Skip to navigation

⌂ ∞ ▽ Elite on the 6502

Save and load: LOD

[BBC Master version]

       Name: LOD                                                     [Show more]
       Type: Subroutine
   Category: Save and load
    Summary: Load a commander file

    Context: See this subroutine in context in the source code
 Variations: See code variations for this subroutine in the different versions
 References: This subroutine is called as follows:
             * SVE calls LOD
             * GTDRV calls via LOR




 The filename should be stored at INWK, terminated with a carriage return (13).



 Other entry points:

   LOR                  Set the C flag and return from the subroutine



.LOD

 JSR rfile              \ Call rfile to load the commander file to the TAP%
                        \ staging area

 LDA TAP%               \ If the first byte of the loaded file has bit 7 set,
 BMI ELT2F              \ jump to ELT2F, as this is an invalid commander file
                        \
                        \ ELT2F contains a BRK instruction, which will force an
                        \ interrupt to call the address in BRKV, which will
                        \ print out the system error at ELT2F

 LDY #NT%               \ We have successfully loaded the commander file to the
                        \ TAP% staging area, so now we want to copy it to the
                        \ last saved commander data block at NA%+8, so we set up
                        \ a counter in Y to copy NT% bytes

.copyme

 LDA TAP%,Y             \ Copy the Y-th byte of TAP% to the Y-th byte of NA%+8
 STA NA%+8,Y

 DEY                    \ Decrement the loop counter

 BPL copyme             \ Loop back until we have copied all NT% bytes

.LOR

 SEC                    \ Set the C flag

 RTS                    \ Return from the subroutine

.ELT2F

 LDA #9                 \ Print extended token 9 ("{cr}{all caps}ILLEGAL ELITE
 JSR DETOK              \ II FILE{sentence case}")

 JSR t                  \ Scan the keyboard until a key is pressed, returning
                        \ the ASCII code in A and X

 JMP SVE                \ Jump to SVE to display the disc access menu and return
                        \ from the subroutine using a tail call