Re: Bug in 1581 ???

On 02/08/2012 07:42 AM, Baltissen, GJPAA (Ruud) wrote:
> Hallo allemaal,
>
>
> I was having a look at the source code of the 1581 to see if it is
> possible to create 1581IDE, the IDE version of the 1581. And I ran in
> this piece of code:
>
> wdstatus				;
> [CD42]
> 		php
>
> 		lda	WDSTAT	; get status
> 		lsr	a
> 		lsr	a
> 		lsr	a
> 		bcs	L93		; [1]
>
> 		and	#bit3+bit1+bit0
> 		tax
>
> 		plp			; restore carry
> 		lda	wdtrans,x
> .by $2C
> L93					;
> [CD53]
> 		lda	#9
> 		sta	ContrStat
>
> 		lda	ContrStat
> 		rts
>
>
>   This code checks the state of the WD177x. Have a look at the point
> marked [1]. If the Carry is set for one or another reason, the branch is
> taken. Then we end up at the RTS. But here it must go terribly wrong as
> the state is still on the stack !!!

Which ROM version did you look at? There were 2 for the 1581, 318045-01 
and 318045-02.

Also, the 1581 doesn't strike me as particularly crash prone, so are you 
sure the WD177x is ever in the state necessary to hit this bug?

  Gerrit




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