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?
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))-- 2.7.4
Alsa-devel mailing list Alsa-devel@alsa-project.org https://mailman.alsa-project.org/mailman/listinfo/alsa-devel