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cc65/libsrc/c64/crt0.s

112 lines
2.4 KiB
ArmAsm

;
; 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