; void reset_brk (void);
;
- .export _set_brk, _reset_brk
- .destructor _reset_brk
- .export _brk_a, _brk_x, _brk_y, _brk_sr, _brk_pc
- .importzp ptr1
+ .export _set_brk, _reset_brk
+ .destructor _reset_brk
+ .export _brk_a, _brk_x, _brk_y, _brk_sr, _brk_pc
+ .importzp ptr1
- .include "c128.inc"
+ .include "c128.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
-
+_brk_a: .res 1
+_brk_x: .res 1
+_brk_y: .res 1
+_brk_sr: .res 1
+_brk_pc: .res 2
.data
-uservec: jmp $FFFF ; Patched at runtime
+uservec: jmp $FFFF ; Patched at runtime
.code
-; Where will we put the break stub?
-stub_addr = $0E00 ; BASIC sprite area
-
-
; Set the break vector
-.proc _set_brk
+.proc _set_brk
- sta uservec+1
- stx uservec+2 ; Set the user vector
+ sta uservec+1
+ stx uservec+2 ; Set the user vector
- lda oldvec
- ora oldvec+1 ; Did we save the vector already?
- bne L2 ; Jump if we installed the handler already
+ lda brk_old+1
+ ora brk_old+2 ; 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
+ lda BRKVec ; Save the old vector
+ sta brk_old+1
+ lda BRKVec+1
+ sta brk_old+2
- ldy #stub_size-1 ; Copy our stub into the low mem area
-L1: lda brk_stub,y
- sta stub_addr,y
- dey
- bpl L1
+ lda #<brk_stub ; Set the break vector to our stub
+ ldx #>brk_stub
+ sta BRKVec
+ stx BRKVec+1
-L2: lda #<stub_addr ; Set the break vector to our stub
- sta BRKVec
- lda #>stub_addr
- sta BRKVec+1
- rts
+ lda #<brk_handler ; Set the indirect vector to our handler
+ ldx #>brk_handler
+ sta brk_ind+1
+ stx brk_ind+2
+
+@L1: rts
.endproc
; Reset the break vector
-.proc _reset_brk
-
- lda oldvec
- bne @L1
- ldx oldvec
- beq @L9 ; Jump if vector not installed
-@L1: sta BRKVec
- stx BRKVec+1
-@L9: rts
+.proc _reset_brk
+
+ lda brk_old+1
+ ldx brk_old+2
+ beq @L9 ; Jump if vector not installed
+ sta BRKVec
+ stx BRKVec+1
+ lda #$00
+ sta brk_old+1 ; Clear the saved vector
+ sta brk_old+2
+@L9: rts
.endproc
; Break handler, called if a break occurs
-.proc brk_handler
-
- pla
- sta _brk_y
- pla
- sta _brk_x
- pla
- sta _brk_a
- pla
- and #$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...
+.proc brk_handler
+
+ pla
+ sta _brk_y
+ pla
+ sta _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
+
+
+; Break stub, must go into low (non banked) memory
+
+.segment "LOWCODE"
+.proc brk_stub
+ pla ; Get original MMU_CR value
+ sta MMU_CR ; And set it
+ jmp brk_ind ; Jump indirect to break
.endproc
+; ------------------------------------------------------------------------
+; Data
+
+.data
+
+; Old break vector preceeded by a jump opcode
+brk_old:
+ jmp $0000
-brk_stub:
- .org stub_addr
- pla ; Get original MMU value
- sta MMU_CR ; Re-enable our config
- jmp brk_handler ; Jump to the user handler
- .reloc
+; Indirect vectors preceeded by a jump opcode
+brk_ind:
+ jmp $0000
-stub_size = * - brk_stub
projects / cc65 / blobdiff