[alsa-devel] snd_pcm_set_params faild on set_buffer_time_near and set_period_time_near

[Raymond Yau]

2015-07-24 19:16 GMT+08:00 Martin Geier <martin.geier at streamunlimited.com>:

> Patch with fixed name and description.
>
> Martin
>
>
>
> On 24.07.2015 10:21, Takashi Iwai wrote:
>
>> On Fri, 24 Jul 2015 09:52:14 +0200,
>> Martin Geier wrote:
>>
>>> Thanks for help,
>>>
>>> in attachment is patch with suggest change.
>>> Is the patch acceptable?
>>>
>> I prefer a bit clearer name like params_saved or such, but yes, it's
>> what I had in my mind, too.  Could you tidy it up and resubmit with
>> the more description -- why it's needed and what does it?  Last but
>> not least, it'd be helpful if you give also signed-off-by tag.
>>
>>
>> thanks,
>>
>> Takashi
>>
>>  Martin
>>>
>>> On 23.07.2015 10:11, Takashi Iwai wrote:
>>>
>>>> On Tue, 21 Jul 2015 10:52:01 +0200,
>>>> Martin Geier wrote:
>>>>
>>>>> Hallo,
>>>>>
>>>>> I tried to configure alsa device with snd_pcm_set_params function,
>>>>> requested
>>>>> parameters was:
>>>>> channel 2, rate: 22050, soft_resample: 1, latency: 50000
>>>>>
>>>>> Function snd_pcm_hw_params_set_buffer_time_near and
>>>>> snd_pcm_hw_param_set_near
>>>>> is called with:
>>>>> min: 50000, max: 50000, mindir: 0, maxdir: -1
>>>>>
>>>>> and input params was:
>>>>>
>>>>> ACCESS:  RW_INTERLEAVED
>>>>> FORMAT:  S16_LE
>>>>> SUBFORMAT:  STD
>>>>> SAMPLE_BITS: 16
>>>>> FRAME_BITS: 32
>>>>> CHANNELS: 2
>>>>> RATE: 22050
>>>>> PERIOD_TIME: (362 743039)
>>>>> PERIOD_SIZE: [8 16384]
>>>>> PERIOD_BYTES: [32 65536]
>>>>> PERIODS: [2 19]
>>>>> BUFFER_TIME: (725 1486078)
>>>>> BUFFER_SIZE: [16 32768]
>>>>> BUFFER_BYTES: [64 131072]
>>>>> TICK_TIME: ALL
>>>>>
>>>>> unfortunately, this function fails, on function
>>>>> snd_pcm_hw_param_set_first:
>>>>>
>>>>> ALSA ERROR hw_params: set_near (BUFFER_TIME)
>>>>>               value = 50000 : Invalid argument
>>>>> ACCESS:  RW_INTERLEAVED
>>>>> FORMAT:  S16_LE
>>>>> SUBFORMAT:  STD
>>>>> SAMPLE_BITS: 16
>>>>> FRAME_BITS: 32
>>>>> CHANNELS: 2
>>>>> RATE: 22050
>>>>> PERIOD_TIME: (4580 5533)
>>>>> PERIOD_SIZE: NONE
>>>>> PERIOD_BYTES: [404 488]
>>>>> PERIODS: 10
>>>>> BUFFER_TIME: (50022 50023)
>>>>> BUFFER_SIZE: 1103
>>>>> BUFFER_BYTES: 4412
>>>>> TICK_TIME: ALL
>>>>>
>>>>> This shouldn't be problem because in snd_pcm_set_params is
>>>>> snd_pcm_hw_params_set_period_time_near called.
>>>>> This function should be called with same params as
>>>>> snd_pcm_hw_params_set_buffer_time_near
>>>>> but the input params are:
>>>>>
>>>>> snd_pcm_hw_param_set_near: min: 12500, max: 12500, mindir: 0, maxdir:
>>>>> -1
>>>>> hw_params: snd_pcm_hw_param_set_near (PERIOD_TIME)
>>>>> ACCESS:  RW_INTERLEAVED
>>>>> FORMAT:  S16_LE
>>>>> SUBFORMAT:  STD
>>>>> SAMPLE_BITS: 16
>>>>> FRAME_BITS: 32
>>>>> CHANNELS: 2
>>>>> RATE: 22050
>>>>> PERIOD_TIME: (4580 5533)
>>>>> PERIOD_SIZE: NONE
>>>>> PERIOD_BYTES: [404 488]
>>>>> PERIODS: 10
>>>>> BUFFER_TIME: (50022 50023)
>>>>> BUFFER_SIZE: 1103
>>>>> BUFFER_BYTES: 4412
>>>>> TICK_TIME: ALL
>>>>>
>>>>

What is the period time and buffer time after applied your patch ?

Are latency always <= 50ms ?