[alsa-devel] snd_pcm_hw_params_set_buffer_time_near: invalid argument

[Raymond Yau]

2011/3/9 Jaroslav Kysela <perex at perex.cz>

> On Wed, 9 Mar 2011, Jean-Yves Avenard wrote:
>
>  Hi
>>
>> On Wednesday, 9 March 2011, Raymond Yau <superquad.vortex2 at gmail.com>
>> wrote:
>>
>>  hda-intel.c only allocate 64Kbytes
>>>
>>>     /* buffer pre-allocation */
>>>     snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV_SG,
>>>                           snd_dma_pci_data(chip->pci),
>>>                           1024 * 64, 32 * 1024 * 1024);
>>>
>>> user or distribution need to change "prealloc" from 64 to a higher value
>>> for
>>> getting 500ms buffer
>>>
>>> echo 1024 > /proc/asound/Intel/pcm0p/sub0/prealloc
>>>
>>
>> It seems you misunderstood my first message.
>>
>> For a start, the default memory allocated to alsa in ubuntu is 4096kB.
>> so the amount of ram isn't the problem.
>>
>> Setting a buffer of
>> 200ms: ok
>> 300ms: ok
>> 400ms: not ok (invalid argument)
>> 500ms: ok
>>
>> Why would 400ms gives invalid argument, when 500ms doesn't nor 300.
>> Memory available is obviously not the issue.
>>
>> If only 64kB is allocated, requesting 200ms gives you 200ms
>> 300ms -> 300ms
>> 400ms -> invalid argument
>> 500ms -> 371ms
>> 600ms -> 371ms
>>
>> You would assume that requesting 400ms would work or return what can
>> fit in what has been pre-allocated.
>>
>
> What is your dir argument (last one) for the near functions? If it's NULL
> or value is zero, it means you request the exact value which may not be
> available. Use -1 to request specified or smaller value or 1 to request
> specified or bigger value.
>
>                                        Jaroslav
>

According to your explanation,  it should fail at 500ms buffer time when
rate is 11025Hz and dir=0 or NULL, since half of 11025 is  5512.5

but

alsa-lib/test/pcm -v -Dhw:CARD=Intel,DEV=0 -r 11025 -c 2 -b 500000

Playback device is hw:CARD=Intel,DEV=0
Stream parameters are 11025Hz, S16_LE, 2 channels
Sine wave rate is 440.0000Hz
Using transfer method: write
Hardware PCM card 1 'HDA Intel' device 0 subdevice 0
Its setup is:
  stream       : PLAYBACK
  access       : RW_INTERLEAVED
  format       : S16_LE
  subformat    : STD
  channels     : 2
  rate         : 11025
  exact rate   : 11025 (11025/1)
  msbits       : 16
  buffer_size  : 5504
  period_size  : 1376
  period_time  : 124807
  tstamp_mode  : NONE
  period_step  : 1
  avail_min    : 1376
  period_event : 0
  start_threshold  : 5504
  stop_threshold   : 5504
  silence_threshold: 0
  silence_size : 0
  boundary     : 1442840576
  appl_ptr     : 0
  hw_ptr       : 0