Main game loop: SetScannerAndPause

       Name: SetScannerAndPause                                      [Show more]
       Type: Subroutine
   Category: Main game loop
    Summary: Set the scanner update status and delay for 40 empty loops of 256
             iterations each (i.e. 10,240 loops)
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * MainGameLoop calls SetScannerAndPause


 Arguments:

   A                    The new value for scannerUpdate (this routine is only
                        ever called from the main game loop with A = 0, so this
                        sets scannerUpdate to zero to prevent scanner updates)


.SetScannerAndPause

 STA scannerUpdate      \ Set scannerUpdate to the new value in A

 LDX #40                \ We now perform a delay with a nested loop, so set X
                        \ as an outer loop counter
                        \
                        \ We use Y as an inner loop counter to count down from
                        \ 255 to 0, though the first loop will depend on the
                        \ initial value of Y, which isn't explicitly set to
                        \ anything before the routine is called

.scup1

 DEY                    \ Decrement the inner loop counter in Y

 BNE scup1              \ Loop back until Y reaches zero

 DEX                    \ Decrement the inner loop counter in X

 BNE scup1              \ Loop back until X reaches zero

 RTS                    \ Return from the subroutine

 EQUB &FF, &FF          \ These bytes appear to be unused
 EQUB &FF, &FF