Version analysis of DEATH - Elite on the BBC Micro and NES

This code appears in the following versions (click to see it in the source code):

Cassette, Disc (flight), 6502 Second Processor, Master and Electron

Code variations between these versions are shown below.

       Name: DEATH
       Type: Subroutine
   Category: Start and end
    Summary: Display the death screen


 We have been killed, so display the chaos of our destruction above a "GAME
 OVER" sign, and clean up the mess ready for the next attempt.


.DEATH

Code variation 1 of 20Specific to an individual platform

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Cassette, Flight, 6502SP, Electron
Master
 JSR EXNO3              \ Make the sound of us dying
 LDY #soexpl            \ 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

Code variation 2 of 20Related to the Electron version

The Electron version doesn't hide the dashboard when you die. This effect is implemented in the BBC versions by programming the 6845 CRTC, which isn't present on the Electron.

See below for more variations related to this code.

This variation is blank in the Electron version.

Cassette, Flight, 6502SP, Master
 LDX #24                \ Set the screen to only show 24 text rows, which hides
 JSR DET1               \ the dashboard, setting A to 6 in the process

Code variation 3 of 20Specific to an individual platform

The Master version has a unique view type for the title screen (13).

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Cassette, Flight, 6502SP, Electron
Master
 JSR TT66               \ Clear the top part of the screen, draw a white border,
                        \ and set the current view type in QQ11 to 6 (death
                        \ screen)
 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

Code variation 4 of 20Specific to an individual platform

This variation is blank in the Cassette, Disc (flight), 6502 Second Processor and Master versions.

Electron
 LDX #50                \ Set the laser count to 50 to act as a counter in the
 STX LASCT              \ D2 loop below, so this setting determines how long the
                        \ death animation lasts (LASCT decreases by 4 for each
                        \ iteration round the main loop, and we also decrement
                        \ it by 1 below to give a total of 5, so this makes the
                        \ animation last for 10 iterations of the main loop)

 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)

Code variation 5 of 20Related to an advanced feature

In the Master version, the "GAME OVER" message is cyan, while in the 6502SP version it is yellow.

See below for more variations related to this code.

This variation is blank in the Cassette, Disc (flight), 6502 Second Processor and Electron versions.

Master
 LDA #CYAN              \ Change the current colour to cyan
 STA COL

Code variation 6 of 20Related to Elite's use of the Tube

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Cassette, Flight, Electron
Master
6502SP
 LDA #12                \ Move the text cursor to column 12 on row 12
 STA YC
 STA XC
 LDA #12                \ Move the text cursor to column 12 on row 12
 STA XC
 STA YC
 LDA #12                \ Move the text cursor to column 12 on row 12
 JSR DOYC
 JSR DOXC

Code variation 7 of 20Related to an advanced feature

See variation 5 above for details.

This variation is blank in the Cassette, Disc (flight), Master and Electron versions.

6502SP
 LDA #YELLOW            \ Send a #SETCOL YELLOW command to the I/O processor to
 JSR DOCOL              \ change the current colour to yellow

Code variation 8 of 20Specific to an individual platform

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Cassette, Flight, 6502SP, Master
Electron
 LDA #146               \ Print recursive token 146 ("{all caps}GAME OVER")
 JSR ex
 LDA #146               \ Print recursive token 146 ("{all caps}GAME OVER")
 STA MCNT               \ and reset the main loop counter to 146, so all
 JSR ex                 \ timer-based calls will be stopped

.D1

 JSR Ze                 \ Call Ze to initialise INWK to a potentially hostile
                        \ ship, and set A and X to random values

Code variation 9 of 20Related to the Electron version

In the Electron version, the cargo canisters we see when we die always spawn at an x-coordinate of magnitude 32, so canisters appear on either side of the view but never in the centre. It's much more random in the other versions.

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Cassette, Flight, 6502SP, Master
Electron
 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
 LDA #32                \ Set x_lo = 32
 STA INWK

Code variation 10 of 20Specific to an individual platform

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Cassette, Flight, 6502SP, Electron
Master
 LDY #0                 \ Set the following to 0: the current view in QQ11
 STY QQ11               \ (space view), x_hi, y_hi, z_hi and the AI flag (no AI
 STY INWK+1             \ or E.C.M. and not hostile)
 STY INWK+4
 STY INWK+7
 STY INWK+32
 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

Code variation 11 of 20Specific to an individual platform

This variation is blank in the Electron version.

Cassette, Flight, 6502SP, Master
 STY MCNT               \ Reset the main loop counter to 255, so all timer-based
                        \ calls will be stopped

Code variation 12 of 20Specific to an individual platform

This variation is blank in the 6502 Second Processor, Master and Electron versions.

Cassette, Flight
 STY LASCT              \ Set the laser count to 255 to act as a counter in the
                        \ D2 loop below, so this setting determines how long the
                        \ death animation lasts (it's 5.1 seconds, as LASCT is
                        \ decremented every vertical sync, or 50 times a second,
                        \ and 255 / 50 = 5.1)

 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 sign in bit 7 to get a number between -15 and +15,
 STA INWK+29            \ and store in byte #29 (roll counter) to give our ship
                        \ a gentle roll with damping

Code variation 13 of 20Specific to an individual platform

This variation is blank in the Cassette, Disc (flight) and Electron versions.

Tap on a block to expand it, and tap it again to revert.

Master
6502SP
 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)
 STY LASCT              \ Set the laser count to 127 to act as a counter in the
 LSR LASCT              \ D2 loop below, so this setting determines how long the
                        \ death animation lasts (it's 127 iterations of the main
                        \ flight loop)

Code variation 14 of 20Related to the Master version

In the cassette, disc and 6502SP versions, our ship is given a gentle pitch up or down when we die; the same is true in the Master version, but the pitch is always downwards so the detritus of our death always rises to the top of the screen.

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Cassette, Flight, 6502SP, Electron
Master
 ROR A                  \ The C flag is randomly set from the above call to Ze,
 AND #%10000111         \ so this sets A to a number between -7 and +7, which
 STA INWK+30            \ we store in byte #30 (the pitch counter) to give our
                        \ ship a very gentle pitch with damping
 SEC                    \ Set the C flag

 ROR A                  \ This sets A to a number between 0 and +7, which we
 AND #%10000111         \ store in byte #30 (the pitch counter) to give our ship
 STA INWK+30            \ a very gentle downwards pitch with damping

Code variation 15 of 20Related to an enhanced feature

On death, the cassette version shows your ship explosion along with up to four cargo canisters; in the enhanced versions, it shows up to five items, which can be a mix of cargo canisters and alloy plates.

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Cassette, Electron
Flight, 6502SP, Master
 PHP                    \ Store the processor flags

 LDX #OIL               \ Call fq1 with X set to #OIL, which adds a new cargo
 JSR fq1                \ canister 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 canister's ship data block in K%

 PLP                    \ Restore the processor flags, including our random C
                        \ flag from before

 LDA #0                 \ Set bit 7 of A to our random C flag and store in byte
 ROR A                  \ #31 of the ship's data block, so this has a 50% chance
 LDY #31                \ of marking our new canister as being killed (so it
 STA (INF),Y            \ will explode)

 LDA FRIN+3             \ 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 fourth slot is empty, and if it
                        \ is we loop back to D1 to add another canister, until
                        \ we have added four of them
 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

Code variation 16 of 20Specific to an individual platform

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Cassette, Flight, 6502SP, Electron
Master
 JSR U%                 \ Clear the key logger, which also sets A = 0

 STA DELTA              \ Set our speed in DELTA to 0, as we aren't going
                        \ anywhere any more
\JSR U%                 \ This instruction is commented out in the original
                        \ source

 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

\JSR NOSPRITES          \ This instruction is commented out in the original
                        \ source

.D2

Code variation 17 of 20A variation in the comments only

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Cassette, Flight, Electron
6502SP, Master
 JSR M%                 \ Call the M% routine to do the main flight loop once,
                        \ which will display our exploding canister scene and
                        \ move everything about
 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

Code variation 18 of 20Specific to an individual platform

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Cassette, Flight
6502SP, Master, Electron
 LDA LASCT              \ Loop back to D2 to run the main flight loop until
 BNE D2                 \ LASCT reaches zero (which will take 5.1 seconds, as
                        \ explained above)
 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

Code variation 19 of 20Related to the Electron version

See variation 2 above for details.

This variation is blank in the Electron version.

Cassette, Flight, 6502SP, Master
 LDX #31                \ Set the screen to show all 31 text rows, which shows
 JSR DET1               \ the dashboard

Code variation 20 of 20Minor and very low-impact

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Cassette, Electron
Flight, 6502SP, Master
                        \ Fall through into DEATH2 to reset and restart the game
 JMP DEATH2             \ Jump to DEATH2 to reset and restart the game