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 && !defined(HAL_BUILD_AP_PERIPH)
#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)
{
float airspeed2 = airspeed;
const float airspeed_ratio = 1.9936f;
const float diff_pressure = sq(airspeed) * 0.5;
// apply noise to the differential pressure. This emulates the way
// airspeed noise reduces with speed
airspeed = sqrtf(fabsf(2*(diff_pressure + _sitl->arspd_noise[0] * rand_float())));
airspeed2 = sqrtf(fabsf(2*(diff_pressure + _sitl->arspd_noise[1] * rand_float())));
// check sensor failure
if (is_positive(_sitl->arspd_fail[0])) {
airspeed = _sitl->arspd_fail[0];
}
if (is_positive(_sitl->arspd_fail[1])) {
airspeed2 = _sitl->arspd_fail[1];
}
if (!is_zero(_sitl->arspd_fail_pressure[0])) {
// 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 = fabsf(_sitl->arspd_fail_pressure[0] - _barometer->get_pressure() + _sitl->arspd_fail_pitot_pressure[0]);
airspeed = 340.29409348 * sqrt(5 * (pow((tube_pressure / SSL_AIR_PRESSURE + 1), 2.0/7.0) - 1.0));
}
if (!is_zero(_sitl->arspd_fail_pressure[1])) {
// 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 = fabsf(_sitl->arspd_fail_pressure[1] - _barometer->get_pressure() + _sitl->arspd_fail_pitot_pressure[1]);
airspeed2 = 340.29409348 * sqrt(5 * (pow((tube_pressure / SSL_AIR_PRESSURE + 1), 2.0/7.0) - 1.0));
}
float airspeed_pressure = (airspeed * airspeed) / airspeed_ratio;
float airspeed2_pressure = (airspeed2 * airspeed2) / airspeed_ratio;
// flip sign here for simulating reversed pitot/static connections
if (_sitl->arspd_signflip) airspeed_pressure *= -1;
if (_sitl->arspd_signflip) airspeed2_pressure *= -1;
// apply airspeed sensor offset in m/s
float airspeed_raw = airspeed_pressure + _sitl->arspd_offset[0];
float airspeed2_raw = airspeed2_pressure + _sitl->arspd_offset[1];
_sitl->state.airspeed_raw_pressure[0] = airspeed_pressure;
_sitl->state.airspeed_raw_pressure[1] = airspeed2_pressure;
if (airspeed_raw / 4 > 0xFFFF) {
airspeed_pin_value = 0xFFFF;
return;
}
if (airspeed2_raw / 4 > 0xFFFF) {
airspeed_2_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
buffer_wind_2[store_index_wind].data = airspeed2_raw; // add data to current index
buffer_wind_2[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;
airspeed2_raw = buffer_wind_2[best_index_wind].data;
}
airspeed_pin_value = airspeed_raw / 4;
airspeed_2_pin_value = airspeed2_raw / 4;
}
#endif