commit b751eef1fdffca5532344285f2fad0c60d2f0158
author Jaroslav Kysela <perex@perex.cz> Thu Dec 13 10:19:42 2007 +0100
committer Jaroslav Kysela <perex@perex.cz> Thu Jan 31 17:29:31 2008 +0100
tree d504104c6315a8abc4b3f657f8f4828fb55a8795
parent 25543fa785a32ce22e7374ba403eb6d38854d037

[ALSA] Use posix clock monotonic for PCM and timer timestamps

We need an accurate and continuous (monotonic) time sources to do
accurate synchronization among more timing sources. This patch allows
to enable monotonic timestamps for ALSA PCM devices and enables monotonic
timestamps for ALSA timer devices.

Signed-off-by: Jaroslav Kysela <perex@perex.cz>

sound/core/timer.c

diff --git a/sound/core/timer.c b/sound/core/timer.c
index e7dc56c..7e5fe2d 100644
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -44,11 +44,14 @@
 #endif
 
 static int timer_limit = DEFAULT_TIMER_LIMIT;
+static int timer_tstamp_monotonic = 1;
 MODULE_AUTHOR("Jaroslav Kysela <perex@perex.cz>, Takashi Iwai <tiwai@suse.de>");
 MODULE_DESCRIPTION("ALSA timer interface");
 MODULE_LICENSE("GPL");
 module_param(timer_limit, int, 0444);
 MODULE_PARM_DESC(timer_limit, "Maximum global timers in system.");
+module_param(timer_tstamp_monotonic, int, 0444);
+MODULE_PARM_DESC(timer_tstamp_monotonic, "Use posix monotonic clock source for timestamps (default).");
 
 struct snd_timer_user {
 	struct snd_timer_instance *timeri;
@@ -381,7 +384,10 @@
 	struct snd_timer_instance *ts;
 	struct timespec tstamp;
 
-	getnstimeofday(&tstamp);
+	if (timer_tstamp_monotonic)
+		do_posix_clock_monotonic_gettime(&tstamp);
+	else
+		getnstimeofday(&tstamp);
 	snd_assert(event >= SNDRV_TIMER_EVENT_START &&
 		   event <= SNDRV_TIMER_EVENT_PAUSE, return);
 	if (event == SNDRV_TIMER_EVENT_START ||
@@ -1182,8 +1188,12 @@
 		spin_unlock(&tu->qlock);
 		return;
 	}
-	if (tu->last_resolution != resolution || ticks > 0)
-		getnstimeofday(&tstamp);
+	if (tu->last_resolution != resolution || ticks > 0) {
+		if (timer_tstamp_monotonic)
+			do_posix_clock_monotonic_gettime(&tstamp);
+		else
+			getnstimeofday(&tstamp);
+	}
 	if ((tu->filter & (1 << SNDRV_TIMER_EVENT_RESOLUTION)) &&
 	    tu->last_resolution != resolution) {
 		r1.event = SNDRV_TIMER_EVENT_RESOLUTION;