On Friday 07 September 2001 03:31, Loren Frank wrote:
> On Wed, 5 Sep 2001, Ron wrote:
> > I guess my first question would be, if your talking NTSC video at
> > 60 fields per second i.e. normal 30 frames per second video, why
> > are you bothering to use RTLinux in the first place, even an
> > old 33mhz 486 can service interrupt rates that low (and do large
> > amounts of processing in the interrupt service routine) without
> > breaking a sweat. I've done it myself some years ago with a frame
> > grabber I designed around the old philips SAA7195 chip set. Try
> > doing what you need to do in userland, just as a test, I'll bet
> > you'll see that 16ms is a very very long time on any newer
> > processor.
>
> The frame grabber can indeed service the interrupts without a problem,
> but I need to know, with an error of at most 1 or 2 ms, exactly when
> the frame was taken. I know that I would be likely to be within that
> margin 99% of the time, but I really need consistent precision....
Ok, you're really better off with an RTL/RTAI solution for the particular
timestamping task, although Linux/lowlatency would easily be within 1 ms
a lot more than 99% of the time. My qualified quess would be that it'll
be in ]+0,+1[ at least 99.99% of the time - even under heavy system
stress.
(I have "a feeling" that it's actually much better in real life, but I'm
not going to promise anything without solid benchmark backup. Benchmarks
are the only way we can analyze such a complex setup - measurement and
analysis tools are planned.)
//David Olofson --- Programmer, Reologica Instruments AB
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.- David Olofson -------------------------------------------.
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