cc65/libsrc/c64/crt0.s

;
; Startup code for cc65 (C64 version)
;

	.export		_exit
	.export		__STARTUP__ : absolute = 1	; Mark as startup
	.import		initlib, donelib
	.import		zerobss
	.import		callmain
	.import		RESTOR, BSOUT, CLRCH
	.import		__RAM_START__, __RAM_SIZE__	; Linker generated
	.import		__STACKSIZE__			; Linker generated
	.importzp	ST

	.include	"zeropage.inc"
	.include	"c64.inc"


; ------------------------------------------------------------------------
; Startup code

.segment	"STARTUP"

Start:

; Save the zero page locations we need

	ldx	#zpspace-1
L1:	lda	sp,x
	sta	zpsave,x
	dex
	bpl	L1

; Switch to second charset

	lda	#14
	jsr	BSOUT

; Switch off the BASIC ROM

	lda	$01
	pha			; Remember the value
	and	#$F8
	ora	#$06		; Enable kernal+I/O, disable basic
	sta	$01

; Clear the BSS data

	jsr	zerobss

; Save system settings and setup the stack

	pla
	sta	mmusave		; Save the memory configuration

	tsx
	stx	spsave		; Save the system stack ptr

	lda	#<(__RAM_START__ + __RAM_SIZE__ + __STACKSIZE__)
	sta	sp
	lda	#>(__RAM_START__ + __RAM_SIZE__ + __STACKSIZE__)
	sta	sp+1		; Set argument stack ptr

; Call module constructors

	jsr	initlib

; Push arguments and call main

	jsr	callmain

; Back from main (This is also the _exit entry). Run module destructors

_exit:	pha			; Save the return code on stack
	jsr	donelib

; Copy back the zero page stuff

	ldx	#zpspace-1
L2:	lda	zpsave,x
	sta	sp,x
	dex
	bpl	L2

; Place the program return code into ST

	pla
	sta	ST

; Restore system stuff

	ldx	spsave
	txs			; Restore stack pointer
	ldx	mmusave
	stx	$01		; Restore memory configuration

; Back to basic

	rts

; ------------------------------------------------------------------------
; Data

.segment	"ZPSAVE"

zpsave:	.res	zpspace

.bss

spsave:	.res	1
mmusave:.res	1