mirror of
https://github.com/cc65/cc65.git
synced 2024-11-03 10:07:02 +00:00
29d1400340
_sys() is supposed to be (primarily) intended to call ROM routines. Leveraging the "file overlay" mechanism of the cc65 build system allows to provide a Apple II specific _sys() implementation that temporarily switches in the ROM.
82 lines
1.7 KiB
ArmAsm
82 lines
1.7 KiB
ArmAsm
;
|
|
; void __fastcall__ _sys (struct regs* r);
|
|
;
|
|
|
|
.export __sys
|
|
.import jmpvec
|
|
|
|
.include "zeropage.inc"
|
|
|
|
.segment "LOWCODE"
|
|
|
|
__sys: sta ptr1
|
|
stx ptr1+1 ; Save the pointer to r
|
|
|
|
; Fetch the PC and store it into the jump vector
|
|
ldy #5
|
|
lda (ptr1),y
|
|
sta jmpvec+2
|
|
dey
|
|
lda (ptr1),y
|
|
sta jmpvec+1
|
|
|
|
; Remember the flags so we can restore them to a known state after calling the
|
|
; routine
|
|
php
|
|
|
|
; Get the flags, keep the state of bit 4 and 5 using the other flags from
|
|
; the flags value passed by the caller. Push the new flags and push A.
|
|
dey
|
|
php
|
|
pla ; Current flags -> A
|
|
eor (ptr1),y
|
|
and #%00110000
|
|
eor (ptr1),y
|
|
pha ; Push new flags value
|
|
ldy #0
|
|
lda (ptr1),y
|
|
pha
|
|
|
|
; Get and assign X and Y
|
|
iny
|
|
lda (ptr1),y
|
|
tax
|
|
iny
|
|
lda (ptr1),y
|
|
tay
|
|
|
|
; Switch in ROM
|
|
bit $C082
|
|
|
|
; Set A and the flags, call the machine code routine
|
|
pla
|
|
plp
|
|
jsr jmpvec
|
|
|
|
; Back from the routine. Save the flags and A.
|
|
php
|
|
pha
|
|
|
|
; Switch in LC bank 2 for R/O
|
|
bit $C080
|
|
|
|
; Put the register values into the regs structure
|
|
tya
|
|
ldy #2
|
|
sta (ptr1),y
|
|
dey
|
|
txa
|
|
sta (ptr1),y
|
|
dey
|
|
pla
|
|
sta (ptr1),y
|
|
ldy #3
|
|
pla
|
|
sta (ptr1),y
|
|
|
|
; Restore the old flags value
|
|
plp
|
|
|
|
; Done
|
|
rts
|