[alsa-devel] Application hangs with different period sizes

[Gustavo da Silva Serra]

I think that snd_pcm_hw_params_set_period_size_near() will not return an 
error, but you must check the "val" parameter, is it returning the same 
value that you passed?

"Some periods are not supported" means that some cards may not support 
periods that aren't power of two. I am not sure, since I am new to ALSA 
and I am working most with aloop.

anuj aggarwal escreveu:
> I am doing the same. I used snd_pcm_hw_params_set_period_size_near() 
> to set the period size and checked the return value also; it was not 
> an error.
>
> I have one more question. When you say 'Some periods are not 
> supported', what does that mean? What are the constraints which make 
> some periods not-supported by the audio codec driver?
>
> On Thu, Jul 3, 2008 at 5:11 PM, Gustavo da Silva Serra 
> <gustavo.serra at tet.com.br <mailto:gustavo.serra at tet.com.br>> wrote:
>
>     Do you check the result of the function that sets the period size?
>     Some periods are not supported and you can't assume that they are
>     valid and proceed in your application. Use
>     snd_pcm_hw_params_set_period_time_near to see what is the nearest
>     possible value for period.
>     <http://www.alsa-project.org/alsa-doc/alsa-lib/group___p_c_m___h_w___params.html#gf5e53bcb748185a4da3b8538720a5792>
>
>     anuj aggarwal escreveu:
>
>         My audio driver supports buffer sizes from 128 to 32768 and
>         period sizes
>         from 8 to 2048. I am trying to set the period size as 1030
>         (just a random
>         number between 8 & 2048, but not multiple of 2^n) and buffer
>         size as
>         16*buffer_size (i.e. 16480). The output is as follows:
>
>         Buffer size range from 128 to 32768
>         Period size range from 8 to 2048
>         Request period size 1030 and got 1030
>         Plug PCM: Hardware PCM card 0 'TWL4030' device 0 subdevice 0
>         Its setup is:
>          stream       : PLAYBACK
>          access       : RW_INTERLEAVED
>          format       : S16_LE
>          subformat    : STD
>          channels     : 2
>          rate         : 44100
>          exact rate   : 44100 (44100/1)
>          msbits       : 16
>          buffer_size  : 16480
>          period_size  : 1030
>          period_time  : 23356
>          tstamp_mode  : NONE
>          period_step  : 1
>          avail_min    : 1030
>          start_threshold  : 16480
>          stop_threshold   : 16480
>          silence_threshold: 0
>          silence_size : 0
>          boundary     : 1080033280
>
>         The problem with this setup is the application just hangs
>         without playing
>         anything. If I use period size as 2048, the app plays the song
>         but clips the
>         last part of it. If I use 1024/512, it works fine.
>
>         I have tried alsa lib version 1.0.15 & 1.0.16 but the problem
>         persists. Is
>         there anything wrong with my app or audio driver?
>
>         Please help.
>
>         Thanks in advance,
>         Anuj Aggarwal
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> -- 
> Best Regards,
> Anuj Aggarwal