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cc65/libsrc/atari/break.s
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git-svn-id: svn://svn.cc65.org/cc65/trunk@3 b7a2c559-68d2-44c3-8de9-860c34a00d81
2000-05-28 13:40:48 +00:00

107 lines
1.5 KiB
ArmAsm

;
; Christian Groessler, 27-Feb-2000
;
; void set_brk (unsigned Addr);
; void reset_brk (void);
;
.export _set_brk, _reset_brk
.export _brk_a, _brk_x, _brk_y, _brk_sr, _brk_pc
.import _atexit
.include "atari.inc"
.bss
_brk_a: .res 1
_brk_x: .res 1
_brk_y: .res 1
_brk_sr: .res 1
_brk_pc: .res 2
oldvec: .res 2 ; Old vector
.data
uservec: jmp $FFFF ; Patched at runtime
.code
; Set the break vector
.proc _set_brk
sta uservec+1
stx uservec+2 ; Set the user vector
lda oldvec
ora oldvec+1 ; Did we save the vector already?
bne L1 ; Jump if we installed the handler already
lda VBREAK
sta oldvec
lda VBREAK+1
sta oldvec+1 ; Save the old vector
lda #<_reset_brk
ldx #>_reset_brk
jsr _atexit ; Install an exit handler
L1: lda #<brk_handler ; Set the break vector to our routine
sta VBREAK
lda #>brk_handler
sta VBREAK+1
rts
.endproc
; Reset the break vector
.proc _reset_brk
lda oldvec
sta VBREAK
lda oldvec+1
sta VBREAK+1
rts
.endproc
; Break handler, called if a break occurs
.proc brk_handler
sty _brk_y
stx _brk_x
pla
sta _brk_a
pla
and #$EF ; Clear break bit
sta _brk_sr
pla ; PC low
sec
sbc #2 ; Point to start of brk
sta _brk_pc
pla ; PC high
sbc #0
sta _brk_pc+1
jsr uservec ; Call the user's routine
lda _brk_pc+1
pha
lda _brk_pc
pha
lda _brk_sr
pha
ldx _brk_x
ldy _brk_y
lda _brk_a
rti ; Jump back...
.endproc