Re: hw_pointer error message triggered without need

[Takashi Iwai <tiwai@suse.de>]

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.


Takashi


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