Version analysis of DKS3

Cassette, Flight, Docked
Master
6502SP
Electron
   * CAPS LOCK toggles keyboard flight damping (&40)
   * A toggles keyboard auto-recentre (&41)
   * X toggles author names on start-up screen (&42)
   * F toggles flashing console bars (&43)
   * Y toggles reverse joystick Y channel (&44)
   * J toggles reverse both joystick channels (&45)
   * K toggles keyboard and joystick (&46)

 The numbers in brackets are the internal key numbers (see p.142 of the
 Advanced User Guide for a list of internal key numbers). We pass the key that
 has been pressed in X, and the configuration option to check it against in Y,
 so this routine is typically called in a loop that loops through the various
 configuration options.
   * CAPS LOCK toggles keyboard flight damping (0)
   * A toggles keyboard auto-recentre (1)
   * X toggles author names on start-up screen (2)
   * F toggles flashing console bars (3)
   * Y toggles reverse joystick Y channel (4)
   * J toggles reverse both joystick channels (5)
   * K toggles keyboard and joystick (6)

 The numbers in brackets are the configuration options that we pass in Y. We
 pass the ASCII code of the key that has been pressed in X, and the option to
 check it against in Y, so this routine is typically called in a loop that
 loops through the various configuration option.
   * CAPS LOCK toggles keyboard flight damping (&40)
   * A toggles keyboard auto-recentre (&41)
   * X toggles author names on start-up screen (&42)
   * F toggles flashing console bars (&43)
   * Y toggles reverse joystick Y channel (&44)
   * J toggles reverse both joystick channels (&45)
   * K toggles keyboard and joystick (&46)

 The Executive version supports two additional configuration options:

   * @ toggles infinite jump range and fuel (&47)
   * : toggles speech (&48)

 The numbers in brackets are the internal key numbers (see p.142 of the
 Advanced User Guide for a list of internal key numbers). We pass the key that
 has been pressed in X, and the configuration option to check it against in Y,
 so this routine is typically called in a loop that loops through the various
 configuration options.
   * CAPS LOCK toggles keyboard flight damping (&40)
   * A toggles keyboard auto-recentre (&41)
   * X toggles author names on start-up screen (&42)
   * F toggles flashing console bars (&43)
   * Y toggles reverse joystick Y channel (&44)
   * J toggles reverse both joystick channels (&45)
   * K toggles keyboard and joystick (&46)

 The numbers in brackets are the internal key numbers (see p.40 of the Electron
 Advanced User Guide for a list of internal key numbers). We pass the key that
 has been pressed in X, and the configuration option to check it against in Y,
 so this routine is typically called in a loop that loops through the various
 configuration options.

 Note that the Electron version doesn't support joysticks, but you can still
 configure them (though this does break the chart views, as they still call the
 joystick routines that are still present in the Electron's codebase).

Cassette, Flight, Docked, 6502SP, Electron
Master
   X                    The internal number of the key that's been pressed

   Y                    The internal number of the configuration key to check
                        against, from the list above (i.e. Y must be from &40 to
                        &46)
   X                    The ASCII code of the key that's been pressed

   Y                    The number of the configuration option to check against
                        from the list above (i.e. Y must be from 0 to 6)

Cassette, Flight, Docked, 6502SP, Electron
Master
 STY T                  \ Store the configuration key argument in T

 CPX T                  \ If X <> Y, jump to Dk3 to return from the subroutine
 BNE Dk3
 TXA                    \ Copy the ASCII code of the key that has been pressed
                        \ into A

 CMP TGINT,Y            \ If the pressed key doesn't match the configuration key
 BNE Dk3                \ for option Y (as listed in the TGINT table), then jump
                        \ to Dk3 to return from the subroutine

Cassette, Flight, Docked, 6502SP, Electron
Master
                        \ We have a match between X and Y, so now to toggle
                        \ the relevant configuration byte. CAPS LOCK has a key
                        \ value of &40 and has its configuration byte at
                        \ location DAMP, A has a value of &41 and has its byte
                        \ at location DJD, which is DAMP+1, and so on. So we
                        \ can toggle the configuration byte by changing the
                        \ byte at DAMP + (X - &40), or to put it in indexing
                        \ terms, DAMP-&40,X. It's no coincidence that the
                        \ game's configuration bytes are set up in this order
                        \ and with these keys (and this is also why the sound
                        \ on/off keys are dealt with elsewhere, as the internal
                        \ key for S and Q are &51 and &10, which don't fit
                        \ nicely into this approach)

 LDA DAMP-&40,X         \ Fetch the byte from DAMP + (X - &40), invert it and
 EOR #&FF               \ put it back (0 means no and &FF means yes in the
 STA DAMP-&40,X         \ configuration bytes, so this toggles the setting)
 LDA DAMP,Y             \ The configuration keys listed in TGINT correspond to
 EOR #&FF               \ the configuration option settings from DAMP onwards,
 STA DAMP,Y             \ so to toggle a setting, we fetch the existing byte
                        \ from DAMP+Y, invert it and put it back (0 means no
                        \ and &FF means yes in the configuration bytes, so
                        \ this toggles the setting)

 BPL P%+5               \ If the result has a clear bit 7 (i.e. we just turned
                        \ the option off), skip the following instruction

 JSR BELL               \ We just turned the option on, so make a standard
                        \ system beep, so in all we make two beeps

Cassette, Flight, Docked, 6502SP
Master
Electron
 JSR DELAY              \ Wait for Y/50 seconds (Y is between 64 and 70, so this
                        \ is always a bit longer than a second)
 TYA                    \ Store Y and A on the stack so we can retrieve them
 PHA                    \ below

 LDY #20                \ Wait for 20/50 of a second (0.4 seconds)
 JSR DELAY
 JSR DELAY              \ Wait for Y delay loops (Y is between 64 and 70)

Cassette, Flight, Docked, 6502SP, Electron
Master
 LDY T                  \ Restore the configuration key argument into Y
 PLA                    \ Restore A and Y from the stack
 TAY