Version analysis of TT170 - Elite on the BBC Micro and NES

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

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

Code variations between these versions are shown below.

       Name: TT170
       Type: Subroutine
   Category: Start and end
    Summary: Main entry point for the Elite game code
  Deep dive: Program flow of the main game loop

Code variation 1 of 3A variation in the comments only

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Cassette, Docked, Master, Electron
6502SP
 This is the main entry point for the main game code.
 This is the main entry point for the main game code. It is called after the
 various setup, decryption and checksum routines in S%, G% and BEGIN have
 successfully completed.



.TT170

Code variation 2 of 3A variation in the comments only

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Cassette, Electron
Docked, 6502SP, Master
 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. We need to do this
                        \ because the loader code in elite-loader.asm pushes
                        \ code onto the stack, and this effectively removes that
                        \ code so we start afresh
 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

Code variation 3 of 3Related to the 6502SP version

The Executive version immediately starts the demo once the game has loaded (though just like the other 6502SP versions, you can still bring it up manually using TAB from the title screen, and it will automatically start after a period of inactivity).

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Cassette, Docked, Electron
Master
6502SP
                        \ Fall through into BR1 to start the game
 JSR RESET              \ Call RESET to initialise most of the game variables

                        \ Fall through into DEATH2 to start the game
 JSR RESET              \ Call RESET to initialise most of the game variables

IF _EXECUTIVE

 JSR DEMON              \ Call DEMON to show the demo

 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

ENDIF

                        \ Fall through into DEATH2 to start the game