Setup: Entry

       Name: Entry                                                   [Show more]
       Type: Subroutine
   Category: Setup
    Summary: The main entry point for the game: move code into upper memory and
             call it
  Deep dive: The jigsaw puzzle binary
    Context: See this subroutine in context in the source code
 References: No direct references to this subroutine in this source file


 ORG &1200

.Entry

 LDY #0                 \ We start by copying the following block in memory:
                        \
                        \   * &1200-&12FF is copied to &7900-&79FF
                        \
                        \ so set up a byte counter in Y
.entr1

 LDA &1200,Y            \ Copy the Y-th byte of &1200 to the Y-th byte of &7900
 STA &7900,Y

 INY                    \ Increment the byte counter

 BNE entr1              \ Loop back until we have copied a whole page of bytes

 JMP SwapCode           \ Jump to the routine that we just moved to continue the
                        \ setup process

 COPYBLOCK &1200, &120E, &7900      \ This code starts out at &1200 and is run
                                    \ there, before it duplicates itself to
                                    \ &7900-&790D along with the rest of the
                                    \ page, so we need to move this code next to
                                    \ the block that runs at &790E-&79FF

 CLEAR &1200, &120E     \ We also need to clear the code from &1200 so we can
                        \ assemble more code at the same location