Re: [linux-audio-dev] Re: [announce] [patch] Voluntary Kernel Preemption Patch

Lee Revell
2004-07-13T21:45:25Z

On Tue, 2004-07-13 at 17:29, Andrew Morton wrote:
> Lee Revell <rlrevell@joe-job.com> wrote:
> >
> > Would this explain these? When running JACK with settings that need
> > sub-millisecond latencies, I get them when I generate any load at all on
> > the system (typing, switching windows, etc). I also get lots of these
> > if I run JACK from an X terminal, but very few if I run it from a text
> > console, even if X is running in the background.
> >
> > Jul 13 14:36:16 mindpipe kernel: ALSA /usr/src/alsa-cvs-1.0.5/alsa-driver/alsa-kernel/core/pcm_lib.c:199: Unexpected hw_pointer value [1] (stream = 0, delta: -25, max jitter = 32): wrong interrupt acknowledge?
>
> I'm wondering what this message actually means. "Unexpected hw_pointer
> value"?
>
> Does this actually indicate an underrun, or is the debug code screwy?

Not sure. Here is what Takashi had to say about it:

"The message appears when an unexpected DMA pointer is read in the
interrupt handler. Either the handling of irq was delayed more than
the buffer size, an irq is issued at the wrong timing, or the DMA
pointer reigster is somehow screwed up.

Since you're using quite small buffer, I guess the former case."

My response:

"I thought this was what an XRUN was, when the handling of the irq is
delayed more than the buffer size. Sometimes these messages are
associated with XRUNs, sometimes not."

Haven't heard back yet.

Is it possible that I am simply pushing my hardware past its limits?
Keep in mind this is a 600Mhz C3 processor.

Lee