Re: [PATCH] i386: Selectable Frequency of the Timer Interrupt

Martin J. Bligh
2005-07-12T14:58:40Z

--Lee Revell <rlrevell@joe-job.com> wrote (on Tuesday, July 12, 2005 10:24:59 -0400):

> On Mon, 2005-07-11 at 21:30 -0700, Martin J. Bligh wrote:
>> Exactly what problems
>> *does* it cause (in visible effect, not "timers are less granular").
>> Jittery audio/video? How much worse is it?
>
> Yes, exactly. Say you need to deliver a frame of audio or video every
> 5ms.

Ummm. that's a 200HZ refresh rate, is it not? That seems unreasonable
(to a lay-person, as far as video goes).

> You have a rendering thread and a display thread that communicate
> via FIFOs. The main thread waits in select() for the next frame to
> complete rendering or for the deadline to expire. That's next to
> impossible with HZ=100, because the best you can do is the deadline
> +-10ms. With HZ=1000 it's no problem.

So if we have a 50HZ refresh rate, and a HZ rate of 250 or 300, it'll
work fine then, right? I know that's actually some error in the timers,
so it may be 2 or 3 ticks, not 1, but if we're running HZ at 5 or 6
times the frequency of video, presumably that'd still work fine?

M.