EKF: Add a parameter to enable setting of a minimum buffer length to handle large sensor timing jitter

EKF/common.h

@@ -186,6 +186,7 @@ struct parameters {
 	int32_t sensor_interval_min_ms{20};		// minimum time of arrival difference between non IMU sensor updates. Sets the size of the observation buffers.
 
 	// measurement time delays
+	float min_delay_ms{0.0f};			// used to a set a minimum buffer length independent of specified sensor delays
 	float mag_delay_ms{0.0f};		// magnetometer measurement delay relative to the IMU (msec)
 	float baro_delay_ms{0.0f};		// barometer height measurement delay relative to the IMU (msec)
 	float gps_delay_ms{110.0f};		// GPS measurement delay relative to the IMU (msec)

EKF/estimator_interface.cpp

@@ -350,13 +350,14 @@ void EstimatorInterface::setExtVisionData(uint64_t time_usec, ext_vision_message
 
 bool EstimatorInterface::initialise_interface(uint64_t timestamp)
 {
-	// find the maximum time delay required to compensate for
+	// find the maximum time delay the buffers are required to handle
 	uint16_t max_time_delay_ms = math::max(_params.mag_delay_ms,
 					 math::max(_params.range_delay_ms,
 					     math::max(_params.gps_delay_ms,
 						 math::max(_params.flow_delay_ms,
 						     math::max(_params.ev_delay_ms,
-							 math::max(_params.airspeed_delay_ms, _params.baro_delay_ms))))));
+							 math::max(_params.min_delay_ms,
+								math::max(_params.airspeed_delay_ms, _params.baro_delay_ms)))))));
 
 	// calculate the IMU buffer length required to accomodate the maximum delay with some allowance for jitter
 	_imu_buffer_length = (max_time_delay_ms / FILTER_UPDATE_PERIOD_MS) + 1;