Use delta between FPGA time and ALSA time for SR timestamps

ALSA reports monotonic timestamps regardles of the time stamps type set
by snd_pcm_params_set_tstamp_type(). Calculate delta between FPGA time
and ALSA time when audio stream starts and use this delta to correct
time stamps in SR packets.

src/audio.h

@@ -52,10 +52,10 @@ public:
 	void Stop(void);
 protected:
 //	int fd;
-	snd_pcm_t *capture_handle;                                  // PCM handle, returned from snd_pcm_open
-	short *sbuffer;
+	snd_pcm_t *capture_handle;                                  //< PCM handle, returned from snd_pcm_open
+	short *sbuffer;                                             //< buffer for sound data
 	long sbuffer_len;
-	bool _present;                                              // flag indicating that audio interface has been initialized
+	bool _present;                                              //< flag indicating that audio interface has been initialized
 	long _sample_rate;
 	long _channels;
 	long _volume;
@@ -66,9 +66,13 @@ protected:
 	void set_capture_volume(int volume);
 
 	uint64_t timestamp_rtcp;
-	long delta_fpga_sys;	                                    // A/V clocks delta for RTCP
+	long delta_fpga_sys;	                                    //< A/V clocks delta for RTCP
 //	bool is_first;
 //	bool is_first2;
+	long long delta_fpga_alsa;                                  //< time delta between FPGA time and time reported by ALSA, in microseconds
+	unsigned char *packet_buffer;                               //< buffer for RTP packet data (header plus PCM samples)
+private:
+	long long get_delta_fpga_alsa(void);                        //< return time delta between FPGA time and time stamps reported by ALSA, in microseconds
 };
 
 #endif // _AUDIO__H_

src/helper.h

 /**
- * @file FILENAME
- * @brief BRIEF DESCRIPTION
- * @copyright Copyright (C) YEAR Elphel Inc.
+ * @file helper.h
+ * @brief Various time helper functions to work with \e timeval structures
+ * @copyright Copyright (C) 2017 Elphel Inc.
  * @author AUTHOR <EMAIL>
  *
  * @par License:
@@ -54,4 +54,19 @@ inline struct timeval time_minus(struct timeval tv_1, const struct timeval &tv_2
 	return tv_1;
 }
 
-#endif
+/**
+ * @brief Add microseconds to a value represented by \e timeval structure
+ * @param   tv   time to which microseconds should be added
+ * @param   us   the value of microseconds
+ * @return  The sum of two values
+ */
+inline struct timeval time_plus_us(struct timeval &tv, unsigned long us)
+{
+	tv.tv_usec += us;
+	tv.tv_sec += tv.tv_usec / 1000000;
+	tv.tv_usec = tv.tv_usec % 1000000;
+
+	return tv;
+}
+
+#endif /* __H_HELPER__ */

src/parameters.cpp

@@ -119,3 +119,19 @@ bool Parameters::daemon_enabled(void) {
 void Parameters::setPValue(unsigned long *val_array, int count) {
 	this->write(val_array, sizeof(unsigned long) * count);
 }
+
+/**
+ * @brief Get current FPGA time
+ * @return   Time value in \e timeval structure
+ */
+struct timeval Parameters::get_fpga_time(void)
+{
+	struct timeval tv;
+	unsigned long write_data[] = {FRAMEPARS_GETFPGATIME, 0};
+
+	write(write_data, sizeof(unsigned long) * 2);
+	tv.tv_sec = getGPValue(G_SECONDS);
+	tv.tv_usec = getGPValue(G_MICROSECONDS);
+
+	return tv;
+}

src/parameters.h

@@ -48,6 +48,7 @@ public:
 	bool daemon_enabled(void);
 	void setPValue(unsigned long *val_array, int count);
 	inline int get_port_num() const {return sensor_port;}
+	struct timeval get_fpga_time(void);
 protected:
 //	static Parameters *_parameters;
 

src/rtp_stream.h

@@ -50,21 +50,19 @@ protected:
 	static void *pthread_f(void *_this);
 	void *thread(void);
 	pthread_mutex_t pthm_flow;
-//	virtual bool process(void) = 0;
 	virtual long process(void) = 0;
 
 	int _ptype;
 	bool _play;
-	/// semaphore to wait 'play' event
-	sem_t sem_play;
+	sem_t sem_play;                                             //< semaphore to wait 'play' event
 	Socket *rtp_socket;
 	Socket *rtcp_socket;
 
-	unsigned short packet_num;
+	unsigned short packet_num;                                  //< sequence number in RTP packet header
 	unsigned long SSRC;
 
 	struct timeval f_tv;
-	struct timeval rtcp_tv; // time of last SR
+	struct timeval rtcp_tv;                                     //< time of last SR
 	long rtcp_delay;
 	unsigned long timestamp;
 

src/streamer.cpp

@@ -278,7 +278,8 @@ int Streamer::update_settings(bool apply) {
 		f_audio_channels = true;
 	if ((audio_proc || session->process_audio) && (f_audio_rate || f_audio_channels))
 		audio_was_changed = true;
-	D(sensor_port, cerr << "audio_proc = " << audio_proc << ", process_audio = " << session->process_audio << ", f_audio_rate = " << f_audio_rate << "f_audio_channels = " << f_audio_channels << endl);
+	D(sensor_port, cerr << "audio_proc = " << audio_proc << ", process_audio = " << session->process_audio << ", f_audio_rate = " << f_audio_rate
+			<< ", f_audio_channels = " << f_audio_channels << endl);
 	if (apply) {
 		bool audio_restarted = false;
 		if (audio_was_changed) {