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;
; Ullrich von Bassewitz, 27.09.1998
;
; void __fastcall__ set_brk (unsigned Addr);
; void reset_brk (void);
;
.export _set_brk, _reset_brk
.destructor _reset_brk
; Be sure to export the following variables absolute
.export _brk_a: abs, _brk_x: abs, _brk_y: abs
.export _brk_sr: abs, _brk_pc: abs
.include "apple2.inc"
_brk_a = $45
_brk_x = $46
_brk_y = $47
_brk_sr = $48
_brk_sp = $49
_brk_pc = $3A
.bss
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 BRKVec
sta oldvec
lda BRKVec+1
sta oldvec+1 ; Save the old vector
L1: lda #<brk_handler ; Set the break vector to our routine
ldx #>brk_handler
sta BRKVec
stx BRKVec+1
rts
.endproc
; Reset the break vector
.proc _reset_brk
lda oldvec
ldx oldvec+1
beq @L9 ; Jump if vector not installed
sta BRKVec
stx BRKVec+1
lda #$00
sta oldvec ; Clear the old vector
stx oldvec+1
@L9: rts
.endproc
; Break handler, called if a break occurs
.proc brk_handler
sec
lda _brk_pc
sbc #$02 ; Point to start of brk
sta _brk_pc
lda _brk_pc+1
sbc #$00
sta _brk_pc+1
clc
lda _brk_sp
adc #$04 ; Adjust stack pointer
sta _brk_sp
lda _brk_sr ; Clear brk
and #$EF
sta _brk_sr
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
|
