Re: very strange C64 fault

From: Pete Rittwage <peter_at_rittwage.com>
Date: Tue, 18 Apr 2017 08:31:38 -0400
Message-ID: <7a6824631c411ba6dfac211b093123fe.squirrel@rittwage.com>
>
>> On 2017-04-18, at 13:56, afachat@gmx.de wrote:
>>
>> From your description of a sprite "almost?" touching the bottom of the
>> screen... And the fact that it's always at the same position, so that
>> it's
>> really repeatable points to a logic error, not a timing error.
>>
>> Maybe it's a stuck sprite collision bit, that once set is not reset and
>> keeps
>> the interrupt low?
>
> For one, good example.
>
>> You could write a simple test program for that.
>
> Or check with the scope what happens with e. g. _IRQ line when it freezes.
> Putting in a freezer car and checking if you get a repeatable freeze state
> when it happens may also help. Provided you have an AR or similar.

VIC-II can exhibit very strange failures. I have a stack of "partially
failed" chips. One I recall works fine with everything, except programs
that have sprites on the bottom border (like Paperboy). Any sprite moved
down there displays as trash.

-Pete


       Message was sent through the cbm-hackers mailing list
Received on 2017-04-18 13:00:43

Archive generated by hypermail 2.2.0.