Loader: RunGMA

       Name: RunGMA                                                  [Show more]
       Type: Subroutine
   Category: Loader
    Summary: Load and run the GMA1 loader file
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * basicVectors calls RunGMA
             * RelocateLoader calls RunGMA


.RunGMA

 LDA #%00000000         ; Call the Kernal's SETMSG function to set the system
 JSR KERNALSETMSG       ; error display switch as follows:
                        ;
                        ;   * Bit 6 clear = do not display I/O error messages
                        ;
                        ;   * Bit 7 clear = do not display system messages
                        ;
                        ; This ensures that any file system errors are hidden

 LDA #2                 ; Call the Kernal's SETLFS function to set the file
 LDX #8                 ; parameters as follows:
 LDY #$FF               ;
 JSR KERNALSETLFS       ;   * A = logical number 2
                        ;
                        ;   * X = device number 8 (disk)
                        ;
                        ;   * Y = secondary address $FF
                        ;
                        ; The last setting ensures that the Kernal's LOAD
                        ; function loads files using the addresses in their PRG
                        ; headers

 LDA #3                 ; Call SETNAM to set the filename parameters as follows:
 LDX #LO(filename)      ;
 LDY #HI(filename)      ;   * A = filename length of 3
 JSR KERNALSETNAM       ;
                        ;   * (Y X) = address of filename
                        ;
                        ; So this sets the filename to "GM*"

 LDA #0                 ; Call the Kernal's LOAD function to load the GMA* file
 JSR KERNALLOAD         ; as follows:
                        ;
                        ;   * A = 0 to initiate a load operation
                        ;
                        ; So this loads the first GM* file we find on disk at
                        ; the address in its PRG header, which will be GMA1 at
                        ; $0334

 LDA #$FF               ; Set the high byte of the execution address of STOP to
 STA $0329              ; $FF, from the default $F6ED to $FFED
                        ;
                        ; The address $FFED in the Kernal ROM simply returns
                        ; without doing anything, so this effectively disables
                        ; the RUN/STOP key

 NOP                    ; These NOPs pad out the rest of this routine to ensure
 NOP                    ; that the BASIC vectors in basicVectors end up in the
 NOP                    ; correct addresses for overriding BASIC, for when this
 NOP                    ; file is loaded at its PRG address of $02A7
 NOP
 NOP
 NOP
 NOP
 NOP
 NOP
 NOP
 NOP
 NOP
 NOP
 NOP
 NOP
 NOP
 NOP
 NOP
 NOP
 NOP
 NOP
 NOP
 NOP

 JMP $0334              ; Jump to the start of the GMA1 loader file that we just
                        ; loaded, which loads the game