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
        .import         callmain, zerobss
        .import         MEMTOP, RESTOR, BSOUT, CLRCH
        .importzp       ST

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

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

.segment        "STARTUP"

Start:

; Save the zero-page locations that we need.

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

; Switch to the second charset.

        lda     #14
        jsr     BSOUT

; Clear the BSS data.

        jsr     zerobss

; Save some system stuff; and, set up 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

; Call the module constructors.

        jsr     initlib

; Push the command-line arguments; and, call main().

        jsr     callmain

; Call the module destructors. This is also the exit() entry.

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

; Copy back the zero-page stuff.

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

; Store the return code into BASIC's status variable.

        pla
        sta     ST

; Restore the stack pointer.

        ldx     spsave
        txs

; Back to BASIC.

        rts

; ------------------------------------------------------------------------

.segment        "ZPSAVE"

zpsave: .res    zpspace

; ------------------------------------------------------------------------

.bss

spsave: .res    1