On Tue, 21 Oct 2003, Takashi Iwai wrote:
> At Tue, 21 Oct 2003 17:37:30 +0200,
> Tobias Peters wrote:
> >
> > I'm using linux-2.4.22 with alsa drivers 0.9.7c. Sound card driver in
> > use was intel 8x0 (but I doubt it's responsible in this case).
> >
> > ALSA ../alsa-kernel/core/pcm_lib.c:216: Unexpected hw_pointer value
> > (stream = 0, delta: -255, max jitter = 256): wrong interrupt acknowledge?
> >
> > If I understand the relevant code correctly, then this error message is
> > triggered unnecessarily if the hardware buffer is only two periods in
> > size. It is triggered when the hardware pointer has already been
> > increased by one sample since the last period completed.
> >
> > Not so if there are more periods per buffer.
>
> well, it's not unnecessary but too strict.
> especially, if the hardware generates too late (often seen on onboard
> chips), and if only two periods are used, this situation can happen.
>
> i think delta < (runtime->period_size/2) would be enough to check the
> negative (invalid) hwptr rather than delta < (runtime->buffer_size/2)
> as it is.
Nope. This check will be wrong because we will fall to the wrap point and
increase hw_ptr_base with buffer_size.
Looking to code, it seems that an interrupt was lost. Its quite impossible
to create a realiable check for lost interrupts when you have only two
periods in the midlevel code. Or the interrupt was generated too early.
Anyway, I think that we should leave the check as is for debugging
purposes (we should know that something is failing).
Jaroslav
-----
Jaroslav Kysela <[EMAIL PROTECTED]>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs
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