@@ -333,16 +333,16 @@ static int snd_pcm_dshare_reset(snd_pcm_t *pcm)
snd_pcm_direct_t *dshare = pcm->private_data;
dshare->hw_ptr %= pcm->period_size;
dshare->appl_ptr = dshare->last_appl_ptr = dshare->hw_ptr;
- dshare->slave_appl_ptr = dshare->slave_hw_ptr = *dshare->spcm->hw.ptr;
+ snd_pcm_direct_reset_slave_ptr(pcm, dshare);
return 0;
}
-static int snd_pcm_dshare_start_timer(snd_pcm_direct_t *dshare)
+static int snd_pcm_dshare_start_timer(snd_pcm_t *pcm, snd_pcm_direct_t *dshare)
{
int err;
snd_pcm_hwsync(dshare->spcm);
- dshare->slave_appl_ptr = dshare->slave_hw_ptr = *dshare->spcm->hw.ptr;
+ snd_pcm_direct_reset_slave_ptr(pcm, dshare);
err = snd_timer_start(dshare->timer);
if (err < 0)
return err;
@@ -364,7 +364,8 @@ static int snd_pcm_dshare_start(snd_pcm_t *pcm)
else if (avail < 0)
return 0;
else {
- if ((err = snd_pcm_dshare_start_timer(dshare)) < 0)
+ err = snd_pcm_dshare_start_timer(pcm, dshare);
+ if (err < 0)
return err;
snd_pcm_dshare_sync_area(pcm);
}
@@ -547,7 +548,8 @@ static snd_pcm_sframes_t snd_pcm_dshare_mmap_commit(snd_pcm_t *pcm,
return 0;
snd_pcm_mmap_appl_forward(pcm, size);
if (dshare->state == STATE_RUN_PENDING) {
- if ((err = snd_pcm_dshare_start_timer(dshare)) < 0)
+ err = snd_pcm_dshare_start_timer(pcm, dshare);
+ if (err < 0)
return err;
} else if (dshare->state == SND_PCM_STATE_RUNNING ||
dshare->state == SND_PCM_STATE_DRAINING) {
@@ -755,6 +757,7 @@ int snd_pcm_dshare_open(snd_pcm_t **pcmp, const char *name,
dshare->slowptr = opts->slowptr;
dshare->max_periods = opts->max_periods;
dshare->var_periodsize = opts->var_periodsize;
+ dshare->hw_ptr_alignment = opts->hw_ptr_alignment;
dshare->sync_ptr = snd_pcm_dshare_sync_ptr;
retry:
@@ -912,6 +915,12 @@ pcm.name {
ipc_key INT # unique IPC key
ipc_key_add_uid BOOL # add current uid to unique IPC key
ipc_perm INT # IPC permissions (octal, default 0600)
+ hw_ptr_alignment STR # Slave application and hw pointer alignment type
+ # STR can be one of the below strings :
+ # no
+ # roundup
+ # rounddown
+ # auto (default)
slave STR
# or
slave { # Slave definition
@@ -936,6 +945,27 @@ pcm.name {
}
\endcode
+<code>hw_ptr_alignment</code> specifies slave application and hw
+pointer alignment type. By default hw_ptr_alignment is auto. Below are
+the possible configurations:
+- no: minimal latency with minimal frames dropped at startup. But
+ wakeup of application (return from snd_pcm_wait() or poll()) can
+ take up to 2 * period.
+- roundup: It is guaranteed that all frames will be played at
+ startup. But the latency will increase upto period-1 frames.
+- rounddown: It is guaranteed that a wakeup will happen for each
+ period and frames can be written from application. But on startup
+ upto period-1 frames will be dropped.
+- auto: Selects the best approach depending on the used period and
+ buffer size.
+ If the application buffer size is < 2 * application period,
+ "roundup" will be selected to avoid under runs. If the slave_period
+ is < 10ms we could expect that there are low latency
+ requirements. Therefore "rounddown" will be chosen to avoid long
+ wakeup times. Such wakeup delay could otherwise end up with Xruns in
+ case of a dependency to another sound device (e.g. forwarding of
+ microphone to speaker). Else "no" will be chosen.
+
\subsection pcm_plugins_dshare_funcref Function reference
<UL>