On Thu, 03 Sep 2015 05:20:54 +0200, Koro Chen wrote:
When we use a ping-ping buffer in capture, and if hw_ptr reported at IRQ is a little smaller than period_size:
|xxxxxxxxxxxxxxxxxxxxxxxxxxxx--|-----------------------------| hw_ptr < period_size
How this happens? The period size is the size where irq (or wakeup) wakes up for read/write. Why the driver wakes up even if there is no enough data?
This available buffer will not be read since its size is smaller than avail_min (which is set to be period_size), and read thread continues to sleep. If the next hw_ptr is just a little larger than buffer_size, overrun occurs.
This could be resolved by setting a small avail_min to kernel, for example, 1, so read thread wakes up and reads every data at IRQ. But current alsa-lib only allows avail_min to be at least period_size. Remove the constraint and only check for zero case.
The restriction was introduced for avoiding CPU hogs with rate plugin in many years ago. avail_min=1 *might* work now because of the later fix for rate plugin, but this must be verified.
thanks,
Takashi
Signed-off-by: Koro Chen koro.chen@mediatek.com
src/pcm/pcm.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-)
diff --git a/src/pcm/pcm.c b/src/pcm/pcm.c index f5fc728..8492689 100644 --- a/src/pcm/pcm.c +++ b/src/pcm/pcm.c @@ -5958,12 +5958,8 @@ int snd_pcm_sw_params_set_avail_min(snd_pcm_t *pcm, snd_pcm_sw_params_t *params, #endif { assert(pcm && params);
- /* Fix avail_min if it's below period size. The period_size
* defines the minimal wake-up timing accuracy, so it doesn't* make sense to set below that.*/- if (val < pcm->period_size)
val = pcm->period_size;
- if (!val)
val = 1;}
1.7.9.5