Re: hw_pointer error message triggered without need

[Manuel Jander <manuel.jander@mat.utfsm.cl>]

Hallo,

There really something wrong. 

718, max jitter = 8192): wrong interrupt acknowledge?
ALSA sound/core/pcm_lib.c:157: Unexpected hw_pointer value (stream = 0,
delta: -297, max jitter = 1024): wrong interrupt acknowledge?
ALSA sound/core/pcm_lib.c:157: Unexpected hw_pointer value (stream = 0,
delta: -722, max jitter = 8192): wrong interrupt acknowledge?
ALSA sound/core/pcm_lib.c:157: Unexpected hw_pointer value (stream = 0,
delta: -301, max jitter = 1024): wrong interrupt acknowledge?
ALSA sound/core/pcm_lib.c:157: Unexpected hw_pointer value (stream = 0,
delta: -726, max jitter = 8192): wrong interrupt acknowledge?
ALSA sound/core/pcm_lib.c:157: Unexpected hw_pointer value (stream = 0,
delta: -305, max jitter = 1024): wrong interrupt acknowledge?
ALSA sound/core/pcm_lib.c:157: Unexpected hw_pointer value (stream = 0,
delta: -730, max jitter = 8192): wrong interrupt acknowledge?

How do you explain this ???

At first i would vote for eliminating that "-" since it leads one to
think into negative deltas, that really dones make any sense.

And why is the "max jitter" changing all the time ? And the delta is
smaller than the "max jitter", so why should it complain ??

I just want to know if me soundboard is smoking crack or what ?

Best Regards

Manuel Jander.

On Tue, 2003-10-21 at 13:55, Takashi Iwai wrote:
> At Tue, 21 Oct 2003 19:24:04 +0200 (CEST),
> Jaroslav wrote:
> > 
> > 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.
> 
> the problem is that this check is too strict when only two periods are
> used.  since buffer_size/2 == period_size, if the update of hwptr is
> delayed even for one sample, it won't pass.
> 
> > 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.
> 
> there is a little difference between snd_pcm_update_hw_ptr() and
> snd_pcm_update_hw_ptr_interrupt(), and this problem doesn't happen in
> the former but only in the latter function, which is invoked by
> snd_pcm_lib_write1().
> 
> in the former function, delta is the difference between the expected
> pointer (lastptr + period_size) and the current pointer.  meanwhile,
> in the latter function, delta is the difference between the last
> pointer and the new pointer.
> hence, the calculation of delta in the latter function can be easily
> less than buffer_size/2 when nperiods = 2.
> 
> > Anyway, I think that we should leave the check as is for debugging
> > purposes (we should know that something is failing).
> 
> sure, it's harmless message (as long as it comes from
> snd_pcm_update_hw_ptr()) but too annoying.  there are too many
> sloppy hardwares...
> 
> 
> Takashi
> 
> 
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