On Thu, 06 Feb 2020 09:44:58 +0100, Takashi Iwai wrote:

On Thu, 06 Feb 2020 09:14:42 +0100, Channaiah Vanitha (RBEI/ECF3) wrote:

...

Hello Takashi-san,

This patch is regarding the fix for rounding down/up of slave pointers. For buffer_size >= 2*period_size, round down of slave pointers and for buffer_size < 2*period_size, round up of slave pointers will avoid xruns. which otherwise causes snd_pcm_wait() to block for more than expected snd_pcm_period_elapsed() which leads to xruns.

We had similar discussion for same issue in below link: https://mailman.alsa-project.org/pipermail/alsa-devel/2019-June/151169.html

Yes, and I still don't get why this must be required. Doesn't this imply that you drop the samples instead?

Actually, in such an extreme situation, there is no perfect solution with dmix. That's the reason we introduced the explicit hw_ptr_alignment option to specify the behavior. The default value is to keep the current behavior for compatibility; i.e. unless you are 100% sure that this change won't break any existing usage, there is no big reason to change the behavior, too.

thanks,

Takashi

Takashi

...

Regards, Vanitha

-----Original Message----- From: Channaiah Vanitha (RBEI/ECF3) Vanitha.Channaiah@in.bosch.com Sent: Thursday, February 6, 2020 1:43 PM To: Channaiah Vanitha (RBEI/ECF3) Vanitha.Channaiah@in.bosch.com; patch@alsa-project.org Cc: alsa-devel@alsa-project.org; Wischer Timo (ADITG/ESS) twischer@de.adit-jv.com Subject: [PATCH - 1/1] pcm: direct: Round down of slave_hw_ptr when buffer size is two period size

From: Vanitha Channaiah vanitha.channaiah@in.bosch.com

For buffer size equal to two period size, the start position of slave_hw_ptr is rounded down in order to avoid xruns

For e.g.: Considering below parameters and its values: Period size = 96 (0x60) Buffer size = 192 (0xC0) Timer ticks = 1 avail_min = 0x60 slave_hw_ptr = unaligned value during dmix_start()

Issue:

• Initial, app_ptr = hw_ptr = 0
• Application fills buffer size of data. so app_ptr = 0xC0, hw_ptr = 0
• During dmix_start(), current slave_hw_ptr is not rounded down. current slave_hw_ptr would be 0x66
• slave_hw_ptr is keep on updating at the hardware 0x67, 0x68, 0x69
• The diff calculation between old_slave_hw_ptr(0x66) and new_slave_hw_ptr(0x69) results in avail = 0x6
• After 1 snd_pcm_period_elapsed(), slave_hw_ptr = 0xC0
• The result of avail = 0x5A which is less than avail_min(0x60)
• Here, xruns will be observed

Fix:

• Initial, app_ptr = hw_ptr = 0
• Application fills buffer size of data. so app_ptr = 0xC0, hw_ptr = 0
• Round down of slave_hw_ptr during dmix_start() leads to below calculation:
• During dmix_start(), slave_hw_ptr rounded to 0x60 (old slave_hw_ptr)
• The diff calculation between old_slave_hw_ptr(0x60) and new_slave_hw_ptr(0x69) results in avail = 0x9
• After 1 snd_pcm_period_elapsed(), slave_hw_ptr = 0xC0
• The result of avail = 0x60 which is avail_min(0x60)
• Here, xruns can be avoided

Signed-off-by: Vanitha Channaiah vanitha.channaiah@in.bosch.com

diff --git a/src/pcm/pcm_direct.c b/src/pcm/pcm_direct.c index 54d9900..a201fa3 100644 --- a/src/pcm/pcm_direct.c +++ b/src/pcm/pcm_direct.c @@ -2043,10 +2043,14 @@ int snd_pcm_direct_parse_open_conf(snd_config_t *root, snd_config_t *conf,

void snd_pcm_direct_reset_slave_ptr(snd_pcm_t *pcm, snd_pcm_direct_t *dmix) {

• /*

• * For buffer size equal to two period size, slave_hw_ptr is rounded down
  

• * to avoid xruns
  

• */
  
  

  if (dmix->hw_ptr_alignment == SND_PCM_HW_PTR_ALIGNMENT_ROUNDUP || (dmix->hw_ptr_alignment == SND_PCM_HW_PTR_ALIGNMENT_AUTO &&

• pcm->buffer_size <= pcm->period_size * 2))
  

• pcm->buffer_size < pcm->period_size * 2))
  

  dmix->slave_appl_ptr = ((dmix->slave_appl_ptr + dmix->slave_period_size - 1) / dmix->slave_period_size) * dmix->slave_period_size;

-- 2.7.4

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