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⌂ ∞ ▽ Elite on the BBC Micro and NES

Version analysis of QUS1

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

Code variations between these versions are shown below.

       Name: QUS1
       Type: Subroutine
   Category: Save and load
    Summary: Save or load the commander file
  Deep dive: Commander save files



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

Code variation 1 of 8A variation in the comments only

Tap on a block to expand it, and tap it again to revert.

Cassette, Docked, Electron
6502SP
 The routine should be called with Y set to &C.

 The routine asks for a drive number and updates the filename accordingly
 before performing the load or save.




 Arguments:

   A                    File operation to be performed. Can be one of the
                        following:

                          * 0 (save file)

                          * &FF (load file)

Code variation 2 of 8A variation in the comments only

Tap on a block to expand it, and tap it again to revert.

Cassette, Docked, Electron
6502SP
   Y                    Points to the page number containing the OSFILE block,
                        which must be &C because that's where the pointer to the
                        filename in INWK is stored below (by the STX &0C00
                        instruction)

 Returns:

   C flag               Set if an invalid drive number was entered


.QUS1

Code variation 3 of 8Related to an enhanced feature

The enhanced versions support the entering of disc drive numbers when loading or saving.

This variation is blank in the Cassette and Electron versions.

Docked, 6502SP
 PHA                    \ Store A on the stack so we can restore it after the
                        \ call to GTDRV

 JSR GTDRV              \ Get an ASCII disc drive number from the keyboard in A,
                        \ setting the C flag if an invalid drive number was
                        \ entered

 STA INWK+1             \ Store the ASCII drive number in INWK+1, which is the
                        \ drive character of the filename string ":0.E."

 PLA                    \ Restore A from the stack

 BCS QUR                \ If the C flag is set, then an invalid drive number was
                        \ entered, so jump to QUR to return from the subroutine

Code variation 4 of 8Related to Elite's use of the Tube

This variation is blank in the Cassette, Disc (docked) and Electron versions.

6502SP
 PHA                    \ Store A on the stack so we can restore it after the
                        \ call to DODOSVN

 LDA #255               \ Set the SVN flag to 255 to indicate that disc access
 JSR DODOSVN            \ is in progress

 PLA                    \ Restore A from the stack

Code variation 5 of 8Specific to an individual platform

Tap on a block to expand it, and tap it again to revert.

Cassette, Docked, 6502SP
Electron
 LDX #INWK              \ Store a pointer to INWK at the start of the block at
 STX &0C00              \ &0C00, storing #INWK in the low byte because INWK is
                        \ in zero page

 LDX #INWK              \ Store a pointer to INWK at the start of the block at
 STX &0A00              \ &0A00, storing #INWK in the low byte because INWK is
                        \ in zero page

Code variation 6 of 8Minor and very low-impact

Tap on a block to expand it, and tap it again to revert.

Cassette
Docked, 6502SP
Electron
 LDX #0                 \ Set X to 0 so (Y X) = &0C00

 JMP OSFILE             \ Jump to OSFILE to do the file operation specified in
                        \ &0C00 (i.e. save or load a file depending on the value
                        \ of A), returning from the subroutine using a tail call

 LDX #0                 \ Set (Y X) = &0C00
 LDY #&C

 JSR OSFILE             \ Call OSFILE to do the file operation specified in
                        \ &0C00 (i.e. save or load a file depending on the value
                        \ of A)

 LDX #&FF               \ Set KEYB = &FF to indicate that we are reading from
 STX KEYB               \ the keyboard using an OS command

 INX                    \ Set X = 0

 JSR OSFILE             \ Call OSFILE to do the file operation specified in
                        \ &0A00 (i.e. save or load a file depending on the value
                        \ of A)

 INC KEYB               \ Increment KEYB back to 0 to indicate we are done
                        \ reading the keyboard

 RTS                    \ Return from the subroutine

Code variation 7 of 8Related to Elite's use of the Tube

This variation is blank in the Cassette, Disc (docked) and Electron versions.

6502SP
 JSR CLDELAY            \ Pause for 1280 empty loops

 LDA #0                 \ Set the SVN flag to 0 indicate that disc access has
 JSR DODOSVN            \ finished

Code variation 8 of 8Specific to an individual platform

This variation is blank in the Cassette and Electron versions.

Docked, 6502SP
 CLC                    \ Clear the C flag

.QUR

 RTS                    \ Return from the subroutine