On Thu, 02 Aug 2018 16:31:13 +0200, Chakravarthi Pradeep wrote:

I'm working on ALSA driver for PCIe card. My ALSA driver and it's initializing struct snd_pcm_hardware with below parameter.

/************************ code start ************************************************/ static struct snd_pcm_hardware audio_pcm_hardware = { .info = (SNDRV_PCM_INFO_INTERLEAVED | SNDRV_PCM_INFO_MMAP | SNDRV_PCM_INFO_MMAP_VALID | SNDRV_PCM_INFO_BLOCK_TRANSFER | SNDRV_PCM_INFO_RESUME ), .formats = (SNDRV_PCM_FORMAT_S16_LE | SNDRV_PCM_FORMAT_S24_LE), .rates = (SNDRV_PCM_RATE_44100 | SNDRV_PCM_RATE_48000 | SNDRV_PCM_RATE_96000 | SNDRV_PCM_RATE_192000), .rate_min = 44100, .rate_max = 192000, .channels_min = 2, .channels_max = 8, .buffer_bytes_max = 76800, /*75 kbytes */ .period_bytes_min = 512,//4410, /* (channel (2) * sample_rate (44100)

• bit width (24)) / (60 * 8) */

.period_bytes_max = 16*1024, .periods_min = 10, .periods_max = 255,

}; /************************ code end ************************************************/

1. I did not understand what is significance of periods_min ,

period_bytes_min , period_bytes_max and periods_max. Can you please tell me what is importance of these parameter and what value should be mentioned according into ALSA.

These three defines the values your hardware may accept: periods_min = the minimal number of periods period_bytes_min = the minimal size of bytes for one period period_bytes_max = the maximal size of bytes for one period

2. snd_pcm_ops trigger callback is getting called in the driver when

application sends "start" command. But ALSA driver is stopping by itself after one frame is copied to ALSA framework, without waiting for "stop" command.

For instance: In trigger callback , I'm getting these logs after one frame is copied. Trigger:Start (When Play button is selected/clicked in application, Start command is sent to ALSA driver) Dma transfer is completed. Trigger:Stop. (When Stop button is selected/clicked in application, Stop command is sent to ALSA driver. But stop button is not clicked in this case)

It's most likely the ALSA PCM core's safety stop; your driver seem to have missed snd_pcm_period_elapsed() calls, so the hwptr isn't updated, resulting in XRUN. ALSA PCM core checks such XRUN condition with the own timer.

Takashi