git.sur5r.net Git - cc65/blob - libsrc/osic1p/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 .include  "osic1p.inc"
  18
  19 ; ---------------------------------------------------------------------------
  20 ; Place the startup code in a special segment
  21
  22 .segment  "STARTUP"
  23
  24 ; ---------------------------------------------------------------------------
  25 ; A little light 6502 housekeeping
  26
  27 _init:    ldx     #$FF                 ; Initialize stack pointer to $01FF
  28           txs
  29           cld                          ; Clear decimal mode
  30
  31 ; ---------------------------------------------------------------------------
  32 ; Set cc65 argument stack pointer
  33
  34           lda     #<(__RAM_START__ + __RAM_SIZE__)
  35           sta     sp
  36           lda     #>(__RAM_START__ + __RAM_SIZE__)
  37           sta     sp+1
  38
  39 ; ---------------------------------------------------------------------------
  40 ; Initialize memory storage
  41 ; copydata seems to be only necessary for special systems
  42
  43           jsr     zerobss              ; Clear BSS segment
  44           ; jsr     copydata           ; Initialize DATA segment
  45           jsr     initlib              ; Run constructors
  46
  47 ; ---------------------------------------------------------------------------
  48 ; Call main()
  49
  50           jsr     _main
  51
  52 ; ---------------------------------------------------------------------------
  53 ; Back from main (this is also the _exit entry):  force a software break
  54
  55 _exit:    jsr     donelib              ; Run destructors
  56           jmp     RESET                ; Display boot menu after program exit