[alsa-devel] [PATCH] ALSA: provide a simple mechanism to start playback at a given time
Nick Stoughton
nstoughton at aether.com
Tue Oct 14 10:29:31 CEST 2014
Given an absolute time based on the clock used by the substream
setup a high resolution timer to cause playback to be triggered
at that time.
Signed-off-by: Nick Stoughton <nstoughton at aether.com>
---
include/uapi/sound/asound.h | 6 ++
sound/core/pcm_native.c | 142 ++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 148 insertions(+)
diff --git a/include/uapi/sound/asound.h b/include/uapi/sound/asound.h
index 6ee5867..92d5856 100644
--- a/include/uapi/sound/asound.h
+++ b/include/uapi/sound/asound.h
@@ -462,6 +462,11 @@ struct snd_xfern {
snd_pcm_uframes_t frames;
};
+struct snd_clock_time {
+ clockid_t clock;
+ struct timespec time;
+};
+
enum {
SNDRV_PCM_TSTAMP_TYPE_GETTIMEOFDAY = 0, /* gettimeofday equivalent */
SNDRV_PCM_TSTAMP_TYPE_MONOTONIC, /* posix_clock_monotonic equivalent */
@@ -547,6 +552,7 @@ 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 _IOW('A', 0x62, struct snd_clock_time)
/*****************************************************************************
* *
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 85fe1a2..f16ac3c 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -27,6 +27,7 @@
#include <linux/pm_qos.h>
#include <linux/aio.h>
#include <linux/dma-mapping.h>
+#include <linux/time.h>
#include <sound/core.h>
#include <sound/control.h>
#include <sound/info.h>
@@ -38,6 +39,9 @@
#if defined(CONFIG_MIPS) && defined(CONFIG_DMA_NONCOHERENT)
#include <dma-coherence.h>
#endif
+#if defined(CONFIG_HIGH_RES_TIMERS)
+#include <linux/hrtimer.h>
+#endif
/*
* Compatibility
@@ -1016,6 +1020,142 @@ static struct action_ops snd_pcm_action_start = {
.post_action = snd_pcm_post_start
};
+#ifdef CONFIG_HIGH_RES_TIMERS
+/**
+ * ktime_get_raw_offset - get the offset in ktime format between
+ * the monotonic_raw clock and the monotonic clock
+ */
+static ktime_t ktime_get_raw_offset(void)
+{
+ struct timespec rawtime = {0,0};
+ struct timespec now = {0,0};
+ struct timespec delta;
+
+ ktime_get_ts(&now);
+ getrawmonotonic(&rawtime);
+ delta = timespec_sub(now, rawtime);
+ return timespec_to_ktime(delta);
+}
+
+/*
+ * hrtimer interface
+ */
+
+struct hrtimer_pcm {
+ struct hrtimer timer;
+ struct snd_pcm_substream *substream;
+};
+
+/*
+ * called from a hard irq context - no need for locks.
+ */
+enum hrtimer_restart snd_pcm_do_start_time(struct hrtimer *timer)
+{
+ struct hrtimer_pcm *pcm_timer;
+ struct snd_pcm_substream *substream;
+ struct snd_pcm_runtime *runtime;
+ int ret;
+
+ pcm_timer = container_of(timer, struct hrtimer_pcm, timer);
+ substream = pcm_timer->substream;
+ runtime = substream->runtime;
+
+ /* Check that the stream is still open and in the right state. */
+ if (runtime && runtime->status->state == SNDRV_PCM_STATE_PREPARED) {
+
+ ret = snd_pcm_do_start(substream, SNDRV_PCM_STATE_RUNNING);
+ if (ret == 0) {
+ snd_pcm_post_start(substream, SNDRV_PCM_STATE_RUNNING);
+ }
+ }
+ kfree(pcm_timer);
+
+ return HRTIMER_NORESTART;
+}
+
+int snd_pcm_start_at(struct snd_pcm_substream *substream,
+ struct timespec __user *_start_time)
+{
+ struct hrtimer_pcm *pcm_timer;
+ struct timespec start_time;
+ int clock;
+ ktime_t start_kt;
+ ktime_t raw_offset;
+ int ret;
+
+ if (copy_from_user(&start_time, _start_time, sizeof(start_time)))
+ return -EFAULT;
+
+ if (!timespec_valid(&start_time))
+ return -EINVAL;
+
+ start_kt = timespec_to_ktime(start_time);
+ switch (substream->runtime->tstamp_type) {
+ case SNDRV_PCM_TSTAMP_TYPE_GETTIMEOFDAY:
+ clock = CLOCK_REALTIME;
+ break;
+ case SNDRV_PCM_TSTAMP_TYPE_MONOTONIC:
+ clock = CLOCK_MONOTONIC;
+ break;
+ case SNDRV_PCM_TSTAMP_TYPE_MONOTONIC_RAW:
+ clock = CLOCK_MONOTONIC_RAW;
+ break;
+ default:
+ return -EINVAL;
+ }
+ switch(clock) {
+ case CLOCK_MONOTONIC_RAW:
+ /*
+ * convert to clock monotonic:
+ * the raw clock and the monotonic clock run at different
+ * rates. Currently there is no timer based on the
+ * monotonic_raw clock but for our purposes, we assume that
+ * the divergence between the raw and the monotonic clock
+ * over the life of the timer will be minimal.
+ * Typically the difference is less than 20PPM.
+ * TODO: implement high res timer based on CLOCK_MONOTONIC_RAW
+ */
+ raw_offset = ktime_get_raw_offset();
+ start_kt = ktime_add(raw_offset, start_kt);
+ clock = CLOCK_MONOTONIC;
+ /* and fall through ... */
+ case CLOCK_MONOTONIC:
+ if (ktime_compare(start_kt, ktime_get()) <= 0)
+ return -ETIME;
+ break;
+ case CLOCK_REALTIME:
+ if (ktime_compare(start_kt,
+ ktime_get_with_offset(TK_OFFS_REAL)) <= 0)
+ return -EINVAL;
+ }
+
+ /* Fail if not playback substream */
+ if (substream->stream != SNDRV_PCM_STREAM_PLAYBACK)
+ return -EBADFD;
+
+ ret = snd_pcm_pre_start(substream, SNDRV_PCM_STATE_PREPARED);
+ if (ret != 0)
+ return ret;
+
+ pcm_timer = kmalloc(sizeof(*pcm_timer), GFP_KERNEL);
+ hrtimer_init(&pcm_timer->timer, clock, HRTIMER_MODE_ABS);
+
+ pcm_timer->timer.function = snd_pcm_do_start_time;
+ pcm_timer->substream = substream;
+
+ hrtimer_start(&pcm_timer->timer, start_kt, HRTIMER_MODE_ABS);
+
+ return 0;
+}
+#else
+/* without high res time, interface is identical to snd_pcm_start() */
+int snd_pcm_start_at(struct snd_pcm_substream *substream,
+ struct snd_clock_time __user *_start_time)
+{
+ return -ENOSYS;
+}
+#endif
+
/**
* snd_pcm_start - start all linked streams
* @substream: the PCM substream instance
@@ -2698,6 +2838,8 @@ static int snd_pcm_common_ioctl1(struct file *file,
return snd_pcm_reset(substream);
case SNDRV_PCM_IOCTL_START:
return snd_pcm_action_lock_irq(&snd_pcm_action_start, substream, SNDRV_PCM_STATE_RUNNING);
+ case SNDRV_PCM_IOCTL_START_AT:
+ return snd_pcm_start_at(substream, arg);
case SNDRV_PCM_IOCTL_LINK:
return snd_pcm_link(substream, (int)(unsigned long) arg);
case SNDRV_PCM_IOCTL_UNLINK:
--
1.9.3
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