Version analysis of MJP - Elite on the 6502

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

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

Code variations between these versions are shown below.

       Name: MJP
       Type: Subroutine
   Category: Flight
    Summary: Process a mis-jump into witchspace


 Process a mis-jump into witchspace (which happens very rarely). Witchspace has
 a strange, almost dust-free aspect to it, and it is populated by hostile
 Thargoids. Using our escape pod will be fatal, and our position on the
 galactic chart is in-between systems. It is a scary place...

 There is a 0.78% chance that this routine is called from TT18 instead of doing
 a normal hyperspace, or we can manually trigger a mis-jump by holding down
 CTRL after first enabling the "author display" configuration option ("X") when
 paused.


 Other entry points:

   ptg                  Called when the user manually forces a mis-jump

Code variation 1 of 8A variation in the comments only

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

6502SP, Master
   RTS111               Contains an RTS


.ptg

 LSR COK                \ Set bit 0 of the competition flags in COK, so that the
 SEC                    \ competition code will include the fact that we have
 ROL COK                \ manually forced a mis-jump into witchspace

.MJP

Code variation 2 of 8A variation in the comments only

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

6502SP, Master
\JSR CATLOD             \ This instruction is commented out in the original
                        \ source

Code variation 3 of 8Specific to an individual platform

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

Flight
 LDA #3                 \ Call SHIPinA to load ship blueprints file D, which is
 JSR SHIPinA            \ one of the two files that contain Thargoids

Code variation 4 of 8Minor and very low-impact

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

Cassette
Flight, 6502SP, Master
\LDA #1                 \ This instruction is commented out in the original
                        \ source - it is not required as a call to TT66-2 sets
                        \ A to 1 for us. This is presumably an example of the
                        \ authors saving a couple of bytes by calling TT66-2
                        \ instead of TT66, while leaving the original LDA
                        \ instruction in place

 JSR TT66-2             \ Clear the top part of the screen, draw a border box,
                        \ and set the current view type in QQ11 to 1
 LDA #3                 \ Clear the top part of the screen, draw a border box,
 JSR TT66               \ and set the current view type in QQ11 to 3

 JSR LL164              \ Call LL164 to show the hyperspace tunnel and make the
                        \ hyperspace sound for a second time (as we already
                        \ called LL164 in TT18)

 JSR RES2               \ Reset a number of flight variables and workspaces, as
                        \ well as setting Y to &FF

 STY MJ                 \ Set the mis-jump flag in MJ to &FF, to indicate that
                        \ we are now in witchspace

Code variation 5 of 8Related to the 6502SP version

If speech is enabled on the Executive version, it will say "Oh shit, it's a mis-jump" when we mis-jump into witchspace (this happens with both accidental and manually triggered mis-jumps).

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

6502SP
IF _EXECUTIVE

 LDX #4                 \ Call TALK with X = 4 to say "Oh shit, it's a mis-jump"
 JSR TALK               \ using the Watford Electronics Beeb Speech Synthesiser
                        \ (if one is fitted and speech has been enabled)

ENDIF

.MJP1

 JSR GTHG               \ Call GTHG to spawn a Thargoid ship and a Thargon
                        \ companion

Code variation 6 of 8Related to the Master version

The Master version spawns three Thargoid motherships in witchspace, while the other versions spawn four.

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

Cassette, Flight, 6502SP
Master
 LDA #3                 \ Fetch the number of Thargoid ships from MANY+THG, and
 CMP MANY+THG           \ if it is less than or equal to 3, loop back to MJP1 to
 BCS MJP1               \ spawn another one, until we have four Thargoids
 LDA #2                 \ Fetch the number of Thargoid ships from MANY+THG, and
 CMP MANY+THG           \ if it is less than or equal to 2, loop back to MJP1 to
 BCS MJP1               \ spawn another one, until we have three Thargoids

 STA NOSTM              \ Set NOSTM (the maximum number of stardust particles)
                        \ to 3, so there are fewer bits of stardust in
                        \ witchspace (normal space has a maximum of 18)

 LDX #0                 \ Initialise the front space view
 JSR LOOK1

 LDA QQ1                \ Fetch the current system's galactic y-coordinate in
 EOR #%00011111         \ QQ1 and flip bits 0-5, so we end up somewhere in the
 STA QQ1                \ vicinity of our original destination, but above or
                        \ below it in the galactic chart

Code variation 7 of 8Specific to an individual platform

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

Master
 RTS                    \ Return from the subroutine

Code variation 8 of 8A variation in the labels only

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

6502SP, Master
.RTS111

 RTS                    \ Return from the subroutine