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Re: [Qemu-devel] Re: OSS audio debugging

From: Fabrice Bellard
Subject: Re: [Qemu-devel] Re: OSS audio debugging
Date: Mon, 14 Jun 2004 21:01:16 +0200
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.4) Gecko/20030624

Mike Nordell wrote:

DOOM Shareware - this one needs no introduction.
Crashes, hangs and plays really "choppy" sound.
The crashes and hangs (depending on moon-phase) seems to be due to
incomplete detection of self-modifying code. When it does run for more than
1 second, the choppy sound I suspect might be, as for many cases here, due
to timing or incorrect SB16, PIC or DMA emulation. That it also run as in
molasses (the seconds I got it to run) further strengthen my suspicions of
timing or PIC - even that it could be a large amount of self-modifying code
invalidating the TB all the time too. I haven't dug deeper into it.

It should work now. The problem was linked to self modifying code and cpu interrupts.

DOOM is a rather pathological case for self-modifying code and it slows QEMU a lot (although DOOM remains fully playable on my PC). Since only some instruction constants are modified in the code, I could optimize this case specifically in the dynamic compiler.


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