[0.99.11] ALSA latency patch

git-svn-id: svn+ssh://jackaudio.org/trunk/jack@799 0c269be4-1314-0410-8aa9-9f06e86f4224

configure.ac

@@ -15,7 +15,7 @@ dnl                 changes are made
 dnl ---
 JACK_MAJOR_VERSION=0
 JACK_MINOR_VERSION=99
-JACK_MICRO_VERSION=10
+JACK_MICRO_VERSION=11
 
 dnl ---
 dnl HOWTO: updating the jack protocol version

drivers/alsa/alsa_driver.c

@@ -325,6 +325,7 @@ alsa_driver_configure_stream (alsa_driver_t *driver, char *device_name,
 			      snd_pcm_t *handle, 
 			      snd_pcm_hw_params_t *hw_params, 
 			      snd_pcm_sw_params_t *sw_params, 
+			      unsigned int *nperiodsp,
 			      unsigned long *nchns,unsigned long sample_width)
 {
 	int err, format;
@@ -436,13 +437,23 @@ alsa_driver_configure_stream (alsa_driver_t *driver, char *device_name,
 		return -1;
 	}
 
-	if ((err = snd_pcm_hw_params_set_periods (handle, hw_params,
-						  driver->user_nperiods, 0))
+	*nperiodsp = driver->user_nperiods;
+	snd_pcm_hw_params_set_periods_min (handle, hw_params, nperiodsp, NULL);
+	*nperiodsp = driver->user_nperiods;
+	if ((*nperiodsp = snd_pcm_hw_params_set_periods_near (handle, hw_params,
+							      *nperiodsp, NULL))
 	    < 0) {
 		jack_error ("ALSA: cannot set number of periods to %u for %s",
-			    driver->user_nperiods, stream_name);
+			    *nperiodsp, stream_name);
 		return -1;
 	}
+
+	if (*nperiodsp < driver->user_nperiods) {
+		jack_error ("ALSA: got smaller periods %u than %u for %s",
+			    *nperiodsp, (unsigned int)driver->user_nperiods, stream_name);
+		return -1;
+	}
+	fprintf(stderr, "nperiods = %d for %s\n", *nperiodsp, stream_name);
 	
 	if (!jack_power_of_two(driver->frames_per_cycle)) {
 		jack_error("JACK: frames must be a power of two "
@@ -451,12 +462,12 @@ alsa_driver_configure_stream (alsa_driver_t *driver, char *device_name,
 	}
 
 	if ((err = snd_pcm_hw_params_set_buffer_size (handle, hw_params,
-						      driver->user_nperiods *
+						      *nperiodsp *
 						      driver->frames_per_cycle))
 	    < 0) {
 		jack_error ("ALSA: cannot set buffer length to %" PRIu32
 			    " for %s",
-			    driver->user_nperiods * driver->frames_per_cycle,
+			    *nperiodsp * driver->frames_per_cycle,
 			    stream_name);
 		return -1;
 	}
@@ -475,7 +486,7 @@ alsa_driver_configure_stream (alsa_driver_t *driver, char *device_name,
 		return -1;
 	}
 
-	stop_th = driver->user_nperiods * driver->frames_per_cycle;
+	stop_th = *nperiodsp * driver->frames_per_cycle;
 	if (driver->soft_mode) {
 		stop_th = (snd_pcm_uframes_t)-1;
 	}
@@ -496,20 +507,27 @@ alsa_driver_configure_stream (alsa_driver_t *driver, char *device_name,
 
 #if 0
 	fprintf (stderr, "set silence size to %lu * %lu = %lu\n",
-		 driver->frames_per_cycle, driver->user_nperiods,
-		 driver->frames_per_cycle * driver->user_nperiods);
+		 driver->frames_per_cycle, *nperiodsp,
+		 driver->frames_per_cycle * *nperiodsp);
 
 	if ((err = snd_pcm_sw_params_set_silence_size (
 		     handle, sw_params,
-		     driver->frames_per_cycle * driver->user_nperiods)) < 0) {
+		     driver->frames_per_cycle * *nperiodsp)) < 0) {
 		jack_error ("ALSA: cannot set silence size for %s",
 			    stream_name);
 		return -1;
 	}
 #endif
 
-	if ((err = snd_pcm_sw_params_set_avail_min (
-		     handle, sw_params, driver->frames_per_cycle)) < 0) {
+	if (handle == driver->playback_handle)
+		err = snd_pcm_sw_params_set_avail_min (
+			handle, sw_params,
+			driver->frames_per_cycle * (*nperiodsp - driver->user_nperiods + 1));
+	else
+		err = snd_pcm_sw_params_set_avail_min (
+			handle, sw_params, driver->frames_per_cycle);
+			
+	if (err < 0) {
 		jack_error ("ALSA: cannot set avail min for %s", stream_name);
 		return -1;
 	}
@@ -532,8 +550,6 @@ alsa_driver_set_parameters (alsa_driver_t *driver,
 	int dir;
 	unsigned int p_period_size = 0;
 	unsigned int c_period_size = 0;
-	unsigned int p_nfragments = 0;
-	unsigned int c_nfragments = 0;
 	channel_t chn;
 	unsigned int pr = 0;
 	unsigned int cr = 0;
@@ -554,6 +570,7 @@ alsa_driver_set_parameters (alsa_driver_t *driver,
 			    driver->capture_handle,
 			    driver->capture_hw_params,
 			    driver->capture_sw_params,
+			    &driver->capture_nperiods,
 			    &driver->capture_nchannels,
 			    driver->capture_sample_bytes)) {
 			jack_error ("ALSA: cannot configure capture channel");
@@ -569,6 +586,7 @@ alsa_driver_set_parameters (alsa_driver_t *driver,
 			    driver->playback_handle,
 			    driver->playback_hw_params,
 			    driver->playback_sw_params,
+			    &driver->playback_nperiods,
 			    &driver->playback_nchannels,
 			    driver->playback_sample_bytes)) {
 			jack_error ("ALSA: cannot configure playback channel");
@@ -623,9 +641,6 @@ alsa_driver_set_parameters (alsa_driver_t *driver,
 		p_period_size =
 			snd_pcm_hw_params_get_period_size (
 				driver->playback_hw_params, &dir);
-		p_nfragments =
-			snd_pcm_hw_params_get_periods (
-				driver->playback_hw_params, &dir);
 		driver->playback_sample_format = (snd_pcm_format_t)
 			snd_pcm_hw_params_get_format (
 				driver->playback_hw_params);
@@ -647,9 +662,6 @@ alsa_driver_set_parameters (alsa_driver_t *driver,
 		c_period_size =
 			snd_pcm_hw_params_get_period_size (
 				driver->capture_hw_params, &dir);
-		c_nfragments =
-			snd_pcm_hw_params_get_periods (
-				driver->capture_hw_params, &dir);
 		driver->capture_sample_format = (snd_pcm_format_t)
 			snd_pcm_hw_params_get_format (
 				driver->capture_hw_params);
@@ -667,26 +679,6 @@ alsa_driver_set_parameters (alsa_driver_t *driver,
 		}
 	}
 
-	if (driver->capture_handle && driver->playback_handle) {
-		if (p_nfragments != c_nfragments) {
-			jack_error ("alsa_pcm: different period counts for "
-				    "playback and capture!");
-			return -1;
-		}
-
-		driver->nfragments = c_nfragments;
-
-	} else if (driver->capture_handle) {
-
-		driver->nfragments = c_nfragments;
-
-	} else {
-
-		driver->nfragments = p_nfragments;
-
-	}
-
-	driver->buffer_frames = driver->frames_per_cycle * driver->nfragments;
 	driver->playback_sample_bytes =
 		snd_pcm_format_physical_width (driver->playback_sample_format)
 		/ 8;
@@ -965,7 +957,7 @@ alsa_driver_start (alsa_driver_t *driver)
 		
 		pavail = snd_pcm_avail_update (driver->playback_handle);
 
-		if (pavail != driver->buffer_frames) {
+		if (pavail != driver->frames_per_cycle * driver->playback_nperiods) {
 			jack_error ("ALSA: full buffer not available at start");
 			return -1;
 		}
@@ -986,11 +978,11 @@ alsa_driver_start (alsa_driver_t *driver)
 		
 		for (chn = 0; chn < driver->playback_nchannels; chn++) {
 			alsa_driver_silence_on_channel (driver, chn,
-							driver->buffer_frames);
+							driver->user_nperiods * driver->frames_per_cycle);
 		}
 		
 		snd_pcm_mmap_commit (driver->playback_handle, poffset,
-				     driver->buffer_frames);
+				     driver->user_nperiods * driver->frames_per_cycle);
 		
 		if ((err = snd_pcm_start (driver->playback_handle)) < 0) {
 			jack_error ("could not start playback (%s)",
@@ -1107,10 +1099,11 @@ alsa_driver_silence_untouched_channels (alsa_driver_t *driver,
 					jack_nframes_t nframes)
 {
 	channel_t chn;
+	jack_nframes_t buffer_frames = driver->frames_per_cycle * driver->playback_nperiods;
 
 	for (chn = 0; chn < driver->playback_nchannels; chn++) {
 		if ((driver->channels_not_done & (1<<chn))) { 
-			if (driver->silent[chn] < driver->buffer_frames) {
+			if (driver->silent[chn] < buffer_frames) {
 				alsa_driver_silence_on_channel_no_mark (
 					driver, chn, nframes);
 				driver->silent[chn] += nframes;
@@ -1685,7 +1678,7 @@ alsa_driver_attach (alsa_driver_t *driver)
 		 * (external) latency
 		*/
 		jack_port_set_latency (port, driver->frames_per_cycle
-				       * driver->nfragments);
+				       * driver->user_nperiods);
 
 		driver->playback_ports =
 			jack_slist_append (driver->playback_ports, port);
@@ -1900,7 +1893,6 @@ alsa_driver_new (char *name, char *playback_alsa_device,
 	driver->ctl_handle = 0;
 	driver->hw = 0;
 	driver->capture_and_playback_not_synced = FALSE;
-	driver->nfragments = 0;
 	driver->max_nchannels = 0;
 	driver->user_nchannels = 0;
 	driver->playback_nchannels = user_playback_nchnls;

drivers/alsa/alsa_driver.h

@@ -84,14 +84,14 @@ typedef struct {
     char                         *alsa_name_playback;
     char                         *alsa_name_capture;
     char                         *alsa_driver;
-    snd_pcm_uframes_t             buffer_frames;
     unsigned long                 channels_not_done;
     unsigned long                 channel_done_bits;
     snd_pcm_format_t              playback_sample_format;
     snd_pcm_format_t              capture_sample_format;
     float                         max_sample_val;
     unsigned long                 user_nperiods;
-    unsigned long                 nfragments;
+    unsigned int                  playback_nperiods;
+    unsigned int                  capture_nperiods;
     unsigned long                 last_mask;
     snd_ctl_t                    *ctl_handle;
     snd_pcm_t                    *playback_handle;

jackd/jackd.1.in

@@ -145,10 +145,20 @@ Number of capture channels.  Default is maximum supported by hardware.
 .TP
 \fB\-n, \-\-nperiods \fIint\fR
 .br
-Specify the number of periods in the hardware buffer.  The default is
-2.  The period size (\fB\-p\fR) times \fB\-\-nperiods\fR times four is
-the JACK buffer size in bytes.  The JACK output latency in seconds is
-\fB\-\-nperiods\fR times \fB\-\-period\fR divided by \fB\-\-rate\fR.
+Specify the number of periods of playback latency.  In seconds, this
+corresponds to \fB\-\-nperiods\fR times \fB\-\-period\fR divided by
+\fB\-\-rate\fR.  The default is 2, the minimum allowable.  For most
+devices, there is no need for any other value with the
+\fB\-\-realtime\fR option.  Without realtime privileges or with boards
+providing unreliable interrupts (like ymfpci), a larger value may
+yield fewer xruns.  This can also help if the system is not tuned for
+reliable realtime scheduling.
+
+For most ALSA devices, the hardware buffer has exactly
+\fB\-\-period\fR times \fB\-\-nperiods\fR frames.  Some devices demand
+a larger buffer.  If so, JACK will use the smallest possible buffer
+containing at least \fB\-\-nperiods\fR, but the playback latency does
+not increase.
 .TP
 \fB\-o, \-\-outchannels \fIint\fR
 .br
@@ -163,7 +173,7 @@ playback device name.
 Specify the number of frames between JACK \fBprocess()\fR calls.  The
 default is 1024.  If you need low latency, set \fB\-p\fR as low as you
 can go without seeing xruns.  A larger period size yields higher
-latency, but makes xruns less likely.  The JACK input latency in
+latency, but makes xruns less likely.  The JACK capture latency in
 seconds is \fB\-\-period\fR divided by \fB\-\-rate\fR.
 .TP
 \fB\-r, \-\-rate \fIint\fR
@@ -221,10 +231,10 @@ Specify number of playback ports. The default value is 2.
 Specify sample rate. The default value is 48000.
 .TP
 \fB\-p, \-\-period \fIint\fR
-Specify number of frames per period. THe default value is 1024.
+Specify number of frames per period. The default value is 1024.
 If you need low latency, set \fB\-p\fR as low as you
 can go without seeing xruns.  A larger period size yields higher
-latency, but makes xruns less likely.  The JACK input latency in
+latency, but makes xruns less likely.  The JACK capture latency in
 seconds is \fB\-\-period\fR divided by \fB\-\-rate\fR.
 .TP
 \fB\-w, \-\-wait \fIint\fR 
@@ -239,7 +249,7 @@ Specify the sample rate.  The default is 48000.
 Specify number of frames between JACK \fBprocess()\fR calls.  The
 default is 1024.  If you need low latency, set \fB\-p\fR as low as you
 can go without seeing xruns.  A larger period size yields higher
-latency, but makes xruns less likely.  The JACK input latency in
+latency, but makes xruns less likely.  The JACK capture latency in
 seconds is \fB\-\-period\fR divided by \fB\-\-rate\fR.
 .TP
 \fB\-n, \-\-nperiods \fIint\fR
@@ -324,7 +334,7 @@ system for low latency can be challenging.  The JACK FAQ,
 .I http://jackit.sourceforge.net/docs/faq.php\fR
 has some useful suggestions.
 .IP
-\fBjackstart \-Rv \-d alsa \-p 128 \-n 3 \-r 44100\fR
+\fBjackstart \-Rv \-d alsa \-p 128 \-n 2 \-r 44100\fR
 .PP
 Run \fBjackd\fR with realtime priority using the "sblive" ALSA device
 defined in ~/.asoundrc.  Apply shaped dithering to playback audio.