Re: [alsa-devel] [RFC] pcm: provide a simple mechanism to start playback at a given time

Hi Nick,

Some more comments :)

On 14/10/14 09:34, Nick Stoughton wrote:

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.

/** } */

#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...

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.

#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...

• */

+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);