Recently I studied tuna audio HAL reference codes, and summarized
parameters configuration in the following table:
screen status ALSA parameters AF parameters period size period count
start
threshold avail min write size write threshold buffer size buffer count screen
ON 308ms 2 22ms x 2 22ms 22ms 22ms x 4 22ms 28 screen OFF 308ms 2 22ms x 2
308ms 22ms 308ms x 2 22ms 28
According to the codes, the purpose is to simulate 22ms pseudo period size
when screen is ON, and use 308ms period size when screen is OFF, right?
Then I have one question:
Actually ALSA period size is always set to 308ms, so DMA interrupt will
always arrive after each 308ms, right? But according to kernel codes, ALSA
will always wait with 10s timeout, until DMA interrupt signal it. So how
could we simulate 22ms pseudo period size? Need to modify the timeout logic
in kernel codes? Thanks a lot.
------------------------------------------------------------------------
kernel/sound/core/pcm_lib.c (wait_for_avail() functin)
if (runtime->no_period_wakeup)
wait_time = MAX_SCHEDULE_TIMEOUT;
else {
wait_time = 10;
if (runtime->rate) {
long t = runtime->period_size * 2 / runtime->rate;
wait_time = max(t, wait_time);
}
wait_time = msecs_to_jiffies(wait_time * 1000);
}
--------------------------------------------------------------------------
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