Underrun in alsa audio (wake_up() is not working in linux-2.6.25)

chethangm84 · 07-24-2009, 08:28 AM

Issue:

If I play the wav file using "aplay", underrun error occurs.

I am suspecting the issue in driver or in kernel code.

I am using the following setup:

a) Application and Library:
aplay in alsa-utils-1.0.16 and alsa-lib-1.0.16.
b) Platform: imx27
c) kernel: linux-2.6.25

Hardware & Software parameters for aplay:

cat /proc/asound/card0/pcm0p/sub0/sw_params
tstamp_mode: NONE
period_step: 1
avail_min: 2048
start_threshold: 8192
stop_threshold: 8192
silence_threshold: 0
silence_size: 0
boundary: 1073741824

cat /proc/asound/card0/pcm0p/sub0/hw_params
access: RW_INTERLEAVED
format: S16_LE
subformat: STD
channels: 2
rate: 44100 (44100/1)
period_size: 2048
buffer_size: 8192

observation:

1. When the aplay task going to wait state by calling following set of
functions in the audio driver,

static int wait_for_avail_min(struct snd_pcm_substream *substream,
snd_pcm_uframes_t *availp)
{
set_current_state(TASK_INTERRUPTIBLE);
snd_pcm_stream_unlock_irq(substream);
tout = schedule_timeout(msecs_to_jiffies(10000));
.
.
}

(file: linux-2.6.25/sound/core/pcm_lib.c)

Its not coming out from "schedule_timeout()" for a while in error
scenario (underrun condition).

2. What I observed is, in "try_to_wake_up()" of kernel/sched.c
its not enqueueing the "aplay" task in the "runqueue".

3. When the audio buffer is free the callback function
"snd_pcm_update_hw_ptr_post()" is calling "wake_up" to schedule,
here in error scenario its not actually
enqueueing our task in the "runqueue"

4. And Here I observed old_state and current task state (p->state)
mismatch for "aplay" context.

Is any one faced similar problem?

Can any one suggest me if any kernel patch for this issue.

I am stuck up here.

Thanks in advance
Chethan