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Michael Montague
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Tetris Question for Heliophobe
 Posted: Mon Apr 17, 2000 9:46 pm
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In your Tetris game you output 191 to port 0x02.
I haven't seen this port documented, so I was curious what it was for. :)
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- Joined: 25 Oct 1999
- Posts: 2029
- Location: Monterey, California
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Posted: Mon Apr 17, 2000 10:28 pm
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Quote > In your Tetris game you output 191 to port 0x02.
> I haven't seen this port documented, so I was curious what it was for. :)
Um, I do?
Hold on, let me check...
Hmm, I don't see where I do this directly, it must be a bug in the port queue (which is in serious need of an overhaul). It's probably supposed to output two bytes to port $bf (=191), but the port queue pointer is offset incorrectly so it sees 2 as the port , and $bf as the output data.
Come to think of it, I have an idea where that could be going wrong. I'll have at it tonight.
Thanks for pointing that out.
How did you detect this? Did you use MasterGear's port logging feature?
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Michael Montague
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Posted: Mon Apr 17, 2000 11:37 pm
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Quote > > In your Tetris game you output 191 to port 0x02.
> > I haven't seen this port documented, so I was curious what it was for. :)
> Um, I do?
> Hold on, let me check...
>
> Hmm, I don't see where I do this directly, it must be a bug in the port queue (which is in serious need of an overhaul). It's probably supposed to output two bytes to port $bf (=191), but the port queue pointer is offset incorrectly so it sees 2 as the port , and $bf as the output data.
> Come to think of it, I have an idea where that could be going wrong. I'll have at it tonight.
> Thanks for pointing that out.
> How did you detect this? Did you use MasterGear's port logging feature?
Well I was testing the compatibility of my emulator and noticed this happening. My emu currently breaks into debugging mode if it encounters something it doesn't expect.
I figured it was a feature I hadn't heard about, so I wanted to ask you about it. :)
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