apple2a/crt0.s

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2018-07-28 05:30:44 +00:00
; ---------------------------------------------------------------------------
; crt0.s
; ---------------------------------------------------------------------------
;
; Startup code for cc65 (Single Board Computer version)
.export _init, _exit
.import _main
.export __STARTUP__ : absolute = 1 ; Mark as startup
.import __RAM_START__, __RAM_SIZE__ ; Linker generated
.import copydata, zerobss, initlib, donelib
.include "zeropage.inc"
; ---------------------------------------------------------------------------
; Place the startup code in a special segment
.segment "STARTUP"
; ---------------------------------------------------------------------------
; A little light 6502 housekeeping
_init: LDX #$FF ; Initialize stack pointer to $01FF
TXS
CLD ; Clear decimal mode
; ---------------------------------------------------------------------------
; Set cc65 argument stack pointer
LDA #<(__RAM_START__ + __RAM_SIZE__)
STA sp
LDA #>(__RAM_START__ + __RAM_SIZE__)
STA sp+1
; ---------------------------------------------------------------------------
; Initialize memory storage
JSR zerobss ; Clear BSS segment
JSR copydata ; Initialize DATA segment
JSR initlib ; Run constructors
; ---------------------------------------------------------------------------
; Call main()
JSR _main
; ---------------------------------------------------------------------------
; Back from main (this is also the _exit entry): force a software break
_exit: JSR donelib ; Run destructors
BRK