ardupilot/libraries/AP_HAL_SITL/sitl_airspeed.cpp

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/*
SITL handling
This simulates an analog airspeed sensor
Andrew Tridgell November 2011
*/
#include <AP_HAL/AP_HAL.h>
#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
#include "AP_HAL_SITL.h"
#include "AP_HAL_SITL_Namespace.h"
#include "HAL_SITL_Class.h"
#include "SITL_State.h"
#include <SITL/SITL.h>
#include <AP_Math/AP_Math.h>
extern const AP_HAL::HAL& hal;
using namespace HALSITL;
/*
convert airspeed in m/s to an airspeed sensor value
*/
void SITL_State::_update_airspeed(float airspeed)
{
const float airspeed_ratio = 1.9936f;
const float airspeed_offset = 2013.0f;
// Check sensor failure
airspeed = is_zero(_sitl->arspd_fail) ? airspeed : _sitl->arspd_fail;
// Add noise
airspeed = airspeed + (_sitl->arspd_noise * rand_float());
if (!is_zero(_sitl->arspd_fail_pressure)) {
// compute a realistic pressure report given some level of trapper air pressure in the tube and our current altitude
// algorithm taken from https://en.wikipedia.org/wiki/Calibrated_airspeed#Calculation_from_impact_pressure
float tube_pressure = abs(_sitl->arspd_fail_pressure - _barometer->get_pressure() + _sitl->arspd_fail_pitot_pressure);
airspeed = 340.29409348 * sqrt(5 * (pow((tube_pressure / 101325.01576 + 1), 2.0/7.0) - 1.0));
}
float airspeed_pressure = (airspeed * airspeed) / airspeed_ratio;
// flip sign here for simulating reversed pitot/static connections
if (_sitl->arspd_signflip) airspeed_pressure *= -1;
float airspeed_raw = airspeed_pressure + airspeed_offset;
if (airspeed_raw / 4 > 0xFFFF) {
airspeed_pin_value = 0xFFFF;
return;
}
// add delay
const uint32_t now = AP_HAL::millis();
uint32_t best_time_delta_wind = 200; // initialise large time representing buffer entry closest to current time - delay.
uint8_t best_index_wind = 0; // initialise number representing the index of the entry in buffer closest to delay.
// storing data from sensor to buffer
if (now - last_store_time_wind >= 10) { // store data every 10 ms.
last_store_time_wind = now;
if (store_index_wind > wind_buffer_length - 1) { // reset buffer index if index greater than size of buffer
store_index_wind = 0;
}
buffer_wind[store_index_wind].data = airspeed_raw; // add data to current index
buffer_wind[store_index_wind].time = last_store_time_wind; // add time to current index
store_index_wind = store_index_wind + 1; // increment index
}
// return delayed measurement
delayed_time_wind = now - _sitl->wind_delay; // get time corresponding to delay
// find data corresponding to delayed time in buffer
for (uint8_t i = 0; i <= wind_buffer_length - 1; i++) {
// find difference between delayed time and time stamp in buffer
time_delta_wind = abs(
(int32_t)(delayed_time_wind - buffer_wind[i].time));
// if this difference is smaller than last delta, store this time
if (time_delta_wind < best_time_delta_wind) {
best_index_wind = i;
best_time_delta_wind = time_delta_wind;
}
}
if (best_time_delta_wind < 200) { // only output stored state if < 200 msec retrieval error
airspeed_raw = buffer_wind[best_index_wind].data;
}
airspeed_pin_value = airspeed_raw / 4;
}
#endif