From: Vanitha Channaiah <vanitha.channaiah@xxxxxxxxxxxx>
For buffer size less than two period size, the start position
of slave_app_ptr is rounded up in order to avoid xruns
For e.g.:
Considering below parameters and its values
Period size = 96
Buffer size = 191
slave_appl_ptr = slave_hw_ptr = unaligned value
Issue:
- During the start of the stream, app_ptr = hw_ptr = 0
- Application writes one period of data in the buffer i.e
app_ptr = 96, hw_ptr = 0
- Now, the avail is just period-1 frames available.
avail = hw_ptr + buffer_size - app_ptr = 95
i.e. shortage of 1 frame space
- so application is waiting for the 1frame space to be available.
- slave_app_ptr and slave_hw_ptr would get updated to lower values
- This could lead to under run to occur.
Fix:
If we round Up the slave_app_ptr pointer,
- During the start of the stream, app_ptr = hw_ptr = 0
- Application writes one period of data in the buffer i.e
app_ptr = 96, hw_ptr = 0
- Round Up of slave_app_ptr pointer leads to below calculation:
- slave_app_ptr rounded to 96
- slave_app_ptr and slave_hw_ptr would get updated to larger value nearing to 2 period size
- avail = greater than period size.
- Here, there is a lower chance of under run.
Signed-off-by: Vanitha Channaiah <vanitha.channaiah@xxxxxxxxxxxx>
---
src/pcm/pcm_direct.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/src/pcm/pcm_direct.c b/src/pcm/pcm_direct.c
index 54d9900..b56da85 100644
--- a/src/pcm/pcm_direct.c
+++ b/src/pcm/pcm_direct.c
@@ -2043,10 +2043,12 @@ 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 less than two period size, the start position
+ * of slave app ptr is rounded up in order 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
_______________________________________________
Alsa-devel mailing list
Alsa-devel@xxxxxxxxxxxxxxxx
https://mailman.alsa-project.org/mailman/listinfo/alsa-devel
