[visionegg] Random selection of primary and secondary vsync on init in clone mode
- From: Martin Spacek <mspacek@xxxxxxxxxxxxxxx>
- To: visionegg@xxxxxxxxxxxxx
- Date: Tue, 22 Feb 2005 21:58:39 -0800
Greetings,
We have two 800 x 600 x 200Hz screens hooked up to a single dual-head
ATI Radeon card in clone mode. VisionEgg runs perfectly in this setup
with the timing of each frame at 5 ms, and the same image appearing on
both monitors as expected.
Comparing the vsync signals (VGA pin 14) of the two ports on the ATI
card on an oscilloscope, I've noticed that they aren't in phase, even in
clone mode with the same resolution and refresh rate. No big deal, so
long as the timing of the stimulus is always relative to the vsync of
one of the ports (presumably the primary), so that we can use that
port's vsync signal to get precise timing information about our stimuli
on the primary monitor.
I've noticed however that with the setup described above, the screen's
buffer swaps seem to randomly choose on initialization to lock to the
vsync signal of either the primary or the secondary VGA port. This is
bad, because we need to know which port to sample the vsync signal off
of for our timing information, and if the correctly timed port keeps
changing, then half the time we'll be getting the wrong timing info. Has
anyone else noticed this behaviour?
This is in Windows 2000 on a Sapphire ATI Radeon 9800 Pro 128MB. I've
tried all sorts of ATI Catalyst drivers: 4.1, 4.9, 5.2 (most recent)
with no luck. I've tried updating SDL.dll to the latest SDL runtime
(1.2.8), the latest pygame 1.6.2, and the latest pyopengl 2.0.2.01 with
no luck. I realize that pygame/SDL can only init a single screen, but
shouldn't it always init locked to the primary vsync? I'm trying to
figure out the likeliest source of the problem: the driver, SDL, pygame...?
P.S. For any of you out there using the Catalyst drivers, I've noticed
tearing at 800x600 (fullscreen and maybe windowed too, but only at this
resolution) even with buffer swaps locked to vsync, at any refresh rate,
since version 4.10 (October 2004). At least that's the case for the
Radeon 9800. So right now we're sticking with version 4.9 or earlier.
Cheers,
Martin Spacek
PhD student, Swindale lab
Graduate Program in Neuroscience
Dept. of Ophthalmology and Visual Sciences
University of British Columbia, Vancouver, BC, Canada
+1-604-875-4555 ext. 66282
mspacek@xxxxxxxxxxxxxxx | http://swindale.ecc.ubc.ca
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