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alsa: improve audio output to multiple devices

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There are currently several issues when multiple alsa devices are
involved.

For alsa devices that are followers, all data is written via
impl_node_process(). Currently spa_alsa_write() is only called if a new
buffer was queued.
It can happen that all buffers are in the ready list (queued by previous
calls but not yet written because there was no free space in the kernel
ring buffer). In this case writing stalls indefinitely.
To fix this, also call spa_alsa_write() if no new buffer is queued but
there are still buffers in the ready list.

If the ready list of the primary device is not empty then only this
device is handled because spa_alsa_write() is called directly. The other
devices make no progress during this interval.
The clock drift calculation works by comparing the alsa delay with the
expected delay since the last wakeup. This only work if the alsa
ringbuffer was filled completly. If the ready list contains a partial
buffer then the ringbuffer is not filled and the timing calculation
during the next wakeup is incorrect.

To fix all this, remove the special case for the non-empty ready list
and just call spa_node_call_ready() every time.
This commit is contained in:
Michael Olbrich 2023-06-21 11:18:43 +02:00 • committed by Wim Taymans
parent ad5ac964af
commit e808875d60
2 changed files with 10 additions and 12 deletions
Download patch file Download diff file Expand all files Collapse all files

5
spa/plugins/alsa/alsa-pcm-sink.c
View file

@ -820,6 +820,11 @@ static int impl_node_process(void *object)
io->status = SPA_STATUS_OK;
}
else if (!spa_list_is_empty(&this->ready)) {
spa_alsa_write(this);
io->status = SPA_STATUS_OK;
}
return SPA_STATUS_HAVE_DATA;
}

11
spa/plugins/alsa/alsa-pcm.c
View file

@ -2574,6 +2574,7 @@ int spa_alsa_skip(struct state *state)
static int handle_play(struct state *state, uint64_t current_time, snd_pcm_uframes_t avail,
snd_pcm_uframes_t delay, snd_pcm_uframes_t target)
{
struct spa_io_buffers *io = state->io;
int res;
if (state->alsa_started && SPA_UNLIKELY(delay > target + state->max_error)) {
@ -2588,20 +2589,12 @@ static int handle_play(struct state *state, uint64_t current_time, snd_pcm_ufram
if (SPA_UNLIKELY((res = update_time(state, current_time, delay, target, false)) < 0))
return res;
if (spa_list_is_empty(&state->ready)) {
struct spa_io_buffers *io = state->io;
spa_log_trace_fp(state->log, "%p: %d", state, io->status);
update_sources(state, false);
io->status = SPA_STATUS_NEED_DATA;
res = spa_node_call_ready(&state->callbacks, SPA_STATUS_NEED_DATA);
}
else {
res = spa_alsa_write(state);
}
return res;
return spa_node_call_ready(&state->callbacks, SPA_STATUS_NEED_DATA);
}
static int handle_capture(struct state *state, uint64_t current_time, snd_pcm_uframes_t avail,