[RFC] pcm: provide a simple mechanism to start playback at a given time

Tim Cussins

2014-10-16 11:15:18 UTC

Hi Nick,

Some more comments :)

Post by Nick Stoughton
Initial implementation / Request For Comment.
Given an absolute time based on a given clock (CLOCK_MONOTONIC,
CLOCK_MONOTONIC_RAW, CLOCK_REALTIME etc), setup a high resolution timer
to cause playback to be triggered at that time.
---
include/global.h | 10 +++++++++-
include/pcm.h | 2 ++
include/sound/asound.h | 7 +++++++
src/pcm/pcm.c | 22 +++++++++++++++++++++-
src/pcm/pcm_hw.c | 15 +++++++++++++++
src/pcm/pcm_local.h | 1 +
6 files changed, 55 insertions(+), 2 deletions(-)
diff --git a/include/global.h b/include/global.h
index 16a26dc..f0fb661 100644
--- a/include/global.h
+++ b/include/global.h
@@ -144,6 +144,8 @@ struct timespec {
time_t tv_sec; /* seconds */
long tv_nsec; /* nanoseconds */
};
+
+typedef int clockid_t;
#endif
#endif
@@ -151,7 +153,13 @@ struct timespec {
typedef struct timeval snd_timestamp_t;
/** Hi-res timestamp */
typedef struct timespec snd_htimestamp_t;
-
+/** clock type */
+typedef clockid_t snd_clock_t;
+/** a combined clock and time */
+typedef struct {
+ snd_clock_t clock;
+ snd_htimestamp_t time;
+} snd_clock_time_t;

See comments on snd_timestamp_type_t from previous email.

Post by Nick Stoughton
/** \} */
#ifdef __cplusplus
diff --git a/include/pcm.h b/include/pcm.h
index db88ad5..dfaf69f 100644
--- a/include/pcm.h
+++ b/include/pcm.h
@@ -474,6 +474,8 @@ int snd_pcm_prepare(snd_pcm_t *pcm);
int snd_pcm_reset(snd_pcm_t *pcm);
int snd_pcm_status(snd_pcm_t *pcm, snd_pcm_status_t *status);
int snd_pcm_start(snd_pcm_t *pcm);
+int snd_pcm_start_at(snd_pcm_t *pcm, snd_clock_time_t *start_time);
+#define SND_PCM_START_AT(pcm, start_time) snd_pcm_start_at(pcm, start_time)

A debug macro, right? Just checking...

Post by Nick Stoughton
int snd_pcm_drop(snd_pcm_t *pcm);
int snd_pcm_drain(snd_pcm_t *pcm);
int snd_pcm_pause(snd_pcm_t *pcm, int enable);
diff --git a/include/sound/asound.h b/include/sound/asound.h
index 6ee5867..92647ce 100644
--- a/include/sound/asound.h
+++ b/include/sound/asound.h
@@ -434,6 +434,11 @@ struct snd_pcm_mmap_control {
snd_pcm_uframes_t avail_min; /* RW: min available frames for wakeup */
};
+struct snd_clock_time {
+ clockid_t clock;
+ struct timespec time;
+};
+

As above.

Post by Nick Stoughton
#define SNDRV_PCM_SYNC_PTR_HWSYNC (1<<0) /* execute hwsync */
#define SNDRV_PCM_SYNC_PTR_APPL (1<<1) /* get appl_ptr from driver (r/w op) */
#define SNDRV_PCM_SYNC_PTR_AVAIL_MIN (1<<2) /* get avail_min from driver */
@@ -547,6 +552,8 @@ enum {
#define SNDRV_PCM_IOCTL_READN_FRAMES _IOR('A', 0x53, struct snd_xfern)
#define SNDRV_PCM_IOCTL_LINK _IOW('A', 0x60, int)
#define SNDRV_PCM_IOCTL_UNLINK _IO('A', 0x61)
+#define SNDRV_PCM_IOCTL_START_AT _IOR('A', 0x62, struct snd_clock_time)
+
/*****************************************************************************
* *
diff --git a/src/pcm/pcm.c b/src/pcm/pcm.c
index 4a7be6c..7051a22 100644
--- a/src/pcm/pcm.c
+++ b/src/pcm/pcm.c
@@ -1084,6 +1084,25 @@ int snd_pcm_start(snd_pcm_t *pcm)
}
/**
+ * \brief Start a PCM at a specified point in the future
+ * \param pcm PCM handle
+ * \param start_time time to start - based on specified clock
+ * \return 0 on success otherwise a negative error code

Let's figure out what the error codes are going to be:

EINVAL for invalid arguments (broken timespec, invalid clock type)
ENOSYS if start_at isn't supported in this configuration
ETIME if timespec points into the past? Maybe not a great idea...

Post by Nick Stoughton
+ */
+int snd_pcm_start_at(snd_pcm_t *pcm, snd_clock_time_t *start_at)
+{
+ assert(pcm);
+ assert(start_at);
+ if (CHECK_SANITY(! pcm->setup)) {
+ SNDMSG("PCM not set up");
+ return -EIO;
+ }
+ if (pcm->fast_ops->start_at)
+ return pcm->fast_ops->start_at(pcm->fast_op_arg, start_at);
+ return -EINVAL;
+}
+
+/**
* \brief Stop a PCM dropping pending frames
* \param pcm PCM handle
* \return 0 on success otherwise a negative error code
@@ -2444,8 +2463,9 @@ int snd_pcm_wait_nocheck(snd_pcm_t *pcm, int timeout)
continue;
return -errno;
}
- if (! err_poll)
+ if (! err_poll) {
break;
+ }
err = snd_pcm_poll_descriptors_revents(pcm, pfd, npfds, &revents);
if (err < 0)
return err;
diff --git a/src/pcm/pcm_hw.c b/src/pcm/pcm_hw.c
index c34b766..9888253 100644
--- a/src/pcm/pcm_hw.c
+++ b/src/pcm/pcm_hw.c
@@ -620,6 +620,20 @@ static int snd_pcm_hw_start(snd_pcm_t *pcm)
return 0;
}
+static int snd_pcm_hw_start_at(snd_pcm_t *pcm, snd_clock_time_t *start_time)
+{
+ snd_pcm_hw_t *hw = pcm->private_data;
+ int err;
+
+ sync_ptr(hw, 0);
+ if (ioctl(hw->fd, SNDRV_PCM_IOCTL_START_AT, start_time) < 0) {
+ err = -errno;
+ SYSMSG("SNDRV_PCM_IOCTL_START_AT failed (%i)", err);
+ return err;
+ }
+ return 0;
+}
+
static int snd_pcm_hw_drop(snd_pcm_t *pcm)
{
snd_pcm_hw_t *hw = pcm->private_data;
@@ -1336,6 +1350,7 @@ static const snd_pcm_fast_ops_t snd_pcm_hw_fast_ops = {
.prepare = snd_pcm_hw_prepare,
.reset = snd_pcm_hw_reset,
.start = snd_pcm_hw_start,
+ .start_at = snd_pcm_hw_start_at,
.drop = snd_pcm_hw_drop,
.drain = snd_pcm_hw_drain,
.pause = snd_pcm_hw_pause,
diff --git a/src/pcm/pcm_local.h b/src/pcm/pcm_local.h
index 394505f..c3e58af 100644
--- a/src/pcm/pcm_local.h
+++ b/src/pcm/pcm_local.h
@@ -154,6 +154,7 @@ typedef struct {
int (*prepare)(snd_pcm_t *pcm);
int (*reset)(snd_pcm_t *pcm);
int (*start)(snd_pcm_t *pcm);
+ int (*start_at)(snd_pcm_t *pcm, snd_clock_time_t *start_time);
int (*drop)(snd_pcm_t *pcm);
int (*drain)(snd_pcm_t *pcm);
int (*pause)(snd_pcm_t *pcm, int enable);