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109 lines
1.6 KiB
ArmAsm
109 lines
1.6 KiB
ArmAsm
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; Ullrich von Bassewitz, 27.09.1998
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;
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; void set_brk (unsigned Addr);
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; void reset_brk (void);
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;
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.export _set_brk, _reset_brk
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.destructor _reset_brk
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.export _brk_a, _brk_x, _brk_y, _brk_sr, _brk_pc
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.include "vic20.inc"
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.bss
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_brk_a: .res 1
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_brk_x: .res 1
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_brk_y: .res 1
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_brk_sr: .res 1
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_brk_pc: .res 2
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oldvec: .res 2 ; Old vector
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.data
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uservec: jmp $FFFF ; Patched at runtime
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.code
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; Set the break vector
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.proc _set_brk
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sta uservec+1
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stx uservec+2 ; Set the user vector
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lda oldvec
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ora oldvec+1 ; Did we save the vector already?
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bne L1 ; Jump if we installed the handler already
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lda BRKVec
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sta oldvec
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lda BRKVec+1
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sta oldvec+1 ; Save the old vector
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L1: lda #<brk_handler ; Set the break vector to our routine
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ldx #>brk_handler
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sta BRKVec
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stx BRKVec+1
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rts
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.endproc
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; Reset the break vector
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.proc _reset_brk
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lda oldvec
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ldx oldvec+1
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beq @L9 ; Jump if vector not installed
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sta BRKVec
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stx BRKVec+1
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lda #$00
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sta oldvec ; Clear the old vector
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stx oldvec+1
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@L9: rts
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.endproc
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; Break handler, called if a break occurs
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.proc brk_handler
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pla
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sta _brk_y
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pla
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sta _brk_x
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pla
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sta _brk_a
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pla
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and #$EF ; Clear break bit
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sta _brk_sr
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pla ; PC low
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sec
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sbc #2 ; Point to start of brk
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sta _brk_pc
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pla ; PC high
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sbc #0
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sta _brk_pc+1
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jsr uservec ; Call the user's routine
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lda _brk_pc+1
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pha
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lda _brk_pc
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pha
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lda _brk_sr
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pha
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ldx _brk_x
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ldy _brk_y
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lda _brk_a
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rti ; Jump back...
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.endproc
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