This code appears in the following versions (click to see it in the source code):
Code variations between these versions are shown below.
.MLOOPName: Main game loop (Part 5 of 6) 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
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)
The cassette version disables keyboard interrupts at the start of the minimal game loop, though I'm not entirely sure why.
This variation is blank in the Disc (flight), Disc (docked), 6502 Second Processor, Master and Electron versions.
LDA #%00000001 \ Set 6522 System VIA interrupt enable register IER STA VIA+&4E \ (SHEILA &4E) bit 1 (i.e. disable the CA2 interrupt, \ which comes from the keyboard)
This variation is blank in the Cassette, Disc (flight), Disc (docked), 6502 Second Processor and Master versions.
LDA LASCT \ Set A to the value of LASCT, the laser pulse count SBC #4 \ Decrement the value of LASCT by 4 BCS P%+4 \ If we just reduced LASCT below 0, set it to 0 LDA #0 STA LASCT \ Store the decremented value of X in LASCT, so LASCT \ gets reduced by 4, but not into negative territory
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
This variation is blank in the Cassette, Disc (flight), Disc (docked), 6502 Second Processor and Master versions.
INX \ Set KEYB = 0 to indicate we are not currently reading STX KEYB \ the keyboard using an OS command
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
This variation is blank in the Cassette, Disc (flight), Disc (docked) and Electron versions.
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
This variation is blank in the Cassette, Disc (flight), Disc (docked), 6502 Second Processor and Electron versions.
\LDA QQ11 \ These instructions are commented out in the original \BNE P%+5 \ source
JSR DIALS \ Call DIALS to update the dashboard
The 6502SP version supports a printer (holding CTRL when pressing a red function key will send that screen to the printer). As part of this, the code sends line feeds, which is mainly notable for using the longest label name in the entire source code: dontdolinefeedontheprinternow.
This variation is blank in the Cassette, Disc (flight), Disc (docked), Master and Electron versions.
BIT printflag \ If bit 7 of printflag is clear (printer output is not \ enabled), jump to dontdolinefeedontheprinternow to \ skip the following (and en route, why not take a \ short moment to admire this, the longest label name in \ the original Elite source code - presumably they got \ longer when development moved to a 6502 second \ processor system, with all that extra memory...) BPL dontdolinefeedontheprinternow LDA #prilf \ Send a #prilf command to the I/O processor to print a JSR OSWRCH \ blank line on the printer JSR OSWRCH .dontdolinefeedontheprinternow STZ printflag \ Set the printflag to 0 to disable printing