[alsa-devel] snd_pcm_set_params faild on set_buffer_time_near and set_period_time_near

[Martin Geier]

Hi Raymond,

Output parameters with custom logs:
set_buffer_time_near: -22
set period time: 12517
get period size: 276
set buffer size: 1104
get buffer size: 1104

ACCESS:  RW_INTERLEAVED
FORMAT:  S16_LE
SUBFORMAT:  STD
SAMPLE_BITS: 16
FRAME_BITS: 32
CHANNELS: 2
RATE: 22050
PERIOD_TIME: (12517 12518)
PERIOD_SIZE: 276
PERIOD_BYTES: 1104
PERIODS: 4
BUFFER_TIME: (50068 50069)
BUFFER_SIZE: 1104
BUFFER_BYTES: 4416

What do you mean, are latency always <= 50ms? In what cases?

Martin

On 25.07.2015 04:01, Raymond Yau wrote:
>
>
> 2015-07-24 19:16 GMT+08:00 Martin Geier 
> <martin.geier at streamunlimited.com 
> <mailto: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 ?

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