cc65/libsrc/c16/crt0.s

;
; Startup code for cc65 (C16 version)
;
; Note: The C16 is actually the Plus/4 with just 16KB of memory. So many
; things are similar here, and we even use the plus4.inc include file.
;

	.export		_exit
        .export         __STARTUP__ : absolute = 1      ; Mark as startup
	.import		initlib, donelib, callirq
	.import	     	callmain, zerobss
        .import         MEMTOP, RESTOR, BSOUT, CLRCH
	.import	       	__INTERRUPTOR_COUNT__

        .include        "zeropage.inc"
	.include	"plus4.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

; Clear the BSS data

	jsr	zerobss

; Save system stuff and setup the stack

       	tsx
       	stx    	spsave       	; save system stk ptr

	sec
	jsr	MEMTOP		; Get top memory
	cpy	#$80  		; We can only use the low 32K :-(
	bcc	MemOk
	ldy	#$80
	ldx	#$00
MemOk:	stx	sp
      	sty	sp+1  		; set argument stack ptr

; If we have IRQ functions, chain our stub into the IRQ vector

        lda     #<__INTERRUPTOR_COUNT__
      	beq	NoIRQ1
      	lda	IRQVec
       	ldx	IRQVec+1
      	sta	IRQInd+1
      	stx	IRQInd+2
      	lda	#<IRQStub
      	ldx	#>IRQStub
      	sei
      	sta	IRQVec
      	stx	IRQVec+1
      	cli

; Call module constructors

NoIRQ1: jsr     initlib

; Push arguments and call main()

       	jsr    	callmain

; Call module destructors. This is also the _exit entry.

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

; Reset the IRQ vector if we chained it.

        pha  			; Save the return code on stack
	lda     #<__INTERRUPTOR_COUNT__
	beq	NoIRQ2
	lda	IRQInd+1
	ldx	IRQInd+2
	sei
	sta	IRQVec
	stx	IRQVec+1
	cli

; Copy back the zero page stuff

NoIRQ2: ldx     #zpspace-1
L2:	lda	zpsave,x
	sta	sp,x
	dex
       	bpl	L2

; Store the return code into ST

	pla
	sta	ST

; Restore the stack pointer

	ldx	spsave
	txs

; Back to BASIC

	rts

; ------------------------------------------------------------------------
; The IRQ vector jumps here, if condes routines are defined with type 2.

IRQStub:
	cld    	       		   	; Just to be sure
       	jsr    	callirq                 ; Call the functions
       	jmp    	IRQInd			; Jump to the saved IRQ vector

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

.data

IRQInd: jmp     $0000

.segment        "ZPSAVE"

zpsave:	.res	zpspace

.bss

spsave:	.res	1