Version analysis of backtonormal

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

6502 Second Processor and Master

Code variations between these versions are shown below.

       Name: backtonormal
       Type: Subroutine
   Category: Utility routines
    Summary: Disable the keyboard, set the SVN flag to 0, and return with A = 0

Code variation 1 of 2A variation in the comments only

This variation is blank in the 6502 Second Processor version.

Master
 This routine is unused in this version of Elite (it is left over from the
 6502 Second Processor version).


.backtonormal

Code variation 2 of 2Specific to an individual platform

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

Master
6502SP
 RTS                    \ Return from the subroutine, as backtonormal does
                        \ nothing in this version of Elite (it is left over from
                        \ the 6502 Second Processor version)
 LDA #VIAE              \ Send a #VIAE %00000001 command to the I/O processor to
 JSR OSWRCH             \ set 6522 System VIA interrupt enable register IER
 LDA #%00000001         \ (SHEILA &4E) bit 1 (i.e. disable the CA2 interrupt,
 JSR OSWRCH             \ which comes from the keyboard)

 LDA #0                 \ Set the SVN flag to 0 and return from the subroutine
 BEQ DODOSVN            \ using a tail call (this BEQ is effectively a JMP as A
                        \ is always zero)