[stella] Understanding the PIA

[seagtgruff at aol.com]

I had posted about this issue on AtariAge a while back, and had tried it with the different timer intervals. I also looked at the timer interrupt flag. I compared Stella, z26, and my 2600. What I found was that Stella emulates the timer interrupt flag correctly, but z26 does not. On the other hand, z26 emulates the timer wraparound after timeout correctly, but Stella does not. Here is the thread where I posted about it.

http://www.atariage.com/forums/index.php?s=&showtopic=113297&view=findpost&p=1368611

As I recall, the timer interval did make a difference. I would need to go back and review everything again to refresh my memory about it.

Michael


-----Original Message-----
From: Stephen Anthony <sa666666 at gmail.com>
To: Atari 2600 programming list <stella at atari2600.org>
Sent: Thu, 3 Apr 2008 12:52 pm
Subject: Re: [stella] Understanding the PIA



On Thursday 03 April 2008 14:09, bob.montgomery at thomson.com wrote:

> Based on some other tests I just ran, it looks like, in Stella, once
> the  timer hits $FF it counts at *double speed* (!) until you read INTIM
> again, and then it resumes counting at the correct speed.

OK, I'll look into this later tonight.

> Though my 
> tests were all with TIM1T, I don't know if that holds for TIM8T, TIM64T,
> or TIM1024T.
>
> -Bob

If you get a chance, could you also test those  (ie, let me know what *is* 
happening, and what *should* be happening in terms of output)?

Thanks,
Steve

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