@@ -1883,6 +1883,7 @@ int snd_pcm_direct_parse_open_conf(snd_config_t *root, snd_config_t *conf,
rec->max_periods = 0;
rec->var_periodsize = 0;
rec->direct_memory_access = 1;
+ rec->hw_ptr_alignment = SND_PCM_HW_PTR_ALIGNMENT_AUTO;
/* read defaults */
if (snd_config_search(root, "defaults.pcm.dmix_max_periods", &n) >= 0) {
@@ -1924,6 +1925,28 @@ int snd_pcm_direct_parse_open_conf(snd_config_t *root, snd_config_t *conf,
rec->ipc_perm = perm;
continue;
}
+ if (strcmp(id, "hw_ptr_alignment") == 0) {
+ const char *str;
+ err = snd_config_get_string(n, &str);
+ if (err < 0) {
+ SNDERR("Invalid type for %s", id);
+ return -EINVAL;
+ }
+ if (strcmp(str, "no") == 0)
+ rec->hw_ptr_alignment = SND_PCM_HW_PTR_ALIGNMENT_NO;
+ else if (strcmp(str, "roundup") == 0)
+ rec->hw_ptr_alignment = SND_PCM_HW_PTR_ALIGNMENT_ROUNDUP;
+ else if (strcmp(str, "rounddown") == 0)
+ rec->hw_ptr_alignment = SND_PCM_HW_PTR_ALIGNMENT_ROUNDDOWN;
+ else if (strcmp(str, "auto") == 0)
+ rec->hw_ptr_alignment = SND_PCM_HW_PTR_ALIGNMENT_AUTO;
+ else {
+ SNDERR("The field hw_ptr_alignment is invalid : %s", str);
+ return -EINVAL;
+ }
+
+ continue;
+ }
if (strcmp(id, "ipc_gid") == 0) {
char *group;
char *endp;
@@ -49,6 +49,13 @@ typedef void (mix_areas_u8_t)(unsigned int size,
volatile signed int *sum, size_t dst_step,
size_t src_step, size_t sum_step);
+typedef enum snd_pcm_direct_hw_ptr_alignment {
+ SND_PCM_HW_PTR_ALIGNMENT_NO = 0, /* use the hw_ptr as is and do no rounding */
+ SND_PCM_HW_PTR_ALIGNMENT_ROUNDUP = 1, /* round the slave_appl_ptr up to slave_period */
+ SND_PCM_HW_PTR_ALIGNMENT_ROUNDDOWN = 2, /* round slave_hw_ptr and slave_appl_ptr down to slave_period */
+ SND_PCM_HW_PTR_ALIGNMENT_AUTO = 3 /* automatic selection */
+} snd_pcm_direct_hw_ptr_alignment_t;
+
struct slave_params {
snd_pcm_format_t format;
int rate;
@@ -159,6 +166,7 @@ struct snd_pcm_direct {
unsigned int *bindings;
unsigned int recoveries; /* mirror of executed recoveries on slave */
int direct_memory_access; /* use arch-optimized buffer RW */
+ snd_pcm_direct_hw_ptr_alignment_t hw_ptr_alignment;
union {
struct {
int shmid_sum; /* IPC global sum ring buffer memory identification */
@@ -341,6 +349,7 @@ struct snd_pcm_direct_open_conf {
int max_periods;
int var_periodsize;
int direct_memory_access;
+ snd_pcm_direct_hw_ptr_alignment_t hw_ptr_alignment;
snd_config_t *slave;
snd_config_t *bindings;
};
@@ -55,6 +55,9 @@ const char *_snd_module_pcm_dmix = "";
#define STATE_RUN_PENDING 1024
#endif
+#define SEC_TO_MS 1000 /* Seconds representing in Milli seconds */
+#define LOW_LATENCY_PERIOD_TIME 10 /* slave_period time for low latency requirements in ms */
+
/*
*
*/
@@ -560,14 +563,17 @@ static int snd_pcm_dmix_hwsync(snd_pcm_t *pcm)
static void reset_slave_ptr(snd_pcm_t *pcm, snd_pcm_direct_t *dmix)
{
dmix->slave_appl_ptr = dmix->slave_hw_ptr = *dmix->spcm->hw.ptr;
- if (pcm->buffer_size > pcm->period_size * 2)
- return;
- /* If we have too litte periods, better to align the start position
- * to the period boundary so that the interrupt can be handled properly
- * at the right time.
- */
- dmix->slave_appl_ptr = ((dmix->slave_appl_ptr + dmix->slave_period_size - 1)
+
+ if (dmix->hw_ptr_alignment == SND_PCM_HW_PTR_ALIGNMENT_ROUNDUP ||
+ (dmix->hw_ptr_alignment == SND_PCM_HW_PTR_ALIGNMENT_AUTO &&
+ pcm->buffer_size <= pcm->period_size * 2))
+ dmix->slave_appl_ptr = ((dmix->slave_appl_ptr + dmix->slave_period_size - 1)
/ dmix->slave_period_size) * dmix->slave_period_size;
+ else if (dmix->hw_ptr_alignment == SND_PCM_HW_PTR_ALIGNMENT_ROUNDDOWN ||
+ (dmix->hw_ptr_alignment == SND_PCM_HW_PTR_ALIGNMENT_AUTO &&
+ (((dmix->slave_period_size * SEC_TO_MS) / pcm->rate) < LOW_LATENCY_PERIOD_TIME)))
+ dmix->slave_appl_ptr = dmix->slave_hw_ptr = ((dmix->slave_hw_ptr
+ / dmix->slave_period_size) * dmix->slave_period_size);
}
static int snd_pcm_dmix_reset(snd_pcm_t *pcm)
@@ -1086,6 +1092,7 @@ int snd_pcm_dmix_open(snd_pcm_t **pcmp, const char *name,
dmix->slowptr = opts->slowptr;
dmix->max_periods = opts->max_periods;
dmix->var_periodsize = opts->var_periodsize;
+ dmix->hw_ptr_alignment = opts->hw_ptr_alignment;
dmix->sync_ptr = snd_pcm_dmix_sync_ptr;
dmix->direct_memory_access = opts->direct_memory_access;
@@ -1241,6 +1248,12 @@ 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
@@ -1273,6 +1286,24 @@ added to the value set in <code>ipc_key</code>. This will
avoid the confliction of the same IPC key with different users
concurrently.
+<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.
+
Note that the dmix plugin itself supports only a single configuration.
That is, it supports only the fixed rate (default 48000), format
(\c S16), channels (2), and period_time (125000).