Recovering UTC timestamps from ULog without sensor_gps (#25534)

* Added overloaded get_log_time util for fractional seconds

* Added write_info implementation for double info types

* Save boot time to .ulg via info message key boot_time_utc

* Changed time type from double to uint64_t, formatted

* Fixing get_log_time function doc

src/modules/logger/logger.cpp

@@ -1990,6 +1990,11 @@ void Logger::write_info(LogType type, const char *name, uint32_t value)
 	write_info_template<uint32_t>(type, name, value, "uint32_t");
 }
 
+void Logger::write_info(LogType type, const char *name, uint64_t value)
+{
+	write_info_template<uint64_t>(type, name, value, "uint64_t");
+}
+
 
 template<typename T>
 void Logger::write_info_template(LogType type, const char *name, T value, const char *type_str)
@@ -2122,6 +2127,12 @@ void Logger::write_version(LogType type)
 
 	write_info(type, "time_ref_utc", _param_sdlog_utc_offset.get() * 60);
 
+	uint64_t boot_time_utc_us;
+
+	if (util::get_log_time(boot_time_utc_us, _param_sdlog_utc_offset.get() * 60, true)) {
+		write_info(type, "boot_time_utc_us", boot_time_utc_us);
+	}
+
 	if (_replay_file_name) {
 		write_info(type, "replay", _replay_file_name);
 	}

src/modules/logger/logger.h

@@ -267,6 +267,7 @@ private:
 	void write_info_multiple(LogType type, const char *name, int fd);
 	void write_info(LogType type, const char *name, int32_t value);
 	void write_info(LogType type, const char *name, uint32_t value);
+	void write_info(LogType type, const char *name, uint64_t value);
 
 	/** generic common template method for write_info variants */
 	template<typename T>

src/modules/logger/util.cpp

@@ -72,20 +72,19 @@ bool file_exist(const char *filename)
 	return stat(filename, &buffer) == 0;
 }
 
-bool get_log_time(struct tm *tt, int utc_offset_sec, bool boot_time)
+bool get_log_time(uint64_t &utc_time_usec, int utc_offset_sec, bool boot_time)
 {
 	uORB::Subscription vehicle_gps_position_sub{ORB_ID(vehicle_gps_position)};
 
-	time_t utc_time_sec;
 	bool use_clock_time = true;
 
 	/* Get the latest GPS publication */
 	sensor_gps_s gps_pos;
 
 	if (vehicle_gps_position_sub.copy(&gps_pos)) {
-		utc_time_sec = gps_pos.time_utc_usec / 1e6;
+		utc_time_usec = gps_pos.time_utc_usec;
 
-		if (gps_pos.fix_type >= 2 && utc_time_sec >= GPS_EPOCH_SECS) {
+		if (gps_pos.fix_type >= 2 && utc_time_usec >= (uint64_t) GPS_EPOCH_SECS * 1000000ULL) {
 			use_clock_time = false;
 		}
 	}
@@ -94,22 +93,30 @@ bool get_log_time(struct tm *tt, int utc_offset_sec, bool boot_time)
 		/* take clock time if there's no fix (yet) */
 		struct timespec ts = {};
 		px4_clock_gettime(CLOCK_REALTIME, &ts);
-		utc_time_sec = ts.tv_sec + (ts.tv_nsec / 1e9);
+		utc_time_usec = ts.tv_sec * 1000000ULL + ts.tv_nsec / 1000ULL;
 
-		if (utc_time_sec < GPS_EPOCH_SECS) {
+		if (utc_time_usec < (uint64_t) GPS_EPOCH_SECS * 1000000ULL) {
 			return false;
 		}
 	}
 
 	/* strip the time elapsed since boot */
 	if (boot_time) {
-		utc_time_sec -= hrt_absolute_time() / 1e6;
+		utc_time_usec -= hrt_absolute_time();
 	}
 
 	/* apply utc offset */
-	utc_time_sec += utc_offset_sec;
+	utc_time_usec += (int64_t) utc_offset_sec * 1000000LL;
 
-	return gmtime_r(&utc_time_sec, tt) != nullptr;
+	return true;
+}
+
+bool get_log_time(struct tm *tt, int utc_offset_sec, bool boot_time)
+{
+	uint64_t utc_time_usec;
+	bool result = get_log_time(utc_time_usec, utc_offset_sec, boot_time);
+	time_t utc_time_sec = static_cast<time_t>(utc_time_usec / 1000000ULL);
+	return result && gmtime_r(&utc_time_sec, tt) != nullptr;
 }
 
 int check_free_space(const char *log_root_dir, int32_t max_log_dirs_to_keep, orb_advert_t &mavlink_log_pub,

src/modules/logger/util.h

@@ -75,6 +75,16 @@ bool file_exist(const char *filename);
 int check_free_space(const char *log_root_dir, int32_t max_log_dirs_to_keep, orb_advert_t &mavlink_log_pub,
 		     int &sess_dir_index);
 
+
+/**
+ * Utility for fetching UTC time in microseconds from sensor_gps or CLOCK_REALTIME
+ * @param utc_time_usec returned microseconds
+ * @param utc_offset_sec UTC time offset [s]
+ * @param boot_time use time when booted instead of current time
+ * @return true on success, false otherwise (eg. if no gps)
+ */
+bool get_log_time(uint64_t &utc_time_usec, int utc_offset_sec, bool boot_time);
+
 /**
  * Get the time for log file name
  * @param tt returned time