dbgsupp.s

;
; Ullrich von Bassewitz, 08.08.1998
;
; Support routines for the debugger
;

 	.export	       	_DbgInit
       	.export		_DbgSP, _DbgCS, _DbgHI
	.import	       	popax, return0, _DbgEntry, _set_brk, _end_brk
	.import	       	_DbgBreaks
	.import	       	_brk_pc
	.importzp      	sp, sreg, ptr1, tmp1, zpspace

; C callable function, will install the debugger

_DbgInit:
	lda	#<DbgBreak
	ldx	#>DbgBreak
	jmp	_set_brk


; Entry for the break vector.

DbgBreak:
	pla
	sta	retsav
	pla
	sta	retsav+1

 	cli
 	tsx  	       		; Stack pointer
 	stx  	_DbgSP

 	jsr  	DbgSwapZP	; Swap stuff
      	lda	#<DbgStack	; Set new stack
      	sta	sp
      	lda	#>DbgStack
      	sta	sp+1
      	jsr	ResetDbgBreaks	; Reset temporary breakpoints
      	jsr  	_DbgEntry	; Call C code
      	jsr	SetDbgBreaks	; Set temporary breakpoints
       	jsr  	DbgSwapZP	; Swap stuff back

	lda	retsav+1
	pha
	lda	retsav
	pha
	rts



; Stack used when in debugger mode

.bss
       	.res	256
DbgStack:

; Swap space for the the C temporaries

CTemp:
_DbgCS:	.res	2	  	; sp
_DbgHI:	.res	2 	  	; sreg
	.res	22     	  	; Other stuff
_DbgSP:	.res	1
retsav:	.res	2	  	; Save buffer for return address

.code

; Swap the C temporaries

DbgSwapZP:
 	ldy	#zpspace-1
Swap1: 	ldx	CTemp,y
       	lda    	sp,y	      	; ######
       	sta	CTemp,y
       	txa
       	sta	sp,y
       	dey
       	bpl	Swap1
       	rts

; ----------------------------------------------------------------------------
; Utility functions


; Set/reset the breakpoints. We must do that here since the breakpoints
; may be in the runtime stuff, causing the C part to fail before it has
; reset the breakpoints. See declaration of struct breakpoint in the C
; source

MaxBreaks	= 48	      	; 4*12

ResetDbgBreaks:
       	ldy	#0
       	ldx    	#0
L4:    	lda    	_DbgBreaks+3,x	; Get bk_use
       	beq    	L6 	      	; Jump if not set
       	bpl	L5 	      	; Jump if user breakpoint
       	lda	#0
       	sta	_DbgBreaks+3,x	; Clear if temp breakpoint
L5:    	lda    	_DbgBreaks+1,x	; PC hi
       	sta  	ptr1+1
       	lda    	_DbgBreaks,x  	; PC lo
       	sta  	ptr1
       	lda	_DbgBreaks+2,x	; Old OPC
       	sta	(ptr1),y      	; Reset the breakpoint
L6:    	inx
       	inx
       	inx
       	inx
       	cpx    	#MaxBreaks    	; Done?
       	bne	L4
       	rts

SetDbgBreaks:
       	ldx	#0
	ldy	#0
L7:    	lda    	_DbgBreaks+3,x	; Get bk_use
       	beq    	L8 	      	; Jump if not set
    	lda    	_DbgBreaks+1,x	; PC hi
       	sta  	ptr1+1
       	lda    	_DbgBreaks,x  	; PC lo
       	sta  	ptr1
       	lda	(ptr1),y      	; Get the breakpoint OPC...
       	sta	_DbgBreaks+2,x	; ...and save it
	lda	#$00	      	; Load BRK opcode
	sta	(ptr1),y
L8:    	inx
       	inx
       	inx
       	inx
       	cpx	#MaxBreaks    	; Done?
       	bne    	L7
       	rts

; Get a free breakpoint slot or return 0

	.export		_DbgGetBreakSlot

_DbgGetBreakSlot:
       	ldx	#0
L10:	lda    	_DbgBreaks+3,x	; Get bk_use
       	beq    	L11	    	; Jump if not set
	inx
       	inx
       	inx
       	inx
       	cpx	#MaxBreaks   	; Done?
       	bne    	L10
	jmp	return0	     	; No free slot

L11:	stx	tmp1
	lda	#<_DbgBreaks
	ldx	#>_DbgBreaks
	clc
	adc	tmp1
	bcc	L12
	inx
L12:	ldy	#1 	     	; Force != 0
	rts


; Check if a given address has a user breakpoint set, if found, return the
; slot, otherwise return 0.

	.export		_DbgIsBreak

_DbgIsBreak:
      	jsr	popax	     	; Get address
	sta	ptr1
	stx	ptr1+1
       	ldx 	#0
L20:	lda    	_DbgBreaks+3,x 	; Get bk_use
       	beq    	L21  	      	; Jump if not set
	bmi	L21	      	; Jump if temp breakpoint
	lda	_DbgBreaks,x 	; Low byte of address
	cmp	ptr1
	bne	L21
	lda	_DbgBreaks+1,x	; High byte of address
	cmp	ptr1+1
	beq	L22
L21:	inx
       	inx
       	inx
	inx
       	cpx	#MaxBreaks   	; Done?
       	bne    	L20
	jmp	return0	     	; Not found

L22:   	stx	tmp1
	lda	#<_DbgBreaks
	ldx	#>_DbgBreaks
      	clc
      	adc	tmp1
      	bcc	L23
      	inx
L23:   	ldy	#1 	     	; Force != 0
	rts

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