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Elite on the BBC Micro

Elite F source [Master version]

ELITE F FILE
CODE_F% = P% LOAD_F% = LOAD% + P% - CODE%
Name: DJOY [Show more] Type: Subroutine Category: Keyboard Summary: Scan the keyboard for cursor key or digital joystick movement
Context: See this subroutine on its own page References: This subroutine is called as follows: * TT17 calls DJOY
IF _COMPACT .DJOY JSR TT17X \ Call TT17X to read the digital joystick and return \ deltas as appropriate JMP TJ1 \ Jump to TJ1 in the TT17 routine to check for cursor \ key presses and return the combined deltas for the \ digital joystick and cursor keys, returning from the \ subroutine using a tail call ENDIF
Name: KS3 [Show more] Type: Subroutine Category: Universe Summary: Set the SLSP ship heap pointer after shuffling ship slots
Context: See this subroutine on its own page References: This subroutine is called as follows: * KS2 calls KS3

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 [Show more] Type: Subroutine Category: Universe Summary: Remove the current ship from our local bubble of universe
Context: See this subroutine on its own page References: This subroutine is called as follows: * Main flight loop (Part 12 of 16) calls KS1

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 [Show more] Type: Subroutine Category: Universe Summary: Remove the space station and replace it with the sun
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * KILLSHP calls KS4
.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 [Show more] Type: Subroutine Category: Universe Summary: Check the local bubble for missiles with target lock
Context: See this subroutine on its own page References: This subroutine is called as follows: * KILLSHP calls KS2

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 [Show more] Type: Subroutine Category: Universe Summary: Remove a ship from our local bubble of universe
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * KS1 calls KILLSHP

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 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 INC TALLY+1 \ Award 256 kill points for killing the Constrictor .lll CPX #HER \ Did we just kill a rock hermit? If we did, jump to BEQ blacksuspenders \ blacksuspenders to decrease 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, 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. One down, quite a few to \ go... 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: THERE [Show more] Type: Subroutine Category: Missions Summary: Check whether we are in the Constrictor's system in mission 1
Context: See this subroutine on its own page References: This subroutine is called as follows: * Main game loop (Part 4 of 6) calls THERE

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: HEXPRNT [Show more] Type: Subroutine Category: Text Summary: Print a number in hexadecimal (unused)
Context: See this subroutine on its own page References: No direct references to this subroutine in this source file

Arguments: A The number to print
.HEXPRNT PHA \ Store A on the stack so we can grab the lower nibble \ from it later LSR A \ Shift A right so that it contains the upper nibble LSR A \ of the original argument LSR A LSR A JSR HEXP \ Call HEXP below to print 0-F for the upper nibble PLA \ Restore A from the stack AND #%00001111 \ Extract the lower nibble and fall through into HEXP \ to print 0-F for the lower nibble .HEXP CMP #10 \ If A >= 10, skip the next three instructions BCS P%+7 ADC #'0' \ A < 10, so print the number in A as a digit 0-9 and JMP CHPR \ return from the subroutine using a tail call ADC #'6' \ A >= 10, so print the number in A as a digit A-F and JMP CHPR \ return from the subroutine using a tail call
Name: RESET [Show more] Type: Subroutine Category: Start and end Summary: Reset most variables
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * TITLE calls RESET * TT170 calls RESET

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 \ Reset 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 STX JSTGY \ X is now negative - i.e. &FF - so this sets JSTGY to \ &FF to set the joystick Y-channel to the default \ direction 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 [Show more] Type: Subroutine Category: Start and end Summary: Reset a number of flight variables and workspaces
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * DEATH calls RES2 * DEATH2 calls RES2 * DOENTRY calls RES2 * ESCAPE calls RES2 * MJP calls RES2 * TT110 calls RES2 * TT18 calls RES2

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 #0 \ Set XMAX to 0 (though this variable is never used, so STA XMAX \ this has no effect) LDA #191 \ Set YMAX to 191, the number of pixel lines in the STA YMAX \ space view 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 \ Reset 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 \ Finally, fall through into ZINF to reset the INWK \ ship workspace
Name: ZINF [Show more] Type: Subroutine Category: Utility routines Summary: Reset the INWK workspace and orientation vectors Deep dive: Orientation vectors
Context: See this subroutine on its own page References: This subroutine is called as follows: * BRIEF calls ZINF * DOKEY calls ZINF * FRS1 calls ZINF * HAS1 calls ZINF * KS4 calls ZINF * Main game loop (Part 2 of 6) calls ZINF * SOLAR calls ZINF * TITLE calls ZINF * Ze calls ZINF

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 [Show more] Type: Subroutine Category: Dashboard Summary: Display the dashboard's missile indicators in green
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * BR1 (Part 2 of 2) calls msblob * EQSHP calls msblob * SOS1 calls msblob

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 [Show more] Type: Subroutine Category: Text Summary: Remove an in-flight message from the space view
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * Main game loop (Part 2 of 6) calls me2
.me2 LDA QQ11 \ If this is not the space view, jump down to nomess to BNE nomess \ skip displaying the in-flight message 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 me3 .nomess 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 JMP me3 \ Jump back into the main spawning loop at me3
Name: Ze [Show more] Type: Subroutine Category: Universe Summary: Initialise the INWK workspace to a hostile ship Deep dive: Fixing ship positions
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * DEATH calls Ze * GTHG calls Ze * Main game loop (Part 3 of 6) calls Ze * Main game loop (Part 4 of 6) calls Ze

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. Note that because this routine uses the value of X returned by DORND, and X contains the value of A returned by the previous call to DORND, this routine does not necessarily set the new ship to a totally random location. See the deep dive on "Fixing ship positions" for details.
.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 [Show more] Type: Subroutine Category: Utility routines Summary: Generate random numbers Deep dive: Generating random numbers Fixing ship positions
Context: See this subroutine on its own page References: This subroutine is called as follows: * BOMBINIT calls DORND * DEATH calls DORND * DETOK2 calls DORND * GVL calls DORND * HALL calls DORND * HAS1 calls DORND * LASLI calls DORND * LL9 (Part 1 of 12) calls DORND * MT18 calls DORND * Main flight loop (Part 11 of 16) calls DORND * Main flight loop (Part 8 of 16) calls DORND * Main game loop (Part 1 of 6) calls DORND * Main game loop (Part 2 of 6) calls DORND * Main game loop (Part 4 of 6) calls DORND * OUCH calls DORND * SFS1 calls DORND * SOLARX calls DORND * SPIN calls DORND * STARS1 calls DORND * STARS2 calls DORND * STARS6 calls DORND * SUN (Part 3 of 4) calls DORND * TACTICS (Part 1 of 7) calls DORND * TACTICS (Part 2 of 7) calls DORND * TACTICS (Part 3 of 7) calls DORND * TACTICS (Part 4 of 7) calls DORND * TACTICS (Part 5 of 7) calls DORND * TACTICS (Part 7 of 7) calls DORND * TT18 calls DORND * TT210 calls DORND * Ze calls DORND * nWq calls DORND

Set A and X to random numbers (though note that X is set to the random number that was returned in A the last time DORND was called). The C and V flags are also set randomly. If we want to generate a repeatable sequence of random numbers, when generating explosion clouds, for example, then we call DORND2 to ensure that the value of the C flag on entry doesn't affect the outcome, as otherwise we might not get the same sequence of numbers if the C flag changes. Other entry points: DORND2 Make sure the C flag doesn't affect the outcome
.DORND2 CLC \ Clear the C flag so the value of the C flag on entry \ doesn't affect the outcome .DORND LDA RAND \ Calculate the next two values f2 and f3 in the feeder ROL A \ sequence: TAX \ ADC RAND+2 \ * f2 = (f1 << 1) mod 256 + C flag on entry STA RAND \ * f3 = f0 + f2 + (1 if bit 7 of f1 is set) STX RAND+2 \ * C flag is set according to the f3 calculation LDA RAND+1 \ Calculate the next value m2 in the main sequence: TAX \ ADC RAND+3 \ * A = m2 = m0 + m1 + C flag from feeder calculation STA RAND+1 \ * X = m1 STX RAND+3 \ * C and V flags set according to the m2 calculation RTS \ Return from the subroutine
Name: Main game loop (Part 1 of 6) [Show more] Type: Subroutine Category: Main loop Summary: Spawn a trader (a Cobra Mk III, Python, Boa or Anaconda) Deep dive: Program flow of the main game loop Ship data blocks
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: No direct references to this subroutine in this source file

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 a 50% chance of it having a missile, a 50% chance of it having an E.C.M., a 50% chance of it docking and being aggressive if attacked, 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 and set the C \ flag to bit 0 of A, which os random 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 the ship's missile count ramdomly (as the \ C flag was set), giving the ship either no missiles or \ 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) [Show more] Type: Subroutine Category: Main loop Summary: Call the main flight loop, and potentially spawn a trader, an asteroid, or a cargo canister Deep dive: Program flow of the main game loop Ship data blocks Fixing ship positions
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * Main game loop (Part 2 of 6) calls entry point me3 * me2 calls entry point me3 * Main game loop (Part 1 of 6) calls entry point TT100 * Main game loop (Part 6 of 6) calls entry point TT100

This section covers the following: * Call M% to do the main flight loop * Potentially spawn a trader, 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 \ \ Note that because we use the value of X returned by \ DORND, and X contains the value of A returned by the \ previous call to DORND, this does not set the new ship \ to a totally random location. See the deep dive on \ "Fixing ship positions" for details 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 1 of x_hi to the C flag, which is random, so ROL INWK+1 \ this randomly moves us off-centre by 512 (as if x_hi \ is %00000010, then (x_hi x_lo) is 512 + x_lo) 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) [Show more] Type: Subroutine Category: Main loop Summary: Potentially spawn a cop, particularly if we've been bad Deep dive: Program flow of the main game loop Ship data blocks Fixing ship positions
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: No direct references to this subroutine in this source file

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 \ \ Note that because Ze uses the value of X returned by \ DORND, and X contains the value of A returned by the \ previous call to DORND, this does not set the new ship \ to a totally random location. See the deep dive on \ "Fixing ship positions" for details 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 to stop spawning, otherwise fall \ through into the next part to look at spawning \ something else
Name: Main game loop (Part 4 of 6) [Show more] Type: Subroutine Category: Main loop Summary: Potentially spawn a lone bounty hunter, a Thargoid, or up to four pirates Deep dive: Program flow of the main game loop Ship data blocks Fixing ship positions
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: No direct references to this subroutine in this source file

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 if BPL MLOOPS \ it is still positive, jump to MLOOPS to stop spawning, \ 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 #220 \ If the random number in A < 220 (86% 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 \ 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 \ \ Note that because Ze uses the value of X returned by \ DORND, and X contains the value of A returned by the \ previous call to DORND, this does not set the new ship \ to a totally random location. See the deep dive on \ "Fixing ship positions" for details 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 \ Set A to the new ship type in Y 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 \ Try adding 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) [Show more] Type: Subroutine Category: Main loop Summary: Cool down lasers, make calls to update the dashboard Deep dive: Program flow of the main game loop The dashboard indicators
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * Main game loop (Part 2 of 6) calls entry point MLOOP * Main game loop (Part 3 of 6) calls entry point MLOOP * Main game loop (Part 4 of 6) calls entry point MLOOP * Main game loop (Part 6 of 6) calls entry point MLOOP

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 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) [Show more] Type: Subroutine Category: Main loop Summary: Process non-flight key presses (red function keys, docked keys) Deep dive: Program flow of the main game loop
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * BAY calls entry point FRCE * TT219 calls entry point FRCE

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 BEQ P%+5 \ If we are docked, loop back up to MLOOP just above JMP MLOOP \ 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 [Show more] Type: Subroutine Category: Keyboard Summary: Process function key, save key, hyperspace and chart key presses and update the hyperspace counter
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * Main game loop (Part 6 of 6) calls TT102 * HME2 calls entry point T95

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). This routine also checks for the "F" key press (search for a system), which applies to enhanced versions only. 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 set ZZ to JMP TT25 \ the system number, and then jump to TT25 to show the \ Data on System screen (along with an extended system \ description for the system in ZZ if we're docked), \ 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 #&40 \ If "@" was not pressed, skip to nosave BNE nosave JSR SVE \ "@" was pressed, so call SVE to show the disc access \ 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 red key f1 was pressed, jump to BVIEW BEQ BVIEW CMP #f2 \ If red key f2 was pressed, jump to LVIEW BEQ LVIEW CMP #f3 \ If red key f3 was not pressed, jump to LABEL_3 to keep BNE LABEL_3 \ checking for which key was pressed LDX #3 \ Red key f3 was pressed, so set the view number in X to \ 3 for the right view EQUB &2C \ Skip the next instruction by turning it into \ &2C &A2 &02, or BIT &02A2, which does nothing apart \ from affect the flags .LVIEW LDX #2 \ If we jump to here, red key f2 was pressed, so set the \ view number in X to 2 for the left view EQUB &2C \ Skip the next instruction by turning it into \ &2C &A2 &01, or BIT &02A2, which does nothing apart \ from affect the flags .BVIEW LDX #1 \ If we jump to here, red key f1 was pressed, so set the \ view number in X to 1 for the rear view JMP LOOK1 \ Jump to LOOK1 to switch to view X (rear, left or \ right), returning from the subroutine using a tail \ call .LABEL_3 LDA KL \ If "H" was not pressed, jump to NWDAV5 to skip the CMP #'H' \ following BNE NWDAV5 JMP hyp \ Jump to hyp to do a hyperspace jump (if we are in \ space), returning from the subroutine using a tail \ call .NWDAV5 CMP #&44 \ 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 #&46 \ 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 #&4F \ If "O" was pressed, do the following three jumps, BNE ee2 \ otherwise skip to ee2 to continue 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) JSR hm \ Call hm to move the crosshairs to the target system \ in (QQ9, QQ10), returning with A = 0 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 #12 \ Print a line feed to move the text cursor down a line JSR TT26 JMP TT146 \ Print the distance to the selected system and return \ from the subroutine using a tail call
Name: BAD [Show more] Type: Subroutine Category: Status Summary: Calculate how bad we have been
Context: See this subroutine on its own page References: This subroutine is called as follows: * Main game loop (Part 3 of 6) calls BAD * TT110 calls BAD

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 [Show more] Type: Subroutine Category: Maths (Geometry) Summary: Compare x_hi, y_hi and z_hi with 224
Context: See this subroutine on its own page References: This subroutine is called as follows: * Main flight loop (Part 12 of 16) calls FAROF

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 [Show more] Type: Subroutine Category: Maths (Geometry) Summary: Compare x_hi, y_hi and z_hi with A
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * Main flight loop (Part 14 of 16) calls FAROF2

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 [Show more] Type: Subroutine Category: Maths (Geometry) Summary: Calculate a cap on the maximum distance to a ship
Context: See this subroutine on its own page References: This subroutine is called as follows: * Main flight loop (Part 7 of 16) calls MAS4 * TACTICS (Part 1 of 7) calls MAS4 * TACTICS (Part 6 of 7) calls MAS4

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: stack [Show more] Type: Variable Category: Save and load Summary: Temporary storage for the stack pointer when switching the BRKV handler between BRBR and MEBRK
Context: See this variable on its own page Variations: See code variations for this variable in the different versions References: This variable is used as follows: * BRBR calls stack * SVE calls stack
.stack EQUB &FF
Name: BRBR [Show more] Type: Subroutine Category: Utility routines Summary: The standard BRKV handler for the game
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * BRKBK calls BRBR

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.
.BRBR 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 change it in the SVE routine JSR SWAPZP \ Call SWAPZP to restore the top part of zero page STZ CATF \ Set the CATF flag to 0, so the TT26 routine reverts to \ standard formatting LDY #0 \ Set Y to 0, which we use as a loop counter below LDA #7 \ Set A = 7 to generate a beep before we print the error \ message .BRBRLOOP JSR CHPR \ 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) JSR t \ Scan the keyboard until a key is pressed, returning \ the ASCII code in A and X JMP SVE \ Jump to SVE to display the disc access menu and return \ from the subroutine using a tail call
Name: DEATH [Show more] Type: Subroutine Category: Start and end Summary: Display the death screen
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * Main flight loop (Part 15 of 16) calls DEATH * Main flight loop (Part 9 of 16) calls DEATH * OOPS calls DEATH

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 LDY #4 \ Call the NOISE routine with Y = 4 to make the sound of JSR NOISE \ 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 LDA #13 \ Clear the top part of the screen, draw a white border, JSR TT66 \ and set the current view type in QQ11 to 13 (which \ is not a space view, though I'm not quite sure why \ this value is chosen, as it gets overwritten by the \ next instruction anyway) STZ QQ11 \ Set QQ11 to 0, so from here on we are using a space \ view 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 #CYAN \ Change the current colour to cyan STA COL LDA #12 \ Move the text cursor to column 12 on row 12 STA XC STA YC 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: x_hi, y_hi, z_hi and the AI STY INWK+1 \ flag (no AI 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 LDY #64 \ Set the laser count to 64 to act as a counter in the STY LASCT \ D2 loop below, so this setting determines how long the \ death animation lasts (it's 64 * 2 iterations of the \ main flight loop) SEC \ Set the C flag ROR A \ This sets A to a number between 0 and +7, which we AND #%10000111 \ we store in byte #30 (the pitch counter) to give our STA INWK+30 \ ship a very gentle downwards 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 LDA #0 \ Set our speed in DELTA to 0, as we aren't going STA DELTA \ anywhere any more \ JSR M% \ Call the M% routine to do the main flight loop once, \ which will display our exploding canister scene and \ move everything about, as well as decrementing the \ value in LASCT .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, as well as decrementing the \ value in LASCT DEC LASCT \ Decrement the counter in LASCT, which we set above, \ so for each loop around D2, we decrement LASCT by 5 \ (the main loop decrements it by 4, and this one makes \ it 5) 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 JMP DEATH2 \ Jump to DEATH2 to reset and restart the game
Name: spasto [Show more] Type: Variable Category: Universe Summary: Contains the address Coriolis space station's ship blueprint
Context: See this variable on its own page References: This variable is used as follows: * BEGIN calls spasto * NWSPS calls spasto
.spasto EQUW &8888 \ This variable is set by routine BEGIN to the address \ of the Coriolis space station's ship blueprint
Name: BEGIN [Show more] Type: Subroutine Category: Loader Summary: Initialise the configuration variables and start the game
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * S% calls BEGIN
.BEGIN LDX #(DTAPE-COMC) \ We start by zeroing all the configuration variables \ between COMC and DTAPE, to set them to their default \ values, so set a counter in X for DTAPE - 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 JSR JAMESON \ Call JAMESON to set the last saved commander to the \ default "JAMESON" commander \ Fall through into TT170 to start the game
Name: TT170 [Show more] Type: Subroutine Category: Start and end Summary: Main entry point for the Elite game code Deep dive: Program flow of the main game loop
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: No direct references to this subroutine in this source file

This is the main entry point for the main game code.
.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 JSR RESET \ Call RESET to initialise most of the game variables \ Fall through into DEATH2 to start the game
Name: DEATH2 [Show more] Type: Subroutine Category: Start and end Summary: Reset most of the game and restart from the title screen
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * DEATH calls DEATH2 * DK4 calls DEATH2

This routine is called following death, and when the game is quit by pressing ESCAPE when paused.
.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 (Part 1 of 2) [Show more] Type: Subroutine Category: Start and end Summary: Start or restart the game
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * BR1 (Part 1 of 2) calls entry point QU5 * TT102 calls entry point QU5

BRKV is set to point to BR1 by the loading process. Other entry points: QU5 Restart the game using the last saved commander without asking whether to load a new commander file
.BR1 JSR U% \ Call U% to clear the key logger LDA #3 \ Set XC = 3 (set text cursor to column 3) STA XC LDX #CYL \ Call TITLE to show a rotating Cobra Mk III (#CYL) and LDA #6 \ token 6 ("LOAD NEW {single cap}COMMANDER {all caps} LDY #200 \ (Y/N)?{sentence case}{cr}{cr}"), with the ship at a JSR TITLE \ distance of 200, returning with the internal number \ of the key pressed in A CPX #'Y' \ 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
Name: BR1 (Part 2 of 2) [Show more] Type: Subroutine Category: Start and end Summary: Show the "Load New Commander (Y/N)?" screen and start the game
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: No direct references to this subroutine in this source file

BRKV is set to point to BR1 by the loading process.
JSR msblob \ Reset the dashboard's missile indicators so none of \ them are targeted LDA #7 \ Call TITLE to show a rotating Cougar (#COU) and LDX #COU \ token 7 ("LOAD NEW {single cap}COMMANDER {all caps} LDY #100 \ (Y/N)?{sentence case}{cr}{cr}""), with the ship at a JSR TITLE \ distance of 100, returning with the internal number \ of the key pressed in A JSR ping \ Set the target system coordinates (QQ9, QQ10) to the \ current system coordinates (QQ0, QQ1) we just loaded 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 hyp1 \ routine .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 \ Fall through into the docking bay routine below
Name: BAY [Show more] Type: Subroutine Category: Status Summary: Go to the docking bay (i.e. show the Status Mode screen)
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * BRP calls BAY * DOENTRY calls BAY * EQSHP calls BAY * TT102 calls BAY

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)
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) \ If the commander check below fails, we keep jumping \ back to here to crash the game with an infinite loop 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 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 \ The checksum CHK is correct, so now we check whether \ CHK2 = CHK EOR A9, and if this check fails, bit 7 of \ the competition flags at COK gets set, to indicate \ to Acornsoft via the competition code that there has \ been some hacking going on with this competition entry 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 #%00001000 \ Set bit 3 of A to denote that this is the Master \ version STA COK \ Store the updated competition flags in COK RTS \ Return from the subroutine
Name: TITLE [Show more] Type: Subroutine Category: Start and end Summary: Display a title screen with a rotating ship and prompt
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * BR1 (Part 1 of 2) calls TITLE * BR1 (Part 2 of 2) calls TITLE

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) Y The distance to show the ship rotating, once it has finished moving towards us Returns: X If a key is being pressed, X contains the ASCII code of the key pressed
.TITLE STY SDIST \ Store the ship distance in SDIST 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 U% \ Call U% to clear the key logger JSR ZINF \ Call ZINF to reset the INWK ship workspace LDA #32 \ Set the mode 1 palette to yellow (colour 1), white JSR DOVDU19 \ (colour 2) and cyan (colour 3) LDA #13 \ Clear the top part of the screen, draw a white border, JSR TT66 \ and set the current view type in QQ11 to 13 (rotating \ ship view) LDA #RED \ Switch to colour 2, which is white in the title screen STA COL LDA #0 \ Set QQ11 to 0, so from here on we are using a space STA QQ11 \ view LDA #96 \ Set nosev_z hi = 96 (96 is the value of unity in the STA INWK+14 \ rotation vector) LDA #96 \ Set A = 96 as the distance that the ship starts at 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 \ Set roll counter = 127, so don't dampen the roll STX INWK+29 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 STA XC 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 STA XC 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 LDY #0 \ Set DELTA = 0 (i.e. ship speed = 0) STY DELTA STY JSTK \ Set JSTK = 0 (i.e. keyboard, not joystick) LDA #20 \ Move the text cursor to row 20 STA YC LDA #1 \ Move the text cursor to column 1 STA XC PLA \ Restore the recursive token number we stored on the \ stack at the start of this subroutine JSR DETOK \ Print the extended token in A LDA #7 \ Move the text cursor to column 7 STA XC LDA #12 \ Print extended token 12 ("({single cap}C) ACORNSOFT JSR DETOK \ 1986") 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 STZ JSTK \ Set JSTK = 0 (i.e. keyboard, not joystick) .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 SDIST \ Set z_lo to the distance value we passed to the STX INWK+6 \ routine, so this is the closest the ship gets to us LDA #0 \ Set x_lo = 0, so the ship remains in the screen centre STA INWK STA INWK+3 \ Set y_lo = 0, so the ship remains in the screen centre JSR LL9 \ Call LL9 to display the ship DEC MCNT \ Decrement the main loop counter IF _SNG47 LDA VIA+&40 \ Read 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 ELIF _COMPACT JSR RDFIRE \ Call RDFIRE to check whether the joystick's fire \ button is being pressed BCS TL2 \ If the C flag is set then the joystick fire button \ is being pressed, so jump to TL2 ENDIF IF _SNG47 BEQ TL2 \ If the joystick fire button is pressed, jump to TL2 ENDIF JSR RDKEY \ Scan the keyboard for a key press BEQ TLL2 \ If no key was pressed, loop back up to move/rotate \ the ship and check again for a key press RTS \ Return from the subroutine .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 RTS \ Return from the subroutine
Name: CHECK [Show more] Type: Subroutine Category: Save and load Summary: Calculate the checksum for the last saved commander data block Deep dive: Commander save files
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * SVE calls CHECK

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%-3 \ Set X to the size of the commander data block, less \ 3 (as there are two checksum bytes and the save count) 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: JAMESON [Show more] Type: Subroutine Category: Save and load Summary: Restore the default JAMESON commander
Context: See this subroutine on its own page References: This subroutine is called as follows: * BEGIN calls JAMESON * SVE calls JAMESON
.JAMESON LDY #96 \ We are going to copy the default commander at DEFAULT% \ over the top of the last saved commander at NA%, so \ set a counter to copy 97 bytes .JAMESL LDA DEFAULT%,Y \ Copy the Y-th byte of DEFAULT% to the Y-th byte of STA NA%,Y \ NA% DEY \ Decrement the loop counter BPL JAMESL \ Loop back until we have copied the whole commander LDY #7 \ Set NAMELEN2 to 7, the length of the commander name STY NAMELEN2 \ "JAMESON" RTS \ Return from the subroutine
Name: TRNME [Show more] Type: Subroutine Category: Save and load Summary: Copy the last saved commander's name from INWK to NA%
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * SVE calls TRNME
.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 LDA NAMELEN1 \ Copy the length of the commander's name from NAMELEN1 STA NAMELEN2 \ to NAMELEN2 (though this is never used, so this \ doesn't have any effect) .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 [Show more] Type: Subroutine Category: Save and load Summary: Copy the last saved commander's name from NA% to INWK
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * GTNMEW calls TR1
.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 [Show more] Type: Subroutine Category: Save and load Summary: Fetch the name of a commander file to save or load
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * SVE calls GTNMEW

Get the commander's name for loading or saving a commander file. The name is stored in the INWK workspace and is terminated by a return character (13). If ESCAPE is pressed or a blank name is entered, then the name stored is set to the name from the last saved commander block. Returns: INWK The full filename, including drive and directory, in the form ":0.E.JAMESON", for example, terminated by a return character (13)
.GTNMEW .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 \ The OSWORD call returns the length of the commander's \ name in Y, so transfer this to A BEQ TR1 \ If A = 0, no name was entered, so jump to TR1 to copy \ the last saved commander's name from NA% to INWK \ and return from the subroutine there STY NAMELEN1 \ Store the length of the length of the commander's that \ was entered in NAMELEN1 RTS \ Return from the subroutine
Name: MT26 [Show more] Type: Subroutine Category: Text Summary: Fetch a line of text from the keyboard Deep dive: Extended text tokens
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * DELT calls MT26 * GTDIR calls MT26 * GTNMEW calls MT26 * JMTB calls MT26

Returns: Y The size of the entered text, or 0 if none was entered INWK+5 The entered text, terminated by a carriage return C flag Set if ESCAPE was pressed
.MT26 LDA COL \ Store the current colour on the stack PHA LDA #RED \ Switch to colour 2, which is magenta in the trade view STA COL LDY #8 \ Wait for 8/50 of a second (0.16 seconds) JSR DELAY JSR FLKB \ Call FLKB to flush the keyboard buffer LDY #0 \ Set Y = 0 to hold the length of the text entered .MT26L JSR TT217 \ Scan the keyboard until a key is pressed, and return \ the key's ASCII code in A (and X) CMP #13 \ If RETURN was pressed, jump to MT26ret BEQ MT26ret CMP #27 \ If ESCAPE was pressed, jump to MT26esc BEQ MT26esc CMP #127 \ If DELETE was pressed, jump to MT26ret BEQ MT26del IF _COMPACT PHX \ Store X on the stack so we can retrieve it after the \ call to SHIFT PHA \ Store the number of the key being pressed on the stack JSR SHIFT \ If SHIFT is not being pressed, jump to noshift to skip BPL noshift \ the following PLA \ SHIFT is being pressed, so fetch the number of the key \ being pressed from the stack CMP #'@' \ If A >= ASCII "@", then we are pressing a letter key, BCS P%+4 \ so skip the following instruction EOR #%00010000 \ We are pressing SHIFT and a number key, so flip bit 4 \ of the key number, which flips the letter betweeen the \ ASCII code of the number being pressed and the ASCII \ code of the number being pressed when SHIFT is being \ held down (so SHIFT-1 will enter !, SHIFT-2 will enter \ ", and so on) PHA \ Push the updated key number onto the stack .noshift PLA \ Retrieve the values of X and A we stored on the stack PLX \ above ENDIF CPY RLINE+2 \ If Y >= RLINE+2 (the maximum line length from the BCS MT26err \ OSWORD configuration block at RLINE), then jump to \ MT26err to give an error beep as we have reached the \ character limit CMP RLINE+3 \ If the key pressed is less than the character in BCC MT26err \ RLINE+3 (the lowest allowed character from the OSWORD \ configuration block at RLINE), then jump to MT26err \ to give an error beep as the key pressed is out of \ range CMP RLINE+4 \ If the key pressed is geater than or equal to the BCS MT26err \ character in RLINE+4 (the highest allowed character \ from the OSWORD configuration block at RLINE), then \ jump to MT26err to give an error beep as the key \ pressed is out of range STA INWK+5,Y \ Store the key's ASCII code in the Y-th byte of INWK+5 INY \ Increment Y to point to the next free byte in INWK+5 EQUB &2C \ Skip the next instruction by turning it into \ &2C &A9 &07, or BIT &07A9, which does nothing apart \ from affect the flags .MT26err LDA #7 \ Set A to the beep character, so the next instruction \ makes a system beep .MT26LS JSR CHPR \ Print the character in A (and clear the C flag) BCC MT26L \ Loop back to MT26L to fetch another key press (this \ BCC is effectively a JMP as CHPR clears the C flag) .MT26ret STA INWK+5,Y \ Store the return character in the Y-th byte of INWK+5 LDA #12 \ Print a newline JSR CHPR EQUB &24 \ Skip the next instruction by turning it into &24 &38, \ or BIT &0038, which does nothing apart from affect the \ flags .MT26esc SEC \ Set the C flag as ESCAPE was pressed PLA \ Restore the original colour from the stack and set it STA COL \ as the current colour RTS \ Return from the subroutine .MT26del TYA \ If the length of the line so far in Y is 0, then we BEQ MT26err \ just pressed DELETE on an empty line, so jump to \ MT26err give an error beep DEY \ Otherwise we want to delete a character, so decrement \ the length of the line so far in Y LDA #127 \ Set A = 127 and jump back to MT26LS to print the BNE MT26LS \ character in A (i.e. the DELETE character) and listen \ for the next key press
Name: RLINE [Show more] Type: Variable Category: Text Summary: The OSWORD configuration block used to fetch a line of text from the keyboard
Context: See this variable on its own page Variations: See code variations for this variable in the different versions References: This variable is used as follows: * GTDIR calls RLINE * GTNMEW calls RLINE * MT26 calls RLINE
.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, as that's the maximum size \ for a commander's name including a directory name EQUB '!' \ Allow ASCII characters from "!" through to "{" in {' \ the input
Name: MT30 [Show more] Type: Subroutine Category: Text Summary: Display the currently selected media (disc or tape) Deep dive: Extended text tokens
Context: See this subroutine on its own page References: This subroutine is called as follows: * JMTB calls MT30
.MT30 LDA #3 \ Print extended token 3 + DTAPE, i.e. token 3 or 2 (as CLC \ DTAPE can be 0 or &FF). In other versions of the game, ADC DTAPE \ such as the Commodore 64 version, token 2 is "disk" JMP DETOK \ and token 3 is "tape", so this displays the currently \ selected media, but this system is unused in the \ Master version and tokens 2 and 3 contain different \ text
Name: MT31 [Show more] Type: Subroutine Category: Text Summary: Display the non-selected media (disc or tape) Deep dive: Extended text tokens
Context: See this subroutine on its own page References: This subroutine is called as follows: * JMTB calls MT31
.MT31 LDA #2 \ Print extended token 2 - DTAPE, i.e. token 2 or 3 (as SEC \ DTAPE can be 0 or &FF). In other versions of the game, SBC DTAPE \ such as the Commodore 64 version, token 2 is "disk" JMP DETOK \ and token 3 is "tape", so this displays the other, \ non-selected media, but this system is unused in the \ Master version and tokens 2 and 3 contain different \ text
Name: ZERO [Show more] Type: Subroutine Category: Utility routines Summary: Reset the local bubble of universe and ship status
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * RES2 calls ZERO * RESET calls ZERO

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: GTDIR [Show more] Type: Subroutine Category: Save and load Summary: Fetch the name of an ADFS directory on the Master Compact and change to that directory
Context: See this subroutine on its own page References: This subroutine is called as follows: * CATS calls GTDIR
IF _COMPACT .GTDIR LDA #2 \ Print extended token 2 ("{cr}WHICH DRIVE?") JSR DETOK LDA #19 \ 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 19 (as that's the longest directory name \ allowed) 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 directory name LDA #9 \ Reset the maximum length in RLINE+2 to the original STA RLINE+2 \ value of 9 TYA \ The OSWORD call returns the length of the commander's \ name in Y, so transfer this to A BEQ GTDIR-1 \ If A = 0, no name was entered, so jump to DIR-1 to \ return from the subroutine (as GTDIR-1 contains an \ RTS) \ We now copy the entered filename from INWK to DIRI, so \ that it overwrites the filename part of the string, \ i.e. the "12345678901234567890" part of \ "DIR 12345678901234567890" LDX #18 \ Set up a counter in X to count from 18 to 0, so that \ we copy the string starting at INWK+5 to DIRI+4 \ onwards (i.e. "12345678901234567890") .DIRL LDA INWK+5,X \ Copy the X-th byte of INWK+5 to the X-th byte of STA DIRI+4,X \ DIRI+4 DEX \ Decrement the loop counter BPL DIRL \ Loop back to DIRL to copy the next character until we \ have copied the whole filename JSR NMIRELEASE \ Release the NMI workspace (&00A0 to &00A7) LDX #LO(DIRI) \ Set (Y X) to point to DIRI ("DIR ") LDY #HI(DIRI) JSR OSCLI \ Call OSCLI to run the OS command in DIRI, which \ changes the disc directory to the name entered JMP SWAPZP \ Call SWAPZP to restore the top part of zero page \ and return from the subroutine using a tail call ENDIF
Name: CATS [Show more] Type: Subroutine Category: Save and load Summary: Ask for a disc drive number and print a catalogue of that drive
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * DELT calls CATS * SVE calls CATS

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 IF _SNG47 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+4 \ Store the drive number in the fifth byte of the \ command string at CTLI, so it overwrites the "1" in \ "CAT 1" 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) ELIF _COMPACT JSR GTDIR \ Get a directory name from the keyboard and change to \ that directory ENDIF LDA #3 \ Print extended token 3, which clears the screen and JSR DETOK \ prints the boxed-out title "DRIVE {drive number} \ CATALOGUE" LDA #1 \ Set the CATF flag to 1, so that the TT26 routine will STA CATF \ print out the disc catalogue correctly STA XC \ Move the text cursor to column 1 IF _SNG47 JSR SWAPZP \ Call SWAPZP to restore the top part of zero page ELIF _COMPACT JSR NMIRELEASE \ Release the NMI workspace (&00A0 to &00A7) ENDIF 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 OSCLI \ Call OSCLI to execute the OS command at (Y X), which \ catalogues the disc JSR SWAPZP \ Call SWAPZP to restore the top part of zero page STZ CATF \ Set the CATF flag to 0, so the TT26 routine reverts to \ standard formatting CLC \ Clear the C flag RTS \ Return from the subroutine
Name: DELT [Show more] Type: Subroutine Category: Save and load Summary: Catalogue a disc, ask for a filename to delete, and delete the file
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * SVE calls DELT * CATS calls entry point DELT-1

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 (or a directory \ name on the Master Compact) and catalogue that disc \ or directory 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 IF _SNG47 LDA CTLI+4 \ The call to CATS above put the drive number into STA DELI+8 \ CTLI+4, so copy the drive number into DELI+8 so that \ the drive number in the "DELETE :1.1234567" string \ gets updated (i.e. the number after the colon) ENDIF 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 TYA \ If no text was entered (Y = 0) then jump to SVE to BEQ SVE \ display the disc access menu IF _SNG47 \ 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 :1.1234567" 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+9+1 (i.e. DELI+10 onwards, or "1.1234567") ELIF _COMPACT \ We now copy the entered filename from INWK to DELI, so \ that it overwrites the filename part of the string, \ i.e. the "1234567890" part of "DELETE 1234567890" LDX #8 \ Set up a counter in X to count from 8 to 0, so that we \ copy the string starting at INWK+5+0 (i.e. INWK+5) to \ DELI+7+0 (i.e. DELI+7 onwards, or "1234567890") ENDIF .DELL1 IF _SNG47 LDA INWK+4,X \ Copy the X-th byte of INWK+4 to the X-th byte of STA DELI+9,X \ DELI+9 DEX \ Decrement the loop counter BNE DELL1 \ Loop back to DELL1 to copy the next character until we \ have copied the whole filename JSR SWAPZP \ Call SWAPZP to restore the top part of zero page ELIF _COMPACT LDA INWK+5,X \ Copy the X-th byte of INWK+5 to the X-th byte of STA DELI+7,X \ DELI+7 DEX \ Decrement the loop counter BPL DELL1 \ Loop back to DELL1 to copy the next character until we \ have copied the whole filename JSR NMIRELEASE \ Release the NMI workspace (&00A0 to &00A7) ENDIF 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 OSCLI \ Call OSCLI to execute the OS command at (Y X), which \ catalogues the disc JSR SWAPZP \ Call SWAPZP to restore the top part of zero page JMP SVE \ Jump to SVE to display the disc access menu and return \ from the subroutine using a tail call
Name: SVE [Show more] Type: Subroutine Category: Save and load Summary: Display the disc access menu and process saving of commander files Deep dive: Commander save files The competition code
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * BR1 (Part 1 of 2) calls SVE * BRBR calls SVE * DELT calls SVE * LOD calls SVE * TT102 calls SVE
.SVE TSX \ Transfer the stack pointer to X and store it in stack, STX stack \ so we can restore it in the BRBR routine JSR TRADE \ Set the palette for trading screens and switch the \ current colour to white 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. Default JAMESON \ 6. Exit JSR t \ Scan the keyboard until a key is pressed, returning \ the ASCII code in A and X CMP #'1' \ Option 1 was chosen, so jump to LD1 to load a new BEQ LD1 \ commander CMP #'2' \ Option 2 was chosen, so jump to LD1 to save the BEQ SV1 \ current commander CMP #'3' \ Option 3 was chosen, so jump to CAT to catalogue a BEQ CAT \ disc CMP #'4' \ If option 4 wasn't chosen, skip the next two BNE P%+8 \ instructions JSR DELT \ Option 4 was chosen, so call DELT to delete a file JMP SVE \ Jump to SVE to display the disc access menu again and \ return from the subroutine using a tail call CMP #'5' \ If option 5 wasn't chosen, skip to exit to exit the BNE exit \ menu LDA #224 \ Print extended token 224 ("ARE YOU SURE?") JSR DETOK JSR GETYN \ Call GETYN to wait until either "Y" or "N" is pressed BCC exit \ If "N" was pressed, jump to exit JSR JAMESON \ Otherwise "Y" was pressed, so call JAMESON to set the \ last saved commander to the default "JAMESON" \ commander JMP DFAULT \ Jump to DFAULT to reset the current commander data \ block to the last saved commander, returning from the \ subroutine using a tail call .exit CLC \ Option 5 was chosen, so clear the C flag to indicate \ that nothing was loaded RTS \ Return from the subroutine .CAT JSR CATS \ Call CATS to ask for a drive number (or a directory \ name on the Master Compact) and catalogue that disc \ or directory JSR t \ Scan the keyboard until a key is pressed, returning \ the ASCII code in A and X JMP SVE \ Jump to SVE to display the disc access menu and return \ from the subroutine using a tail call .LD1 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 IF _SNG47 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 LDdone \ 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 LDLI+6 \ Store the ASCII drive number in LDLI+6, which is the \ drive character of the load filename string ":1.E." ENDIF 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 .LDdone RTS \ Return from the subroutine .SV1 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 #4 \ Print extended token 4, which is blank (this was where JSR DETOK \ the competition number was printed in older versions, \ but the competition was long gone by the time of the \ BBC Master version 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 .SVL1 LDA TP,X \ Copy the X-th byte of TP to the X-th byte of NA%+8 STA NA%+8,X DEX \ Decrement the loop counter BPL SVL1 \ Loop back until we have copied all the bytes in the \ commander data block 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 TT67 \ Call TT67 twice to print two newlines JSR TT67 PLA \ Restore the checksum from the stack EOR #&A9 \ Store the checksum EOR &A9 in CHK2, the penultimate STA CHK2 \ byte of the last saved commander block LDY #NT% \ We now want to copy the current commander data block \ to location &0791 so we can do a file save operation, \ so set a counter in X to copy the NT% bytes in the \ commander data block .SVL2 LDA NA%+8,Y \ Copy the X-th byte of NA% to the X-th byte of &0791 STA &0791,Y DEY \ Decrement the loop counter BPL SVL2 \ Loop back until we have copied all the bytes in the \ commander data block IF _SNG47 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 P%+8 \ If the C flag is set, then an invalid drive number was \ entered, so skip the next two instructions STA SVLI+6 \ Store the ASCII drive number in SVLI+6, which is the \ drive character of the save filename string ":1.E." ENDIF JSR SAVE \ Call SAVE to save the commander file JSR DFAULT \ Call DFAULT to reset the current commander data \ block to the last saved commander CLC \ Clear the C flag to indicate that no new commander \ file was loaded RTS \ Return from the subroutine
Name: NAMELEN1 [Show more] Type: Variable Category: Save and load Summary: Contains the length of the most recently entered commander name
Context: See this variable on its own page References: This variable is used as follows: * GTNMEW calls NAMELEN1 * TRNME calls NAMELEN1
.NAMELEN1 EQUB 7
Name: NAMELEN2 [Show more] Type: Variable Category: Save and load Summary: Contains the length of the last saved commander name
Context: See this variable on its own page References: This variable is used as follows: * JAMESON calls NAMELEN2 * TRNME calls NAMELEN2
.NAMELEN2 EQUB 7
Name: GTDRV [Show more] Type: Subroutine Category: Save and load Summary: Get an ASCII disc drive drive number from the keyboard
Context: See this subroutine on its own page References: This subroutine is called as follows: * CATS calls GTDRV * SVE calls GTDRV

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 [Show more] Type: Subroutine Category: Save and load Summary: Load a commander file
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * SVE calls LOD * GTDRV calls entry point LOR

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 JSR LOAD \ Call LOAD to load the commander file to address &0791 LDA &0791 \ 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 LDY #NT% \ We have successfully loaded the commander file at \ &0791, so now we want to copy it to the last saved \ commander data block at NA%+8, so we set up a counter \ in Y to copy NT% bytes .LOL1 LDA &0791,Y \ Copy the Y-th byte of &0791 to the Y-th byte of NA%+8 STA NA%+8,Y DEY \ 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 LDA #9 \ Print extended token 9 ("{cr}{all caps}ILLEGAL ELITE JSR DETOK \ II FILE{sentence case}") JSR t \ Scan the keyboard until a key is pressed, returning \ the ASCII code in A and X JMP SVE \ Jump to SVE to display the disc access menu and return \ from the subroutine using a tail call RTS \ Return from the subroutine RTS \ This instruction has no effect as we already returned \ from the subroutine
Name: CTLI [Show more] Type: Variable Category: Save and load Summary: The OS command string for cataloguing a disc
Context: See this variable on its own page Variations: See code variations for this variable in the different versions References: This variable is used as follows: * CATS calls CTLI * DELT calls CTLI
.CTLI IF _SNG47 EQUS "CAT 1" \ The "1" part of the string is overwritten with the EQUB 13 \ actual drive number by the CATS routine ELIF _COMPACT EQUS "CAT" \ The Master Compact only had one drive, so the CAT EQUB 13 \ command always catalogues that drive ENDIF
Name: DELI [Show more] Type: Variable Category: Save and load Summary: The OS command string for deleting a file
Context: See this variable on its own page Variations: See code variations for this variable in the different versions References: This variable is used as follows: * DELT calls DELI
.DELI IF _SNG47 EQUS "DELETE :1.1234567" EQUB 13 ELIF _COMPACT EQUS "DELETE 1234567890" EQUB 13 ENDIF
Name: DIRI [Show more] Type: Variable Category: Save and load Summary: The OS command string for changing directory on the Master Compact
Context: See this variable on its own page References: This variable is used as follows: * GTDIR calls DIRI
IF _COMPACT .DIRI EQUS "DIR 12345678901234567890" EQUB 13 ENDIF
Name: SVLI [Show more] Type: Variable Category: Save and load Summary: The OS command string for saving a commander file
Context: See this variable on its own page References: This variable is used as follows: * SAVE calls SVLI * SVE calls SVLI
.SVLI IF _SNG47 EQUS "SAVE :1.E.JAMESON E7E +100 0 0" EQUB 13 ELIF _COMPACT EQUS "SAVE JAMESON E7E +100 0 0" EQUB 13 ENDIF
Name: LDLI [Show more] Type: Variable Category: Save and load Summary: The OS command string for loading a commander file
Context: See this variable on its own page References: This variable is used as follows: * LOAD calls LDLI * SVE calls LDLI
.LDLI IF _SNG47 EQUS "LOAD :1.E.JAMESON E7E" EQUB 13 ELIF _COMPACT EQUS "LOAD JAMESON E7E" EQUB 13 ENDIF
Name: SAVE [Show more] Type: Subroutine Category: Save and load Summary: Save the commander file
Context: See this subroutine on its own page References: This subroutine is called as follows: * SVE calls SAVE
.SAVE LDY #NT% \ We first want to copy the current commander data block \ to location &0E7E so we can do a file save operation, \ so we set a counter in Y to copy the NT% bytes in the \ commander data block .SAVEL1 LDA NA%+8,Y \ Copy the Y-th byte of NA%+8 to the Y-th byte of &0E7E STA &0E7E,Y DEY \ Decrement the loop counter BPL SAVEL1 \ Loop back until we have copied all the bytes in the \ commander data block LDA #0 \ The save file is 256 bytes long but only NT% (76) of \ those contain data, so before we save we need to zero \ out the rest of the 256-byte block, so we set A = 0 to \ do this LDY #NT% \ Set an index in Y to point the byte after the end of \ the first NT% bytes in the commander data block .SAVEL2 STA &0E7E,Y \ Zero the Y-th byte of &0E7E INY \ Increment the loop counter BNE SAVEL2 \ Loop back until we have zeroed the rest of the \ 256-byte block LDY #0 \ Now we need to change the save command at SVLI to \ contain the commander name as the filename, so set an \ index in Y so we can copy the commander name from NA% \ into the SVLI command .SAVEL3 LDA NA%,Y \ Fetch the Y-th character of the commander name at NA% CMP #13 \ If the character is a carriage return then we have BEQ SAVEL4 \ reached the end of the name, so jump to SAVEL4 as we \ have now copied the whole name IF _SNG47 STA SVLI+10,Y \ Store the Y-th character of the commander name in the \ Y-th character of SVLI+10, where SVLI+10 points to the \ JAMESON part of the save command in SVLI: \ \ "SAVE :1.E.JAMESON E7E +100 0 0" ELIF _COMPACT STA SVLI+5,Y \ Store the Y-th character of the commander name in the \ Y-th character of SVLI+5, where SVLI+5 points to the \ JAMESON part of the save command in SVLI: \ \ "SAVE JAMESON E7E +100 0 0" ENDIF INY \ Increment the loop counter CPY #7 \ If Y < 7 then there may be more characters in the BCC SAVEL3 \ name, so loop back to SAVEL3 to fetch the next one .SAVEL4 LDA #' ' \ We have copied the name into the SVLI command string, \ but the new name might be shorter then the previous \ one, so we now need to blank out the rest of the name \ with spaces, so we load the space character into A IF _SNG47 STA SVLI+10,Y \ Store the Y-th character of the commander name in the \ Y-th character of SVLI+10, which will be directly \ after the last letter we copied above ELIF _COMPACT STA SVLI+5,Y \ Store the Y-th character of the commander name in the \ Y-th character of SVLI+5, which will be directly \ after the last letter we copied above ENDIF INY \ Increment the loop counter CPY #7 \ If Y < 7 then we haven't yet blanked out the whole BCC SAVEL4 \ name, so loop back to SAVEL4 to blank the next one \ until the save string is ready for use IF _SNG47 JSR SWAPZP \ Call SWAPZP to store the top part of zero page, as it \ gets corrupted by the MOS during the saving process ELIF _COMPACT JSR NMIRELEASE \ Release the NMI workspace (&00A0 to &00A7) ENDIF LDX #LO(SVLI) \ Set (Y X) to point to the OS command at SVLI, which LDY #HI(SVLI) \ contains the DFS command for saving the commander file JSR OSCLI \ Call OSCLI to execute the OS command at (Y X), which \ saves the commander file JMP SWAPZP \ Call SWAPZP to restore the top part of zero page \ and return from the subroutine using a tail call
Name: LOAD [Show more] Type: Subroutine Category: Save and load Summary: Load the commander file
Context: See this subroutine on its own page References: This subroutine is called as follows: * LOD calls LOAD

Arguments: INWK+5 The filename, terminated by a carriage return
.LOAD LDY #0 \ We start by changing the load command at LDLI to \ contain the filename that was just entered by the \ user, so we set an index in Y so we can copy the \ filename from INWK+5 into the LDLI command .LOADL1 LDA INWK+5,Y \ Fetch the Y-th character of the filename CMP #13 \ If the character is a carriage return then we have BEQ LOADL2 \ reached the end of the filename, so jump to LOADL2 as \ we have now copied the whole filename IF _SNG47 STA LDLI+10,Y \ Store the Y-th character of the filename in the Y-th \ character of LDLI+10, where LDLI+10 points to the \ JAMESON part of the load command in LDLI: \ \ "LOAD :1.E.JAMESON E7E" ELIF _COMPACT STA LDLI+5,Y \ Store the Y-th character of the filename in the Y-th \ character of LDLI+5, where LDLI+5 points to the \ JAMESON part of the load command in LDLI: \ \ "LOAD JAMESON E7E" ENDIF INY \ Increment the loop counter CPY #7 \ If Y < 7 then there may be more characters in the BCC LOADL1 \ name, so loop back to LOADL1 to fetch the next one .LOADL2 LDA #' ' \ We have copied the name into the LDLI command string, \ but the new name might be shorter then the previous \ one, so we now need to blank out the rest of the name \ with spaces, so we load the space character into A IF _SNG47 STA LDLI+10,Y \ Store the Y-th character of the filename in the Y-th \ character of LDLI+10, which will be directly after \ the last letter we copied above ELIF _COMPACT STA LDLI+5,Y \ Store the Y-th character of the filename in the Y-th \ character of LDLI+5, which will be directly after \ the last letter we copied above ENDIF INY \ Increment the loop counter CPY #7 \ If Y < 7 then we haven't yet blanked out the whole BCC LOADL2 \ name, so loop back to LOADL2 to blank the next one \ until the load string is ready for use IF _SNG47 JSR SWAPZP \ Call SWAPZP to store the top part of zero page, as it \ gets corrupted by the MOS during the loading process ELIF _COMPACT JSR NMIRELEASE \ Release the NMI workspace (&00A0 to &00A7) ENDIF LDX #LO(LDLI) \ Set (Y X) to point to the OS command at LDLI, which LDY #HI(LDLI) \ contains the DFS command for loading the commander \ file JSR OSCLI \ Call OSCLI to execute the OS command at (Y X), which \ loads the commander file JSR SWAPZP \ Call SWAPZP to restore the top part of zero page LDY #NT% \ We now want to copy the newly loaded commander data \ block to location &0791, so we set a counter in Y to \ copy the NT% bytes in the commander data block .LOADL3 LDA &0E7E,Y \ Copy the Y-th byte of &0E7E to the Y-th byte of &0791 STA &0791,Y DEY \ Decrement the loop counter BPL LOADL3 \ Loop back until we have copied all the bytes in the \ newly loaded commander data block RTS \ Return from the subroutine RTS \ This instruction has no effect as we already returned \ from the subroutine
Name: SPS1 [Show more] Type: Subroutine Category: Maths (Geometry) Summary: Calculate the vector to the planet and store it in XX15
Context: See this subroutine on its own page References: This subroutine is called as follows: * COMPAS calls SPS1 * Main flight loop (Part 9 of 16) calls SPS1 * TACTICS (Part 3 of 7) calls SPS1

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 [Show more] Type: Subroutine Category: Maths (Geometry) Summary: Normalise the three-coordinate vector in K3
Context: See this subroutine on its own page References: This subroutine is called as follows: * DOCKIT calls TAS2 * SPS4 calls TAS2 * TACTICS (Part 3 of 7) calls TAS2 * DOCKIT calls entry point TA2

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 [Show more] Type: Subroutine Category: Maths (Geometry) Summary: Normalise the three-coordinate vector in XX15 Deep dive: Tidying orthonormal vectors Orientation vectors
Context: See this subroutine on its own page References: This subroutine is called as follows: * TIDY calls NORM

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: WARP [Show more] Type: Subroutine Category: Flight Summary: Perform an in-system jump
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * Main flight loop (Part 3 of 16) calls WARP

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, Transporters 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) 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 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 JMP LOWBEEP \ Call the LOWBEEP routine to make a long, low beep, and \ return from the subroutine using a tail call RTS \ This instruction has no effect as we already returned \ from the subroutine
Name: DKS3 [Show more] Type: Subroutine Category: Keyboard Summary: Toggle a configuration setting and emit a beep
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * DK4 calls DKS3

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 (0) * A toggles keyboard auto-recentre (1) * X toggles author names on start-up screen (2) * F toggles flashing console bars (3) * Y toggles reverse joystick Y channel (4) * J toggles reverse both joystick channels (5) * K toggles keyboard and joystick (6) The numbers in brackets are the configuration options that we pass in Y. We pass the ASCII code of the key that has been pressed in X, and the option to check it against in Y, so this routine is typically called in a loop that loops through the various configuration option. Arguments: X The ASCII code of the key that's been pressed Y The number of the configuration option to check against from the list above (i.e. Y must be from 0 to 6)
.DKS3 TXA \ Copy the ASCII code of the key that has been pressed \ into A CMP CKEYS,Y \ If the pressed key doesn't match the configuration key BNE Dk3 \ for option Y (as listed in the CKEYS table), then jump \ to Dk3 to return from the subroutine LDA DAMP,Y \ The configuration keys listed in CKEYS correspond to EOR #&FF \ the configuration option settings from DAMP onwards, STA DAMP,Y \ so to toggle a setting, we fetch the existing byte \ from DAMP+Y, invert it and put it back (0 means no \ and &FF means yes in the configuration bytes, so \ this toggles the setting) BPL P%+5 \ If the result has a clear bit 7 (i.e. we just turned \ the option off), skip the following instruction JSR BELL \ We just turned the option on, so make a standard \ system beep, so in all we make two beeps JSR BELL \ Make a beep sound so we know something has happened TYA \ Store Y and A on the stack so we can retrieve them PHA \ below LDY #20 \ Wait for 20 vertical syncs (20/50 = 0.4 seconds) JSR DELAY PLA \ Restore A and Y from the stack TAY .Dk3 RTS \ Return from the subroutine
Name: DOKEY [Show more] Type: Subroutine Category: Keyboard Summary: Scan for the seven primary flight controls Deep dive: The key logger The docking computer
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * TT17 calls DOKEY

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.
.DOKEY JSR RDKEY-1 \ Scan the keyboard for a key press and return the \ ASCII code of the key pressed in X LDA auto \ If auto is 0, then the docking computer is not BEQ DK16 \ currently activated, so jump to DK16 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 #15 \ Set X = 0, so we "press" KY+15, i.e. KY1, below \ ("?", slow down) LDY INWK+28 \ If the updated acceleration in byte #28 is zero, skip BEQ DK11 \ to DK11 BMI P%+4 \ If the updated acceleration is negative, skip the \ following instruction LDX #11 \ Set X = 11, so we "press" KY+11, i.e. KY2, with the \ next instruction (Space, speed up) STA KL,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 #13 \ Set X = 13, so we "press" KY+13, i.e. 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%+4 \ If the C flag is clear, skip the following instruction LDX #14 \ The C flag is set, i.e. the direction of the updated \ roll counter is negative, so set X to 14 so we \ "press" KY+14. i.e. 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 KL,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 #6 \ Set X = 6, so we "press" KY+6, i.e. 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%+4 \ If the C flag is set, skip the following instruction LDX #8 \ Set X = 6, so we "press" KY+8, i.e. KY6, with the next \ instruction ("S", increase pitch) STA KL,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 IF _COMPACT JMP DK15 \ Jump to DK15 to skip reading the joystick, as this is \ a Master Compact that doesn't support an analogue \ joystick (instead it supports a digital joystick, \ which is read elsewhere) ENDIF .DK16 LDA JSTK \ If JSTK is zero, then we are configured to use the BEQ DK15 \ keyboard rather than the joystick, so jump to DK15 to \ skip reading the joystick IF _SNG47 LDA ADCH1 \ Fetch the high byte of the joystick X value 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) ORA #1 \ Ensure the value is at least 1 STA JSTX \ Store the resulting joystick X value in JSTX LDA ADCH2 \ Fetch the high byte of the joystick Y value EOR #&FF \ This EOR is used in conjunction with the EOR JSTGY \ below, as having a value of 0 in JSTGY means we have \ to invert the joystick Y value, and this EOR does \ that part 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) EOR JSTGY \ JSTGY will be 0 if the game is configured to reverse \ the joystick Y channel, so this EOR along with the \ EOR #&FF above does exactly that STA JSTY \ Store the resulting joystick Y value in JSTY LDA VIA+&40 \ Read 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 BNE DK4 \ If the joystick fire button is not being pressed, \ jump to DK4 to scan for other keys LDA #&FF \ Update the key logger at KY7 to "press" the "A" (fire) STA KY7 \ button BNE DK4 \ Jump to DK4 to scan for other keys (this BNE is \ effectively a JMP as A is never 0) ELIF _COMPACT JSR RDJOY \ Call RDJOY to read from either the analogue or digital \ joystick BCC DK4 \ If we just read from the analogue joystick, the C flag \ will be clear, so jump to DK4 to scan for other keys \ Otherwise we just read the digital joystick, so we now \ update the pitch and roll ENDIF .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 KY3 \ If the "<" key is not being pressed, skip the next BEQ P%+5 \ instruction JSR BUMP2 \ The "<" key is being pressed, so call the BUMP2 \ routine to increase the roll rate in X by A LDY KY4 \ If the ">" key is not being pressed, skip the next BEQ P%+5 \ instruction JSR REDU2 \ The "<" key is being pressed, so call the REDU2 \ routine to decrease the roll rate in X by A, taking \ 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 KY5 \ If the "X" key is not being pressed, skip the next BEQ P%+5 \ instruction JSR REDU2 \ The "X" key is being pressed, so call the REDU2 \ routine to decrease the pitch rate in X by A, taking \ the keyboard auto re-centre setting into account LDY KY6 \ If the "S" key is not being pressed, skip the next BEQ P%+5 \ instruction JSR BUMP2 \ The "S" key is being pressed, so call the BUMP2 \ routine to increase the pitch rate in X by A STX JSTY \ Store the updated roll rate in JSTY \ Fall through into DK4 to scan for other keys
Name: DK4 [Show more] Type: Subroutine Category: Keyboard Summary: Scan for pause, configuration and secondary flight keys Deep dive: The key logger
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * DOKEY calls DK4

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
.DK4 LDX KL \ Fetch the key pressed from byte #0 of the key logger CPX #&8B \ 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 \ ASCII code of the key pressed in X (or 0 for no key \ press) CPX #'Q' \ If "Q" is not being pressed, skip to DK6 BNE DK6 LDX #&FF \ "Q" is being pressed, so set DNOIZ to &FF to turn the STX DNOIZ \ sound off LDX #&51 \ Set X to &51, which is the internal key for "S" on the \ BBC Micro. This is set to ensure that X has the same \ value at this point as the BBC Micro version of this \ routine would .DK6 LDY #0 \ We now want to loop through the keys that toggle \ various settings, so set a counter in Y to work our \ way through them .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 #9 \ Check to see whether we have reached the last toggle \ key BNE DKL4 \ If not, loop back to check for the next toggle key LDA VOLUME \ Fetch the current volume setting into A CPX #'.' \ If "." is being pressed (i.e. the ">" key) then jump BEQ VOLUP \ to VOLUP to increase the volume CPX #',' \ If "," is not being pressed (i.e. the "<" key) then BNE NOVOL \ jump to NOVOL to skip the following DEC A \ The volume down key is being pressed, so decrement the \ volume level in A EQUB &24 \ Skip the next instruction by turning it into &24 &1A, \ or BIT &001A, which does nothing apart from affect the \ flags .VOLUP INC A \ The volume up key is being pressed, so increment the \ volume level in A TAY \ Copy the new volumen level to Y AND #%11111000 \ If any of bits 3-7 are set, skip to MAXVOL as we have BNE MAXVOL \ either increased the volume past the maximum volume of \ 7, or we have decreased it below 0 to -1, and in \ neither case do we want to change the volume as we are \ already at the maximum or minimum level STY VOLUME \ Store the new volume level in VOLUME .MAXVOL PHX \ Store X on the stack so we can retrieve it below after \ making a beep JSR BEEP \ Call the BEEP subroutine to make a short, high beep at \ the new volume level LDY #10 \ Wait for 10/50 of a second (0.2 seconds) JSR DELAY PLX \ Restore the value of X we stored above .NOVOL CPX #'B' \ 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 BPL P%+5 \ If we just toggled the Bitstik off (i.e. to 0, which \ is positive), then skip the following two instructions JSR BELL \ We just enabled the Bitstik, so give two standard JSR BELL \ system beeps .nobit CPX #'S' \ If "S" is not being pressed, jump to DK7 BNE DK7 LDA #0 \ "S" is being pressed, so set DNOIZ to 0 to turn the STA DNOIZ \ sound on .DK7 CPX #&1B \ 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 #&7F \ 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 RTS \ Return from the subroutine
Name: TT217 [Show more] Type: Subroutine Category: Keyboard Summary: Scan the keyboard until a key is pressed
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * MT26 calls TT217 * TT214 calls TT217 * gnum calls TT217 * qv calls TT217 * BRBR calls entry point t * GETYN calls entry point t * GTDRV calls entry point t * LOD calls entry point t * SVE calls entry point t * OUCH calls entry point out * mes9 calls entry point out

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 \ ASCII code of the key pressed 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 \ ASCII code of the key pressed in X (or 0 for no key \ press) BEQ t2 \ Keep looping up to t2 until a key is pressed LDY YSAV \ Restore the original value of Y we stored above TAX \ Copy A into X .out RTS \ Return from the subroutine
Name: me1 [Show more] Type: Subroutine Category: Text Summary: Erase an old in-flight message and display a new one
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * MESS calls me1

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 #YELLOW \ Switch to colour 1, which is yellow STA COL 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 [Show more] Type: Subroutine Category: Text Summary: Display an in-flight message
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * EXNO2 calls MESS * FR1 calls MESS * Ghy calls MESS * KILLSHP calls MESS * Main flight loop (Part 12 of 16) calls MESS * Main flight loop (Part 15 of 16) calls MESS * Main flight loop (Part 8 of 16) calls MESS * OUCH calls MESS * SFRMIS calls MESS * me2 calls MESS * ou2 calls MESS * ou3 calls MESS

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 LDX QQ11 \ If this is the space view, skip the following BEQ P%+5 \ instruction 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 LDA #21 \ Move the text cursor to row 21 STA YC LDA #YELLOW \ Switch to colour 1, which is yellow STA COL LDX #0 \ Set QQ17 = 0 to switch to ALL CAPS STX QQ17 LDA messXC \ Move the text cursor to column messXC, in case we STA XC \ 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) PLA \ Restore A from the stack LDY #20 \ Set Y = 20 for setting the message delay below 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 20 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 STA XC \ 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 [Show more] Type: Subroutine Category: Text Summary: Print a text token, possibly followed by " DESTROYED"
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * me1 calls mes9

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 0 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 [Show more] Type: Subroutine Category: Flight Summary: Potentially lose cargo or equipment following damage
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * OOPS calls OUCH

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 (91% 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 JMP 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 [Show more] Type: Subroutine Category: Text Summary: Display "E.C.M.SYSTEM DESTROYED" as an in-flight message
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * OUCH calls ou2
.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 [Show more] Type: Subroutine Category: Text Summary: Display "FUEL SCOOPS DESTROYED" as an in-flight message
Context: See this subroutine on its own page Variations: See code variations for this subroutine in the different versions References: This subroutine is called as follows: * OUCH calls ou3
.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 [Show more] Type: Macro Category: Market Summary: Macro definition for the market prices table Deep dive: Market item prices and availability
Context: See this macro on its own page References: No direct references to this macro in this source file

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 [Show more] Type: Variable Category: Market Summary: Market prices table
Context: See this variable on its own page References: This variable is used as follows: * GVL calls QQ23 * TT151 calls QQ23 * TT210 calls QQ23

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: TIDY [Show more] Type: Subroutine Category: Maths (Geometry) Summary: Orthonormalise the orientation vectors for a ship Deep dive: Tidying orthonormal vectors Orientation vectors
Context: See this subroutine on its own page References: This subroutine is called as follows: * HAS1 calls TIDY * MVEIT (Part 1 of 9) calls TIDY

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 [Show more] Type: Subroutine Category: Maths (Arithmetic) Summary: Calculate A = A / Q Deep dive: Shift-and-subtract division
Context: See this subroutine on its own page References: This subroutine is called as follows: * NORM calls TIS2

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 [Show more] Type: Subroutine Category: Maths (Arithmetic) Summary: Calculate -(nosev_1 * roofv_1 + nosev_2 * roofv_2) / nosev_3
Context: See this subroutine on its own page References: This subroutine is called as follows: * TIDY calls TIS3

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 [Show more] Type: Subroutine Category: Maths (Arithmetic) Summary: Calculate (P+1 A) = (A P) / Q
Context: See this subroutine on its own page References: No direct references to this subroutine in this source file

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 [Show more] Type: Variable Category: Keyboard Summary: The key logger buffer that gets updated by the OSWORD 240 command
Context: See this variable on its own page References: No direct references to this variable in this source file

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)
Save 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 "3-assembled-output/ELTF.bin", CODE_F%, P%, LOAD%