replay: update & add some comments

msg/ekf2_replay.msg

@@ -1,5 +1,4 @@
-# uint64 timestamp 			# ekf2 reference time. This is a timestamp passed to the
-					# estimator which it uses a absolute reference.
+
 float32 gyro_integral_dt		# gyro integration period in s
 float32 accelerometer_integral_dt 	# accelerometer integration period in s
 uint64 magnetometer_timestamp 		# timestamp of magnetometer measurement in us

msg/ekf2_timestamps.msg

@@ -1,8 +1,8 @@
 # this message contains the (relative) timestamps of the sensor inputs used by
 # ekf2. It can be used for reproducible replay.
 
-# timestamp             # ekf2 reference time. This matches the timestamp of the
-                        # sensor_combined topic.
+# the timestamp field (auto-generated) is the ekf2 reference time and matches
+# the timestamp of the sensor_combined topic.
 
 
 int16 RELATIVE_TIMESTAMP_INVALID = 32767 # (0x7fff) If one of the relative timestamps

src/modules/replay/replay.hpp

@@ -231,6 +231,7 @@ protected:
 	 * handle ekf2 topic publication in ekf2 replay mode
 	 * @param sub
 	 * @param data
+	 * @param replay_file file currently replayed (file seek position should be considered arbitrary after this call)
 	 * @return true if published, false otherwise
 	 */
 	bool handleTopicUpdate(Subscription &sub, void *data, std::ifstream &replay_file) override;
@@ -245,6 +246,7 @@ private:
 	 * find the next message for a subscription that matches a given timestamp and publish it
 	 * @param timestamp in 0.1 ms
 	 * @param msg_id
+	 * @param replay_file file currently replayed (file seek position should be considered arbitrary after this call)
 	 * @return true if timestamp found and published
 	 */
 	bool findTimestampAndPublish(uint64_t timestamp, uint16_t msg_id, std::ifstream &replay_file);

src/modules/replay/replay_main.cpp

@@ -885,6 +885,7 @@ bool ReplayEkf2::publishEkf2Topics(const ekf2_timestamps_s &ekf2_timestamps, std
 {
 	auto handle_sensor_publication = [&](int16_t timestamp_relative, uint16_t msg_id) {
 		if (timestamp_relative != ekf2_timestamps_s::RELATIVE_TIMESTAMP_INVALID) {
+			// timestamp_relative is already given in 0.1 ms
 			uint64_t t = timestamp_relative + ekf2_timestamps.timestamp / 100; // in 0.1 ms
 			findTimestampAndPublish(t, msg_id, replay_file);
 		}