[alsa-devel] [PATCH - Intervals 1/1] interval: Interpret (x x+1] correctly and return x+1

[Takashi Iwai]

On Thu, 18 Oct 2018 12:50:26 +0200,
<twischer at de.adit-jv.com> wrote:
> 
> From: Timo Wischer <twischer at de.adit-jv.com>
> 
> Without this change an interval of (x x+1] will be interpreted as an
> empty interval but the right value would be x+1.
> This leads to a failing snd_pcm_hw_params() call which returns -EINVAL.
> 
> An example issue log is given in the following:
> snd_pcm_hw_params failed with err -22 (Invalid argument)
> ACCESS: MMAP_NONINTERLEAVED
> FORMAT: S16_LE
> SUBFORMAT: STD
> SAMPLE_BITS: 16
> FRAME_BITS: 16
> CHANNELS: 1
> RATE: 16000
> PERIOD_TIME: (15999 16000]
> PERIOD_SIZE: (255 256]
> PERIOD_BYTES: (510 512]
> PERIODS: [2 3)
> BUFFER_TIME: 32000
> BUFFER_SIZE: 512
> BUFFER_BYTES: 1024
> 
> In case of (x x+1) we have to interpret it anyway as a single value of x to
> compensate rounding issues.
> For example the period size will result in an interval of (352 353) when
> the period time is 16ms and the sample rate 22050 Hz
> (16ms * 22,05 kHz = 352,8 frames). But 352 has to be chosen to allow a
> buffer size of 705 (32ms * 22,05 kHz = 705,6 frames) which has to be >= 2x
> period size to avoid Xruns. The buffer size will not end up with an
> interval of (705 706) similar to the period size because
> snd_pcm_rate_hw_refine_cchange() calls snd_interval_floor() for the buffer
> size. Therefore this value will be interpreted as an integer interval
> instead of a real interval further on.
> 
> This issue seems to exist since the change of 9bb985c38 ("pcm:
> snd_interval_refine_first/last: exclude value only if also excluded
> before")
> 
> Signed-off-by: Timo Wischer <twischer at de.adit-jv.com>
> 
> diff --git a/src/pcm/interval_inline.h b/src/pcm/interval_inline.h
> index a68e292..5e59d72 100644
> --- a/src/pcm/interval_inline.h
> +++ b/src/pcm/interval_inline.h
> @@ -51,12 +51,14 @@ INTERVAL_INLINE int snd_interval_single(const snd_interval_t *i)
>  {
>  	assert(!snd_interval_empty(i));
>  	return (i->min == i->max || 
> -		(i->min + 1 == i->max && i->openmax));
> +		(i->min + 1 == i->max && (i->openmin || i->openmax)));
>  }

This change looks reasonable, but....


>  INTERVAL_INLINE int snd_interval_value(const snd_interval_t *i)
>  {
>  	assert(snd_interval_single(i));
> +	if (!i->openmax)
> +		return i->max;
>  	return i->min;

This change looks risky.  The snd_interval_value() might be called
even if the interval isn't reduced to a single value.  Rather check
openmin instead.


thanks,

Takashi