git.sur5r.net Git - cc65/blob - libsrc/c1p/crt0.s

   1 ; ---------------------------------------------------------------------------
   2 ; crt0.s
   3 ; ---------------------------------------------------------------------------
   4 ;
   5 ; Startup code for Ohio Scientific Challenger 1P
   6
   7 .export   _init, _exit
   8 .import   _main
   9
  10 .export   __STARTUP__ : absolute = 1        ; Mark as startup
  11 .import   __RAM_START__, __RAM_SIZE__       ; Linker generated
  12
  13 .import    zerobss, initlib, donelib
  14
  15 .include  "zeropage.inc"
  16 .include  "extzp.inc"
  17
  18 ; ---------------------------------------------------------------------------
  19 ; Place the startup code in a special segment
  20
  21 .segment  "STARTUP"
  22
  23 ; ---------------------------------------------------------------------------
  24 ; A little light 6502 housekeeping
  25
  26 _init:    ldx     #$FF                 ; Initialize stack pointer to $01FF
  27           txs
  28           cld                          ; Clear decimal mode
  29
  30 ; ---------------------------------------------------------------------------
  31 ; Initialize screen width
  32 ; TODO: Can initialization be done in a more idiomatic way?
  33 ; TODO: Create function for changing screen width
  34           lda     #$18
  35           sta     SCR_LINELEN
  36
  37 ; ---------------------------------------------------------------------------
  38 ; Set cc65 argument stack pointer
  39
  40           lda     #<(__RAM_START__ + __RAM_SIZE__)
  41           sta     sp
  42           lda     #>(__RAM_START__ + __RAM_SIZE__)
  43           sta     sp+1
  44
  45 ; ---------------------------------------------------------------------------
  46 ; Initialize memory storage
  47 ; copydata seems to be only necessary for special systems
  48
  49           jsr     zerobss              ; Clear BSS segment
  50           ; jsr     copydata           ; Initialize DATA segment
  51           jsr     initlib              ; Run constructors
  52
  53 ; ---------------------------------------------------------------------------
  54 ; Call main()
  55
  56           jsr     _main
  57
  58 ; ---------------------------------------------------------------------------
  59 ; Back from main (this is also the _exit entry):  force a software break
  60
  61 _exit:    jsr     donelib              ; Run destructors
  62           brk