Work down this list and hope for the best:
<
http://psychtoolbox.org/wikka.php?wakka=FaqPerformanceTuning1>
Additionally you may try to use the Priority(2) command instead of Priority(MaxPriority..., and be logged in as system administrator. That will give the code an extra priority boost, which may either help, not help, or cause really severe malfunctions on your system, up to the point of system crashes and data loss, very dependent on your script and the exact system setup.
> I am trying to figure out why 1) the errors only happen occassionally and 2)
> how to fix something intermittent.
This is simple. It is because <citing myself> "...Windows has much more timing variability in most cases. We try to compensate for that with some tricks, but there is only so much you can do. Macs and Linux usually have better timing..." <end cite>
The intermittent glitches could be anything: A random burst of network activity on a connected network, wifi or bluetooth link, a mouse movement at the wrong moment, some background system process which is part of the OS deciding to do some regular maintenance work, a bad and inefficient device driver for one of the connected (or internal) devices. Power management kicking in and reducing processor speed at the wrong moment. An inefficient hardware configuration. Matlab deciding to check its license if you run a network license manager, whatever...
You have to understand that nobody in the technical computing area with a strong need for exact and deterministic timing (aka realtime) ever had the weird idea of using a normal desktop MS-Windows as operating system. Well nobody except 2/3 of our users, a fact that amazes me over and over again.
That doesn't mean that you can't get lucky. Some selected combinations of pc hardware, carefully configured, can allow Windows to reach a sufficient level of precision for not too demanding tasks. It's just largely a matter of luck if your specific hardware and software configuration is such a lucky choice for your tasks. And if you got lucky, any given software update (drivers, security updates, service packs, new installed software...) may change the situation to the better or worse.
-mario
--- In psychtoolbox@yahoogroups.com, "Anna E. M. Holt" <aeholt@...> wrote:
>
> I see more than one missed deadline-- I see 2-5. This doesn't ALWAYS happen.
> Sometimes it is zero or 1, but sometimes it is 2-5 missed stimulus
> presentation deadlines.
>
>
> ~Anna
> --
> Anna E. Holt
> PhD Candidate
> Cognitive Development Lab
> UC San Diego Dept. of Cognitive Science
> Vice President of Communications
> MIT Alumni Club of San Diego
> mitsandiego.org
> Cell: 913-406-3527
>
>
> On Wed, Sep 23, 2009 at 7:00 PM, Mario <mario.kleiner@...>wrote:
>
> >
> >
> > As the test states at the end, "one missed deadline is ok and an artifact
> > of the test", and everything else seems to work well, so you're good.
> >
> > There are optimization tips in the FAQ section of our Wiki. And as far as
> > MS-Windows is concerned, only real ASIO soundcards are recommended
> > soundcards if you need exact timing and control. ASIO4ALL may work for less
> > demanding tasks if you are lucky. Non-Asio stuff is really only for very
> > basic things like playing some sounds or a feedback tone for the subject.
> >
> > But again, you are lucky if you only see the occassional missed deadline.
> > If a large fraction of the tested 600 samples goes wrong, then you have a
> > problem. Windows has much more timing variability in most cases. We try to
> > compensate for that with some tricks, but there is only so much you can do.
> > Macs and Linux usually have better timing.
> >
> > -mario
> >
> >
> > --- In psychtoolbox@yahoogroups.com <psychtoolbox%40yahoogroups.com>,
> > "Anna E. M. Holt" <aeholt@> wrote:
> > >
> > > I have an ATI Radeon 3100 series graphics card, and an ASIO-enabled
> > > soundcard (which is detected by psychtoolbox with InitializePyschSound.)
> > >
> > > I don't get sync errors. My computer passes the PerceptualVBLSyncTest. It
> > > doesn't look weird, and the yellow lines are clustered tightly and at the
> > > very top of the screen. Yet, when I run VBLSyncTest, I sometimes get a
> > > "missed stimulus presentation deadline" of 2/600 or some other small
> > single
> > > digit number.
> > >
> > > I've looked through the documentation, but I can't really tell what is
> > left
> > > to do at that point. I have sound and graphics cards that are recommended
> > on
> > > the website, and my computer is brand new. All drivers are up to date. Is
> > > there anything else I CAN do for a VBLSyncTest output that isn't 1 or 0?
> > >
> > >
> > > Anna E. Holt
> > > PhD Candidate
> > > Cognitive Development Lab
> > > UC San Diego Dept. of Cognitive Science
> > > Vice President of Communications
> > > MIT Alumni Club of San Diego
> > > mitsandiego.org
> > > Cell: 913-406-3527
> > >
> >
> >
> >
>