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Elite on the BBC Micro

Version analysis of MJP

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

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 1% 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 7A 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 \ copmpetition code will include the fact that we have ROL COK \ manually forced a mis-jump into witchspace .MJP

Code variation 2 of 7Specific 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 3 of 7Minor and very low-impact

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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 white border, \ and set the current view type in QQ11 to 1
LDA #3 \ Clear the top part of the screen, draw a white border, 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 4 of 7Related 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

Code variation 5 of 7Related to the Master version

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

Tap on a version to expand it, and tap it again to show to all variations.

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 6 of 7Specific 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 7 of 7A variation in the labels only

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

6502SP, Master

.RTS111
 RTS                    \ Return from the subroutine

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