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Re: [Qemu-devel] How to Simulate hardware that counts scanlines?


From: Steve Ellenoff
Subject: Re: [Qemu-devel] How to Simulate hardware that counts scanlines?
Date: Wed, 02 Aug 2006 21:47:37 +0000

Thanks malc-

Turns out I didn't need it after all. Once I pumped up my RTC Frequency to 4096 from 1024 (thanks Brad), my 'fake' scanline counting code seemed to satisfy the machine and all looks perfect. Thanks for the help anyway, it was much appreciated, and may serve useful for future projects.

Regards-
Steve


From: malc <address@hidden>
To: Steve Ellenoff <address@hidden>
Subject: Re: [Qemu-devel] How to Simulate hardware that counts scanlines?
Date: Tue, 1 Aug 2006 04:16:32 +0400 (MSD)

On Mon, 31 Jul 2006, Steve Ellenoff wrote:

You misunderstand, I have no control over the running program. I didn't write it, I don't have source code, and I surely wouldn't have used a polling mechanism for determining the vblank as you suggested.

My problem is that I wish to run this program through qemu. I've made a bunch of hardware specific additions to qemu to emulate the specific hardware this program runs on. I'm just not sure the best way to simulate the scanline counting the hardware does.

Seems nobody here has any ideas either, which is kind of hard to believe. I don't know if this would work, but one idea I had was to divide up the gui timer into 260 slices (that's the # of scanlines the hardware expects), and simply update the hardware register that counts the scanlines this way.

Does anyone thing that's the way to go, or if there's a better way?


I don't know wether this is applicable or not, but it might help:
http://www.boblycat.org/~malc/code/patches/qemu/5c_rqemu.patch.gz

Is the patch that does something that sounds a bit like what you
want. Basically this tries to provide a bit better h/v retrace
polling support than what qemu orignally does (needed for some
old DOS applications) Each time guest reads the VGA register
that contains h/v retrace bits the virtual time is calculated
and that gives some indication where the beam might be at the
current point in time, with a bit of tweaking this can report
current scanline and whatnot too.

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