Warning/error from ALSA’s pcm_min.c example. Possible problem?

Warning/error from ALSA’s pcm_min.c example. Possible problem?

[Louise Hoffman]

Dear ALSA developers,

When I compile ALSA's pcm_min.c[0] example with

gcc -Wall -lasound pcm_min.c -o pcm_min

Everything is fine, but running it, I get the white noise as expected,
but I also get this warning/error:

Short write (expected 16384, wrote 7616)

Which comes from the last if-statement.

One bug is in this line

                frames = snd_pcm_writei(handle, buffer, sizeof(buffer));

where "sizeof(buffer)" should be "number of frames in the buffer".

But there are still some strange things going on. I still get those
errors, and if I remove the for-loop, nothing is played.

Here is my code. [1]

Can someone see what's wrong?

Hugs,
Louise


[0] http://www.google.com/codesearch/p?hl=en&sa=N&cd=1&ct=rc#4FSOSMZ6Pxc/distfiles/alsa-lib-1.0.14rc2.tar.bz2|ZScnKi-LryE/alsa-lib-1.0.14rc2/test/pcm_min.c&q=pcm_min.c

[1] http://pastebin.com/m2f28b578

Re: Warning/error from ALSA’s pcm_min.c example. Possible problem?

[Raymond Yau]

2010/1/31 Louise Hoffman <louise.hoffman@gmail.com>

> Dear ALSA developers,
>
> When I compile ALSA's pcm_min.c[0] example with
>
> gcc -Wall -lasound pcm_min.c -o pcm_min
>
> Everything is fine, but running it, I get the white noise as expected,
> but I also get this warning/error:
>
> Short write (expected 16384, wrote 7616)
>
> Which comes from the last if-statement.
>
> One bug is in this line
>
>                frames = snd_pcm_writei(handle, buffer, sizeof(buffer));
>
> where "sizeof(buffer)" should be "number of frames in the buffer".
>
> But there are still some strange things going on. I still get those
> errors, and if I remove the for-loop, nothing is played.
>
> Here is my code. [1]
>
> Can someone see what's wrong?
>
> Hugs,
> Louise
>
>
> [0]
> http://www.google.com/codesearch/p?hl=en&sa=N&cd=1&ct=rc#4FSOSMZ6Pxc/distfiles/alsa-lib-1.0.14rc2.tar.bz2|ZScnKi-LryE/alsa-lib-1.0.14rc2/test/pcm_min.c&q=pcm_min.c<http://www.google.com/codesearch/p?hl=en&sa=N&cd=1&ct=rc#4FSOSMZ6Pxc/distfiles/alsa-lib-1.0.14rc2.tar.bz2%7CZScnKi-LryE/alsa-lib-1.0.14rc2/test/pcm_min.c&q=pcm_min.c>
>
> [1] http://pastebin.com/m2f28b578
>
> The correct way is to use snd_pcm_get_params() to get buffer_size and
period_size

*snd_pcm_set_params() has limitation

The most common sound card (e.g. HDA ) has the following constraints
on period bytes and buffer bytes

     snd_pcm_hw_constraint_step(runtime, 0, SNDRV_PCM_HW_PARAM_BUFFER_BYTES,
                                    128);
     snd_pcm_hw_constraint_step(runtime, 0, SNDRV_PCM_HW_PARAM_PERIOD_BYTES,
                                   128);
*

you cannot get exactly 0.5 second period time when rate is multiple of 3 (
e.g. 48000 Hz )

Re: Warning/error from ALSA’s pcm_min.c example. Possible problem?

[Louise Hoffman]

>> The correct way is to use snd_pcm_get_params() to get buffer_size and
> period_size
>
> *snd_pcm_set_params() has limitation
>
> The most common sound card (e.g. HDA ) has the following constraints
> on period bytes and buffer bytes
>
>     snd_pcm_hw_constraint_step(runtime, 0, SNDRV_PCM_HW_PARAM_BUFFER_BYTES,
>                                    128);
>     snd_pcm_hw_constraint_step(runtime, 0, SNDRV_PCM_HW_PARAM_PERIOD_BYTES,
>                                   128);

I am probably not good enough to understand these changes =( Pretty
hard core stuff =)


> you cannot get exactly 0.5 second period time when rate is multiple of 3 (
> e.g. 48000 Hz )

Does this mean, that I shouldn't give snd_pcm_writei() the number of
all the frames in the buffer, but only

sample_rate * latency = frames

?

So if I e.g. have:
sample_rate = 44100
latency = 0.5 [s]
all_frames = 100000

The number of frames that I should give to snd_pcm_writei() would be

sample_rate * latency = frames
44100*0.5 = 22050

and the number of iterations the for-loop should be?:

(int) 100000/22050 = 4; with frames=22050

and one extra, but only with

100000 mod 22050 = 11800

frames?

Re: Warning/error from ALSA’s pcm_min.c example. Possible problem?

[Jaroslav Kysela]

On Sat, 30 Jan 2010, Louise Hoffman wrote:

> Dear ALSA developers,
>
> When I compile ALSA's pcm_min.c[0] example with
>
> gcc -Wall -lasound pcm_min.c -o pcm_min
>
> Everything is fine, but running it, I get the white noise as expected,
> but I also get this warning/error:
>
> Short write (expected 16384, wrote 7616)

It was a bug in alsa-lib. I fixed it in patch bellow. Thank you for your 
report.

http://git.alsa-project.org/?p=alsa-lib.git;a=commitdiff;h=2e48439ad93f6c8d99a2d72928ac71285b5211bb

 					Jaroslav

-----
Jaroslav Kysela <perex@perex.cz>
Linux Kernel Sound Maintainer
ALSA Project, Red Hat, Inc.

Re: Warning/error from ALSA’s pcm_min.c example. Possible problem?

[Louise Hoffman]

> It was a bug in alsa-lib. I fixed it in patch bellow. Thank you for your
> report.

Cool. And that was the big one, you fixed there =)

Can you also patch pcm_min.c ?

Re: Warning/error from ALSA’s pcm_min.c example. Possible problem?

[Raymond Yau]

>> On Sat, 30 Jan 2010, Louise Hoffman wrote:

>> Dear ALSA developers,
>>
>> When I compile ALSA's pcm_min.c[0] example with
>>
>> gcc -Wall -lasound pcm_min.c -o pcm_min
>>
>> Everything is fine, but running it, I get the white noise as expected,
>> but I also get this warning/error:
>>
>> Short write (expected 16384, wrote 7616)

>It was a bug in alsa-lib. I fixed it in patch bellow. Thank you for your
>report.

> http://git.alsa-project.org/?p=alsa-lib.git;a=commitdiff;h=2e48439ad93f6c8d99a2d72928ac71285b5211bb <http://git.alsa-project.org/?p=alsa-lib.git;a=commitdiff;h=2e48439ad93f6c8d99a2d72928ac71285b5211bb>

Add snd_pcm_dump() after call snd_pcm_set_params in pcm_min.c

The start threshold is equal to buffer size , so there should be a
short write at the second write since
16384 + 7616 = 24000  ( start threshold )

your patch had changed the behaviour


 ./pcm_min
ALSA <-> PulseAudio PCM I/O Plugin
Its setup is:
  stream       : PLAYBACK
  access       : RW_INTERLEAVED
  format       : U8
  subformat    : STD
  channels     : 1
  rate         : 48000
  exact rate   : 48000 (48000/1)
  msbits       : 8
  buffer_size  : 24000
  period_size  : 6000
  period_time  : 125000
  tstamp_mode  : NONE
  period_step  : 1
  avail_min    : 6000
  period_event : 0
  start_threshold  : 24000
  stop_threshold   : 24000
  silence_threshold: 0
  silence_size : 0
  boundary     : 1572864000
state = 2
write 16384 frames
state = 2
write 16384 frames
state = 3
write 16384 frames
state = 3
write 16384 frames
state = 3

Re: Warning/error from ALSA’s pcm_min.c example. Possible problem?

[Jaroslav Kysela]

On Fri, 29 Oct 2010, Raymond Yau wrote:

>>> On Sat, 30 Jan 2010, Louise Hoffman wrote:
>
>>> Dear ALSA developers,
>>>
>>> When I compile ALSA's pcm_min.c[0] example with
>>>
>>> gcc -Wall -lasound pcm_min.c -o pcm_min
>>>
>>> Everything is fine, but running it, I get the white noise as expected,
>>> but I also get this warning/error:
>>>
>>> Short write (expected 16384, wrote 7616)
>
>> It was a bug in alsa-lib. I fixed it in patch bellow. Thank you for your
>> report.
>
>> http://git.alsa-project.org/?p=alsa-lib.git;a=commitdiff;h=2e48439ad93f6c8d99a2d72928ac71285b5211bb <http://git.alsa-project.org/?p=alsa-lib.git;a=commitdiff;h=2e48439ad93f6c8d99a2d72928ac71285b5211bb>
>
> Add snd_pcm_dump() after call snd_pcm_set_params in pcm_min.c
>
> The start threshold is equal to buffer size , so there should be a
> short write at the second write since
> 16384 + 7616 = 24000  ( start threshold )
>
> your patch had changed the behaviour

The pcm_min uses the blocked mode, so all layers tries to queue all given 
samples and wait for the ring buffer.

>  buffer_size  : 24000
>  start_threshold  : 24000

> state = 2
> write 16384 frames
> state = 2
> write 16384 frames
> state = 3

This looks correct.

 					Jaroslav


-----
Jaroslav Kysela <perex@perex.cz>
Linux Kernel Sound Maintainer
ALSA Project, Red Hat, Inc.