Skip to navigation

BBC Micro Elite

Elite F source (6502SP version)

ELITE F FILE Produces the binary file ELTF.bin that gets loaded by elite-bcfs.asm.
CODE_F% = P% LOAD_F% = LOAD% + P% - CODE%
Name: KS3 [View individually] Type: Subroutine Category: Universe Summary: Set the SLSP ship heap pointer after shuffling ship slots
The final part of the KILLSHP routine, called after we have shuffled the ship slots and sorted out our missiles. This simply sets SLSP to the new bottom of the ship heap space. Arguments: P(1 0) Points to the ship line heap of the ship in the last occupied slot (i.e. it points to the bottom of the descending heap)
.KS3 LDA P \ After shuffling the ship slots, P(1 0) will point to STA SLSP \ the new bottom of the ship heap, so store this in LDA P+1 \ SLSP(1 0), which stores the bottom of the heap STA SLSP+1 RTS \ Return from the subroutine
Name: KS1 [View individually] Type: Subroutine Category: Universe Summary: Remove the current ship from our local bubble of universe
Part 12 of the main flight loop calls this routine to remove the ship that is currently being analysed by the flight loop. Once the ship is removed, it jumps back to MAL1 to re-join the main flight loop, with X pointing to the same slot that we just cleared (and which now contains the next ship in the local bubble of universe). Arguments: XX0 The address of the blueprint for this ship INF The address of the data block for this ship
.KS1 LDX XSAV \ Store the current ship's slot number in XSAV JSR KILLSHP \ Call KILLSHP to remove the ship in slot X from our \ local bubble of universe LDX XSAV \ Restore the current ship's slot number from XSAV, \ which now points to the next ship in the bubble JMP MAL1 \ Jump to MAL1 to re-join the main flight loop at the \ start of the ship analysis loop
Name: KS4 [View individually] Type: Subroutine Category: Universe Summary: Remove the space station and replace it with the sun
Remove the space station from our local bubble of universe, and replace it with the sun.
.KS4 JSR ZINF \ Call ZINF to reset the INWK ship workspace JSR FLFLLS \ Reset the LSO block, returns with A = 0 STA FRIN+1 \ Set the second slot in the FRIN table to 0, which \ sets this slot to empty, so when we call NWSHP below \ the new sun that gets created will go into FRIN+1 STA SSPR \ Set the "space station present" flag to 0, as we are \ no longer in the space station's safe zone JSR SPBLB \ Call SPBLB to redraw the space station bulb, which \ will erase it from the dashboard LDA #6 \ Set the sun's y_sign to 6 STA INWK+5 LDA #129 \ Set A = 129, the "ship" type for the sun JMP NWSHP \ Call NWSHP to set up the sun's data block and add it \ to FRIN, where it will get put in the second slot as \ we just cleared out the second slot, and the first \ slot is already taken by the planet
Name: KS2 [View individually] Type: Subroutine Category: Universe Summary: Check the local bubble for missiles with target lock
Check the local bubble of universe to see if there are any missiles with target lock in the vicinity. If there are, then check their targets; if we just removed their target in the KILLSHP routine, then switch off their AI so they just drift in space, otherwise update their targets to reflect the newly shuffled slot numbers. This is called from KILLSHP once the slots have been shuffled down, following the removal of a ship. Arguments: XX4 The slot number of the ship we removed just before calling this routine
.KS2 LDX #&FF \ We want to go through the ships in our local bubble \ and pick out all the missiles, so set X to &FF to \ use as a counter .KSL4 INX \ Increment the counter (so it starts at 0 on the first \ iteration) LDA FRIN,X \ If slot X is empty, loop round again until it isn't, BEQ KS3 \ at which point A contains the ship type in that slot CMP #MSL \ If the slot does not contain a missile, loop back to BNE KSL4 \ KSL4 to check the next slot \ We have found a slot containing a missile, so now we \ want to check whether it has target lock TXA \ Set Y = X * 2 and fetch the Y-th address from UNIV ASL A \ and store it in SC and SC+1 - in other words, set TAY \ SC(1 0) to point to the missile's ship data block LDA UNIV,Y STA SC LDA UNIV+1,Y STA SC+1 LDY #32 \ Fetch byte #32 from the missile's ship data (AI) LDA (SC),Y BPL KSL4 \ If bit 7 of byte #32 is clear, then the missile is \ dumb and has no AI, so loop back to KSL4 to move on \ to the next slot AND #%01111111 \ Otherwise this missile has AI, so clear bit 7 and LSR A \ shift right to set the C flag to the missile's "is \ locked" flag, and A to the target's slot number CMP XX4 \ If this missile's target is less than XX4, then the BCC KSL4 \ target's slot isn't being shuffled down, so jump to \ KSL4 to move on to the next slot BEQ KS6 \ If this missile was locked onto the ship that we just \ removed in KILLSHP, jump to KS6 to stop the missile \ from continuing to hunt it down SBC #1 \ Otherwise this missile is locked and has AI enabled, \ and its target will have moved down a slot, so \ subtract 1 from the target number (we know C is set \ from the BCC above) ASL A \ Shift the target number left by 1, so it's in bits \ 1-6 once again, and also set bit 0 to 1, as the C \ flag is still set, so this makes sure the missile is \ still set to being locked ORA #%10000000 \ Set bit 7, so the missile's AI is enabled STA (SC),Y \ Update the missile's AI flag to the value in A BNE KSL4 \ Loop back to KSL4 to move on to the next slot (this \ BNE is effectively a JMP as A will never be zero) .KS6 LDA #0 \ The missile's target lock just got removed, so set the STA (SC),Y \ AI flag to 0 to make it dumb and not locked BEQ KSL4 \ Loop back to KSL4 to move on to the next slot (this \ BEQ is effectively a JMP as A is always zero)
Name: KILLSHP [View individually] Type: Subroutine Category: Universe Summary: Remove a ship from our local bubble of universe
Remove the ship in slot X from our local bubble of universe. This happens when we kill a ship, collide with a ship and destroy it, or when a ship moves outside our local bubble. We also use this routine when we move out of range of the space station, in which case we replace it with the sun. When removing a ship, this creates a gap in the ship slots at FRIN, so we shuffle all the later slots down to close the gap. We also shuffle the ship data blocks at K% and ship line heap at WP, to reclaim all the memory that the removed ship used to occupy. Arguments: X The slot number of the ship to remove XX0 The address of the blueprint for the ship to remove INF The address of the data block for the ship to remove
.KILLSHP STX XX4 \ Store the slot number of the ship to remove in XX4 \ The following two instructions appear in the BASIC \ source file (ELITEF), but in the text source file \ (ELITEF.TXT) they are replaced by: \ \ CPX MSTG \ \ which does the same thing, but saves two bytes of \ memory (as CPX MSTG is a two-byte opcode, while LDA \ MSTG and CMP XX4 take up four bytes between them) LDA MSTG \ Check whether this slot matches the slot number in CMP XX4 \ MSTG, which is the target of our missile lock BNE KS5 \ If our missile is not locked on this ship, jump to KS5 LDY #GREEN2 \ Otherwise we need to remove our missile lock, so call JSR ABORT \ ABORT to disarm the missile and update the missile \ indicators on the dashboard to green (Y = #GREEN2) LDA #200 \ Print recursive token 40 ("TARGET LOST") as an JSR MESS \ in-flight message .KS5 LDY XX4 \ Restore the slot number of the ship to remove into Y LDX FRIN,Y \ Fetch the contents of the slot, which contains the \ ship type CPX #SST \ If this is the space station, then jump to KS4 to BEQ KS4 \ replace the space station with the sun CPX #CON \ Did we just kill the Constrictor from mission 1? If BNE lll \ not, jump to lll LDA TP \ We just killed the Constrictor from mission 1, so set ORA #%00000010 \ bit 1 of TP to indicate that we have successfully STA TP \ completed mission 1 .lll CPX #HER \ Did we just kill a rock hermit? If we did, jump to BEQ blacksuspenders \ blacksuspenders to increase the junk count CPX #JL \ If JL <= X < JH, i.e. the type of ship we killed in X BCC KS7 \ is junk (escape pod, alloy plate, cargo canister, CPX #JH \ asteroid, splinter, shuttle or transporter), then keep BCS KS7 \ going, otherwise jump to KS7 .blacksuspenders DEC JUNK \ We just killed junk, or a rock hermit, so decrease the \ junk counter .KS7 DEC MANY,X \ Decrease the number of this type of ship in our little \ bubble, which is stored in MANY+X (where X is the ship \ type) LDX XX4 \ Restore the slot number of the ship to remove into X \ We now want to remove this ship and reclaim all the \ memory that it uses. Removing the ship will leave a \ gap in three places, which we need to close up: \ \ * The ship slots in FRIN \ \ * The ship data blocks in K% \ \ * The descending ship line heap at WP down \ \ The rest of this routine closes up these gaps by \ looping through all the occupied ship slots after the \ slot we are removing, one by one, and shuffling each \ ship's slot, data block and line heap down to close \ up the gaps left by the removed ship. As part of this, \ we have to make sure we update any address pointers \ so they point to the newly shuffled data blocks and \ line heaps \ \ In the following, when shuffling a ship's data down \ into the preceding empty slot, we call the ship that \ we are shuffling down the "source", and we call the \ empty slot we are shuffling it into the "destination" \ \ Before we start looping through the ships we need to \ shuffle down, we need to set up some variables to \ point to the source and destination line heaps LDY #5 \ Fetch byte #5 of the removed ship's blueprint into A, LDA (XX0),Y \ which gives the ship's maximum heap size for the ship \ we are removing (i.e. the size of the gap in the heap \ created by the ship removal) \ INF currently contains the ship data for the ship we \ are removing, and INF(34 33) contains the address of \ the bottom of the ship's heap, so we can calculate \ the address of the top of the heap by adding the heap \ size to this address LDY #33 \ First we add A and the address in INF+33, to get the CLC \ low byte of the top of the heap, which we store in P ADC (INF),Y STA P INY \ And next we add A and address in INF+34, with any LDA (INF),Y \ from the previous addition, to get the high byte of ADC #0 \ the top of the heap, which we store in P+1, so P(1 0) STA P+1 \ points to the top of this ship's heap \ Now, we're ready to start looping through the ships \ we want to move, moving the slots, data blocks and \ line heap from the source to the destination. In the \ following, we set up SC to point to the source data, \ and INF (which currently points to the removed ship's \ data that we can now overwrite) points to the \ destination \ \ So P(1 0) now points to the top of the line heap for \ the destination .KSL1 INX \ On entry, X points to the empty slot we want to \ shuffle the next ship into (the destination), so \ this increment points X to the next slot - i.e. the \ source slot we want to shuffle down LDA FRIN,X \ Copy the contents of the source slot into the STA FRIN-1,X \ destination slot BNE P%+5 \ If the slot we just shuffled down is not empty, then \ skip the following instruction JMP KS2 \ The source slot is empty and we are done shuffling, \ so jump to KS2 to move on to processing missiles ASL A \ Otherwise we have a source ship to shuffle down into TAY \ the destination, so set Y = A * 2 so it can act as an \ index into the two-byte ship blueprint lookup table \ at XX21 for the source ship LDA XX21-2,Y \ Set SC(0 1) to point to the blueprint data for the STA SC \ source ship LDA XX21-1,Y STA SC+1 LDY #5 \ Fetch blueprint byte #5 for the source ship, which LDA (SC),Y \ gives us its maximum heap size, and store it in T STA T \ We now subtract T from P(1 0), so P(1 0) will point to \ the bottom of the line heap for the destination \ (which we will use later when closing up the gap in \ the heap space) LDA P \ First, we subtract the low bytes SEC SBC T STA P LDA P+1 \ And then we do the high bytes, for which we subtract SBC #0 \ 0 to include any carry, so this is effectively doing STA P+1 \ P(1 0) = P(1 0) - (0 T) \ Next, we want to set SC(1 0) to point to the source \ ship's data block TXA \ Set Y = X * 2 so it can act as an index into the ASL A \ two-byte lookup table at UNIV, which contains the TAY \ addresses of the ship data blocks. In this case we are \ multiplying X by 2, and X contains the source ship's \ slot number so Y is now an index for the source ship's \ entry in UNIV LDA UNIV,Y \ Set SC(1 0) to the address of the data block for the STA SC \ source ship LDA UNIV+1,Y STA SC+1 \ We have now set up our variables as follows: \ \ SC(1 0) points to the source's ship data block \ \ INF(1 0) points to the destination's ship data block \ \ P(1 0) points to the destination's line heap \ \ so let's start copying data from the source to the \ destination LDY #36 \ We are going to be using Y as a counter for the 37 \ bytes of ship data we want to copy from the source \ to the destination, so we set it to 36 to start things \ off, and will decrement Y for each byte we copy LDA (SC),Y \ Fetch byte #36 of the source's ship data block at SC, STA (INF),Y \ and store it in byte #36 of the destination's block DEY \ at INF, so that's the ship's NEWB flags copied from \ the source to the destination. One down, quite a few \ to go... LDA (SC),Y \ Fetch byte #35 of the source's ship data block at SC, STA (INF),Y \ and store it in byte #35 of the destination's block \ at INF, so that's the ship's energy copied from the \ source to the destination DEY \ Fetch byte #34 of the source ship, which is the LDA (SC),Y \ high byte of the source ship's line heap, and store STA K+1 \ in K+1 LDA P+1 \ Set the low byte of the destination's heap pointer STA (INF),Y \ to P+1 DEY \ Fetch byte #33 of the source ship, which is the LDA (SC),Y \ low byte of the source ship's heap, and store in K STA K \ so now we have the following: \ \ K(1 0) points to the source's line heap LDA P \ Set the low byte of the destination's heap pointer STA (INF),Y \ to P, so now the destination's heap pointer is to \ P(1 0), so that's the heap pointer in bytes #33 and \ #34 done DEY \ Luckily, we can just copy the rest of the source's \ ship data block into the destination, as there are no \ more address pointers, so first we decrement our \ counter in Y to point to the next byte (the AI flag) \ in byte #32) and then start looping .KSL2 LDA (SC),Y \ Copy the Y-th byte of the source to the Y-th byte of STA (INF),Y \ the destination DEY \ Decrement the counter BPL KSL2 \ Loop back to KSL2 to copy the next byte until we have \ copied the whole block \ We have now shuffled the ship's slot and the ship's \ data block, so we only have the heap data itself to do LDA SC \ First, we copy SC into INF, so when we loop round STA INF \ again, INF will correctly point to the destination for LDA SC+1 \ the next iteration STA INF+1 LDY T \ Now we want to move the contents of the heap, as all \ we did above was to update the pointers, so first \ we set a counter in Y that is initially set to T \ (which we set above to the maximum heap size for the \ source ship) \ \ As a reminder, we have already set the following: \ \ K(1 0) points to the source's line heap \ \ P(1 0) points to the destination's line heap \ \ so we can move the heap data by simply copying the \ correct number of bytes from K(1 0) to P(1 0) .KSL3 DEY \ Decrement the counter LDA (K),Y \ Copy the Y-th byte of the source heap at K(1 0) to STA (P),Y \ the destination heap at P(1 0) TYA \ Loop back to KSL3 to copy the next byte, until we BNE KSL3 \ have done them all BEQ KSL1 \ We have now shuffled everything down one slot, so \ jump back up to KSL1 to see if there is another slot \ that needs shuffling down (this BEQ is effectively a \ JMP as A will always be zero)
Name: SFX [View individually] Type: Variable Category: Sound Summary: Sound data
Sound data. To make a sound, the NOS1 routine copies the four relevant sound bytes to XX16, and NO3 then makes the sound. The sound numbers are shown in the table, and are always multiples of 8. Generally, sounds are made by calling the NOISE routine with the sound number in A. These bytes are passed to OSWORD 7, and are the equivalents to the parameters passed to the SOUND keyword in BASIC. The parameters therefore have these meanings: channel/flush, amplitude (or envelope number if 1-4), pitch, duration For the channel/flush parameter, the first byte is the channel while the second is the flush control (where a flush control of 0 queues the sound, while a flush control of 1 makes the sound instantly). When written in hexadecimal, the first figure gives the flush control, while the second is the channel (so &13 indicates flush control = 1 and channel = 3). So when we call NOISE with A = 40 to make a long, low beep, then this is effectively what the NOISE routine does: SOUND &13, &F4, &0C, &08 which makes a sound with flush control 1 on channel 3, and with amplitude &F4 (-12), pitch &0C (2) and duration &08 (8). Meanwhile, to make the hyperspace sound, the NOISE routine does this: SOUND &10, &02, &60, &10 which makes a sound with flush control 1 on channel 0, using envelope 2, and with pitch &60 (96) and duration &10 (16). The four sound envelopes (1-4) are set up in elite-loader.asm.
.SFX EQUB &12,&01,&00,&10 \ 0 - Lasers fired by us EQUB &12,&02,&2C,&08 \ 8 - We're being hit by lasers EQUB &11,&03,&F0,&18 \ 16 - We died 1 / We made a hit or kill 2 EQUB &10,&F1,&07,&1A \ 24 - We died 2 / We made a hit or kill 1 EQUB &03,&F1,&BC,&01 \ 32 - Short, high beep EQUB &13,&F4,&0C,&08 \ 40 - Long, low beep EQUB &10,&F1,&06,&0C \ 48 - Missile launched / Ship launched from station EQUB &10,&02,&60,&10 \ 56 - Hyperspace drive engaged EQUB &13,&04,&C2,&FF \ 64 - E.C.M. on EQUB &13,&00,&00,&00 \ 72 - E.C.M. off
Name: THERE [View individually] Type: Subroutine Category: Missions Summary: Check whether we are in the Constrictor's system in mission 1
The stolen Constrictor is the target of mission 1. We finally track it down to the Orarra system in the second galaxy, which is at galactic coordinates (144, 33). This routine checks whether we are in this system and sets the C flag accordingly. Returns: C flag Set if we are in the Constrictor system, otherwise clear
.THERE LDX GCNT \ Set X = GCNT - 1 DEX BNE THEX \ If X is non-zero (i.e. GCNT is not 1, so we are not in \ the second galaxy), then jump to THEX LDA QQ0 \ Set A = the current system's galactic x-coordinate CMP #144 \ If A <> 144 then jump to THEX BNE THEX LDA QQ1 \ Set A = the current system's galactic y-coordinate CMP #33 \ If A = 33 then set the C flag BEQ THEX+1 \ If A = 33 then jump to THEX+1, so we return from the \ subroutine with the C flag set (otherwise we clear the \ C flag with the next instruction) .THEX CLC \ Clear the C flag RTS \ Return from the subroutine
Name: RESET [View individually] Type: Subroutine Category: Start and end Summary: Reset most variables
Reset our ship and various controls, recharge shields and energy, and then fall through into RES2 to reset the stardust and the ship workspace at INWK. In this subroutine, this means zero-filling the following locations: * Pages &9, &A, &B, &C and &D * BETA to BETA+6, which covers the following: * BETA, BET1 - Set pitch to 0 * XC, YC - Set text cursor to (0, 0) * QQ22 - Set hyperspace counters to 0 * ECMA - Turn E.C.M. off It also sets QQ12 to &FF, to indicate we are docked, recharges the shields and energy banks, and then falls through into RES2.
.RESET JSR ZERO \ Zero-fill pages &9, &A, &B, &C and &D, which clears \ the ship data blocks, the ship line heap, the ship \ slots for the local bubble of universe, and various \ flight and ship status variables LDX #6 \ Set up a counter for zeroing BETA through BETA+6 .SAL3 STA BETA,X \ Zero the X-th byte after BETA DEX \ Decrement the loop counter BPL SAL3 \ Loop back for the next byte to zero TXA \ X is now negative - i.e. &FF - so this sets A and QQ12 STA QQ12 \ to &FF to indicate we are docked LDX #2 \ We're now going to recharge both shields and the \ energy bank, which live in the three bytes at FSH, \ ASH (FSH+1) and ENERGY (FSH+2), so set a loop counter \ in X for 3 bytes .REL5 STA FSH,X \ Set the X-th byte of FSH to &FF to charge up that \ shield/bank DEX \ Decrement the lopp counter BPL REL5 \ Loop back to REL5 until we have recharged both shields \ and the energy bank \ Fall through into RES2 to reset the stardust and ship \ workspace at INWK
Name: RES2 [View individually] Type: Subroutine Category: Start and end Summary: Reset a number of flight variables and workspaces
This is called after we launch from a space station, arrive in a new system after hyperspace, launch an escape pod, or die a cold, lonely death in the depths of space. Returns: Y Y is set to &FF
.RES2 LDA #NOST \ Reset NOSTM, the number of stardust particles, to the STA NOSTM \ maximum allowed (18) LDX #&FF \ Reset LSX2 and LSY2, the ball line heaps used by the STX LSX2 \ BLINE routine for drawing circles, to &FF, to set the STX LSY2 \ heap to empty STX MSTG \ Reset MSTG, the missile target, to &FF (no target) LDA #128 \ Set the current pitch rate to the mid-point, 128 STA JSTY STA ALP2 \ Reset ALP2 (roll sign) and BET2 (pitch sign) STA BET2 \ to negative, i.e. pitch and roll negative ASL A \ This sets A to 0 STA BETA \ Reset BETA (pitch angle alpha) to 0 STA BET1 \ Reset BET1 (magnitude of the pitch angle) to 0 STA ALP2+1 \ Reset ALP2+1 (flipped roll sign) and BET2+1 (flipped STA BET2+1 \ pitch sign) to positive, i.e. pitch and roll negative STA MCNT \ Reset MCNT (the main loop counter) to 0 LDA #3 \ Reset DELTA (speed) to 3 STA DELTA STA ALPHA \ Reset ALPHA (roll angle alpha) to 3 STA ALP1 \ Reset ALP1 (magnitude of roll angle alpha) to 3 LDA SSPR \ Fetch the "space station present" flag, and if we are BEQ P%+5 \ not inside the safe zone, skip the next instruction JSR SPBLB \ Light up the space station bulb on the dashboard LDA ECMA \ Fetch the E.C.M. status flag, and if E.C.M. is off, BEQ yu \ skip the next instruction JSR ECMOF \ Turn off the E.C.M. sound .yu JSR WPSHPS \ Wipe all ships from the scanner JSR ZERO \ Zero-fill pages &9, &A, &B, &C and &D, which clears \ the ship data blocks, the ship line heap, the ship \ slots for the local bubble of universe, and various \ flight and ship status variables LDA #LO(LS%) \ We have reset the ship line heap, so we now point STA SLSP \ SLSP to LS% (the byte below the ship blueprints at D%) LDA #HI(LS%) \ to indicate that the heap is empty STA SLSP+1 JSR DIALS \ Update the dashboard \ Finally, fall through into ZINF to reset the INWK \ ship workspace
Name: ZINF [View individually] Type: Subroutine Category: Utility routines Summary: Reset the INWK workspace and orientation vectors
Zero-fill the INWK ship workspace and reset the orientation vectors, with nosev pointing out of the screen, towards us. Returns: Y Y is set to &FF
.ZINF LDY #NI%-1 \ There are NI% bytes in the INWK workspace, so set a \ counter in Y so we can loop through them LDA #0 \ Set A to 0 so we can zero-fill the workspace .ZI1 STA INWK,Y \ Zero the Y-th byte of the INWK workspace DEY \ Decrement the loop counter BPL ZI1 \ Loop back for the next byte, ending when we have \ zero-filled the last byte at INWK, which leaves Y \ with a value of &FF \ Finally, we reset the orientation vectors as follows: \ \ sidev = (1, 0, 0) \ roofv = (0, 1, 0) \ nosev = (0, 0, -1) \ \ 96 * 256 (&6000) represents 1 in the orientation \ vectors, while -96 * 256 (&E000) represents -1. We \ already set the vectors to zero above, so we just \ need to set up the high bytes of the diagonal values \ and we're done. The negative nosev makes the ship \ point towards us, as the z-axis points into the screen LDA #96 \ Set A to represent a 1 (in vector terms) STA INWK+18 \ Set byte #18 = roofv_y_hi = 96 = 1 STA INWK+22 \ Set byte #22 = sidev_x_hi = 96 = 1 ORA #128 \ Flip the sign of A to represent a -1 STA INWK+14 \ Set byte #14 = nosev_z_hi = -96 = -1 RTS \ Return from the subroutine
Name: msblob [View individually] Type: Subroutine Category: Dashboard Summary: Display the dashboard's missile indicators in green
Display the dashboard's missile indicators, with all the missiles reset to green (i.e. not armed or locked).
.msblob LDX #4 \ Set up a loop counter in X to count through all four \ missile indicators .ss CPX NOMSL \ If the counter is equal to the number of missiles, BEQ SAL8 \ jump down to SQL8 to draw remaining the missiles, as \ the rest of them are present and should be drawn in \ green LDY #0 \ Draw the missile indicator at position X in black JSR MSBAR DEX \ Decrement the counter to point to the next missile BNE ss \ Loop back to ss if we still have missiles to draw RTS \ Return from the subroutine .SAL8 LDY #GREEN2 \ Draw the missile indicator at position X in green JSR MSBAR DEX \ Decrement the counter to point to the next missile BNE SAL8 \ Loop back to SAL8 if we still have missiles to draw RTS \ Return from the subroutine
Name: me2 [View individually] Type: Subroutine Category: Text Summary: Remove an in-flight message from the space view
.me2 LDA MCH \ Fetch the token number of the current message into A JSR MESS \ Call MESS to print the token, which will remove it \ from the screen as printing uses EOR logic LDA #0 \ Set the delay in DLY to 0, so any new in-flight STA DLY \ messages will be shown instantly JMP me3 \ Jump back into the main spawning loop at TT100
Name: Ze [View individually] Type: Subroutine Category: Universe Summary: Initialise the INWK workspace to a hostile ship
Specifically, this routine does the following: * Reset the INWK ship workspace * Set the ship to a fair distance away in all axes, in front of us but randomly up or down, left or right * Give the ship a 4% chance of having E.C.M. * Set the ship to hostile, with AI enabled This routine also sets A, X, T1 and the C flag to random values.
.Ze JSR ZINF \ Call ZINF to reset the INWK ship workspace JSR DORND \ Set A and X to random numbers STA T1 \ Store A in T1 AND #%10000000 \ Extract the sign of A and store in x_sign STA INWK+2 TXA \ Extract the sign of X and store in y_sign AND #%10000000 STA INWK+5 LDA #25 \ Set x_hi = y_hi = z_hi = 25, a fair distance away STA INWK+1 STA INWK+4 STA INWK+7 TXA \ Set the C flag if X >= 245 (4% chance) CMP #245 ROL A \ Set bit 0 of A to the C flag (i.e. there's a 4% \ chance of this ship having E.C.M.) ORA #%11000000 \ Set bits 6 and 7 of A, so the ship is hostile (bit 6 \ and has AI (bit 7) STA INWK+32 \ Store A in the AI flag of this ship \ Fall through into DORND2 to set A, X and the C flag \ randomly
Name: DORND [View individually] Type: Subroutine Category: Utility routines Summary: Generate random numbers Deep dive: Generating random numbers
Set A and X to random numbers. The C and V flags are also set randomly. Other entry points: DORND2 Restricts the value of RAND+2 so that bit 0 is always 0
.DORND2 CLC \ This ensures that bit 0 of r2 is 0 .DORND LDA RAND \ r2´ = ((r0 << 1) mod 256) + C ROL A \ r0´ = r2´ + r2 + bit 7 of r0 TAX ADC RAND+2 \ C = C flag from r0´ calculation STA RAND STX RAND+2 LDA RAND+1 \ A = r1´ = r1 + r3 + C TAX \ X = r3´ = r1 ADC RAND+3 STA RAND+1 STX RAND+3 RTS \ Return from the subroutine
Name: Main game loop (Part 1 of 6) [View individually] Type: Subroutine Category: Main loop Summary: Spawn a trader (a peaceful Cobra Mk III)
This is part of the main game loop. This is where the core loop of the game lives, and it's in two parts. The shorter loop (just parts 5 and 6) is iterated when we are docked, while the entire loop from part 1 to 6 iterates if we are in space. This section covers the following: * Spawn a trader, i.e. a Cobra Mk III, Python, Boa or Anaconda, with one missile, a 50% chance of having an E.C.M., a 50% chance of being hostile, a speed between 16 and 31, and a gentle clockwise roll We call this from within the main loop.
.MTT4 JSR DORND \ Set A and X to random numbers LSR A \ Clear bit 7 of our random number in A STA INWK+32 \ Store this in the ship's AI flag, so this ship does \ not have AI STA INWK+29 \ Store A in the ship's roll counter, giving it a \ clockwise roll (as bit 7 is clear), and a 1 in 127 \ chance of it having no damping ROL INWK+31 \ Set bit 0 of missile count (as we know the C flag is \ set), giving the ship one missile AND #31 \ Set the ship speed to our random number, set to a ORA #16 \ minimum of 16 and a maximum of 31 STA INWK+27 JSR DORND \ Set A and X to random numbers, plus the C flag BMI nodo \ If A is negative (50% chance), jump to nodo to skip \ the following \ If we get here then we are going to spawn a ship that \ is minding its own business and trying to dock LDA INWK+32 \ Set bits 6 and 7 of the ship's AI flag, to make it ORA #%11000000 \ aggressive if attacked, and enable its AI STA INWK+32 LDX #%00010000 \ Set bit 4 of the ship's NEWB flags, to indicate that STX NEWB \ this ship is docking .nodo AND #2 \ If we jumped here with a random value of A from the \ BMI above, then this reduces A to a random value of \ either 0 or 2; if we didn't take the BMI and made the \ ship hostile, then A will be 0 ADC #CYL \ Set A = A + C + #CYL \ \ where A is 0 or 2 and C is 0 or 1, so this gives us a \ ship type from the following: Cobra Mk III, Python, \ Boa or Anaconda CMP #HER \ If A is now the ship type of a rock hermit, jump to BEQ TT100 \ TT100 to skip the following instruction JSR NWSHP \ Add a new ship of type A to the local bubble and fall \ through into the main game loop again
Name: Main game loop (Part 2 of 6) [View individually] Type: Subroutine Category: Main loop Summary: Call main flight loop, potentially spawn trader, asteroid, cargo
This section covers the following: * Call M% to do the main flight loop * Potentially spawn a trader (Cobra Mk III), asteroid or cargo canister Other entry points: TT100 The entry point for the start of the main game loop, which calls the main flight loop and the moves into the spawning routine me3 Used by me2 to jump back into the main game loop after printing an in-flight message
.TT100 JSR M% \ Call M% to iterate through the main flight loop DEC DLY \ Decrement the delay counter in DLY, so any in-flight \ messages get removed once the counter reaches zero BEQ me2 \ If DLY is now 0, jump to me2 to remove any in-flight \ message from the space view, and once done, return to \ me3 below, skipping the following two instructions BPL me3 \ If DLY is positive, jump to me3 to skip the next \ instruction INC DLY \ If we get here, DLY is negative, so we have gone too \ and need to increment DLY back to 0 .me3 DEC MCNT \ Decrement the main loop counter in MCNT BEQ P%+5 \ If the counter has reached zero, which it will do \ every 256 main loops, skip the next JMP instruction \ (or to put it another way, if the counter hasn't \ reached zero, jump down to MLOOP, skipping all the \ following checks) .ytq JMP MLOOP \ Jump down to MLOOP to do some end-of-loop tidying and \ restart the main loop \ We only get here once every 256 iterations of the \ main loop. If we aren't in witchspace and don't \ already have 3 or more asteroids in our local bubble, \ then this section has a 13% chance of spawning \ something benign (the other 87% of the time we jump \ down to consider spawning cops, pirates and bounty \ hunters) \ \ If we are in that 13%, then 50% of the time this will \ be a Cobra Mk III trader, and the other 50% of the \ time it will either be an asteroid (98.5% chance) or, \ very rarely, a cargo canister (1.5% chance) LDA MJ \ If we are in witchspace following a mis-jump, skip the BNE ytq \ following by jumping down to MLOOP (via ytq above) JSR DORND \ Set A and X to random numbers CMP #35 \ If A >= 35 (87% chance), jump down to MTT1 to skip BCS MTT1 \ the spawning of an asteroid or cargo canister and \ potentially spawn something else LDA JUNK \ If we already have 3 or more bits of junk in the local CMP #3 \ bubble, jump down to MTT1 to skip the following and BCS MTT1 \ potentially spawn something else JSR ZINF \ Call ZINF to reset the INWK ship workspace LDA #38 \ Set z_hi = 38 (far away) STA INWK+7 JSR DORND \ Set A, X and C flag to random numbers STA INWK \ Set x_lo = random STX INWK+3 \ Set y_lo = random AND #%10000000 \ Set x_sign = bit 7 of x_lo STA INWK+2 TXA \ Set y_sign = bit 7 of y_lo AND #%10000000 STA INWK+5 ROL INWK+1 \ Set bit 2 of x_hi to the C flag, which is random, so ROL INWK+1 \ this randomly moves us slightly off-centre JSR DORND \ Set A, X and V flag to random numbers BVS MTT4 \ If V flag is set (50% chance), jump up to MTT4 to \ spawn a trader ORA #%01101111 \ Take the random number in A and set bits 0-3 and 5-6, STA INWK+29 \ so the result has a 50% chance of being positive or \ negative, and a 50% chance of bits 0-6 being 127. \ Storing this number in the roll counter therefore \ gives our new ship a fast roll speed with a 50% \ chance of having no damping, plus a 50% chance of \ rolling clockwise or anti-clockwise LDA SSPR \ If we are inside the space station safe zone, jump BNE MTT1 \ down to MTT1 to skip the following and potentially \ spawn something else TXA \ Set A to the random X we set above, which we haven't BCS MTT2 \ used yet, and if the C flag is set (50% chance) jump \ down to MTT2 to skip the following AND #31 \ Set the ship speed to our random number, set to a ORA #16 \ minimum of 16 and a maximum of 31 STA INWK+27 BCC MTT3 \ Jump down to MTT3, skipping the following (this BCC \ is effectively a JMP as we know the C flag is clear, \ having passed through the BCS above) .MTT2 ORA #%01111111 \ Set bits 0-6 of A to 127, leaving bit 7 as random, so STA INWK+30 \ storing this number in the pitch counter means we have \ full pitch with no damping, with a 50% chance of \ pitching up or down .MTT3 JSR DORND \ Set A and X to random numbers CMP #252 \ If random A < 252 (98.8% of the time), jump to thongs BCC thongs \ to skip the following LDA #HER \ Set A to #HER so we spawn a rock hermit 1.2% of the \ time STA INWK+32 \ Set byte #32 to %00001111 to give the rock hermit an \ E.C.M. BNE whips \ Jump to whips (this BNE is effectively a JMP as A will \ never be zero) .thongs CMP #10 \ If random A >= 10 (96% of the time), set the C flag AND #1 \ Reduce A to a random number that's 0 or 1 ADC #OIL \ Set A = #OIL + A + C, so there's a tiny chance of us \ spawning a cargo canister (#OIL) and an even chance of \ us spawning either a boulder (#OIL + 1) or an asteroid \ (#OIL + 2) .whips JSR NWSHP \ Add our new asteroid or canister to the universe
Name: Main game loop (Part 3 of 6) [View individually] Type: Subroutine Category: Main loop Summary: Potentially spawn a cop, particularly if we've been bad
This section covers the following: * Potentially spawn a cop (in a Viper), very rarely if we have been good, more often if have been naughty, and very often if we have been properly bad * Very rarely, consider spawning a Thargoid, or vanishingly rarely, a Cougar
.MTT1 LDA SSPR \ If we are outside the space station's safe zone, skip BEQ P%+5 \ the following instruction .MLOOPS JMP MLOOP \ Jump to MLOOP to skip the following JSR BAD \ Call BAD to work out how much illegal contraband we \ are carrying in our hold (A is up to 40 for a \ standard hold crammed with contraband, up to 70 for \ an extended cargo hold full of narcotics and slaves) ASL A \ Double A to a maximum of 80 or 140 LDX MANY+COPS \ If there are no cops in the local bubble, skip the BEQ P%+5 \ next instruction ORA FIST \ There are cops in the vicinity and we've got a hold \ full of jail time, so OR the value in A with FIST to \ get a new value that is at least as high as both \ values, to reflect the fact that they have almost \ certainly scanned our ship STA T \ Store our badness level in T JSR Ze \ Call Ze to initialise INWK to a potentially hostile \ ship, and set A and X to random values CMP #136 \ If the random number in A = 136 (0.4% chance), jump BEQ fothg \ to fothg in part 4 to spawn either a Thargoid or, very \ rarely, a Cougar CMP T \ If the random value in A >= our badness level, which BCS P%+7 \ will be the case unless we have been really, really \ bad, then skip the following two instructions (so if \ we are really bad, there's a higher chance of \ spawning a cop, otherwise we got away with it, for \ now) LDA #COPS \ Add a new police ship to the local bubble JSR NWSHP LDA MANY+COPS \ If we now have at least one cop in the local bubble, BNE MLOOPS \ jump down to MLOOPS, otherwise fall through into the \ next part to look at spawning something else
Name: Main game loop (Part 4 of 6) [View individually] Type: Subroutine Category: Main loop Summary: Potentially spawn lone bounty hunter, Thargoid, or up to 4 pirates
This section covers the following: * Potentially spawn (35% chance) either a lone bounty hunter (a Cobra Mk III, Asp Mk II, Python or Fer-de-lance), a Thargoid, or a group of up to 4 pirates (a mix of Sidewinders, Mambas, Kraits, Adders, Geckos, Cobras Mk I and III, and Worms) * Also potentially spawn a Constrictor if this is the mission 1 endgame, or Thargoids if mission 2 is in progress
DEC EV \ Decrement EV, the extra vessels spawning delay, and BPL MLOOPS \ jump to MLOOPS if it is still positive, so we only \ do the following when the EV counter runs down INC EV \ EV is negative, so bump it up again, setting it back \ to 0 LDA TP \ Fetch bits 2 and 3 of TP, which contain the status of AND #%00001100 \ mission 2 CMP #%00001000 \ If bit 3 is set and bit 2 is clear, keep going to BNE nopl \ spawn a Thargoid as we are transporting the plans in \ mission 2 and the Thargoids are trying to stop us, \ otherwise jump to nopl to skip spawning a Thargoid JSR DORND \ Set A and X to random numbers CMP #200 \ If the random number in A < 200 (78% chance), jump to BCC nopl \ nopl to skip spawning a Thargoid .fothg2 JSR GTHG \ Call GTHG to spawn a Thargoid ship and a Thargon \ companion .nopl JSR DORND \ Set A and X to random numbers LDY gov \ If the government of this system is 0 (anarchy), jump BEQ LABEL_2 \ straight to LABEL_2 to start spawning pirates or a \ lone bounty hunter CMP #90 \ If the random number in A >= 90 (65% chance), jump to BCS MLOOPS \ MLOOPS to stop spawning (so there's a 35% chance of \ spawning pirates or a lone bounty hunter) AND #7 \ Reduce the random number in A to the range 0-7, and CMP gov \ if A is less than government of this system, jump BCC MLOOPS \ to MLOOPS to stop spawning (so safer governments with \ larger gov numbers have a greater chance of jumping \ out, which is another way of saying that more \ dangerous systems spawn pirates and bounty hunters \ more often) .LABEL_2 \ In the 6502 Second Processor version, the LABEL_2 \ label is actually ` (a backtick), but that doesn't \ compile in BeebAsm and it's pretty cryptic, so \ instead this version sticks with the label LABEL_2 \ from the cassette version \ Now to spawn a lone bounty hunter, a Thargoid or a \ group of pirates JSR Ze \ Call Ze to initialise INWK to a potentially hostile \ ship, and set A and X to random values CMP #100 \ If the random number in A >= 100 (61% chance), jump BCS mt1 \ to mt1 to spawn pirates, otherwise keep going to \ spawn a lone bounty hunter or a Thargoid INC EV \ Increase the extra vessels spawning counter, to \ prevent the next attempt to spawn extra vessels AND #3 \ Set A = random number in the range 0-3, which we \ will now use to determine the type of ship ADC #CYL2 \ Add A to #CYL2 (we know the C flag is clear as we \ passed through the BCS above), so A is now one of the \ lone bounty hunter ships, i.e. Cobra Mk III (pirate), \ Asp Mk II, Python (pirate) or Fer-de-lance TAY \ Copy the new ship type to Y JSR THERE \ Call THERE to see if we are in the Constrictor's \ system in mission 1 BCC NOCON \ If the C flag is clear then we are not in the \ Constrictor's system, so skip to NOCON LDA #%11111001 \ Set the AI flag of this ship so that it has E.C.M., STA INWK+32 \ has a very high aggression level of 28 out of 31, is \ hostile, and has AI enabled - nasty stuff! LDA TP \ Fetch bits 0 and 1 of TP, which contain the status of AND #%00000011 \ mission 1 LSR A \ Shift bit 0 into the C flag BCC NOCON \ If bit 0 is clear, skip to NOCON as mission 1 is not \ in progress ORA MANY+CON \ Bit 0 of A now contains bit 1 of TP, so this will be \ set if we have already completed mission 1, so this OR \ will be non-zero if we have either completed mission \ 1, or there is already a Constrictor in our local \ bubble of universe (in which case MANY+CON will be \ non-zero) BEQ YESCON \ If A = 0 then mission 1 is in progress, we haven't \ completed it yet, and there is no Constrictor in the \ vicinity, so jump to YESCON to spawn the Constrictor .NOCON LDA #%00000100 \ Set bit 2 of the NEWB flags and clear all other bits, STA NEWB \ so the ship we are about to spawn is hostile \ We now build the AI flag for this ship in A JSR DORND \ Set A and X to random numbers CMP #200 \ First, set the C flag if X >= 200 (22% chance) ROL A \ Set bit 0 of A to the C flag (i.e. there's a 22% \ chance of this ship having E.C.M.) ORA #%11000000 \ Set bits 6 and 7 of A, so the ship is hostile (bit 6) \ and has AI (bit 7) STA INWK+32 \ Store A in the AI flag of this ship TYA EQUB &2C \ Skip the next instruction by turning it into \ &2C &A9 &1F, or BIT &1FA9, which does nothing apart \ from affect the flags .YESCON LDA #CON \ If we jump straight here, we are in the mission 1 \ endgame and it's time to spawn the Constrictor, so \ set A to the Constrictor's type .focoug JSR NWSHP \ Spawn the new ship, whether it's a pirate, Thargoid, \ Cougar or Constrictor .mj1 JMP MLOOP \ Jump down to MLOOP, as we are done spawning ships .fothg LDA K%+6 \ Fetch the z_lo coordinate of the first ship in the K% AND #%00111110 \ block (i.e. the planet) and extract bits 1-5 BNE fothg2 \ If any of bits 1-5 are set (96.8% chance), jump up to \ fothg2 to spawn a Thargoid \ If we get here then we're going to spawn a Cougar, a \ very rare event indeed. How rare? Well, all the \ following have to happen in sequence: \ \ * Main loop iteration = 0 (1 in 256 iterations) \ * Skip asteroid spawning (87% chance) \ * Skip cop spawning (0.4% chance) \ * Skip Thargoid spawning (3.2% chance) \ \ so the chances of spawning a Cougar on any single main \ loop iteration are slim, to say the least LDA #18 \ Give the ship we're about to spawn a speed of 27 STA INWK+27 LDA #%01111001 \ Give it an E.C.M., and make it hostile and pretty STA INWK+32 \ aggressive (though don't give it AI) LDA #COU \ Set the ship type to a Cougar and jump up to focoug BNE focoug \ to spawn it .mt1 AND #3 \ It's time to spawn a group of pirates, so set A to a \ random number in the range 0-3, which will be the \ loop counter for spawning pirates below (so we will \ spawn 1-4 pirates) STA EV \ Delay further spawnings by this number STA XX13 \ Store the number in XX13, the pirate counter .mt3 JSR DORND \ Set A and X to random numbers STA T \ Set T to a random number JSR DORND \ Set A and X to random numbers AND T \ Set A to the AND of two random numbers, so each bit \ has 25% chance of being set which makes the chances \ of a smaller number higher AND #7 \ Reduce A to a random number in the range 0-7, though \ with a bigger chance of a smaller number in this range ADC #PACK \ #PACK is set to #SH3, the ship type for a Sidewinder, \ so this sets our new ship type to one of the pack \ hunters, namely a Sidewinder, Mamba, Krait, Adder, \ Gecko, Cobra Mk I, Worm or Cobra Mk III (pirate) JSR NWSHP \ Add a new ship of type A to the local bubble DEC XX13 \ Decrement the pirate counter BPL mt3 \ If we need more pirates, loop back up to mt3, \ otherwise we are done spawning, so fall through into \ the end of the main loop at MLOOP
Name: Main game loop (Part 5 of 6) [View individually] Type: Subroutine Category: Main loop Summary: Cool down lasers, make calls to update the dashboard
This is the first half of the minimal game loop, which we iterate when we are docked. This section covers the following: * Cool down lasers * Make calls to update the dashboard Other entry points: MLOOP The entry point for the main game loop. This entry point comes after the call to the main flight loop and spawning routines, so it marks the start of the main game loop for when we are docked (as we don't need to call the main flight loop or spawning routines if we aren't in space)
.MLOOP LDX #&FF \ Set the stack pointer to &01FF, which is the standard TXS \ location for the 6502 stack, so this instruction \ effectively resets the stack LDX GNTMP \ If the laser temperature in GNTMP is non-zero, BEQ EE20 \ decrement it (i.e. cool it down a bit) DEC GNTMP .EE20 LDX LASCT \ Set X to the value of LASCT, the laser pulse count BEQ NOLASCT \ If X = 0 then jump to NOLASCT to skip reducing LASCT, \ as it can't be reduced any further DEX \ Decrement the value of LASCT in X BEQ P%+3 \ If X = 0, skip the next instruction DEX \ Decrement the value of LASCT in X again STX LASCT \ Store the decremented value of X in LASCT, so LASCT \ gets reduced by 2, but not into negative territory .NOLASCT JSR DIALS \ Call DIALS to update the dashboard BIT printflag \ If bit 7 of printflag is clear (printer output is not \ enabled), jump to dontdolinefeedontheprinternow to \ skip the following (and en route, why not take a \ short moment to admire this, the longest label name in \ the original Elite source code - presumably they got \ longer when development moved to a 6502 second \ processor system, with all that extra memory...) BPL dontdolinefeedontheprinternow LDA #prilf \ Send a #prilf command to the I/O processor to print a JSR OSWRCH \ blank line on the printer JSR OSWRCH .dontdolinefeedontheprinternow STZ printflag \ Set the printflag to 0 to disable printing LDA QQ11 \ If this is a space view, skip the following five BEQ P%+13 \ instructions (i.e. jump to JSR TT17 below) AND PATG \ If PATG = &FF (author names are shown on start-up) LSR A \ and bit 0 of QQ11 is 1 (the current view is type 1), BCS P%+7 \ then skip the following two instructions LDY #2 \ Wait for 2/50 of a second (0.04 seconds), to slow the JSR DELAY \ main loop down a bit JSR TT17 \ Scan the keyboard for the cursor keys or joystick, \ returning the cursor's delta values in X and Y and \ the key pressed in A
Name: Main game loop (Part 6 of 6) [View individually] Type: Subroutine Category: Main loop Summary: Process non-flight key presses (red function keys, docked keys)
This is the second half of the minimal game loop, which we iterate when we are docked. This section covers the following: * Process more key presses (red function keys, docked keys etc.) It also support joining the main loop with a key already "pressed", so we can jump into the main game loop to perform a specific action. In practice, this is used when we enter the docking bay in BAY to display Status Mode (red key f8), and when we finish buying or selling cargo in BAY2 to jump to the Inventory (red key f9). Other entry points: FRCE The entry point for the main game loop if we want to jump straight to a specific screen, by pretending to "press" a key, in which case A contains the internal key number of the key we want to "press"
.FRCE JSR TT102 \ Call TT102 to process the key pressed in A LDA QQ12 \ Fetch the docked flag from QQ12 into A BNE MLOOP \ If we are docked, loop back up to MLOOP just above \ to restart the main loop, but skipping all the flight \ and spawning code in the top part of the main loop JMP TT100 \ Otherwise jump to TT100 to restart the main loop from \ the start
Name: TT102 [View individually] Type: Subroutine Category: Keyboard Summary: Process function key, save, hyperspace and chart key presses
Process function key presses, plus "@" (save commander), "H" (hyperspace), "D" (show distance to system) and "O" (move chart cursor back to current system). We can also pass cursor position deltas in X and Y to indicate that the cursor keys or joystick have been used (i.e. the values that are returned by routine TT17). Arguments: A The internal key number of the key pressed (see p.142 of the Advanced User Guide for a list of internal key numbers) X The amount to move the crosshairs in the x-axis Y The amount to move the crosshairs in the y-axis Other entry points: T95 Print the distance to the selected system
.TT102 CMP #f8 \ If red key f8 was pressed, jump to STATUS to show the BNE P%+5 \ Status Mode screen, returning from the subroutine JMP STATUS \ using a tail call CMP #f4 \ If red key f4 was pressed, jump to TT22 to show the BNE P%+5 \ Long-range Chart, returning from the subroutine using JMP TT22 \ a tail call CMP #f5 \ If red key f5 was pressed, jump to TT23 to show the BNE P%+5 \ Short-range Chart, returning from the subroutine using JMP TT23 \ a tail call CMP #f6 \ If red key f6 was pressed, call TT111 to select the BNE TT92 \ system nearest to galactic coordinates (QQ9, QQ10) JSR TT111 \ (the location of the chart crosshairs) and jump to JMP TT25 \ TT25 to show the Data on System screen, returning \ from the subroutine using a tail call .TT92 CMP #f9 \ If red key f9 was pressed, jump to TT213 to show the BNE P%+5 \ Inventory screen, returning from the subroutine JMP TT213 \ using a tail call CMP #f7 \ If red key f7 was pressed, jump to TT167 to show the BNE P%+5 \ Market Price screen, returning from the subroutine JMP TT167 \ using a tail call CMP #f0 \ If red key f0 was pressed, jump to TT110 to launch our BNE fvw \ ship (if docked), returning from the subroutine using JMP TT110 \ a tail call .fvw BIT QQ12 \ If bit 7 of QQ12 is clear (i.e. we are not docked, but BPL INSP \ in space), jump to INSP to skip the following checks \ for f1-f3 and "@" (save commander file) key presses CMP #f3 \ If red key f3 was pressed, jump to EQSHP to show the BNE P%+5 \ Equip Ship screen, returning from the subroutine using JMP EQSHP \ a tail call CMP #f1 \ If red key f1 was pressed, jump to TT219 to show the BNE P%+5 \ Buy Cargo screen, returning from the subroutine using JMP TT219 \ a tail call CMP #&47 \ If "@" was not pressed, skip to nosave BNE nosave JSR SVE \ "@" was pressed, so call SVE to show the disc menu BCC P%+5 \ If the C flag was set by SVE, then we loaded a new JMP QU5 \ commander file, so jump to QU5 to restart the game \ with the newly loaded commander JMP BAY \ Otherwise the C flag was clear, so jump to BAY to go \ to the docking bay (i.e. show the Status Mode screen) .nosave CMP #f2 \ If red key f2 was pressed, jump to TT208 to show the BNE LABEL_3 \ Sell Cargo screen, returning from the subroutine using JMP TT208 \ a tail call .INSP CMP #f1 \ If the key pressed is < red key f1 or > red key f3, BCC LABEL_3 \ jump to LABEL_3 (so only do the following if the key CMP #f3+1 \ pressed is f1, f2 or f3) BCS LABEL_3 AND #3 \ If we get here then we are either in space, or we are TAX \ docked and none of f1-f3 were pressed, so we can now JMP LOOK1 \ process f1-f3 with their in-flight functions, i.e. \ switching space views \ \ A will contain &71, &72 or &73 (for f1, f2 or f3), so \ set X to the last digit (1, 2 or 3) and jump to LOOK1 \ to switch to view X (back, left or right), returning \ from the subroutine using a tail call .LABEL_3 \ In the 6502 Second Processor version, the LABEL_3 \ label is actually `` (two backticks), but that doesn't \ compile in BeebAsm and it's pretty cryptic, so instead \ this version sticks with the label LABEL_3 from the \ cassette version CMP #&54 \ If "H" was pressed, jump to hyp to do a hyperspace BNE P%+5 \ jump (if we are in space), returning from the JMP hyp \ subroutine using a tail call .NWDAV5 CMP #&32 \ If "D" was pressed, jump to T95 to print the distance BEQ T95 \ to a system (if we are in one of the chart screens) CMP #&43 \ If "F" was not pressed, jump down to HME1, otherwise BNE HME1 \ keep going to process searching for systems LDA QQ12 \ If QQ12 = 0 (we are not docked), we can't search for BEQ t95 \ systems, so return from the subroutine (as t95 \ contains an RTS) LDA QQ11 \ If the current view is a chart (QQ11 = 64 or 128), AND #%11000000 \ keep going, otherwise return from the subroutine (as BEQ t95 \ t95 contains an RTS) JMP HME2 \ Jump to HME2 to let us search for a system, returning \ from the subroutine using a tail call .HME1 STA T1 \ Store A (the key that's been pressed) in T1 LDA QQ11 \ If the current view is a chart (QQ11 = 64 or 128), AND #%11000000 \ keep going, otherwise jump down to TT107 to skip the BEQ TT107 \ following LDA QQ22+1 \ If the on-screen hyperspace counter is non-zero, BNE TT107 \ then we are already counting down, so jump to TT107 \ to skip the following LDA T1 \ Restore the original value of A (the key that's been \ pressed) from T1 CMP #&36 \ If "O" was pressed, do the following three JSRs, BNE ee2 \ otherwise jump to ee2 to skip the following JSR TT103 \ Draw small crosshairs at coordinates (QQ9, QQ10), \ which will erase the crosshairs currently there JSR ping \ Set the target system to the current system (which \ will move the location in (QQ9, QQ10) to the current \ home system JMP TT103 \ Draw small crosshairs at coordinates (QQ9, QQ10), \ which will draw the crosshairs at our current home \ system, and return from the subroutine using a tail \ call .ee2 JSR TT16 \ Call TT16 to move the crosshairs by the amount in X \ and Y, which were passed to this subroutine as \ arguments .TT107 LDA QQ22+1 \ If the on-screen hyperspace counter is zero, return BEQ t95 \ from the subroutine (as t95 contains an RTS), as we \ are not currently counting down to a hyperspace jump DEC QQ22 \ Decrement the internal hyperspace counter BNE t95 \ If the internal hyperspace counter is still non-zero, \ then we are still counting down, so return from the \ subroutine (as t95 contains an RTS) \ If we get here then the internal hyperspace counter \ has just reached zero and it wasn't zero before, so \ we need to reduce the on-screen counter and update \ the screen. We do this by first printing the next \ number in the countdown sequence, and then printing \ the old number, which will erase the old number \ and display the new one because printing uses EOR \ logic LDX QQ22+1 \ Set X = the on-screen hyperspace counter - 1 DEX \ (i.e. the next number in the sequence) JSR ee3 \ Print the 8-bit number in X at text location (0, 1) LDA #5 \ Reset the internal hyperspace counter to 5 STA QQ22 LDX QQ22+1 \ Set X = the on-screen hyperspace counter (i.e. the \ current number in the sequence, which is already \ shown on-screen) JSR ee3 \ Print the 8-bit number in X at text location (0, 1), \ i.e. print the hyperspace countdown in the top-left \ corner DEC QQ22+1 \ Decrement the on-screen hyperspace countdown BNE t95 \ If the countdown is not yet at zero, return from the \ subroutine (as t95 contains an RTS) JMP TT18 \ Otherwise the countdown has finished, so jump to TT18 \ to do a hyperspace jump, returning from the subroutine \ using a tail call .t95 RTS \ Return from the subroutine .T95 \ If we get here, "D" was pressed, so we need to show \ the distance to the selected system (if we are in a \ chart view) LDA QQ11 \ If the current view is a chart (QQ11 = 64 or 128), AND #%11000000 \ keep going, otherwise return from the subroutine (as BEQ t95 \ t95 contains an RTS) LDA #CYAN \ Send a #SETCOL CYAN command to the I/O processor to JSR DOCOL \ switch to colour 3, which is white in the chart view JSR hm \ Call hm to move the crosshairs to the target system \ in (QQ9, QQ10), returning with A = 0 STA QQ17 \ Set QQ17 = 0 to switch to ALL CAPS JSR cpl \ Print control code 3 (the selected system name) LDA #%10000000 \ Set bit 7 of QQ17 to switch to Sentence Case, with the STA QQ17 \ next letter in capitals LDA #10 \ Print a line feed to move the text cursor down a line JSR TT26 LDA #1 \ Move the text cursor to column 1 JSR DOXC JSR INCYC \ Move the text cursor down one line JMP TT146 \ Print the distance to the selected system and return \ from the subroutine using a tail call
Name: BAD [View individually] Type: Subroutine Category: Status Summary: Calculate how bad we have been
Work out how bad we are from the amount of contraband in our hold. The formula is: (slaves + narcotics) * 2 + firearms so slaves and narcotics are twice as illegal as firearms. The value in FIST (our legal status) is set to at least this value whenever we launch from a space station, and a FIST of 50 or more gives us fugitive status, so leaving a station carrying 25 tonnes of slaves/narcotics, or 50 tonnes of firearms across multiple trips, is enough to make us a fugitive. Returns: A A value that determines how bad we are from the amount of contraband in our hold
.BAD LDA QQ20+3 \ Set A to the number of tonnes of slaves in the hold CLC \ Clear the C flag so we can do addition without the \ C flag affecting the result ADC QQ20+6 \ Add the number of tonnes of narcotics in the hold ASL A \ Double the result and add the number of tonnes of ADC QQ20+10 \ firearms in the hold RTS \ Return from the subroutine
Name: FAROF [View individually] Type: Subroutine Category: Maths (Geometry) Summary: Compare x_hi, y_hi and z_hi with 224
Compare x_hi, y_hi and z_hi with 224, and set the C flag if all three <= 224, otherwise clear the C flag. Returns: C flag Set if x_hi <= 224 and y_hi <= 224 and z_hi <= 224 Clear otherwise (i.e. if any one of them are bigger than 224)
.FAROF LDA #224 \ Set A = 224 and fall through into FAROF2 to do the \ comparison
Name: FAROF2 [View individually] Type: Subroutine Category: Maths (Geometry) Summary: Compare x_hi, y_hi and z_hi with A
Compare x_hi, y_hi and z_hi with A, and set the C flag if all three <= A, otherwise clear the C flag. Returns: C flag Set if x_hi <= A and y_hi <= A and z_hi <= A Clear otherwise (i.e. if any one of them are bigger than A)
.FAROF2 CMP INWK+1 \ If A < x_hi, C will be clear so jump to FA1 to BCC FA1 \ return from the subroutine with C clear, otherwise \ C will be set so move on to the next one CMP INWK+4 \ If A < y_hi, C will be clear so jump to FA1 to BCC FA1 \ return from the subroutine with C clear, otherwise \ C will be set so move on to the next one CMP INWK+7 \ If A < z_hi, C will be clear, otherwise C will be set .FA1 RTS \ Return from the subroutine
Name: MAS4 [View individually] Type: Subroutine Category: Maths (Geometry) Summary: Calculate a cap on the maximum distance to a ship
Logical OR the value in A with the high bytes of the ship's position (x_hi, y_hi and z_hi). Returns: A A OR x_hi OR y_hi OR z_hi
.MAS4 ORA INWK+1 \ OR A with x_hi, y_hi and z_hi ORA INWK+4 ORA INWK+7 RTS \ Return from the subroutine
Name: brkd [View individually] Type: Subroutine Category: Utility routines Summary: The brkd counter for error handling
This counter starts at zero, and is decremented whenever the BRKV handler at BRBR prints an error message. It is incremented every time an error message is printer out as part of the TITLE routine.
.brkd EQUB 0
Name: BRBR [View individually] Type: Subroutine Category: Utility routines Summary: The standard BRKV handler for the game
This routine is used to display error messages, before restarting the game. When called, it makes a beep and prints the system error message in the block pointed to by (&FD &FE), which is where the MOS will put any system errors. It then waits for a key press and restarts the game. BRKV is set to this routine in the decryption routine at DEEOR just before the game is run for the first time, and at the end of the SVE routine after the disc access menu has been processed. In other words, this is the standard BRKV handler for the game, and it's swapped out to MRBRK for disc access operations only. When it is the BRKV handler, the routine can be triggered using a BRK instruction. The main differences between this routine and the MEBRK handler that is used during disc access operations are that this routine restarts the game rather than returning to the disc access menu, and this handler decrements the brkd counter.
.BRBR DEC brkd \ Decrement the brkd counter LDX #&FF \ Set the stack pointer to &01FF, which is the standard TXS \ location for the 6502 stack, so this instruction \ effectively resets the stack JSR backtonormal \ Disable the keyboard and set the SVN flag to 0 TAY \ The call to backtonormal sets A to 0, so this sets Y \ to 0, which use as a loop counter below LDA #7 \ Set A = 7 to generate a beep before we print the error \ message .BRBRLOOP JSR OSWRCH \ Print the character in A, which contains a line feed \ on the first loop iteration, and then any non-zero \ characters we fetch from the error message INY \ Increment the loop counter LDA (&FD),Y \ Fetch the Y-th byte of the block pointed to by \ (&FD &FE), so that's the Y-th character of the message \ pointed to by the MOS error message pointer BNE BRBRLOOP \ If the fetched character is non-zero, loop back to the \ JSR OSWRCH above to print the it, and keep looping \ until we fetch a zero (which marks the end of the \ message) JMP BR1 \ Jump to BR1 to restart the game
Name: DEATH [View individually] Type: Subroutine Category: Start and end Summary: Display the death screen
We have been killed, so display the chaos of our destruction above a "GAME OVER" sign, and clean up the mess ready for the next attempt.
.DEATH JSR EXNO3 \ Make the sound of us dying JSR RES2 \ Reset a number of flight variables and workspaces ASL DELTA \ Divide our speed in DELTA by 4 ASL DELTA LDX #24 \ Set the screen to only show 24 text rows, which hides JSR DET1 \ the dashboard, setting A to 6 in the process JSR TT66 \ Clear the top part of the screen, draw a white border, \ and set the current view type in QQ11 to 6 (death \ screen) JSR BOX \ Call BOX to redraw the same white border (BOX is part \ of TT66), which removes the border as it is drawn \ using EOR logic JSR nWq \ Create a cloud of stardust containing the correct \ number of dust particles (i.e. NOSTM of them) LDA #12 \ Move the text cursor to column 12 on row 12 JSR DOYC JSR DOXC LDA #YELLOW \ Send a #SETCOL YELLOW command to the I/O processor to JSR DOCOL \ change the current colour to yellow LDA #146 \ Print recursive token 146 ("{all caps}GAME OVER") JSR ex .D1 JSR Ze \ Call Ze to initialise INWK to a potentially hostile \ ship, and set A and X to random values LSR A \ Set A = A / 4, so A is now between 0 and 63, and LSR A \ store in byte #0 (x_lo) STA INWK LDY #0 \ Set the following to 0: the current view in QQ11 STY QQ11 \ (space view), x_hi, y_hi, z_hi and the AI flag (no AI STY INWK+1 \ or E.C.M. and not hostile) STY INWK+4 STY INWK+7 STY INWK+32 DEY \ Set Y = 255 STY MCNT \ Reset the main loop counter to 255, so all timer-based \ calls will be stopped EOR #%00101010 \ Flip bits 1, 3 and 5 in A (x_lo) to get another number STA INWK+3 \ between 48 and 63, and store in byte #3 (y_lo) ORA #%01010000 \ Set bits 4 and 6 of A to bump it up to between 112 and STA INWK+6 \ 127, and store in byte #6 (z_lo) TXA \ Set A to the random number in X and keep bits 0-3 and AND #%10001111 \ the bit 7 to get a number between -15 and +15, and STA INWK+29 \ store in byte #29 (roll counter) to give our ship a \ gentle roll with damping STY LASCT \ Set the laser count to 127 to act as a counter in the LSR LASCT \ D2 loop below, so this setting determines how long the \ death animation lasts (it's 127 iterations of the main \ flight loop) ROR A \ The C flag is randomly set from the above call to Ze, AND #%10000111 \ so this sets A to a number between -7 and +7, which STA INWK+30 \ we store in byte #30 (the pitch counter) to give our \ ship a very gentle pitch with damping LDX #OIL \ Set X to #OIL, the ship type for a cargo canister LDA XX21-1+2*PLT \ Fetch the byte from location XX21 - 1 + 2 * PLT, which \ equates to XX21 + 7 (the high byte of the address of \ SHIP_PLATE), which seems a bit odd. It might make more \ sense to do LDA (XX21-2+2*PLT) as this would fetch the \ first byte of the alloy plate's blueprint (which \ determines what happens when alloys are destroyed), \ but there aren't any brackets, so instead this always \ returns &D0, which is never zero, so the following \ BEQ is never true. (If the brackets were there, then \ we could stop plates from spawning on death by setting \ byte #0 of the blueprint to 0... but then scooping \ plates wouldn't give us alloys, so who knows what this \ is all about?) BEQ D3 \ If A = 0, jump to D3 to skip the following instruction BCC D3 \ If the C flag is clear, which will be random following \ the above call to Ze, jump to D3 to skip the following \ instruction DEX \ Decrement X, which sets it to #PLT, the ship type for \ an alloy plate .D3 JSR fq1 \ Call fq1 with X set to #OIL or #PLT, which adds a new \ cargo canister or alloy plate to our local bubble of \ universe and points it away from us with double DELTA \ speed (i.e. 6, as DELTA was set to 3 by the call to \ RES2 above). INF is set to point to the new arrival's \ ship data block in K% JSR DORND \ Set A and X to random numbers and extract bit 7 from A AND #%10000000 LDY #31 \ Store this in byte #31 of the ship's data block, so it STA (INF),Y \ has a 50% chance of marking our new arrival as being \ killed (so it will explode) LDA FRIN+4 \ The call we made to RES2 before we entered the loop at BEQ D1 \ D1 will have reset all the ship slots at FRIN, so this \ checks to see if the fifth slot is empty, and if it \ is we loop back to D1 to add another canister, until \ we have added five of them JSR U% \ Clear the key logger, which also sets A = 0 STA DELTA \ Set our speed in DELTA to 3, so all the cargo \ canisters we just added drift away from us .D2 JSR M% \ Call the M% routine to do the main flight loop once, \ which will display our exploding canister scene and \ move everything about DEC LASCT \ Decrement the counter in LASCT, which we set above BNE D2 \ Loop back to call the main flight loop again, until we \ have called it 127 times LDX #31 \ Set the screen to show all 31 text rows, which shows JSR DET1 \ the dashboard, and fall through into DEATH2 to reset \ and restart the game JMP DEATH2 \ Jump to DEATH2 to reset and restart the game
Name: spasto [View individually] Type: Subroutine Category: Universe Summary: Contains the address Coriolis space station's ship blueprint
.spasto EQUW &8888 \ This variable is set by routine BEGIN to the address \ of the Coriolis space station's ship blueprint
Name: BEGIN [View individually] Type: Subroutine Category: Loader Summary: Initialise the configuration variables and start the game
.BEGIN \JSR BRKBK \ This instruction is commented out in the original \ source LDX #(CATF-COMC) \ We start by zeroing all the configuration variables \ between COMC and CATF, to set them to their default \ values, so set a counter in X for CATF - COMC bytes LDA #0 \ Set A = 0 so we can zero the variables .BEL1 STA COMC,X \ Zero the X-th configuration variable DEX \ Decrement the loop counter BPL BEL1 \ Loop back to BEL1 to zero the next byte, until we have \ zeroed them all LDA XX21+SST*2-2 \ Set spasto(1 0) to the Coriolis space station entry STA spasto \ from the ship blueprint lookup table at XX21 (so LDA XX21+SST*2-1 \ spasto(1 0) points to the Coriolis blueprint) STA spasto+1 \ Fall through into TT170 to start the game
Name: TT170 [View individually] Type: Subroutine Category: Start and end Summary: Main entry point for the Elite game code Deep dive: Program flow of the main game loop
This is the main entry point for the main game code. It is called after the various setup, decryption and checksum routines in S%, G% and BEGIN have successfully completed. It is also called following death, and when the game is quit by pressing ESCAPE when paused.
.TT170 LDX #&FF \ Set the stack pointer to &01FF, which is the standard TXS \ location for the 6502 stack, so this instruction \ effectively resets the stack. We need to do this \ because the loader code in elite-loader.asm pushes \ code onto the stack, and this effectively removes that \ code so we start afresh JSR RESET \ Call RESET to initialise most of the game variables \ Fall through into DEATH2 to start the game
Name: DEATH2 [View individually] Type: Subroutine Category: Start and end Summary: Reset most of the game and restart from the title screen
.DEATH2 LDX #&FF \ Set the stack pointer to &01FF, which is the standard TXS \ location for the 6502 stack, so this instruction \ effectively resets the stack JSR RES2 \ Reset a number of flight variables and workspaces \ and fall through into the entry code for the game \ to restart from the title screen
Name: BR1 [View individually] Type: Subroutine Category: Start and end Summary: Restart the game
Other entry points: QU5 Restart the game using the last saved commander without asking whether to load a new commander file
.BR1 JSR ZEKTRAN \ Reset the key logger buffer that gets returned from \ the I/O processor LDA #3 \ Move the text cursor to column 3 JSR DOXC LDX #3 \ Disable the ESCAPE key and clear memory if the BREAK JSR FX200 \ key is pressed (*FX 200,3) LDX #CYL \ Call the TITLE subroutine to show the rotating ship LDA #6 \ and load prompt. The arguments sent to TITLE are: JSR TITLE \ \ X = type of ship to show, #CYL is a Cobra Mk III \ \ A = text token to show below the rotating ship, 6 \ is "LOAD NEW {single cap}COMMANDER {all caps} \ (Y/N)?{sentence case}{cr}{cr}" \ \ The TITLE subroutine returns with the internal number \ of the key pressed in A (see p.142 of the Advanced \ User Guide for a list of internal key number) CMP #&60 \ Did we press TAB? If not, skip the following BNE P%+5 \ instruction .BRGO JMP DEMON \ We pressed TAB, so jump to DEMON to show the demo CMP #&44 \ Did we press "Y"? If not, jump to QU5, otherwise BNE QU5 \ continue on to load a new commander JSR DFAULT \ Call DFAULT to reset the current commander data block \ to the last saved commander JSR SVE \ Call SVE to load a new commander into the last saved \ commander data block .QU5 JSR DFAULT \ Call DFAULT to reset the current commander data block \ to the last saved commander JSR msblob \ Reset the dashboard's missile indicators so none of \ them are targeted LDA #7 \ Call the TITLE subroutine to show the rotating ship LDX #ASP \ and load prompt. The arguments sent to TITLE are: JSR TITLE \ \ X = type of ship to show, #ASP is an Asp Mk II \ \ A = text token to show below the rotating ship, 6 \ is "LOAD NEW {single cap}COMMANDER {all caps} \ (Y/N)?{sentence case}{cr}{cr}" JSR ping \ Set the target system coordinates (QQ9, QQ10) to the \ current system coordinates (QQ0, QQ1) we just loaded \ The rest of this routine is almost identical to the \ hyp routine in the cassette version JSR TT111 \ Select the system closest to galactic coordinates \ (QQ9, QQ10) JSR jmp \ Set the current system to the selected system LDX #5 \ We now want to copy the seeds for the selected system \ in QQ15 into QQ2, where we store the seeds for the \ current system, so set up a counter in X for copying \ 6 bytes (for three 16-bit seeds) \ The label below is called likeTT112 because this code \ is almost identical to the TT112 loop in the hyp \ routine in the cassette version .likeTT112 LDA QQ15,X \ Copy the X-th byte in QQ15 to the X-th byte in QQ2, STA QQ2,X DEX \ Decrement the counter BPL likeTT112 \ Loop back to likeTT112 if we still have more bytes to \ copy INX \ Set X = 0 (as we ended the above loop with X = &FF) STX EV \ Set EV, the extra vessels spawning counter, to 0, as \ we are entering a new system with no extra vessels \ spawned LDA QQ3 \ Set the current system's economy in QQ28 to the STA QQ28 \ selected system's economy from QQ3 LDA QQ5 \ Set the current system's tech level in tek to the STA tek \ selected system's economy from QQ5 LDA QQ4 \ Set the current system's government in gov to the STA gov \ selected system's government from QQ4
Name: BAY [View individually] Type: Subroutine Category: Status Summary: Go to the docking bay (i.e. show the Status Mode screen)
We end up here after the start-up process (load commander etc.), as well as after a successful save, an escape pod launch, a successful docking, the end of a cargo sell, and various errors (such as not having enough cash, entering too many items when buying, trying to fit an item to your ship when you already have it, running out of cargo space, and so on).
.BAY LDA #&FF \ Set QQ12 = &FF (the docked flag) to indicate that we STA QQ12 \ are docked LDA #f8 \ Jump into the main loop at FRCE, setting the key JMP FRCE \ that's "pressed" to red key f8 (so we show the Status \ Mode screen)
Name: DFAULT [View individually] Type: Subroutine Category: Start and end Summary: Reset the current commander data block to the last saved commander
.DFAULT LDX #NT%+8 \ The size of the last saved commander data block is NT% \ bytes, and it is preceded by the 8 bytes of the \ commander name (seven characters plus a carriage \ return). The commander data block at NAME is followed \ by the commander data block, so we need to copy the \ name and data from the "last saved" buffer at NA% to \ the current commander workspace at NAME. So we set up \ a counter in X for the NT% + 8 bytes that we want to \ copy .QUL1 LDA NA%-1,X \ Copy the X-th byte of NA%-1 to the X-th byte of STA NAME-1,X \ NAME-1 (the -1 is because X is counting down from \ NT% + 8 to 1) DEX \ Decrement the loop counter BNE QUL1 \ Loop back for the next byte of the commander data \ block STX QQ11 \ X is 0 by the end of the above loop, so this sets QQ11 \ to 0, which means we will be showing a view without a \ boxed title at the top (i.e. we're going to use the \ screen layout of a space view in the following) JSR CHECK \ Call the CHECK subroutine to calculate the checksum \ for the current commander block at NA%+8 and put it \ in A CMP CHK \ Test the calculated checksum against CHK IF _REMOVE_CHECKSUMS NOP \ If we have disabled checksums, then ignore the result NOP \ of the comparison and fall through into the next part ELSE BNE P%-6 \ If commander check is enabled and the calculated \ checksum does not match CHK, then loop back to repeat \ the check - in other words, we enter an infinite loop \ here, as the checksum routine will keep returning the \ same incorrect value ENDIF \JSR BELL \ This instruction is commented out in the original \ source. It would make a standard system beep EOR #&A9 \ X = checksum EOR &A9 TAX LDA COK \ Set A to the competition flags in COK CPX CHK2 \ If X = CHK2, then skip the next instruction BEQ tZ ORA #%10000000 \ Set bit 7 of A to indicate this commander file has \ been tampered with .tZ ORA #4 \ Set bit 2 of A to denote this is the 6502 second \ processor version (which is the same bit as for the \ disc version) STA COK \ Store the updated competition flags in COK RTS \ Retirn from the subroutine
Name: TITLE [View individually] Type: Subroutine Category: Start and end Summary: Display a title screen with a rotating ship and prompt
Display the title screen, with a rotating ship and a text token at the bottom of the screen. Arguments: A The number of the extended token to show below the rotating ship (see variable TKN1 for details of recursive tokens) X The type of the ship to show (see variable XX21 for a list of ship types)
.TITLE PHA \ Store the token number on the stack for later STX TYPE \ Store the ship type in location TYPE JSR RESET \ Reset our ship so we can use it for the rotating \ title ship JSR ZEKTRAN \ Reset the key logger buffer that gets returned from \ the I/O processor LDA #32 \ Send a #SETVDU19 32 command to the I/O processor to JSR DOVDU19 \ set the mode 1 palette to yellow (colour 1), white \ (colour 2) and cyan (colour 3) LDA #1 \ Clear the top part of the screen, draw a white border, JSR TT66 \ and set the current view type in QQ11 to 1 LDA #RED \ Send a #SETCOL RED command to the I/O processor to JSR DOCOL \ switch to colour 2, which is white in the title screen STZ QQ11 \ Set QQ11 to 0, so from here on we are using a space \ view LDA #96 \ Set nosev_z hi = 96 (96 is the value of unity in the STA INWK+14 \ rotation vector) \LSR A \ This instruction is commented out in the original \ source. It would halve the value of z_hi to 48, so the \ ship would start off closer to the viewer STA INWK+7 \ Set z_hi, the high byte of the ship's z-coordinate, \ to 96, which is the distance at which the rotating \ ship starts out before coming towards us LDX #127 STX INWK+29 \ Set roll counter = 127, so don't dampen the roll STX INWK+30 \ Set pitch counter = 127, so don't dampen the pitch INX \ Set QQ17 to 128 (so bit 7 is set) to switch to STX QQ17 \ Sentence Case, with the next letter printing in upper \ case LDA TYPE \ Set up a new ship, using the ship type in TYPE JSR NWSHP LDA #6 \ Move the text cursor to column 6 JSR DOXC LDA #30 \ Print recursive token 144 ("---- E L I T E ----") JSR plf \ followed by a newline LDA #10 \ Print a line feed to move the text cursor down a line JSR TT26 LDA #6 \ Move the text cursor to column 6 again JSR DOXC LDA PATG \ If PATG = 0, skip the following two lines, which BEQ awe \ print the author credits (PATG can be toggled by \ pausing the game and pressing "X") LDA #13 \ Print extended token 13 ("BY D.BRABEN & I.BELL") JSR DETOK .awe LDA brkd \ If brkd = 0, jump to BRBR2 to skip the following, as BEQ BRBR2 \ we do not have a system error message to display INC brkd \ Increment the brkd counter LDA #7 \ Move the text cursor to column 7 JSR DOXC LDA #10 \ Move the text cursor to row 10 JSR DOYC \ The following loop prints out the null-terminated \ message pointed to by (&FD &FE), which is the MOS \ error message pointer - so this prints the error \ message on the next line LDY #0 \ Set Y = 0 to act as a character counter JSR OSWRCH \ Print the character in A (which contains a line feed \ on the first loop iteration, and then any non-zero \ characters we fetch from the error message INY \ Increment the loop counter LDA (&FD),Y \ Fetch the Y-th byte of the block pointed to by \ (&FD &FE), so that's the Y-th character of the message \ pointed to by the MOS error message pointer BNE P%-6 \ If the fetched character is non-zero, loop back to the \ JSR OSWRCH above to print the it, and keep looping \ until we fetch a zero (which marks the end of the \ message) .BRBR2 JSR CLYNS \ Clear the bottom three text rows of the upper screen, \ and move the text cursor to column 1 on row 21, i.e. \ the start of the top row of the three bottom rows. \ It also returns with Y = 0 STY DELTA \ Set DELTA = 0 (i.e. ship speed = 0) STY JSTK \ Set KSTK = 0 (i.e. keyboard, not joystick) PLA \ Restore the recursive token number we stored on the \ stack at the start of this subroutine \JSR ex \ This instruction is commented out in the original \ source (it would print the recursive token in A) JSR DETOK \ Print the extended token in A LDA #7 \ Move the text cursor to column 7 JSR DOXC LDA #12 \ Print extended token 12 ("({single cap}C) ACORNSOFT JSR DETOK \ 1984") LDA #12 \ Set CNT2 = 12 as the outer loop counter for the loop STA CNT2 \ starting at TLL2 LDA #5 \ Set the main loop counter in MCNT to 5, to act as the STA MCNT \ inner loop counter for the loop starting at TLL2 .TLL2 LDA INWK+7 \ If z_hi (the ship's distance) is 1, jump to TL1 to CMP #1 \ skip the following decrement BEQ TL1 DEC INWK+7 \ Decrement the ship's distance, to bring the ship \ a bit closer to us .TL1 JSR MVEIT \ Move the ship in space according to the orientation \ vectors and the new value in z_hi LDX #128 \ Set z_lo = 128 (so the closest the ship gets to us is STX INWK+6 \ z_hi = 1, z_lo = 128, or 256 + 128 = 384 LDA MCNT \ This value will be zero on one out of every four AND #3 \ iterations, so for the other three, skip to nodesire BNE nodesire \ so we only scan for key presses once every four loops STX NEEDKEY \ Set NEEDKEY = 128, so the call to LL9 below draw the \ ship and scans for key presses (LL9 resets NEEDKEY to \ 0 so we have to reset NEEDKEY every four iterations \ round the inner loop) .nodesire STZ INWK \ Set x_lo = 0, so the ship remains in the screen centre STZ INWK+3 \ Set y_lo = 0, so the ship remains in the screen centre JSR LL9 \ Call LL9 to display the ship LDA KTRAN+12 \ Fetch the key press state for the joystick 1 fire \ button from the key logger buffer, which contains \ the value of the 6522 System VIA input register IRB \ (SHEILA &40) AND #%00010000 \ Bit 4 of IRB (PB4) is clear if joystick 1's fire \ button is pressed, otherwise it is set, so AND'ing \ the value of IRB with %10000 extracts this bit TAX \ Copy the joystick fire button state to X BEQ TL2 \ If the joystick fire button is pressed, jump to BL2 LDA KTRAN \ Fetch the internal key number of the current key \ press from the key logger buffer BNE TL3 \ If a key is being pressed, jump to TL3 DEC MCNT \ Decrement the inner loop counter BNE TLL2 \ Loop back to keep the ship rotating, until the inner \ loop counter is zero DEC CNT2 \ Decrement the outer loop counter in CNT2 BNE TLL2 \ Loop back to keep the ship rotating, until the outer \ loop counter is zero JMP DEMON \ Once we have iterated through CNT2 iterations of MCNT, \ jump to DEMON to start the demo .TL2 DEC JSTK \ Joystick fire button was pressed, so set JSTK to &FF \ (it was set to 0 above), to disable keyboard and \ enable joysticks .TL3 RTS \ Return from the subroutine
Name: CHECK [View individually] Type: Subroutine Category: Save and load Summary: Calculate the checksum for the last saved commander data block
The checksum for the last saved commander data block is saved as part of the commander file, in two places (CHK AND CHK2), to protect against file tampering. This routine calculates the checksum and returns it in A. This algorithm is also implemented in elite-checksum.py. Returns: A The checksum for the last saved commander data block
.CHECK LDX #NT%-2 \ Set X to the size of the commander data block, less \ 2 (as there are two checksum bytes) CLC \ Clear the C flag so we can do addition without the \ C flag affecting the result TXA \ Seed the checksum calculation by setting A to the \ size of the commander data block, less 2 \ We now loop through the commander data block, \ starting at the end and looping down to the start \ (so at the start of this loop, the X-th byte is the \ last byte of the commander data block, i.e. the save \ count) .QUL2 ADC NA%+7,X \ Add the X-1-th byte of the data block to A, plus the \ C flag EOR NA%+8,X \ EOR A with the X-th byte of the data block DEX \ Decrement the loop counter BNE QUL2 \ Loop back for the next byte in the calculation, until \ we have added byte #0 and EOR'd with byte #1 of the \ data block RTS \ Return from the subroutine
Name: TRNME [View individually] Type: Subroutine Category: Save and load Summary: Copy the last saved commander's name from INWK to NA%
.TRNME LDX #7 \ The commander's name can contain a maximum of 7 \ characters, and is terminated by a carriage return, \ so set up a counter in X to copy 8 characters .GTL1 LDA INWK+5,X \ Copy the X-th byte of INWK+5 to the X-th byte of NA% STA NA%,X DEX \ Decrement the loop counter BPL GTL1 \ Loop back until we have copied all 8 bytes \ Fall through into TR1 to copy the name back from NA% \ to INWK. This isn't necessary as the name is already \ there, but it does save one byte, as we don't need an \ RTS here
Name: TR1 [View individually] Type: Subroutine Category: Save and load Summary: Copy the last saved commander's name from NA% to INWK
.TR1 LDX #7 \ The commander's name can contain a maximum of 7 \ characters, and is terminated by a carriage return, \ so set up a counter in X to copy 8 characters .GTL2 LDA NA%,X \ Copy the X-th byte of NA% to the X-th byte of INWK+5 STA INWK+5,X DEX \ Decrement the loop counter BPL GTL2 \ Loop back until we have copied all 8 bytes RTS \ Return from the subroutine
Name: GTNMEW [View individually] Type: Subroutine Category: Save and load Summary: Fetch the name of a commander file to save or load
Returns: INWK The full filename, including drive and directory, in the form ":0.E.JAMESON", for example
.GTNMEW \LDY #8 \ These instructions are commented out in the original \JSR DELAY \ source .GTNME LDX #4 \ First we want to copy the drive and directory part of \ the commander file from S1% (which equals NA%-5), so \ set a counter in x for 5 bytes, as the string is of \ the form ":0.E." .GTL3 LDA NA%-5,X \ Copy the X-th byte from NA%-5 to INWK STA INWK,X DEX \ Decrement the loop counter BPL GTL3 \ Loop back until the whole drive and directory string \ has been copied to INWK to INWK+4 LDA #7 \ The call to MT26 below uses the OSWORD block at RLINE STA RLINE+2 \ to fetch the line, and RLINE+2 defines the maximum \ line length allowed, so this changes the maximum \ length to 7 (as that's the longest commander name \ allowed) LDA #8 \ Print extended token 8 ("{single cap}COMMANDER'S JSR DETOK \ NAME? ") JSR MT26 \ Call MT26 to fetch a line of text from the keyboard \ to INWK+5, with the text length in Y, so INWK now \ contains the full pathname of the file, as in \ ":0.E.JAMESON", for example LDA #9 \ Reset the maximum length in RLINE+2 to the original STA RLINE+2 \ value of 9 TYA \ Copy the length of the entered name into A BEQ TR1 \ If A = 0, no name was entered, so jump to TR1 to \ restore the original name from NA% to INWK+5 RTS \ Return from the subroutine
Name: MT26 [View individually] Type: Subroutine Category: Text Summary: Fetch a line of text from the keyboard
If ESCAPE is pressed or a blank name is entered, then an empty string is returned. Returns: Y The size of the entered text, or 0 if ESCAPE was pressed INWK+5 The entered text, terminated by a carriage return
.MT26 LDA #VIAE \ Send a #VIAE %10000001 command to the I/O processor to JSR OSWRCH \ clear 6522 System VIA interrupt enable register IER LDA #%10000001 \ (SHEILA &4E) bit 1 (i.e. enable the CA2 interrupt, \ which comes from the keyboard) JSR OSWRCH LDY #8 \ Wait for 8/50 of a second (0.16 seconds) JSR DELAY JSR FLKB \ Call FLKB to flush the keyboard buffer LDX #LO(RLINE) \ Set (Y X) to point to the RLINE parameter block LDY #HI(RLINE) LDA #0 \ Call OSWORD with A = 0 to read a line from the current JSR OSWORD \ input stream (i.e. the keyboard) BCC P%+4 \ The C flag will be set if we pressed ESCAPE when \ entering the name, otherwise it will be clear, so \ skip the next instruction is ESCAPE is not pressed LDY #0 \ ESCAPE was pressed, so set Y = 0 (as the OSWORD call \ returns the length of the entered string in Y) LDA #VIAE \ Send a #VIAE %00000001 command to the I/O processor to JSR OSWRCH \ set 6522 System VIA interrupt enable register IER LDA #%00000001 \ (SHEILA &4E) bit 1 (i.e. disable the CA2 interrupt, JSR OSWRCH \ which comes from the keyboard) JMP FEED \ Jump to FEED to print a newline, returning from the \ subroutine using a tail call
Name: RLINE [View individually] Type: Variable Category: Text Summary: The OSWORD configuration block used to fetch a line of text from the keyboard
.RLINE EQUW INWK+5 \ The address to store the input, so the text entered \ will be stored in INWK+5 as it is typed EQUB 9 \ Maximum line length = 9 EQUB '!' \ Allow ASCII characters from "!" through to "{" in {' \ the input
Name: ZERO [View individually] Type: Subroutine Category: Utility routines Summary: Reset the local bubble of universe and ship status
This resets the following workspaces to zero: * UP workspace variables from FRIN to de, which include the ship slots for the local bubble of universe, and various flight and ship status variables
.ZERO LDX #(de-FRIN) \ We're going to zero the UP workspace variables from \ FRIN to de, so set a counter in X for the correct \ number of bytes LDA #0 \ Set A = 0 so we can zero the variables .ZEL2 STA FRIN,X \ Zero the X-th byte of FRIN to de DEX \ Decrement the loop counter BPL ZEL2 \ Loop back to zero the next variable until we have done \ them all RTS \ Return from the subroutine
Name: ZEBC [View individually] Type: Subroutine Category: Utility routines Summary: Zero-fill pages &B and &C
.ZEBC LDX #&C \ Call ZES1 with X = &C to zero-fill page &C JSR ZES1 DEX \ Decrement X to &B \ Fall through into ZES1 to zero-fill page &B
Name: ZES1 [View individually] Type: Subroutine Category: Utility routines Summary: Zero-fill the page whose number is in X
Arguments: X The page we want to zero-fill
.ZES1 LDY #0 \ If we set Y = SC = 0 and fall through into ZES2 STY SC \ below, then we will zero-fill 255 bytes starting from \ SC - in other words, we will zero-fill the whole of \ page X
Name: ZES2 [View individually] Type: Subroutine Category: Utility routines Summary: Zero-fill a specific page
Zero-fill from address (X SC) + Y to (X SC) + &FF. Arguments: X The high byte (i.e. the page) of the starting point of the zero-fill Y The offset from (X SC) where we start zeroing, counting up to to &FF SC The low byte (i.e. the offset into the page) of the starting point of the zero-fill Returns: Z flag Z flag is set
.ZES2 LDA #0 \ Load A with the byte we want to fill the memory block \ with - i.e. zero STX SC+1 \ We want to zero-fill page X, so store this in the \ high byte of SC, so the 16-bit address in SC and \ SC+1 is now pointing to the SC-th byte of page X .ZEL1 STA (SC),Y \ Zero the Y-th byte of the block pointed to by SC, \ so that's effectively the Y-th byte before SC INY \ Increment the loop counter BNE ZEL1 \ Loop back to zero the next byte RTS \ Return from the subroutine
Name: CTLI [View individually] Type: Variable Category: Save and load Summary: The OS command string for cataloguing a disc
.CTLI EQUS ".0" \ The "0" part of the string is overwritten with the EQUB 13 \ actual drive number by the CATS routine
Name: DELI [View individually] Type: Variable Category: Save and load Summary: The OS command string for deleting a file
.DELI EQUS "DELETE:0.E.1234567" EQUB 13
Name: CATS [View individually] Type: Subroutine Category: Save and load Summary: Ask for a disc drive number and print a catalogue of that drive
This routine asks for a disc drive number, and if it is a valid number (0-3) it displays a catalogue of the disc in that drive. It also updates the OS command at CTLI so that when that command is run, it catalogues the correct drive. Returns: C flag Clear if a valid drive number was entered (0-3), set otherwise
.CATS JSR GTDRV \ Get an ASCII disc drive drive number from the keyboard \ in A, setting the C flag if an invalid drive number \ was entered BCS DELT-1 \ If the C flag is set, then an invalid drive number was \ entered, so return from the subroutine (as DELT-1 \ contains an RTS) STA CTLI+1 \ Store the drive number in the second byte of the \ command string at CTLI, so it overwrites the "0" in \ ".0" with the drive number to catalogue STA DTW7 \ Store the drive number in DTW7, so printing extended \ token 4 will show the correct drive number (as token 4 \ contains the {drive number} jump code, which calls \ MT16 to print the character in DTW7) LDA #4 \ Print extended token 4, which clears the screen and JSR DETOK \ prints the boxed-out title "DRIVE {drive number} \ CATALOGUE" LDA #DOCATF \ Send a #DOCATF 1 command to the I/O processor to set JSR OSWRCH \ the CATF flag to 1, so that the TT26 routine on the LDA #1 \ I/O processor prints out the disc catalogue correctly JSR OSWRCH STA XC \ Move the text cursor to column 1 LDX #LO(CTLI) \ Set (Y X) to point to the OS command at CTLI, which LDY #HI(CTLI) \ contains a dot and the drive number, which is the \ DFS command for cataloguing that drive (*. being short \ for *CAT) JSR SCLI2 \ Call SCLI2 to execute the OS command at (Y X), which \ catalogues the disc, setting the SVN flag while it's \ running to indicate disc access is in progress LDA #DOCATF \ Send a #DOCATF 0 command to the I/O processor to set JSR OSWRCH \ the CATF flag to 0, so that TT26 returns to normal LDA #0 \ printing JSR OSWRCH CLC \ Clear the C flag RTS \ Return from the subroutine
Name: DELT [View individually] Type: Subroutine Category: Save and load Summary: Catalogue a disc, ask for a filename to delete, and delete the file
This routine asks for a disc drive number, and if it is a valid number (0-3) it displays a catalogue of the disc in that drive. It then asks for a filename to delete, updates the OS command at DELI so that when that command is run, it it deletes the correct file, and then it does the deletion. Other entry points: DELT-1 \ Contains an RTS
.DELT JSR CATS \ Call CATS to ask for a drive number, catalogue that \ disc and update the catalogue command at CTLI BCS SVE \ If the C flag is set then an invalid drive number was \ entered as part of the catalogue process, so jump to \ SVE to display the disc access menu LDA CTLI+1 \ The call to CATS above put the drive number into STA DELI+7 \ CTLI+1, so copy the drive number into DELI+7 so that \ the drive number in the "DELETE:0.E.1234567" string \ gets updated (i.e. the number after the colon) LDA #9 \ Print extended token 9 ("{clear bottom of screen}FILE JSR DETOK \ TO DELETE?") JSR MT26 \ Call MT26 to fetch a line of text from the keyboard \ to INWK+5, with the text length in Y TYA \ If no text was entered (Y = 0) then jump to SVE to BEQ SVE \ display the disc access menu \ We now copy the entered filename from INWK to DELI, so \ that it overwrites the filename part of the string, \ i.e. the "E.1234567" part of "DELETE:0.E.1234567" LDX #9 \ Set up a counter in X to count from 9 to 1, so that we \ copy the string starting at INWK+4+1 (i.e. INWK+5) to \ DELI+8+1 (i.e. DELI+9 onwards, or "E.1234567") .DELL1 LDA INWK+4,X \ Copy the X-th byte of INWK+4 to the X-th byte of STA DELI+8,X \ DELI+8 DEX \ Decrement the loop counter BNE DELL1 \ Loop back to DELL1 to copy the next character until we \ have copied the whole filename LDX #LO(DELI) \ Set (Y X) to point to the OS command at DELI, which LDY #HI(DELI) \ contains the DFS command for deleting this file JSR SCLI2 \ Call SCLI2 to execute the OS command at (Y X), which \ deletes the file, setting the SVN flag while it's \ running to indicate disc access is in progress JMP SVE \ Jump to SVE to display the disc access menu and return \ from the subroutine using a tail call
Name: stack [View individually] Type: Subroutine Category: Save and load Summary: Temporary storage for the stack pointer when switching the BRKV handler between BRBR and MEBRK
.stack EQUB 0
Name: MEBRK [View individually] Type: Subroutine Category: Save and load Summary: The BRKV handler for disc access operations
This routine is used to display error messages from the disc filing system while disc access operations are being performed. When called, it makes a beep and prints the system error message in the block pointed to by (&FD &FE), which is where the disc filing system will put any disc errors (such as "File not found", "Disc error" and so on). It then waits for a key press and returns to the disc access menu. BRKV is set to this routine at the start of the SVE routine, just before the disc access menu is shown, and it reverts to BRBR at the end of the SVE routine after the disc access menu has been processed. In other words, BRBR is the standard BRKV handler for the game, and it's swapped out to MRBRK for disc access operations only. When it is the BRKV handler, the routine can be triggered using a BRK instruction. The main difference between this routine and the standard BRKV handler in BRBR is that this routine returns to the disc access menu rather than restarting the game, and it doesn't decrement the brkd counter.
.MEBRK LDX stack \ Set the stack pointer to the value that we stored in TXS \ location stack, so that's back to the value it had \ before we set BRKV to point to MEBRK in the SVE \ routine JSR backtonormal \ Disable the keyboard and set the SVN flag to 0 TAY \ The call to backtonormal sets A to 0, so this sets Y \ to 0, which use as a loop counter below LDA #7 \ Set A = 7 to generate a beep before we print the error \ message .MEBRKL JSR OSWRCH \ Print the character in A (which contains a line feed \ on the first loop iteration, and then any non-zero \ characters we fetch from the error message INY \ Increment the loop counter BEQ retry \ If A = 0 then we have reached the end of the error \ message, so jump to retry to wait for a key press and \ display the disc access menu (this BEQ is effectively \ a JMP, as we didn't take the BNE branch above) LDA (&FD),Y \ Fetch the Y-th byte of the block pointed to by \ (&FD &FE), so that's the Y-th character of the message \ pointed to by the MOS error message pointer BNE MEBRKL \ If the fetched character is non-zero, loop back to the \ JSR OSWRCH above to print the it, and keep looping \ until we fetch a zero (which marks the end of the \ message) BEQ retry \ Jump to retry to wait for a key press and display the \ disc access menu (this BEQ is effectively a JMP, as we \ didn't take the BNE branch above)
Name: CAT [View individually] Type: Subroutine Category: Save and load Summary: Catalogue a disc, wait for a key press and display the disc access menu
.CAT JSR CATS \ Call CATS to ask for a drive number, catalogue that \ disc and update the catalogue command at CTLI \ Fall through into retry to wait for a key press and \ display the disc access menu
Name: retry [View individually] Type: Subroutine Category: Save and load Summary: Scan the keyboard until a key is pressed and display the disc access menu
.retry JSR t \ Scan the keyboard until a key is pressed, returning \ the ASCII code in A and X \ Fall through into SVE to display the disc access menu
Name: SVE [View individually] Type: Subroutine Category: Save and load Summary: Display the disc access menu and process saving of commander files Deep dive: The competition code
Returns: C flag Set if we loaded a new file, clear otherwise
.SVE JSR ZEBC \ Call ZEBC to zero-fill pages &B and &C TSX \ Transfer the stack pointer to X and store it in stack, STX stack \ so we can restore it in the MRBRK routine LDA #LO(MEBRK) \ Set BRKV to point to the MEBRK routine, disabling SEI \ while we make the change and re-enabling them once we STA BRKV \ are done. MEBRK is the BRKV handler for disc access LDA #HI(MEBRK) \ operations, and replaces the standard BRKV handler in STA BRKV+1 \ BRBR while disc access operations are happening CLI LDA #1 \ Print extended token 1, the disc access menu, which JSR DETOK \ presents these options: \ \ 1. Load New Commander \ 2. Save Commander {commander name} \ 3. Catalogue \ 4. Delete A File \ 5. Exit JSR t \ Scan the keyboard until a key is pressed, returning \ the ASCII code in A and X CMP #'1' \ If A < ASCII "1", jump to SVEX to exit as the key BCC SVEX \ press doesn't match a menu option CMP #'4' \ If "4" was pressed, jump to DELT to process option 4 BEQ DELT \ (delete a file) BCS SVEX \ If A >= ASCII "4", jump to SVEX to exit as the key \ press is either option 5 (exit), or it doesn't match a \ menu option (as we already checked for "4" above) CMP #'2' \ If A >= ASCII "2" (i.e. save or catalogue), skip to BCS SV1 \ SV1 JSR GTNMEW \ If we get here then option 1 (load) was chosen, so \ call GTNMEW to fetch the name of the commander file \ to load (including drive number and directory) into \ INWK JSR LOD \ Call LOD to load the commander file JSR TRNME \ Transfer the commander filename from INWK to NA% SEC \ Set the C flag to indicate we loaded a new commander BCS SVEX+1 \ file, and return from the subroutine (as SVEX+1 \ contains an RTS) .SV1 BNE CAT \ We get here following the CMP #'2' above, so this \ jumps to CAT if option 2 was not chosen - in other \ words, if option 3 (catalogue) was chosen JSR GTNMEW \ If we get here then option 2 (save) was chosen, so \ call GTNMEW to fetch the name of the commander file \ to save (including drive number and directory) into \ INWK JSR TRNME \ Transfer the commander filename from INWK to NA% LSR SVC \ Halve the save count value in SVC LDA #3 \ Print extended token 3 ("COMPETITION NUMBER:") JSR DETOK LDX #NT% \ We now want to copy the current commander data block \ from location TP to the last saved commander block at \ NA%+8, so set a counter in X to copy the NT% bytes in \ the commander data block \ \ We also want to copy the data block to another \ location &0B00, which is normally used for the ship \ lines heap .SVL1 LDA TP,X \ Copy the X-th byte of TP to the X-th byte of &B00 STA &B00,X \ and NA%+8 STA NA%+8,X DEX \ Decrement the loop counter BPL SVL1 \ Loop back until we have copied all NT% bytes JSR CHECK \ Call CHECK to calculate the checksum for the last \ saved commander and return it in A STA CHK \ Store the checksum in CHK, which is at the end of the \ last saved commander block PHA \ Store the checksum on the stack ORA #%10000000 \ Set K = checksum with bit 7 set STA K EOR COK \ Set K+2 = K EOR COK (the competition flags) STA K+2 EOR CASH+2 \ Set K+1 = K+2 EOR CASH+2 (the third cash byte) STA K+1 EOR #&5A \ Set K+3 = K+1 EOR &5A EOR TALLY+1 (the high byte of EOR TALLY+1 \ the kill tally) STA K+3 CLC \ Clear the C flag so the call to BPRNT does not include \ a decimal point JSR BPRNT \ Print the competition number stored in K to K+3. The \ value of U might affect how this is printed, and as \ it's a temporary variable in zero page that isn't \ reset by ZERO, it might have any value, but as the \ competition code is a 10-digit number, this just means \ it may or may not have an extra space of padding JSR TT67 \ Print a newline PLA \ Restore the checksum from the stack STA &B00+NT% \ Store the checksum in the last byte of the save file \ at &0B00 (the equivalent of CHK in the last saved \ block) EOR #&A9 \ Store the checksum EOR &A9 in CHK2, the penultimate STA CHK2 \ byte of the last saved commander block STA &AFF+NT% \ Store the checksum EOR &A9 in the penultimate byte of \ the save file at &0B00 (the equivalent of CHK2 in the \ last saved block) LDY #&B \ Set up an OSFILE block at &0C00, containing: STY &C0B \ INY \ Start address for save = &00000B00 in &0C0A to &0C0D STY &C0F \ \ End address for save = &00000C00 in &0C0E to &0C11 \ \ Y is left containing &C which we use below LDA #0 \ Call QUS1 with A = 0, Y = &C to save the commander JSR QUS1 \ file with the filename we copied to INWK at the start \ of this routine IF _SNG45 JSR DFAULT \ Call DFAULT to reset the current commander data block \ to the last saved commander ENDIF .SVEX CLC \ Clear the C flag to indicate we didn't just load a new \ commander file JMP BRKBK \ Jump to BRKBK to set BRKV back to the standard BRKV \ handler for the game, and return from the subroutine \ using a tail call
Name: QUS1 [View individually] Type: Subroutine Category: Save and load Summary: Save or load the commander file
The filename should be stored at INWK, terminated with a carriage return (13). The routine asks for a drive number and updates the filename accordingly before performing the load or save. Arguments: A File operation to be performed. Can be one of the following: * 0 (save file) * &FF (load file) Returns: C flag Set if an invalid drive number was entered
.QUS1 PHA \ Store A on the stack so we can restore it after the \ call to GTDRV JSR GTDRV \ Get an ASCII disc drive drive number from the keyboard \ in A, setting the C flag if an invalid drive number \ was entered STA INWK+1 \ Store the ASCII drive number in INWK+1, which is the \ drive character of the filename string ":0.E." PLA \ Restore A from the stack BCS QUR \ If the C flag is set, then an invalid drive number was \ entered, so jump to QUR to return from the subroutine PHA \ Store A on the stack so we can restore it after the \ call to DODOSVN LDA #255 \ Set the SVN flag to 255 to indicate that disc access JSR DODOSVN \ is in progress PLA \ Restore A from the stack LDX #INWK \ Store a pointer to INWK at the start of the block at STX &0C00 \ &0C00, storing #INWK in the low byte because INWK is \ in zero page LDX #0 \ Set (Y X) = &0C00 LDY #&C JSR OSFILE \ Call OSFILE to do the file operation specified in \ &0C00 (i.e. save or load a file depending on the value \ of A) JSR CLDELAY \ Pause for 1280 empty loops LDA #0 \ Set the SVN flag to 0 indicate that disc access has JSR DODOSVN \ finished CLC \ Clear the C flag .QUR RTS \ Return from the subroutine
Name: GTDRV [View individually] Type: Subroutine Category: Save and load Summary: Get an ASCII disc drive drive number from the keyboard
Returns: A The ASCII value of the entered drive number ("0" to "3") C flag Clear if a valid drive number was entered (0-3), set otherwise
.GTDRV LDA #2 \ Print extended token 2 ("{cr}WHICH DRIVE?") JSR DETOK JSR t \ Scan the keyboard until a key is pressed, returning \ the ASCII code in A and X ORA #%00010000 \ Set bit 4 of A, perhaps to avoid printing any control \ characters in the next instruction JSR CHPR \ Print the character in A PHA \ Store A on the stack so we can retrieve it after the \ call to FEED JSR FEED \ Print a newline PLA \ Restore A from the stack CMP #'0' \ If A < ASCII "0", then it is not a valid drive number, BCC LOR \ so jump to LOR to set the C flag and return from the \ subroutine CMP #'4' \ If A >= ASCII "4", then it is not a valid drive \ number, and this CMP sets the C flag, otherwise it is \ a valid drive number in the range 0-3, so clear it RTS \ Return from the subroutine
Name: LOD [View individually] Type: Subroutine Category: Save and load Summary: Load a commander file
The filename should be stored at INWK, terminated with a carriage return (13). Other entry points: LOR Set the C flag and return from the subroutine
.LOD \LDX #LO(MINI) \ These instructions are commented out in the original \LDY #HI(MINI) \ source, but they would load a commander file called \JSR SCLI \ "E.MINING" and continue below, so presumably this is \JMP LOL1-2 \ code for loading a test commander file \LDX #2 \ These instructions are commented out in the original \JSR FX200 \ source, but they would enable the ESCAPE key and clear \ memory if the BREAK key is pressed (*FX 200,2) JSR ZEBC \ Call ZEBC to zero-fill pages &B and &C LDY #&B \ Set up an OSFILE block at &0C00, containing: STY &0C03 \ INC &0C0B \ Load address = &00000B00 in &0C02 to &0C05 \ \ Length of file = &00000100 in &0C0A to &0C0D LDA #&FF \ Call QUS1 with A = &FF, Y = &C to load the commander JSR QUS1 \ file at address &0B00 BCS LOR \ If the C flag is set then an invalid drive number was \ entered during the call to QUS1 and the file wasn't \ loaded, so jump to LOR to return from the subroutine LDA &B00 \ If the first byte of the loaded file has bit 7 set, BMI ELT2F \ jump to ELT2F, as this is an invalid commander file \ \ ELT2F contains a BRK instruction, which will force an \ interrupt to call the address in BRKV, which will \ print out the system error at ELT2F LDX #NT% \ We have successfully loaded the commander file at \ &0B00, so now we want to copy it to the last saved \ commander data block at NA%+8, so we set up a counter \ in X to copy NT% bytes .LOL1 LDA &B00,X \ Copy the X-th byte of &0B00 to the X-th byte of NA%+8 STA NA%+8,X DEX \ Decrement the loop counter BPL LOL1 \ Loop back until we have copied all NT% bytes .LOR SEC \ Set the C flag RTS \ Return from the subroutine .ELT2F BRK \ The error that is printed if we try to load an EQUS "IIllegal " \ invalid commander file with bit 7 of byte #0 set EQUS "ELITE II file" \ (the spelling mistake is in the original source) BRK \.MINI \ These instructions are commented out in the original \EQUS "L.E.MINING B00" \ source, and form part of the commented section above \EQUB 13
Name: FX200 [View individually] Type: Subroutine Category: Utility routines Summary: Set the behaviour of the ESCAPE and BREAK keys
This is the equivalent of a *FX 200 command, which controls the behaviour of the ESCAPE and BREAK keys. Arguments: X Controls the behaviour as follows: * 0 = Enable ESCAPE key Normal BREAK key action * 1 = Disable ESCAPE key Normal BREAK key action * 2 = Enable ESCAPE key Clear memory if the BREAK key is pressed * 3 = Disable ESCAPE key Clear memory if the BREAK key is pressed
.FX200 LDY #0 \ Call OSBYTE 200 with Y = 0, so the new value is set to LDA #200 \ X, and return from the subroutine using a tail call JMP OSBYTE
Name: backtonormal [View individually] Type: Subroutine Category: Utility routines Summary: Disable the keyboard, set the SVN flag to 0, and return with A = 0
.backtonormal LDA #VIAE \ Send a #VIAE %00000001 command to the I/O processor to JSR OSWRCH \ set 6522 System VIA interrupt enable register IER LDA #%00000001 \ (SHEILA &4E) bit 1 (i.e. disable the CA2 interrupt, JSR OSWRCH \ which comes from the keyboard) LDA #0 \ Set the SVN flag to 0 and return from the subroutine BEQ DODOSVN \ using a tail call (this BEQ is effectively a JMP as A \ is always zero)
Name: SCLI2 [View individually] Type: Subroutine Category: Utility routines Summary: Execute an OS command, setting the SVN flag while it's running
SVN is set to 255 before the command is run, to indicate that disc access is in progress, and is reset to 0 once it has finished. Arguments: (Y X) The address of a string containing the command to run, terminated by a carriage return (ASCII 13)
.SCLI2 LDA #255 \ Set the SVN flag to 255 JSR DODOSVN JSR SCLI \ Call OSCLI to execute the OS command at (Y X) LDA #0 \ Set A = 0 for the new value of the SVN flag \ Fall through into DODOSVN to set the SVN flag to 0
Name: DODOSVN [View individually] Type: Subroutine Category: Save and load Summary: Set the SVN ("save in progress") flag by sending a #DOsvn command to the I/O processor
Arguments: A The new value of SVN
.DODOSVN PHA \ Store A and Y on the stack PHY LDA #DOsvn \ Send the first part of a #DOsvn command to the I/O JSR OSWRCH \ processor PLY \ Retrieve the values of A and Y from the stack PLA JSR OSWRCH \ Send the new value of SVN to the I/O processor, so \ we've now sent a #DOsvn command \ Fall through into CLDELAY to pause for 1280 empty \ loops
Name: CLDELAY [View individually] Type: Subroutine Category: Utility routines Summary: Delay by iterating through 5 * 256 (1280) empty loops
.CLDELAY PHX \ Store A, X and Y on the stack PHY PHA LDY #5 \ We are going to loop for 5 * 256 empty loops, so set a \ counter in Y for the outer loop LDX #0 \ And set a counter in X for the inner loop .CLDEL1 DEX \ Decrement the inner loop counter BNE CLDEL1 \ Loop back to CLDEL1 until the inner loop counter has \ rolled around to 0 again DEY \ Decrement the outer loop counter BNE CLDEL1 \ Loop back to CLDEL1 until the outer loop counter has \ reached 0 PLA \ Retrieve A, X and Y from the stack PLY PLX RTS \ Return from the subroutine
Name: ZEKTRAN [View individually] Type: Subroutine Category: Keyboard Summary: Reset the key logger buffer at KTRAN
.ZEKTRAN LDX #11 \ We use the first 12 bytes of the key logger buffer at \ KTRAN, so set a loop counter accordingly LDA #0 \ We want to zero the key logger buffer, so set A % 0 .ZEKLOOP STA KTRAN,X \ Reset the X-th byte of the key logger buffer to 0 DEX \ Decrement the loop counter BPL ZEKLOOP \ Loop back until we have zeroed bytes #11 through #0 RTS \ Return from the subroutine RTS \ This instruction has no effect
Name: SPS1 [View individually] Type: Subroutine Category: Maths (Geometry) Summary: Calculate the vector to the planet and store it in XX15
Other entry points: SPS1+1 A BRK instruction
.SPS1 LDX #0 \ Copy the two high bytes of the planet's x-coordinate JSR SPS3 \ into K3(2 1 0), separating out the sign bit into K3+2 LDX #3 \ Copy the two high bytes of the planet's y-coordinate JSR SPS3 \ into K3(5 4 3), separating out the sign bit into K3+5 LDX #6 \ Copy the two high bytes of the planet's z-coordinate JSR SPS3 \ into K3(8 7 6), separating out the sign bit into K3+8 \ Fall through into TAS2 to build XX15 from K3
Name: TAS2 [View individually] Type: Subroutine Category: Maths (Geometry) Summary: Normalise the three-coordinate vector in K3
Normalise the vector in K3, which has 16-bit values and separate sign bits, and store the normalised version in XX15 as a signed 8-bit vector. A normalised vector (also known as a unit vector) has length 1, so this routine takes an existing vector in K3 and scales it so the length of the new vector is 1. This is used in two places: when drawing the compass, and when applying AI tactics to ships. We do this in two stages. This stage shifts the 16-bit vector coordinates in K3 to the left as far as they will go without losing any bits off the end, so we can then take the high bytes and use them as the most accurate 8-bit vector to normalise. Then the next stage (in routine NORM) does the normalisation. Arguments: K3(2 1 0) The 16-bit x-coordinate as (x_sign x_hi x_lo), where x_sign is just bit 7 K3(5 4 3) The 16-bit y-coordinate as (y_sign y_hi y_lo), where y_sign is just bit 7 K3(8 7 6) The 16-bit z-coordinate as (z_sign z_hi z_lo), where z_sign is just bit 7 Returns: XX15 The normalised vector, with: * The x-coordinate in XX15 * The y-coordinate in XX15+1 * The z-coordinate in XX15+2 Other entry points: TA2 Calculate the length of the vector in XX15 (ignoring the low coordinates), returning it in Q
.TAS2 LDA K3 \ OR the three low bytes and 1 to get a byte that has ORA K3+3 \ a 1 wherever any of the three low bytes has a 1 ORA K3+6 \ (as well as always having bit 0 set), and store in ORA #1 \ K3+9 STA K3+9 LDA K3+1 \ OR the three high bytes to get a byte in A that has a ORA K3+4 \ 1 wherever any of the three high bytes has a 1 ORA K3+7 \ (A K3+9) now has a 1 wherever any of the 16-bit \ values in K3 has a 1 .TAL2 ASL K3+9 \ Shift (A K3+9) to the left, so bit 7 of the high byte ROL A \ goes into the C flag BCS TA2 \ If the left shift pushed a 1 out of the end, then we \ know that at least one of the coordinates has a 1 in \ this position, so jump to TA2 as we can't shift the \ values in K3 any further to the left ASL K3 \ Shift K3(1 0), the x-coordinate, to the left ROL K3+1 ASL K3+3 \ Shift K3(4 3), the y-coordinate, to the left ROL K3+4 ASL K3+6 \ Shift K3(6 7), the z-coordinate, to the left ROL K3+7 BCC TAL2 \ Jump back to TAL2 to do another shift left (this BCC \ is effectively a JMP as we know bit 7 of K3+7 is not a \ 1, as otherwise bit 7 of A would have been a 1 and we \ would have taken the BCS above) .TA2 LDA K3+1 \ Fetch the high byte of the x-coordinate from our left- LSR A \ shifted K3, shift it right to clear bit 7, stick the ORA K3+2 \ sign bit in there from the x_sign part of K3, and STA XX15 \ store the resulting signed 8-bit x-coordinate in XX15 LDA K3+4 \ Fetch the high byte of the y-coordinate from our left- LSR A \ shifted K3, shift it right to clear bit 7, stick the ORA K3+5 \ sign bit in there from the y_sign part of K3, and STA XX15+1 \ store the resulting signed 8-bit y-coordinate in \ XX15+1 LDA K3+7 \ Fetch the high byte of the z-coordinate from our left- LSR A \ shifted K3, shift it right to clear bit 7, stick the ORA K3+8 \ sign bit in there from the z_sign part of K3, and STA XX15+2 \ store the resulting signed 8-bit z-coordinate in \ XX15+2 \ Now we have a signed 8-bit version of the vector K3 in \ XX15, so fall through into NORM to normalise it
Name: NORM [View individually] Type: Subroutine Category: Maths (Geometry) Summary: Normalise the three-coordinate vector in XX15
We do this by dividing each of the three coordinates by the length of the vector, which we can calculate using Pythagoras. Once normalised, 96 (&E0) is used to represent a value of 1, and 96 with bit 7 set (&E0) is used to represent -1. This enables us to represent fractional values of less than 1 using integers. Arguments: XX15 The vector to normalise, with: * The x-coordinate in XX15 * The y-coordinate in XX15+1 * The z-coordinate in XX15+2 Returns: XX15 The normalised vector Q The length of the original XX15 vector Other entry points: NO1 Contains an RTS
.NORM LDA XX15 \ Fetch the x-coordinate into A JSR SQUA \ Set (A P) = A * A = x^2 STA R \ Set (R Q) = (A P) = x^2 LDA P STA Q LDA XX15+1 \ Fetch the y-coordinate into A JSR SQUA \ Set (A P) = A * A = y^2 STA T \ Set (T P) = (A P) = y^2 LDA P \ Set (R Q) = (R Q) + (T P) = x^2 + y^2 ADC Q \ STA Q \ First, doing the low bytes, Q = Q + P LDA T \ And then the high bytes, R = R + T ADC R STA R LDA XX15+2 \ Fetch the z-coordinate into A JSR SQUA \ Set (A P) = A * A = z^2 STA T \ Set (T P) = (A P) = z^2 LDA P \ Set (R Q) = (R Q) + (T P) = x^2 + y^2 + z^2 ADC Q \ STA Q \ First, doing the low bytes, Q = Q + P LDA T \ And then the high bytes, R = R + T ADC R STA R JSR LL5 \ We now have the following: \ \ (R Q) = x^2 + y^2 + z^2 \ \ so we can call LL5 to use Pythagoras to get: \ \ Q = SQRT(R Q) \ = SQRT(x^2 + y^2 + z^2) \ \ So Q now contains the length of the vector (x, y, z), \ and we can normalise the vector by dividing each of \ the coordinates by this value, which we do by calling \ routine TIS2. TIS2 returns the divided figure, using \ 96 to represent 1 and 96 with bit 7 set for -1 LDA XX15 \ Call TIS2 to divide the x-coordinate in XX15 by Q, JSR TIS2 \ with 1 being represented by 96 STA XX15 LDA XX15+1 \ Call TIS2 to divide the y-coordinate in XX15+1 by Q, JSR TIS2 \ with 1 being represented by 96 STA XX15+1 LDA XX15+2 \ Call TIS2 to divide the z-coordinate in XX15+2 by Q, JSR TIS2 \ with 1 being represented by 96 STA XX15+2 .NO1 RTS \ Return from the subroutine
Name: RDKEY [View individually] Type: Subroutine Category: Keyboard Summary: Scan the keyboard for key presses by sending an OSWORD 240 command to the I/O processor
This routine sends an OSWORD 240 command to the I/O processor to ask it to scan the keyboard, starting with internal key number 16 ("Q") and working through the set of internal key numbers (see p.142 of the Advanced User Guide for a list of internal key numbers). The results are copied from the I/O processor into the key logger buffer at KTRAN. This routine is effectively the same as OSBYTE 122, though the OSBYTE call preserves A, unlike this routine. Returns: X If a key is being pressed, X contains the internal key number, otherwise it contains 0 A Contains the same as X
.RDKEY LDA #240 \ Set A in preparation for sending an OSWORD 240 command LDY #HI(buf) \ Set (Y X) to point to the parameter block at buf LDX #LO(buf) JSR OSWORD \ Send an OSWORD 240 command to the I/O processor to \ scan the keyboard and joysticks, and populate the key \ logger buffer in KTRAN, which is the part of the buf \ buffer just after the two OSWORD size bytes LDX KTRAN \ Set X to the first byte of the updated KTRAN, which \ contains the internal key number of the key being \ pressed, or 0 if there is no keypress TXA \ Copy X into A RTS \ Return from the subroutine
Name: WARP [View individually] Type: Subroutine Category: Flight Summary: Perform an in-system jump
This is called when we press "J" during flight. The following checks are performed: * Make sure we don't have any ships or space stations in the vicinity * Make sure we are not in witchspace * If we are facing the planet, make sure we aren't too close * If we are facing the sun, make sure we aren't too close If the above checks are passed, then we perform an in-system jump by moving the sun and planet in the opposite direction to travel, so we appear to jump in space. This means that any asteroids, cargo canisters or escape pods get dragged along for the ride.
.WARP LDX JUNK \ Set X to the total number of junk items in the \ vicinity (e.g. asteroids, escape pods, cargo \ canisters, shuttles, transportes and so pn) LDA FRIN+2,X \ If the slot at FRIN+2+X is non-zero, then we have \ something else in the vicinity besides asteroids, \ escape pods and cargo canisters, so to check whether \ we can jump, we first grab the slot contents into A ORA SSPR \ If there is a space station nearby, then SSPR will \ be non-zero, so OR'ing with SSPR will produce a \ a non-zero result if either A or SSPR are non-zero ORA MJ \ If we are in witchspace, then MJ will be non-zero, so \ OR'ing with MJ will produce a non-zero result if \ either A or SSPR or MJ are non-zero BNE WA1 \ A is non-zero if we have either a ship or a space \ station in the vicinity, or we are in witchspace, in \ which case jump to WA1 to make a low beep to show that \ we can't do an in-system jump LDY K%+8 \ Otherwise we can do an in-system jump, so now we fetch \ the byte at K%+8, which contains the z_sign for the \ first ship slot, i.e. the distance of the planet BMI WA3 \ If the planet's z_sign is negative, then the planet \ is behind us, so jump to WA3 to skip the following TAY \ Set A = Y = 0 (as we didn't BNE above) so the call \ to MAS2 measures the distance to the planet JSR MAS2 \ Call MAS2 to set A to the largest distance to the \ planet in any of the three axes (we could also call \ routine m to do the same thing, as A = 0) \ The following two instructions appear in the BASIC \ source file (ELITEC), but in the text source file \ (ELITEC.TXT) they are replaced by: \ \ LSR A \ BEQ WA1 \ \ which does the same thing, but saves one byte of \ memory (as LSR A is a one-byte opcode, while CMP #2 \ takes up two bytes) CMP #2 \ If A < 2 then jump to WA1 to abort the in-system jump BCC WA1 \ with a low beep, as we are facing the planet and are \ too close to jump in that direction .WA3 LDY K%+NI%+8 \ Fetch the z_sign (byte #8) of the second ship in the \ ship data workspace at K%, which is reserved for the \ sun or the space station (in this case it's the \ former, as we already confirmed there isn't a space \ station in the vicinity) BMI WA2 \ If the sun's z_sign is negative, then the sun is \ behind us, so jump to WA2 to skip the following LDY #NI% \ Set Y to point to the offset of the ship data block \ for the sun, which is NI% (as each block is NI% bytes \ long, and the sun is the second block) JSR m \ Call m to set A to the largest distance to the sun \ in any of the three axes \ The following two instructions appear in the BASIC \ source file (ELITEC), but in the text source file \ (ELITEC.TXT) they are replaced by: \ \ LSR A \ BEQ WA1 \ \ which does the same thing, but saves one byte of \ memory (as LSR A is a one-byte opcode, while CMP #2 \ takes up two bytes) CMP #2 \ If A < 2 then jump to WA1 to abort the in-system jump BCC WA1 \ with a low beep, as we are facing the sun and are too \ close to jump in that direction .WA2 \ If we get here, then we can do an in-system jump, as \ we don't have any ships or space stations in the \ vicinity, we are not in witchspace, and if we are \ facing the planet or the sun, we aren't too close to \ jump towards it \ \ We do an in-system jump by moving the sun and planet, \ rather than moving our own local bubble (this is why \ in-system jumps drag asteroids, cargo canisters and \ escape pods along for the ride). Specifically, we move \ them in the z-axis by a fixed amount in the opposite \ direction to travel, thus performing a jump towards \ our destination LDA #&81 \ Set R = R = P = &81 STA S STA R STA P LDA K%+8 \ Set A = z_sign for the planet JSR ADD \ Set (A X) = (A P) + (S R) \ = (z_sign &81) + &8181 \ = (z_sign &81) - &0181 \ \ This moves the planet against the direction of travel \ by reducing z_sign by 1, as the above maths is: \ \ z_sign 00000000 \ + 00000000 10000001 \ - 00000001 10000001 \ \ or: \ \ z_sign 00000000 \ + 00000000 00000000 \ - 00000001 00000000 \ \ i.e. the high byte is z_sign - 1, making sure the sign \ is preserved STA K%+8 \ Set the planet's z_sign to the high byte of the result LDA K%+NI%+8 \ Set A = z_sign for the sun JSR ADD \ Set (A X) = (A P) + (S R) \ = (z_sign &81) + &8181 \ = (z_sign &81) - &0181 \ \ which moves the sun against the direction of travel \ by reducing z_sign by 1 STA K%+NI%+8 \ Set the planet's z_sign to the high byte of the result LDA #1 \ These instructions have no effect, as the call to STA QQ11 \ LOOK1 below starts by setting QQ11 to 0; instead they \ just set the current view type in QQ11 to 1 for the \ duration of the next three instructions STA MCNT \ Set the main loop counter to 1, so the next iteration \ through the main loop will potentially spawn ships \ (see part 2 of the main game loop at me3) LSR A \ Set EV, the extra vessels spawning counter, to 0 STA EV \ (the LSR produces a 0 as A was previously 1) LDX VIEW \ Set X to the current view (front, rear, left or right) JMP LOOK1 \ and jump to LOOK1 to initialise that view, returning \ from the subroutine using a tail call .WA1 LDA #40 \ If we get here then we can't do an in-system jump, so BNE NOISE \ call the NOISE routine with A = 40 to make a long, low \ beep and return from the subroutine using a tail call \ (the BNE is effectively a JMP as A is never zero)
Name: ECMOF [View individually] Type: Subroutine Category: Sound Summary: Switch off the E.C.M.
Switch the E.C.M. off, turn off the dashboard bulb and make the sound of the E.C.M. switching off).
.ECMOF LDA #0 \ Set ECMA and ECMB to 0 to indicate that no E.C.M. is STA ECMA \ currently running STA ECMP JSR ECBLB \ Update the E.C.M. indicator bulb on the dashboard LDA #72 \ Call the NOISE routine with A = 72 to make the sound BNE NOISE \ of the E.C.M. being turned off and return from the \ subroutine using a tail call (this BNE is effectively \ a JMP as A will never be zero)
Name: EXNO3 [View individually] Type: Subroutine Category: Sound Summary: Make an explosion sound
Make the sound of death in the cold, hard vacuum of space. Apparently, in Elite space, everyone can hear you scream. This routine also makes the sound of a destroyed cargo canister if we don't get scooping right, the sound of us colliding with another ship, and the sound of us being hit with depleted shields. It is not a good sound to hear.
.EXNO3 LDA #16 \ Call the NOISE routine with A = 16 to make the first JSR NOISE \ death sound LDA #24 \ Call the NOISE routine with A = 24 to make the second BNE NOISE \ death sound and return from the subroutine using a \ tail call (this BNE is effectively a JMP as A will \ never be zero)
Name: BEEP [View individually] Type: Subroutine Category: Sound Summary: Make a short, high beep
.BEEP LDA #32 \ Call NOISE with A = 32 to make a short, high beep, BNE NOISE \ returning from the subroutine using a tail call (this \ BNE is effectively a JMP as A will never be zero)
Name: SFRMIS [View individually] Type: Subroutine Category: Tactics Summary: Add an enemy missile to our local bubble of universe
An enemy has fired a missile, so add the missile to our universe if there is room, and if there is, make the appropriate warnings and noises.
.SFRMIS LDX #MSL \ Set X to the ship type of a missile, and call SFS1-2 JSR SFS1-2 \ to add the missile to our universe with an AI flag \ of %11111110 (AI enabled, hostile, no E.C.M.) BCC KYTB \ The C flag will be set if the call to SFS1-2 was a \ success, so if it's clear, jump to KYTB to return from \ the subroutine (as KYTB contains an RTS) LDA #120 \ Print recursive token 120 ("INCOMING MISSILE") as an JSR MESS \ in-flight message LDA #48 \ Call the NOISE routine with A = 48 to make the sound BNE NOISE \ of the missile being launched and return from the \ subroutine using a tail call (this BNE is effectively \ a JMP as A will never be zero)
Name: EXNO2 [View individually] Type: Subroutine Category: Sound Summary: Process us making a kill
We have killed a ship, so increase the kill tally, displaying an iconic message of encouragement if the kill total is a multiple of 256, and then make a nearby explosion sound. Other entry points: EXNO-2 Set X = 7 and fall through into EXNO to make the sound of a ship exploding
.EXNO2 INC TALLY \ Increment the low byte of the kill count in TALLY BNE EXNO-2 \ If there is no carry, jump to the LDX #7 below (at \ EXNO-2) INC TALLY+1 \ Increment the high byte of the kill count in TALLY LDA #101 \ The kill total is a multiple of 256, so it's time JSR MESS \ for a pat on the back, so print recursive token 101 \ ("RIGHT ON COMMANDER!") as an in-flight message LDX #7 \ Set X = 7 and fall through into EXNO to make the \ sound of a ship exploding
Name: EXNO [View individually] Type: Subroutine Category: Sound Summary: Make the sound of a laser strike or ship explosion
Make the two-part explosion sound of us making a laser strike, or of another ship exploding. The volume of the first explosion is affected by the distance of the ship being hit, with more distant ships being quieter. The value in X also affects the volume of the first explosion, with a higher X giving a quieter sound (so X can be used to differentiate a laser strike from an explosion). Arguments: X The larger the value of X, the fainter the explosion. Allowed values are: * 7 = explosion is louder (i.e. the ship has just exploded) * 15 = explosion is quieter (i.e. this is just a laser strike)
.EXNO STX T \ Store the distance in T LDA #24 \ Set A = 24 to denote the sound of us making a hit or JSR NOS1 \ kill (part 1 of the explosion), and call NOS1 to set \ up the sound block in XX16 LDA INWK+8 \ Fetch z_sign, the distance of the ship being hit in ASL A \ terms of the z-axis (in and out of the screen), and \ shift it left by 1 to get rid of the sign bit BEQ P%+5 \ If the result is 0, skip the next two instructions \ so that we load A with z_hi below LDA #0 \ Set A = 0 EQUB &2C \ Skip the next instruction by turning it into \ &2C &A5 &4C, or BIT &4CA5, which does nothing apart \ from affect the flags \ So, by this point, if any of bits 0-6 of z_sign are \ non-zero, which means the ship is a long way away, \ then A will be set to 0 rather than z_hi, and the \ SOUND amplitude below will be -15 (%11110001), or \ full volume... which seems a little odd LDA INWK+7 \ Fetch z_hi, the distance of the ship being hit in LSR A \ terms of the z-axis (in and out of the screen), and LSR A \ divide by 4. If z_hi has either bit 6 or 7 set then \ that ship is too far away to be shown on the scanner \ (as per the SCAN routine), so we know the maximum \ z_hi at this point is %00111111, and shifting z_hi \ to the right twice gives us a maximum value of \ %00001111 AND T \ This reduces A to a maximum of X; X can be either \ 7 = %0111 or 15 = %1111, so AND'ing with 15 will \ not affect A, while AND'ing with 7 will clear bit \ 3, reducing the maximum value in A to 7 ORA #%11110001 \ The SOUND statement's amplitude ranges from 0 (for no \ sound) to -15 (full volume), so we can set bits 0 and \ 4-7 in A, and keep bits 1-3 from the above to get \ a value between -15 (%11110001) and -1 (%11111111), \ with lower values of z_hi and argument X leading \ to a more negative, or quieter number (so the closer \ the ship, i.e. the smaller the value of X, the louder \ the sound) STA XX16+2 \ The amplitude byte of the sound block in XX16 is in \ byte #3 (where it's the low byte of the amplitude), so \ this sets the amplitude to the value in A JSR NO3 \ Make the sound from our updated sound block in XX16 LDA #16 \ Set A = 16 to denote we have made a hit or kill \ (part 2 of the explosion), and fall through into NOISE \ to make the sound
Name: NOISE [View individually] Type: Subroutine Category: Sound Summary: Make the sound whose number is in A
Arguments: A The number of the sound to be made. See the documentation for variable SFX for a list of sound numbers
.NOISE JSR NOS1 \ Set up the sound block in XX16 for the sound in A and \ fall through into NO3 to make the sound
Name: NO3 [View individually] Type: Subroutine Category: Sound Summary: Make a sound from a prepared sound block
Make a sound from a prepared sound block in XX16 (if sound is enabled). See routine NOS1 for details of preparing the XX16 sound block.
.NO3 LDX DNOIZ \ Set X to the DNOIZ configuration setting BNE KYTB \ If DNOIZ is non-zero, then sound is disabled, so \ return from the subroutine (as KYTB contains an RTS) LDX #LO(XX16) \ Otherwise set (Y X) to point to the sound block in LDY #HI(XX16) \ XX16 LDA #7 \ Call OSWORD 7 to makes the sound, as described in the JMP OSWORD \ documentation for variable SFX, and return from the \ subroutine using a tail call
Name: NOS1 [View individually] Type: Subroutine Category: Sound Summary: Prepare a sound block
Copy four sound bytes from SFX into XX16, interspersing them with null bytes, with Y indicating the sound number to copy (from the values in the sound table at SFX). So, for example, if we call this routine with A = 40 (long, low beep), the following bytes will be set in XX16 to XX16+7: &13 &00 &F4 &00 &0C &00 &08 &00 This block will be passed to OSWORD 7 to make the sound, which expects the four sound attributes as 16-bit big-endian values - in other words, with the low byte first. So the above block would pass the values &0013, &00F4, &000C and &0008 to the SOUND statement when used with OSWORD 7, or: SOUND &13, &F4, &0C, &08 as the high bytes are always zero. Arguments: A The sound number to copy from SFX to XX16, which is always a multiple of 8
.NOS1 LSR A \ Divide A by 2, and also clear the C flag, as bit 0 of \ A is always zero (as A is a multiple of 8) ADC #3 \ Set Y = A + 3, so Y now points to the last byte of TAY \ four within the block of four-byte values LDX #7 \ We want to copy four bytes, spread out into an 8-byte \ block, so set a counter in Y to cover 8 bytes .NOL1 LDA #0 \ Set the X-th byte of XX16 to 0 STA XX16,X DEX \ Decrement the destination byte pointer LDA SFX,Y \ Set the X-th byte of XX16 to the value from SFX+Y STA XX16,X DEY \ Decrement the source byte pointer again DEX \ Decrement the destination byte pointer again BPL NOL1 \ Loop back for the next source byte \ Fall through into KYTB to return from the subroutine, \ as the first byte of KYTB is an RTS
Name: KYTB [View individually] Type: Variable Category: Keyboard Summary: Lookup table for in-flight keyboard controls Deep dive: The key logger
Keyboard table for in-flight controls. This table contains the internal key codes for the flight keys (see p.142 of the Advanced User Guide for a list of internal key numbers). The pitch, roll, speed and laser keys (i.e. the seven primary flight control keys) have bit 7 set, so they have 128 added to their internal values. This doesn't appear to be used anywhere. Note that KYTB actually points to the byte before the start of the table, so the offset of the first key value is 1 (i.e. KYTB+1), not 0. Other entry points: KYTB Contains an RTS
.KYTB RTS \ Return from the subroutine (used as an entry point and \ a fall-through from above) \ These are the primary flight controls (pitch, roll, \ speed and lasers): EQUB &68 + 128 \ ? KYTB+1 Slow down EQUB &62 + 128 \ SPACE KYTB+2 Speed up EQUB &66 + 128 \ < KYTB+3 Roll left EQUB &67 + 128 \ > KYTB+4 Roll right EQUB &42 + 128 \ X KYTB+5 Pitch up EQUB &51 + 128 \ S KYTB+6 Pitch down EQUB &41 + 128 \ A KYTB+7 Fire lasers \ These are the secondary flight controls: EQUB &60 \ TAB KYTB+8 Energy bomb EQUB &70 \ ESCAPE KYTB+9 Launch escape pod EQUB &23 \ T KYTB+10 Arm missile EQUB &35 \ U KYTB+11 Unarm missile EQUB &65 \ M KYTB+12 Fire missile EQUB &22 \ E KYTB+13 E.C.M. EQUB &45 \ J KYTB+14 In-system jump EQUB &52 \ C KYTB+15 Docking computer EQUB &37 \ P KYTB+16 Cancel docking computer
Name: CTRL [View individually] Type: Subroutine Category: Keyboard Summary: Scan the keyboard to see if CTRL is currently pressed
Returns: X X = %10000001 (i.e. 129 or -127) if CTRL is being pressed X = 1 if CTRL is not being pressed A Contains the same as X
.CTRL LDX #1 \ Set X to the internal key number for CTRL and fall \ through to DSK4 to scan the keyboard
Name: DKS4 [View individually] Type: Subroutine Category: Keyboard Summary: Scan for a particular key press by sending a #DODKS4 command to the I/O processor
This routine sends a #DODKS4 command to the I/O processor to ask it to scan the keyboard, to see if the key specified in X is currently being pressed. Arguments: X The internal number of the key to check Returns: A If the key is being pressed, A contains the original key number in X but with bit 7 set (i.e. key number + 128). If the key is not being pressed, A contains the unchanged key number
.DKS4 STX DKS4pars+2 \ Store the key number in byte #2 of the parameter block \ below LDX #LO(DKS4pars) \ Set (Y X) to point to the parameter block below LDY #HI(DKS4pars) LDA #DODKS4 \ Send a #DODKS4 command to the I/O processor to check JSR OSWORD \ whether the key in byte #2 of the parameter block is \ being pressed LDA DKS4pars+2 \ Fetch the result from byte#2 of the parameter block, \ which will have bit 7 set if the key is being pressed RTS \ Return from the subroutine .DKS4pars EQUB 3 \ The number of bytes to transmit with this command EQUB 3 \ The number of bytes to receive with this command EQUB 0 \ The key number to check RTS \ End of the parameter block
Name: DKS2 [View individually] Type: Subroutine Category: Keyboard Summary: Read the joystick position
Return the value of ADC channel in X (used to read the joystick). The value will be inverted if the game has been configured to reverse both joystick channels (which can be done by pausing the game and pressing J). Arguments: X The ADC channel to read: * 1 = joystick X * 2 = joystick Y Returns: (A X) The 16-bit value read from channel X, with the value inverted if the game has been configured to reverse the joystick
.DKS2 LDA KTRAN+7,X \ Fetch either the joystick X value or joystick Y value \ from the key logger buffer, depending on the value of \ X (i.e. fetch either KTRAN+8 or KTRAN+0) EOR JSTE \ The high byte A is now EOR'd with the value in \ location JSTE, which contains &FF if both joystick \ channels are reversed and 0 otherwise (so A now \ contains the high byte but inverted, if that's what \ the current settings say) RTS \ Return from the subroutine
Name: DKS3 [View individually] Type: Subroutine Category: Keyboard Summary: Toggle a configuration setting and emit a beep
This is called when the game is paused and a key is pressed that changes the game's configuration. Specifically, this routine toggles the configuration settings for the following keys: * CAPS LOCK toggles keyboard flight damping (&40) * A toggles keyboard auto-recentre (&41) * X toggles author names on start-up screen (&42) * F toggles flashing console bars (&43) * Y toggles reverse joystick Y channel (&44) * J toggles reverse both joystick channels (&45) * K toggles keyboard and joystick (&46) The numbers in brackets are the internal key numbers (see p.142 of the Advanced User Guide for a list of internal key numbers). We pass the key that has been pressed in X, and the configuration option to check it against in Y, so this routine is typically called in a loop that loops through the various configuration options. Arguments: X The internal number of the key that's been pressed Y The internal number of the configuration key to check against, from the list above (i.e. Y must be from &40 to &46)
.DKS3 STY T \ Store the configuration key argument in T CPX T \ If X <> Y, jump to Dk3 to return from the subroutine BNE Dk3 \ We have a match between X and Y, so now to toggle \ the relevant configuration byte. CAPS LOCK has a key \ value of &40 and has its configuration byte at \ location DAMP, A has a value of &41 and has its byte \ at location DJD, which is DAMP+1, and so on. So we \ can toggle the configuration byte by changing the \ byte at DAMP + (X - &40), or to put it in indexing \ terms, DAMP-&40,X. It's no coincidence that the \ game's configuration bytes are set up in this order \ and with these keys (and this is also why the sound \ on/off keys are dealt with elsewhere, as the internal \ key for S and Q are &51 and &10, which don't fit \ nicely into this approach) LDA DAMP-&40,X \ Fetch the byte from DAMP + (X - &40), invert it and EOR #&FF \ put it back (0 means no and &FF means yes in the STA DAMP-&40,X \ configuration bytes, so this toggles the setting) JSR BELL \ Make a beep sound so we know something has happened JSR DELAY \ Wait for Y vertical syncs (Y is between 64 and 70, so \ this is always a bit longer than a second) LDY T \ Restore the configuration key argument into Y .Dk3 RTS \ Return from the subroutine
Name: DKJ1 [View individually] Type: Subroutine Category: Keyboard Summary: Read joystick and flight controls
Specifically, scan the keyboard for the speed up and slow down keys, and read the joystick's fire button and X and Y axes, storing the results in the key logger and the joystick position variables. This routine is only called if joysticks are enabled (JSTK = non-zero).
.DKJ1 LDA auto \ If auto is non-zero, then the docking computer is BNE auton \ currently activated, so jump to auton in DOKEY so the \ docking computer can "press" the flight keys for us LDA KTRAN+1 \ Copy the key press state for the "?" key from the STA KL+1 \ key logger buffer to the key logger LDA KTRAN+2 \ Copy the key press state for the SPACE key from the STA KL+2 \ key logger buffer to the key logger .BS1 LDA KTRAN+12 \ Fetch the key press state for the joystick 1 fire \ button from the key logger buffer, which contains \ the value of the 6522 System VIA input register IRB \ (SHEILA &40) TAX \ This instruction doesn't seem to have any effect, as \ X is overwritten in a few instructions. When the \ joystick is checked in a similar way in the TITLE \ subroutine for the "Press Fire Or Space,Commander." \ stage of the start-up screen, there's another \ unnecessary TAX instruction present, but there it's \ commented out AND #%00010000 \ Bit 4 of IRB (PB4) is clear if joystick 1's fire \ button is pressed, otherwise it is set, so AND'ing \ the value of IRB with %10000 extracts this bit EOR #%00010000 \ Flip bit 4 so that it's set if the fire button has STA KY7 \ been pressed, and store the result in the keyboard \ logger at location KY7, which is also where the A key \ (fire lasers) key is logged LDX #1 \ Call DKS2 to fetch the value of ADC channel 1 (the JSR DKS2 \ joystick X value) into (A X), and OR A with 1. This ORA #1 \ ensures that the high byte is at least 1, and then we STA JSTX \ store the result in JSTX LDX #2 \ Call DKS2 to fetch the value of ADC channel 2 (the JSR DKS2 \ joystick Y value) into (A X), and EOR A with JSTGY. EOR JSTGY \ JSTGY will be &FF if the game is configured to STA JSTY \ reverse the joystick Y channel, so this EOR does \ exactly that, and then we store the result in JSTY JMP DK4 \ We are done scanning the joystick flight controls, \ so jump to DK4 to scan for other keys, using a tail \ call so we can return from the subroutine there
Name: U% [View individually] Type: Subroutine Category: Keyboard Summary: Clear the key logger (from KY1 through KY19)
Returns: A A is set to 0
.U% LDA #0 \ Set A to 0, as this means "key not pressed" in the \ key logger at KL LDY #16 \ We want to clear the 16 key logger locations from \ KY1 to KY19, so set a counter in Y .DKL3 STA KL,Y \ Store 0 in the Y-th byte of the key logger DEY \ Decrement the counter BNE DKL3 \ And loop back for the next key, until we have just \ KL+1. We don't want to clear the first key logger \ location at KL, as the keyboard table at KYTB starts \ with offset 1, not 0, so KL is not technically part of \ the key logger (it's actually used for logging keys \ that don't appear in the keyboard table, and which \ therefore don't use the key logger) RTS \ Return from the subroutine
Name: DOKEY [View individually] Type: Subroutine Category: Keyboard Summary: Scan for the seven primary flight controls
Scan for the seven primary flight controls (or the equivalent on joystick), pause and configuration keys, and secondary flight controls, and update the key logger accordingly. Specifically: * If we are on keyboard configuration, clear the key logger and update it for the seven primary flight controls, and update the pitch and roll rates accordingly. * If we are on joystick configuration, clear the key logger and jump to DKJ1, which reads the joystick equivalents of the primary flight controls. Both options end up at DK4 to scan for other keys, beyond the seven primary flight controls. Other entry points: auton Get the docking computer to "press" the flight keys to dock the ship
.DOKEY LDA NEEDKEY \ If NEEDKEY is zero, skip the next insruction BEQ P%+5 JSR RDKEY \ NEEDKEY is non-zero, so call RDKEY to ask the I/O \ processor to scan the keyboard for key presses and \ update the key logger buffer at KTRAN LDA #&FF \ Set NEEDKEY to &FF, so the next call to DOKEY updates STA NEEDKEY \ the key logger buffer JSR U% \ Call U% to clear the key logger LDA JSTK \ If JSTK is non-zero, then we are configured to use BNE DKJ1 \ the joystick rather than keyboard, so jump to DKJ1 \ to read the joystick flight controls, before jumping \ to DK4 below STA BSTK \ Set BSTK = 0 to disable the Bitstik LDX #7 \ We're now going to copy key press data for the primary \ flight keys from the key logger buffer at KTRAN to the \ key logger at KL, so set a loop counter in X so we can \ count down from KTRAN + 7 to KTRAN + 1 .DKL2 LDA KTRAN,X \ Copy the X-th byte of KTRAN to the X-th byte of KL STA KL,X DEX \ Decrement the loop counter BNE DKL2 \ Loop back until we have copied all seven primary \ flight control key presses to KL LDA auto \ If auto is 0, then the docking computer is not BEQ DK15 \ currently activated, so jump to DK15 to skip the \ docking computer manoeuvring code below .auton JSR ZINF \ Call ZINF to reset the INWK ship workspace LDA #96 \ Set nosev_z_hi = 96 STA INWK+14 ORA #%10000000 \ Set sidev_x_hi = -96 STA INWK+22 STA TYPE \ Set the ship type to -96, so the negative value will \ let us check in the DOCKIT routine whether this is our \ ship that is activating its docking computer, rather \ than an NPC ship docking LDA DELTA \ Set the ship speed to DELTA (our speed) STA INWK+27 JSR DOCKIT \ Call DOCKIT to calculate the docking computer's moves \ and update INWK with the results \ We now "press" the relevant flight keys, depending on \ the results from DOCKIT, starting with the pitch keys LDA INWK+27 \ Fetch the updated ship speed from byte #27 into A CMP #22 \ If A < 22, skip the next instruction BCC P%+4 LDA #22 \ Set A = 22, so the maximum speed during docking is 22 STA DELTA \ Update DELTA to the new value in A LDA #&FF \ Set A = &FF, which we can insert into the key logger \ to "fake" the docking computer working the keyboard LDX #0 \ Set X = 0, so we "press" KY1 below ("?", slow down) LDY INWK+28 \ If the updated acceleration in byte #28 is zero, skip BEQ DK11 \ to DK11 BMI P%+3 \ If the updated acceleration is negative, skip the \ following instruction INX \ The updated acceleration is positive, so increment X \ to 1, so we "press" KY2 below (Space, speed up) STA KY1,X \ Store &FF in either KY1 or KY2 to "press" the relevant \ key, depending on whether the updated acceleration is \ negative (in which case we "press" KY1, "?", to slow \ down) or positive (in which case we "press" KY2, \ Space, to speed up) .DK11 \ We now "press" the relevant roll keys, depending on \ the results from DOCKIT LDA #128 \ Set A = 128, which indicates no change in roll when \ stored in JSTX (i.e. the centre of the roll indicator) LDX #0 \ Set X = 0, so we "press" KY3 below ("<", increase \ roll) ASL INWK+29 \ Shift ship byte #29 left, which shifts bit 7 of the \ updated roll counter (i.e. the roll direction) into \ the C flag BEQ DK12 \ If the remains of byte #29 is zero, then the updated \ roll counter is zero, so jump to DK12 set JSTX to 128, \ to indicate there's no change in the roll BCC P%+3 \ If the C flag is clear, skip the following instruction INX \ The C flag is set, i.e. the direction of the updated \ roll counter is negative, so increment X to 1 so we \ "press" KY4 below (">", decrease roll) BIT INWK+29 \ We shifted the updated roll counter to the left above, BPL DK14 \ so this tests bit 6 of the original value, and if it \ is is clear (i.e. the magnitude is less than 64), jump \ to DK14 to "press" the key and leave JSTX unchanged LDA #64 \ The magnitude of the updated roll is 64 or more, so STA JSTX \ set JSTX to 64 (so the roll decreases at half the \ maximum rate) LDA #0 \ And set A = 0 so we do not "press" any keys (so if the \ docking computer needs to make a serious roll, it does \ so by setting JSTX directly rather than by "pressing" \ a key) .DK14 STA KY3,X \ Store A in either KY3 or KY4, depending on whether \ the updated roll rate is increasing (KY3) or decreasing \ (KY4) LDA JSTX \ Fetch A from JSTX so the next instruction has no effect .DK12 STA JSTX \ Store A in JSTX to update the current roll rate \ We now "press" the relevant pitch keys, depending on \ the results from DOCKIT LDA #128 \ Set A = 128, which indicates no change in pitch when \ stored in JSTX (i.e. the centre of the pitch indicator) LDX #0 \ Set X = 0, so we "press" KY5 below ("X", decrease \ pitch) ASL INWK+30 \ Shift ship byte #30 left, which shifts bit 7 of the \ updated pitch counter (i.e. the pitch direction) into \ the C flag BEQ DK13 \ If the remains of byte #30 is zero, then the updated \ pitch counter is zero, so jump to DK13 set JSTY to \ 128, to indicate there's no change in the pitch BCS P%+3 \ If the C flag is set, skip the following instruction INX \ The C flag is clear, i.e. the direction of the updated \ pitch counter is positive, so increment X to 1 so we \ "press" KY6 below ("S", increase pitch) STA KY5,X \ Store 128 in either KY5 or KY6 to "press" the relevant \ key, depending on whether the pitch direction is \ negative (in which case we "press" KY5, "X", to \ decrease the pitch) or positive (in which case we \ "press" KY6, "S", to increase the pitch) LDA JSTY \ Fetch A from JSTY so the next instruction has no effect .DK13 STA JSTY \ Store A in JSTY to update the current pitch rate .DK15 LDX JSTX \ Set X = JSTX, the current roll rate (as shown in the \ RL indicator on the dashboard) LDA #7 \ Set A to 7, which is the amount we want to alter the \ roll rate by if the roll keys are being pressed LDY KL+3 \ If the "<" key is being pressed, then call the BUMP2 BEQ P%+5 \ routine to increase the roll rate in X by A JSR BUMP2 LDY KL+4 \ If the ">" key is being pressed, then call the REDU2 BEQ P%+5 \ routine to decrease the roll rate in X by A, taking JSR REDU2 \ the keyboard auto re-centre setting into account STX JSTX \ Store the updated roll rate in JSTX ASL A \ Double the value of A, to 14 LDX JSTY \ Set X = JSTY, the current pitch rate (as shown in the \ DC indicator on the dashboard) LDY KL+5 \ If the "X" key is being pressed, then call the REDU2 BEQ P%+5 \ routine to decrease the pitch rate in X by A, taking JSR REDU2 \ the keyboard auto re-centre setting into account LDY KL+6 \ If the "S" key is being pressed, then call the BUMP2 BEQ P%+5 \ routine to increase the pitch rate in X by A JSR BUMP2 STX JSTY \ Store the updated roll rate in JSTY \ Fall through into DK4 to scan for other keys
Name: DK4 [View individually] Type: Subroutine Category: Keyboard Summary: Scan for pause, configuration and secondary flight keys
Scan for pause and configuration keys, and if this is a space view, also scan for secondary flight controls. Specifically: * Scan for the pause button (COPY) and if it's pressed, pause the game and process any configuration key presses until the game is unpaused (DELETE) * If this is a space view, scan for secondary flight keys and update the relevant bytes in the key logger Other entry points: FREEZE Rejoin the pause routine after processing a screen save
.DK4 LDX KTRAN \ Fetch the internal key number of the current key \ press from the key logger buffer STX KL \ Store X in KL, byte #0 of the key logger CPX #&69 \ If COPY is not being pressed, jump to DK2 below, BNE DK2 \ otherwise let's process the configuration keys .FREEZE \ COPY is being pressed, so we enter a loop that \ listens for configuration keys, and we keep looping \ until we detect a DELETE key press. This effectively \ pauses the game when COPY is pressed, and unpauses \ it when DELETE is pressed JSR WSCAN \ Call WSCAN to wait for the vertical sync, so the whole \ screen gets drawn JSR RDKEY \ Scan the keyboard for a key press and return the \ internal key number in X (or 0 for no key press) CPX #&51 \ If S is not being pressed, skip to DK6 BNE DK6 LDA #0 \ S is being pressed, so set DNOIZ to 0 to turn the STA DNOIZ \ sound on .DK6 LDY #&40 \ We now want to loop through the keys that toggle \ various settings. These have internal key numbers \ between &40 (CAPS LOCK) and &46 ("K"), so we set up \ the first key number in Y to act as a loop counter. \ See subroutine DKS3 for more details on this .DKL4 JSR DKS3 \ Call DKS3 to scan for the key given in Y, and toggle \ the relevant setting if it is pressed INY \ Increment Y to point to the next toggle key CPY #&47 \ The last toggle key is &46 (K), so check whether we \ have just done that one BNE DKL4 \ If not, loop back to check for the next toggle key CPX #&10 \ If "Q" is not being pressed, skip to DK7 BNE DK7 STX DNOIZ \ "Q" is being pressed, so set DNOIZ to X, which is \ non-zero (&10), so this will turn the sound off .DK7 CPX #&70 \ If ESCAPE is not being pressed, skip over the next BNE P%+5 \ instruction JMP DEATH2 \ ESCAPE is being pressed, so jump to DEATH2 to end \ the game CPX #&64 \ If "B" is not being pressed, skip to DK7 BNE nobit LDA BSTK \ Toggle the value of BSTK between 0 and &FF EOR #&FF STA BSTK STA JSTK \ Configure JSTK to the same value, so when the Bitstik \ is enabled, so is the joystick STA JSTE \ Configure JSTE to the same value, so when the Bitstik \ is enabled, the joystick is configured with reversed \ channels .nobit CPX #&32 \ If "D" is being pressed, jump to savscr to save a BEQ savscr \ screenshot CPX #&59 \ If DELETE is not being pressed, we are still paused, BNE FREEZE \ so loop back up to keep listening for configuration \ keys, otherwise fall through into the rest of the \ key detection code, which unpauses the game .DK2 LDA QQ11 \ If the current view is non-zero (i.e. not a space BNE out \ view), return from the subroutine (as out contains \ an RTS) LDY #16 \ This is a space view, so now we want to check for all \ the secondary flight keys. The internal key numbers \ are in the keyboard table KYTB from KYTB+8 to \ KYTB+16, and their key logger locations are from KL+8 \ to KL+16. So set a decreasing counter in Y for the \ index, starting at 16, so we can loop through them LDA #&FF \ Set A to &FF so we can store this in the keyboard \ logger for keys that are being pressed .DKL1 LDX KYTB,Y \ Get the internal key value of the Y-th flight key \ the KYTB keyboard table CPX KL \ We stored the key that's being pressed in KL above, \ so check to see if the Y-th flight key is being \ pressed BNE DK1 \ If it is not being pressed, skip to DK1 below STA KL,Y \ The Y-th flight key is being pressed, so set that \ key's location in the key logger to &FF .DK1 DEY \ Decrement the loop counter CPY #7 \ Have we just done the last key? BNE DKL1 \ If not, loop back to process the next key RTS \ Return from the subroutine
Name: savscr [View individually] Type: Subroutine Category: Save and load Summary: Save a screenshot if CTRL-D is pressed when the game is paused
Screen memory from &4000 to &8000 is saved to disc with an incremental filename, starting with ":0.X.SCREEN1" for the first screenshot, then ":0.X.SCREEN2" for the next, and so on.
.savscr JSR CTRL \ Scan the keyboard to see if CTRL is currently pressed, \ returning a negative value in A if it is BPL FREEZE \ If CTRL is not being pressed, jump to FREEZE to keep \ listening for configuration keys while we're paused LDX #17 \ We start by copying the 18 bytes in oscobl2 to oscobl, \ so set a counter in X for 18 bytes. The oscobl block \ is not altered by this routine or any other, so it \ isn't clear why we copy oscobl2 to oscobl, but perhaps \ there was a reason at some point .savscl LDA oscobl2,X \ Copy the X-th byte of oscobl2 to the X-th byte of STA oscobl,X \ oscobl DEX \ Decrement the byte counter BPL savscl \ Loop back for the next byte until we have copied all \ 18 bytes LDX #LO(oscobl) \ Set (Y X) to point to the oscobl parameter block LDY #HI(oscobl) LDA #0 \ Call OSFILE with A = 0 to save a file containing the JSR OSFILE \ screen memory from &4000 to &8000 INC scname+11 \ Increment the screenshot number in the filename at \ scname, so ":0.X.SCREEN1" becomes ":0.X.SCREEN2" and \ so on JMP FREEZE \ Jump back into the pause loop to keep listening for \ configuration key presses
Name: TT217 [View individually] Type: Subroutine Category: Keyboard Summary: Scan the keyboard until a key is pressed
Scan the keyboard until a key is pressed, and return the key's ASCII code. If, on entry, a key is already being held down, then wait until that key is released first (so this routine detects the first key down event following the subroutine call). Returns: X The ASCII code of the key that was pressed A Contains the same as X Y Y is preserved Other entry points: out Contains an RTS t As TT217 but don't preserve Y, set it to YSAV instead
.TT217 STY YSAV \ Store Y in temporary storage, so we can restore it \ later .t LDY #2 \ Delay for 2 vertical syncs (2/50 = 0.04 seconds) so we JSR DELAY \ don't take up too much CPU time while looping round JSR RDKEY \ Scan the keyboard for a key press and return the \ internal key number in X (or 0 for no key press) BNE t \ If a key was already being held down when we entered \ this routine, keep looping back up to t, until the \ key is released .t2 JSR RDKEY \ Any pre-existing key press is now gone, so we can \ start scanning the keyboard again, returning the \ internal key number in X (or 0 for no key press) BEQ t2 \ Keep looping up to t2 until a key is pressed TAY \ Copy A to Y, so Y contains the internal key number \ of the key pressed LDA TRANTABLE,Y \ TRANTABLE points to the MOS key translation table, \ which is used to translate internal key values to \ ASCII, so this fetches the key's ASCII code into A LDY YSAV \ Restore the original value of Y we stored above TAX \ Copy A into X .out RTS \ Return from the subroutine
Name: me1 [View individually] Type: Subroutine Category: Text Summary: Erase an old in-flight message and display a new one
Arguments: A The text token to be printed X Must be set to 0
.me1 STX DLY \ Set the message delay in DLY to 0, so any new \ in-flight messages will be shown instantly PHA \ Store the new message token we want to print LDA MCH \ Set A to the token number of the message that is JSR mes9 \ currently on-screen, and call mes9 to print it (which \ will remove it from the screen, as printing is done \ using EOR logic) PLA \ Restore the new message token
Name: MESS [View individually] Type: Subroutine Category: Text Summary: Display an in-flight message
Display an in-flight message in capitals at the bottom of the space view, erasing any existing in-flight message first. Arguments: A The text token to be printed
.MESS PHA \ Store A on the stack so we can restore it after the \ the call to DOCOL LDA #YELLOW \ Send a #SETCOL YELLOW command to the I/O processor to JSR DOCOL \ switch to colour 1, which is yellow PLA \ Restore A from the stack LDX #0 \ Set QQ17 = 0 to switch to ALL CAPS STX QQ17 PHA \ Store A on the stack so we can restore it after the \ the calls to DOXC and DOYC LDA messXC \ Move the text cursor to column messXC, in case we JSR DOXC \ jump to me1 below to erase the current in-flight \ message (whose column we stored in messXC when we \ called MESS to put it there in the first place) LDA #22 \ Move the text cursor to row 22, and set Y = 22 TAY JSR DOYC PLA \ Restore A from the stack CPX DLY \ If the message delay in DLY is not zero, jump up to BNE me1 \ me1 to erase the current message first (whose token \ number will be in MCH) STY DLY \ Set the message delay in DLY to 22 STA MCH \ Set MCH to the token we are about to display \ Before we fall through into mes9 to print the token, \ we need to work out the starting column for the \ message we want to print, so it's centred on-screen, \ so the following doesn't print anything, it just uses \ the justified text mechanism to work out the number of \ characters in the message we are going to print LDA #%11000000 \ Set the DTW4 flag to %11000000 (justify text, buffer STA DTW4 \ entire token including carriage returns) LDA de \ Set the C flag to bit 1 of the destruction flag in de LSR A LDA #0 \ Set A = 0 BCC P%+4 \ If the destruction flag in de is not set, skip the \ following instruction LDA #10 \ Set A = 10 STA DTW5 \ Store A in DTW5, so DTW5 (which holds the size of the \ justified text buffer at BUF) is set to 0 if the \ destruction flag is not set, or 10 if it is (10 being \ the number of characters in the " DESTROYED" token) LDA MCH \ Call TT27 to print the token in MCH into the buffer JSR TT27 \ (this doesn't print it on-screen, it just puts it into \ the buffer and moves the DTW5 pointer along, so DTW5 \ now contains the size of the message we want to print, \ includint the " DESTROYED" part if that's going to be \ included) LDA #32 \ Set A = (32 - DTW5) / 2 SEC \ SBC DTW5 \ so A now contains the column number we need to print LSR A \ our message at for it to be centred on-screen (as \ there are 32 columns) STA messXC \ Store A in messXC, so when we erase the message via \ the branch to me1 above, messXC will tell us where to \ print it JSR DOXC \ Move the text cursor to column messXC JSR MT15 \ Call MT15 to wwitch to left-aligned text when printing \ extended tokens disabling the justify text setting we \ set above LDA MCH \ Set MCH to the token we are about to display \ Fall through into mes9 to print the token in A
Name: mes9 [View individually] Type: Subroutine Category: Text Summary: Print a text token, possibly followed by " DESTROYED"
Print a text token, followed by " DESTROYED" if the destruction flag is set (for when a piece of equipment is destroyed).
.mes9 JSR TT27 \ Call TT27 to print the text token in A LSR de \ If bit 1 of variable de is clear, return from the BCC out \ subroutine (as out contains an RTS) LDA #253 \ Print recursive token 93 (" DESTROYED") and return JMP TT27 \ from the subroutine using a tail call
Name: OUCH [View individually] Type: Subroutine Category: Flight Summary: Potentially lose cargo or equipment following damage
Our shields are dead and we are taking damage, so there is a small chance of losing cargo or equipment.
.OUCH JSR DORND \ Set A and X to random numbers BMI out \ If A < 0 (50% chance), return from the subroutine \ (as out contains an RTS) CPX #22 \ If X >= 22 (89% chance), return from the subroutine BCS out \ (as out contains an RTS) LDA QQ20,X \ If we do not have any of item QQ20+X, return from the BEQ out \ subroutine (as out contains an RTS). X is in the range \ 0-21, so this not only checks for cargo, but also for \ E.C.M., fuel scoops, energy bomb, energy unit and \ docking computer, all of which can be destroyed LDA DLY \ If there is already an in-flight message on-screen, BNE out \ return from the subroutine (as out contains an RTS) LDY #3 \ Set bit 1 of de, the equipment destruction flag, so STY de \ that when we call MESS below, " DESTROYED" is appended \ to the in-flight message STA QQ20,X \ A is 0 (as we didn't branch with the BNE above), so \ this sets QQ20+X to 0, which destroys any cargo or \ equipment we have of that type CPX #17 \ If X >= 17 then we just lost a piece of equipment, so BCS ou1 \ jump to ou1 to print the relevant message TXA \ Print recursive token 48 + A as an in-flight token, ADC #208 \ which will be in the range 48 ("FOOD") to 64 ("ALIEN BNE MESS \ ITEMS") as the C flag is clear, so this prints the \ destroyed item's name, followed by " DESTROYED" (as we \ set bit 1 of the de flag above), and returns from the \ subroutine using a tail call .ou1 BEQ ou2 \ If X = 17, jump to ou2 to print "E.C.M.SYSTEM \ DESTROYED" and return from the subroutine using a tail \ call CPX #18 \ If X = 18, jump to ou3 to print "FUEL SCOOPS BEQ ou3 \ DESTROYED" and return from the subroutine using a tail \ call TXA \ Otherwise X is in the range 19 to 21 and the C flag is ADC #113-20 \ set (as we got here via a BCS to ou1), so we set A as \ follows: \ \ A = 113 - 20 + X + C \ = 113 - 19 + X \ = 113 to 115 JMP MESS \ Print recursive token A ("ENERGY BOMB", "ENERGY UNIT" \ or "DOCKING COMPUTERS") as an in-flight message, \ followed by " DESTROYED", and return from the \ subroutine using a tail call
Name: ou2 [View individually] Type: Subroutine Category: Text Summary: Display "E.C.M.SYSTEM DESTROYED" as an in-flight message
.ou2 LDA #108 \ Set A to recursive token 108 ("E.C.M.SYSTEM") JMP MESS \ Print recursive token A as an in-flight message, \ followed by " DESTROYED", and return from the \ subroutine using a tail call
Name: ou3 [View individually] Type: Subroutine Category: Text Summary: Display "FUEL SCOOPS DESTROYED" as an in-flight message
.ou3 LDA #111 \ Set A to recursive token 111 ("FUEL SCOOPS") JMP MESS \ Print recursive token A as an in-flight message, \ followed by " DESTROYED", and return from the \ subroutine using a tail call
Name: ITEM [View individually] Type: Macro Category: Market Summary: Macro definition for the market prices table Deep dive: Market item prices and availability
The following macro is used to build the market prices table: ITEM price, factor, units, quantity, mask It inserts an item into the market prices table at QQ23. See the deep dive on "Market item prices and availability" for more information on how the market system works. Arguments: price Base price factor Economic factor units Units: "t", "g" or "k" quantity Base quantity mask Fluctuations mask
MACRO ITEM price, factor, units, quantity, mask IF factor < 0 s = 1 << 7 ELSE s = 0 ENDIF IF units = 't' u = 0 ELIF units = 'k' u = 1 << 5 ELSE u = 1 << 6 ENDIF e = ABS(factor) EQUB price EQUB s + u + e EQUB quantity EQUB mask ENDMACRO
Name: QQ23 [View individually] Type: Variable Category: Market Summary: Market prices table
Each item has four bytes of data, like this: Byte #0 = Base price Byte #1 = Economic factor in bits 0-4, with the sign in bit 7 Unit in bits 5-6 Byte #2 = Base quantity Byte #3 = Mask to control price fluctuations To make it easier for humans to follow, we've defined a macro called ITEM that takes the following arguments and builds the four bytes for us: ITEM base price, economic factor, units, base quantity, mask So for food, we have the following: * Base price = 19 * Economic factor = -2 * Unit = tonnes * Base quantity = 6 * Mask = %00000001
.QQ23 ITEM 19, -2, 't', 6, %00000001 \ 0 = Food ITEM 20, -1, 't', 10, %00000011 \ 1 = Textiles ITEM 65, -3, 't', 2, %00000111 \ 2 = Radioactives ITEM 40, -5, 't', 226, %00011111 \ 3 = Slaves ITEM 83, -5, 't', 251, %00001111 \ 4 = Liquor/Wines ITEM 196, 8, 't', 54, %00000011 \ 5 = Luxuries ITEM 235, 29, 't', 8, %01111000 \ 6 = Narcotics ITEM 154, 14, 't', 56, %00000011 \ 7 = Computers ITEM 117, 6, 't', 40, %00000111 \ 8 = Machinery ITEM 78, 1, 't', 17, %00011111 \ 9 = Alloys ITEM 124, 13, 't', 29, %00000111 \ 10 = Firearms ITEM 176, -9, 't', 220, %00111111 \ 11 = Furs ITEM 32, -1, 't', 53, %00000011 \ 12 = Minerals ITEM 97, -1, 'k', 66, %00000111 \ 13 = Gold ITEM 171, -2, 'k', 55, %00011111 \ 14 = Platinum ITEM 45, -1, 'g', 250, %00001111 \ 15 = Gem-Stones ITEM 53, 15, 't', 192, %00000111 \ 16 = Alien Items
Name: oscobl [View individually] Type: Variable Category: Save and load Summary: OSFILE configuration block for saving a screenshot
This OSFILE configuration block is overwritten by the block at oscobl2 before being passed to OSFILE to save a screenshot.
.oscobl EQUW scname \ The address of the filename to save EQUD &FFFF4000 \ Load address of the saved file EQUD &FFFF4000 \ Execution address of the saved file EQUD &FFFF4000 \ Start address of the memory block to save EQUD &FFFF8000 \ End address of the memory block to save
Name: scname [View individually] Type: Variable Category: Save and load Summary: Filename to be used when saving a screenshot
.scname EQUS ":0.X.SCREEN1" EQUB 13
Name: oscobl2 [View individually] Type: Variable Category: Save and load Summary: Master OSFILE configuration block for saving a screenshot
This OSFILE configuration block is copied from oscobl2 to oscobl in order to save a screenshot.
.oscobl2 EQUW scname \ The address of the filename to save EQUD &FFFF4000 \ Load address of the saved file EQUD &FFFF4000 \ Execution address of the saved file EQUD &FFFF4000 \ Start address of the memory block to save EQUD &FFFF8000 \ End address of the memory block to save
Name: TIDY [View individually] Type: Subroutine Category: Maths (Geometry) Summary: Orthonormalise the orientation vectors for a ship Deep dive: Tidying orthonormal vectors
This routine orthonormalises the orientation vectors for a ship. This means making the three orientation vectors orthogonal (perpendicular to each other), and normal (so each of the vectors has length 1). We do this because we use the small angle approximation to rotate these vectors in space. It is not completely accurate, so the three vectors tend to get stretched over time, so periodically we tidy the vectors with this routine to ensure they remain as orthonormal as possible.
.TI2 \ Called from below with A = 0, X = 0, Y = 4 when \ nosev_x and nosev_y are small, so we assume that \ nosev_z is big TYA \ A = Y = 4 LDY #2 JSR TIS3 \ Call TIS3 with X = 0, Y = 2, A = 4, to set roofv_z = STA INWK+20 \ -(nosev_x * roofv_x + nosev_y * roofv_y) / nosev_z JMP TI3 \ Jump to TI3 to keep tidying .TI1 \ Called from below with A = 0, Y = 4 when nosev_x is \ small TAX \ Set X = A = 0 LDA XX15+1 \ Set A = nosev_y, and if the top two magnitude bits AND #%01100000 \ are both clear, jump to TI2 with A = 0, X = 0, Y = 4 BEQ TI2 LDA #2 \ Otherwise nosev_y is big, so set up the index values \ to pass to TIS3 JSR TIS3 \ Call TIS3 with X = 0, Y = 4, A = 2, to set roofv_y = STA INWK+18 \ -(nosev_x * roofv_x + nosev_z * roofv_z) / nosev_y JMP TI3 \ Jump to TI3 to keep tidying .TIDY LDA INWK+10 \ Set (XX15, XX15+1, XX15+2) = nosev STA XX15 LDA INWK+12 STA XX15+1 LDA INWK+14 STA XX15+2 JSR NORM \ Call NORM to normalise the vector in XX15, i.e. nosev LDA XX15 \ Set nosev = (XX15, XX15+1, XX15+2) STA INWK+10 LDA XX15+1 STA INWK+12 LDA XX15+2 STA INWK+14 LDY #4 \ Set Y = 4 LDA XX15 \ Set A = nosev_x, and if the top two magnitude bits AND #%01100000 \ are both clear, jump to TI1 with A = 0, Y = 4 BEQ TI1 LDX #2 \ Otherwise nosev_x is big, so set up the index values LDA #0 \ to pass to TIS3 JSR TIS3 \ Call TIS3 with X = 2, Y = 4, A = 0, to set roofv_x = STA INWK+16 \ -(nosev_y * roofv_y + nosev_z * roofv_z) / nosev_x .TI3 LDA INWK+16 \ Set (XX15, XX15+1, XX15+2) = roofv STA XX15 LDA INWK+18 STA XX15+1 LDA INWK+20 STA XX15+2 JSR NORM \ Call NORM to normalise the vector in XX15, i.e. roofv LDA XX15 \ Set roofv = (XX15, XX15+1, XX15+2) STA INWK+16 LDA XX15+1 STA INWK+18 LDA XX15+2 STA INWK+20 LDA INWK+12 \ Set Q = nosev_y STA Q LDA INWK+20 \ Set A = roofv_z JSR MULT12 \ Set (S R) = Q * A = nosev_y * roofv_z LDX INWK+14 \ Set X = nosev_z LDA INWK+18 \ Set A = roofv_y JSR TIS1 \ Set (A ?) = (-X * A + (S R)) / 96 \ = (-nosev_z * roofv_y + nosev_y * roofv_z) / 96 \ \ This also sets Q = nosev_z EOR #%10000000 \ Set sidev_x = -A STA INWK+22 \ = (nosev_z * roofv_y - nosev_y * roofv_z) / 96 LDA INWK+16 \ Set A = roofv_x JSR MULT12 \ Set (S R) = Q * A = nosev_z * roofv_x LDX INWK+10 \ Set X = nosev_x LDA INWK+20 \ Set A = roofv_z JSR TIS1 \ Set (A ?) = (-X * A + (S R)) / 96 \ = (-nosev_x * roofv_z + nosev_z * roofv_x) / 96 \ \ This also sets Q = nosev_x EOR #%10000000 \ Set sidev_y = -A STA INWK+24 \ = (nosev_x * roofv_z - nosev_z * roofv_x) / 96 LDA INWK+18 \ Set A = roofv_y JSR MULT12 \ Set (S R) = Q * A = nosev_x * roofv_y LDX INWK+12 \ Set X = nosev_y LDA INWK+16 \ Set A = roofv_x JSR TIS1 \ Set (A ?) = (-X * A + (S R)) / 96 \ = (-nosev_y * roofv_x + nosev_x * roofv_y) / 96 EOR #%10000000 \ Set sidev_z = -A STA INWK+26 \ = (nosev_y * roofv_x - nosev_x * roofv_y) / 96 LDA #0 \ Set A = 0 so we can clear the low bytes of the \ orientation vectors LDX #14 \ We want to clear the low bytes, so start from sidev_y \ at byte #9+14 (we clear all except sidev_z_lo, though \ I suspect this is in error and that X should be 16) .TIL1 STA INWK+9,X \ Set the low byte in byte #9+X to zero DEX \ Set X = X - 2 to jump down to the next low byte DEX BPL TIL1 \ Loop back until we have zeroed all the low bytes RTS \ Return from the subroutine
Name: TIS2 [View individually] Type: Subroutine Category: Maths (Arithmetic) Summary: Calculate A = A / Q Deep dive: Shift-and-subtract division
Calculate the following division, where A is a sign-magnitude number and Q is a positive integer: A = A / Q The value of A is returned as a sign-magnitude number with 96 representing 1, and the maximum value returned is 1 (i.e. 96). This routine is used when normalising vectors, where we represent fractions using integers, so this gives us an approximation to two decimal places.
.TIS2 TAY \ Store the argument A in Y AND #%01111111 \ Strip the sign bit from the argument, so A = |A| CMP Q \ If A >= Q then jump to TI4 to return a 1 with the BCS TI4 \ correct sign LDX #%11111110 \ Set T to have bits 1-7 set, so we can rotate through 7 STX T \ loop iterations, getting a 1 each time, and then \ getting a 0 on the 8th iteration... and we can also \ use T to catch our result bits into bit 0 each time .TIL2 ASL A \ Shift A to the left CMP Q \ If A < Q skip the following subtraction BCC P%+4 SBC Q \ A >= Q, so set A = A - Q \ \ Going into this subtraction we know the C flag is \ set as we passed through the BCC above, and we also \ know that A >= Q, so the C flag will still be set once \ we are done ROL T \ Rotate the counter in T to the left, and catch the \ result bit into bit 0 (which will be a 0 if we didn't \ do the subtraction, or 1 if we did) BCS TIL2 \ If we still have set bits in T, loop back to TIL2 to \ do the next iteration of 7 \ We've done the division and now have a result in the \ range 0-255 here, which we need to reduce to the range \ 0-96. We can do that by multiplying the result by 3/8, \ as 256 * 3/8 = 96 LDA T \ Set T = T / 4 LSR A LSR A STA T LSR A \ Set T = T / 8 + T / 4 ADC T \ = 3T / 8 STA T TYA \ Fetch the sign bit of the original argument A AND #%10000000 ORA T \ Apply the sign bit to T RTS \ Return from the subroutine .TI4 TYA \ Fetch the sign bit of the original argument A AND #%10000000 ORA #96 \ Apply the sign bit to 96 (which represents 1) RTS \ Return from the subroutine
Name: TIS3 [View individually] Type: Subroutine Category: Maths (Arithmetic) Summary: Calculate -(nosev_1 * roofv_1 + nosev_2 * roofv_2) / nosev_3
Calculate the following expression: A = -(nosev_1 * roofv_1 + nosev_2 * roofv_2) / nosev_3 where 1, 2 and 3 are x, y, or z, depending on the values of X, Y and A. This routine is called with the following values: X = 0, Y = 2, A = 4 -> A = -(nosev_x * roofv_x + nosev_y * roofv_y) / nosev_z X = 0, Y = 4, A = 2 -> A = -(nosev_x * roofv_x + nosev_z * roofv_z) / nosev_y X = 2, Y = 4, A = 0 -> A = -(nosev_y * roofv_y + nosev_z * roofv_z) / nosev_x Arguments: X Index 1 (0 = x, 2 = y, 4 = z) Y Index 2 (0 = x, 2 = y, 4 = z) A Index 3 (0 = x, 2 = y, 4 = z)
.TIS3 STA P+2 \ Store P+2 in A for later LDA INWK+10,X \ Set Q = nosev_x_hi (plus X) STA Q LDA INWK+16,X \ Set A = roofv_x_hi (plus X) JSR MULT12 \ Set (S R) = Q * A \ = nosev_x_hi * roofv_x_hi LDX INWK+10,Y \ Set Q = nosev_x_hi (plus Y) STX Q LDA INWK+16,Y \ Set A = roofv_x_hi (plus Y) JSR MAD \ Set (A X) = Q * A + (S R) \ = (nosev_x,X * roofv_x,X) + \ (nosev_x,Y * roofv_x,Y) STX P \ Store low byte of result in P, so result is now in \ (A P) LDY P+2 \ Set Q = roofv_x_hi (plus argument A) LDX INWK+10,Y STX Q EOR #%10000000 \ Flip the sign of A \ Fall through into DIVDT to do: \ \ (P+1 A) = (A P) / Q \ \ = -((nosev_x,X * roofv_x,X) + \ (nosev_x,Y * roofv_x,Y)) \ / nosev_x,A
Name: DVIDT [View individually] Type: Subroutine Category: Maths (Arithmetic) Summary: Calculate (P+1 A) = (A P) / Q
Calculate the following integer division between sign-magnitude numbers: (P+1 A) = (A P) / Q This uses the same shift-and-subtract algorithm as TIS2.
.DVIDT STA P+1 \ Set P+1 = A, so P(1 0) = (A P) EOR Q \ Set T = the sign bit of A EOR Q, so it's 1 if A and Q AND #%10000000 \ have different signs, i.e. it's the sign of the result STA T \ of A / Q LDA #0 \ Set A = 0 for us to build a result LDX #16 \ Set a counter in X to count the 16 bits in P(1 0) ASL P \ Shift P(1 0) left ROL P+1 ASL Q \ Clear the sign bit of Q the C flag at the same time LSR Q .DVL2 ROL A \ Shift A to the left CMP Q \ If A < Q skip the following subtraction BCC P%+4 SBC Q \ Set A = A - Q \ \ Going into this subtraction we know the C flag is \ set as we passed through the BCC above, and we also \ know that A >= Q, so the C flag will still be set once \ we are done ROL P \ Rotate P(1 0) to the left, and catch the result bit ROL P+1 \ into the C flag (which will be a 0 if we didn't \ do the subtraction, or 1 if we did) DEX \ Decrement the loop counter BNE DVL2 \ Loop back for the next bit until we have done all 16 \ bits of P(1 0) LDA P \ Set A = P so the low byte is in the result in A ORA T \ Set A to the correct sign bit that we set in T above RTS \ Return from the subroutine
Name: KTRAN [View individually] Type: Variable Category: Keyboard Summary: The key logger buffer that gets updated by the OSWORD 240 command
KTRAN is a buffer that is filled with key logger information by the KEYBOARD routine in the I/O processor, which is run when the parasite sends an OSWORD &F0 command to the I/O processor. The buffer contains details of keys being pressed, with KTRAN being filled with bytes #2 to #14 from the KEYBOARD routine (because KEYBOARD is called with OSSC pointing to buf, and buf is equal to KTRAN - 2). The key logger buffer is filled as follows: KTRAN + 0 Internal key number of any non-primary flight control key that is being pressed KTRAN + 1 "?" is being pressed (0 = no, &FF = yes) KTRAN + 2 Space is being pressed (0 = no, &FF = yes) KTRAN + 3 "<" is being pressed (0 = no, &FF = yes) KTRAN + 4 ">" is being pressed (0 = no, &FF = yes) KTRAN + 5 "X" is being pressed (0 = no, &FF = yes) KTRAN + 6 "S" is being pressed (0 = no, &FF = yes) KTRAN + 7 "A" is being pressed (0 = no, &FF = yes) KTRAN + 8 Joystick X value (high byte) KTRAN + 9 Joystick Y value (high byte) KTRAN + 10 Bitstik rotation value (high byte) KTRAN + 12 Joystick 1 fire button is being pressed (Bit 4 set = no, Bit 4 clear = yes) Other entry points: buf The two OSWORD size bytes for transmitting the key logger from the I/O processor to the parasite
.buf EQUB 2 \ Transmit 2 bytes as part of this command EQUB 15 \ Receive 15 bytes as part of this command .KTRAN EQUS "1234567890" \ A 17-byte buffer to hold the key logger data from the EQUS "1234567" \ KEYBOARD routine in the I/O processor (note that only \ 12 of these bytes are actually updated by the KEYBOARD \ routine)
Name: TRANTABLE [View individually] Type: Variable Category: Keyboard Summary: Translation table from internal key number to ASCII
This is a copy of the keyboard translation table from the BBC Micro's MOS 1.20 ROM. The value at offset n is the lower-case ASCII value of the key with internal key number n, so for example the value at offset &10 is &71, which is 113, or ASCII "q", so internal key number &10 is the key number of the "Q" key. Valid internal key numbers are Binary Coded Decimal (BCD) numbers in the range &10 top &79, so they're in the ranges &10 to &19, then &20 to &29, then &30 to &39, and so on. This means that the other locations - i.e. &1A to &1F, &2A to &2F and so on - are unused by the lookup table, but the MOS doesn't let this space go to waste; instead, those gaps contain MOS code, which is replicated below as TRANTABLE contains a copy of this entire block of the MOS, not just the table entries. This table allows code running on the parasite to convert internal key numbers into ASCII codes in an efficient way. Without this table we would have to do a lookup from the table in the I/O processor's MOS ROM, which we would have to access from across the Tube, and this would be a lot slower than doing a simple table lookup in the parasite's user RAM.
.TRANTABLE EQUB &03, &8C, &40 \ MOS code EQUB &FE, &A0, &7F EQUB &8C, &43, &FE EQUB &8E, &4F, &FE EQUB &AE, &4F, &FE EQUB &60 \ Internal key numbers &10 to &19: \ EQUB &71, &33 \ Q 3 EQUB &34, &35 \ 4 5 EQUB &84, &38 \ f4 8 EQUB &87, &2D \ f7 - EQUB &5E, &8C \ ^ Left arrow EQUB &84, &EC, &86 \ MOS code EQUB &ED, &60, &00 \ Internal key numbers &20 to &29: \ EQUB &80, &77 \ f0 W EQUB &65, &74 \ E T EQUB &37, &69 \ 7 I EQUB &39, &30 \ 9 0 EQUB &5F, &8E \ _ Down arrow EQUB &6C, &FE, &FD \ MOS code EQUB &6C, &FA, &00 \ Internal key numbers &30 to &39: \ EQUB &31, &32 \ 1 2 EQUB &64, &72 \ D R EQUB &36, &75 \ 6 U EQUB &6F, &70 \ O P EQUB &5B, &8F \ [ Up arrow EQUB &2C, &B7, &D9 \ MOS code EQUB &6C, &28, &02 \ Internal key numbers &40 to &49: \ EQUB &01, &61 \ CAPS LOCK A EQUB &78, &66 \ X F EQUB &79, &6A \ Y J EQUB &6B, &40 \ K @ EQUB &3A, &0D \ : RETURN EQUB &00, &FF, &01 \ MOS code EQUB &02, &09, &0A \ Internal key numbers &50 to &59: \ EQUB &02, &73 \ SHIFT LOCK S EQUB &63, &67 \ C G EQUB &68, &6E \ H N EQUB &6C, &3B \ L ; EQUB &5D, &7F \ ] DELETE EQUB &AC, &44, &02 \ MOS code EQUB &A2, &00, &60 \ Internal key numbers &60 to &69: \ EQUB &00, &7A \ TAB Z EQUB &20, &76 \ SPACE V EQUB &62, &6D \ B M EQUB &2C, &2E \ , . EQUB &2F, &8B \ / COPY EQUB &AE, &41, &02 \ MOS code EQUB &4C, &AD, &E1 \ Internal key numbers &70 to &79: \ EQUB &1B, &81 \ ESCAPE f1 EQUB &82, &83 \ f2 f3 EQUB &85, &86 \ f5 f6 EQUB &88, &89 \ f8 f9 EQUB &5C, &8D \ \ Right arrow EQUB &6C, &20, &02 \ MOS code EQUB &D0, &EB, &A2 EQUB &08
Save output/ELTF.bin
PRINT "ELITE F" PRINT "Assembled at ", ~CODE_F% PRINT "Ends at ", ~P% PRINT "Code size is ", ~(P% - CODE_F%) PRINT "Execute at ", ~LOAD% PRINT "Reload at ", ~LOAD_F% PRINT "S.ELTF ", ~CODE_F%, " ", ~P%, " ", ~LOAD%, " ", ~LOAD_F% SAVE "output/ELTF.bin", CODE_F%, P%, LOAD%