linuxaudio.org

On Mon, 2008-03-10 at 19:53 +0000, James Stone wrote:

quoted text
> On Mon, Mar 10, 2008 at 12:56:17PM -0500, Lee Revell wrote:

> > On Sun, Mar 9, 2008 at 3:15 AM, James Stone  wrote:

> > > On Sat, Mar 08, 2008 at 07:03:30PM -0500, Lee Revell wrote:

> > >  > On Sat, Mar 8, 2008 at 2:58 AM, James Stone  wrote:

> > >  > > Hi,

> > >  > >

> > >  > >  I am wanting to use the eeepc for a mobile sound generation unit,

> > >  > >  but unfortunately the gfx card and sound card share the same

> > >  > >  interrupt.

> > >  >

> > >  > This is not necessarily a showstopper.  At least in theory.  Do you

> > >  > have any empirical evidence that it's a problem for you?

> > >

> > >  xruns..

> > >

> >

> > OK.  And you're sure the IRQ priorities were set correctly, realtime

> > kernel used, JACK in realtime mode, etc?

> >

>

> Yes. but IRQ tuning is not much use with the video on the same

> interrupt as the sound card. Basically whenever a widget moves,

> sound dropout occurs.

this is not how video display works. they are a lot like audio

interfaces actually. periodically, they interrupt the host CPU to say

"i'm about to start redrawing the screen from the framebuffer you last

told me about". that's about it really. they never redraw the screen at

any other time.
when your GUI toolkit decides to redraw a widget, it doesn't interact

with the h/w. all that happens is that eventually the new image of the

screen gets into the framebuffer, and on the next "VSYNC" cycle, the

video card will push it out to the actual display.
what is an issue is that the drivers and/or h/w associated with the

video card sometimes do not play fair with the PCI bus - they claim

owernship over it for too long while doing a redraw, and this *does*

lead to xruns at low latencies.
--p
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