Setup: MoveCode

       Name: MoveCode                                                [Show more]
       Type: Subroutine
   Category: Setup
    Summary: Move and reset various blocks around in memory
  Deep dive: The jigsaw puzzle binary
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * SwapCode calls MoveCode


.MoveCode

                        \ We are going to process the five memory blocks defined
                        \ in (blockStartHi blockStartLo)-(blockEndHi blockEndLo)
                        \
                        \ We will either zero the memory block (for the first
                        \ block in the table), or move the block to the address
                        \ in (blockToHi blockToLo)
                        \
                        \ We work through the blocks from the last entry to the
                        \ first, so we end up doing this:
                        \
                        \   * Move &1500-&15DA to &7000-&70DA
                        \   * Move &1300-&14FF to &0B00-&0CFF
                        \   * Move &5A80-&645B to &0D00-&16DB
                        \   * Move &64D0-&6BFF to &5FD0-&63FF
                        \   * Zero &5A80-&5E3F

 LDX #4                 \ Set a block counter in X to work through the five
                        \ memory blocks, starting with the block defined at
                        \ the end of the block tables

 LDY #0                 \ Set Y as a byte counter

.move1

 LDA blockStartLo,X     \ Set (Q P) to the X-th address from (blockStartHi
 STA P                  \ blockStartLo)
 LDA blockStartHi,X
 STA Q

 LDA blockToLo,X        \ Set (S R) to the X-th address from (blockToHi
 STA R                  \ blockToLo)
 LDA blockToHi,X
 STA S

.move2

 LDA (P),Y              \ Copy the Y-th byte of (Q P) to the Y-th byte of (S R)
 STA (R),Y              \
                        \ The LDA (P),Y instruction gets modified to LDA #0 for
                        \ the last block that we process, i.e. when X = 0

 INC P                  \ Increment the address in (Q P), starting with the low
                        \ byte

 BNE move3              \ Increment the high byte if we cross a page boundary
 INC Q

.move3

 INC R                  \ Increment the address in (S R), starting with the low
                        \ byte

 BNE move4              \ Increment the high byte if we cross a page boundary
 INC S

.move4

 LDA P                  \ If (Q P) <> (blockEndHi blockEndLo) then jump back to
 CMP blockEndLo,X       \ move2 to process the next byte in the block
 BNE move2
 LDA Q
 CMP blockEndHi,X
 BNE move2

 DEX                    \ We have finished processing a block, so decrement the
                        \ block counter in X to move on to the next block (i.e.
                        \ the previous entry in the table)

 BMI move5              \ If X < 0 then we have finished processing all five
                        \ blocks, so jump to move5

 BNE move1              \ If X <> 0, i.e. X > 0, then jump up to move1 to move
                        \ the next block

 LDA ldaZero            \ We get here when X = 0, which means we have reached
 STA move2              \ the last block to process (i.e. the first entry in the
 LDA ldaZero+1          \ block tables)
 STA move2+1            \
                        \ We don't want to copy this block, we want to zero it,
                        \ so we modify the instruction at move2 to LDA #0, so
                        \ the code zeroes the block rather than moving it

 JMP move1              \ Jump back to move1 to zero the final block

.move5

IF _ACORNSOFT OR _4TRACKS

 JMP SetupGame          \ If we get here we have processed all the blocks in the
                        \ block tables, so jump to SetupGame to continue setting
                        \ up the game

ELIF _SUPERIOR OR _REVSPLUS

 JMP Protect            \ If we get here we have processed all the blocks in the
                        \ block tables, so jump to Protect to continue setting
                        \ up the game

ENDIF