ardupilot/libraries/AP_Baro/AP_Baro.cpp

194 lines
7.1 KiB
C++

/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
/*
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
/*
* APM_Baro.cpp - barometer driver
*
*/
#include <AP_Math.h>
#include <AP_Common.h>
#include <AP_Baro.h>
#include <AP_HAL.h>
extern const AP_HAL::HAL& hal;
// table of user settable parameters
const AP_Param::GroupInfo AP_Baro::var_info[] PROGMEM = {
// NOTE: Index numbers 0 and 1 were for the old integer
// ground temperature and pressure
// @Param: ABS_PRESS
// @DisplayName: Absolute Pressure
// @Description: calibrated ground pressure in Pascals
// @Increment: 1
AP_GROUPINFO("ABS_PRESS", 2, AP_Baro, _ground_pressure, 0),
// @Param: TEMP
// @DisplayName: ground temperature
// @Description: calibrated ground temperature in degrees Celsius
// @Increment: 1
AP_GROUPINFO("TEMP", 3, AP_Baro, _ground_temperature, 0),
// @Param: ALT_OFFSET
// @DisplayName: altitude offset
// @Description: altitude offset in meters added to barometric altitude. This is used to allow for automatic adjustment of the base barometric altitude by a ground station equipped with a barometer. The value is added to the barometric altitude read by the aircraft. It is automatically reset to 0 when the barometer is calibrated on each reboot or when a preflight calibration is performed.
// @Units: meters
// @Range: -128 127
// @Increment: 1
AP_GROUPINFO("ALT_OFFSET", 4, AP_Baro, _alt_offset, 0),
AP_GROUPEND
};
// calibrate the barometer. This must be called at least once before
// the altitude() or climb_rate() interfaces can be used
void AP_Baro::calibrate()
{
float ground_pressure = 0;
float ground_temperature = 0;
// reset the altitude offset when we calibrate. The altitude
// offset is supposed to be for within a flight
_alt_offset.set_and_save(0);
{
uint32_t tstart = hal.scheduler->millis();
while (ground_pressure == 0 || !healthy) {
read(); // Get initial data from absolute pressure sensor
if (hal.scheduler->millis() - tstart > 500) {
hal.scheduler->panic(PSTR("PANIC: AP_Baro::read unsuccessful "
"for more than 500ms in AP_Baro::calibrate [1]\r\n"));
}
ground_pressure = get_pressure();
ground_temperature = get_temperature();
hal.scheduler->delay(20);
}
}
// let the barometer settle for a full second after startup
// the MS5611 reads quite a long way off for the first second,
// leading to about 1m of error if we don't wait
for (uint8_t i = 0; i < 10; i++) {
uint32_t tstart = hal.scheduler->millis();
do {
read();
if (hal.scheduler->millis() - tstart > 500) {
hal.scheduler->panic(PSTR("PANIC: AP_Baro::read unsuccessful "
"for more than 500ms in AP_Baro::calibrate [2]\r\n"));
}
} while (!healthy);
ground_pressure = get_pressure();
ground_temperature = get_temperature();
hal.scheduler->delay(100);
}
// now average over 5 values for the ground pressure and
// temperature settings
for (uint16_t i = 0; i < 5; i++) {
uint32_t tstart = hal.scheduler->millis();
do {
read();
if (hal.scheduler->millis() - tstart > 500) {
hal.scheduler->panic(PSTR("PANIC: AP_Baro::read unsuccessful "
"for more than 500ms in AP_Baro::calibrate [3]\r\n"));
}
} while (!healthy);
ground_pressure = (ground_pressure * 0.8f) + (get_pressure() * 0.2f);
ground_temperature = (ground_temperature * 0.8f) +
(get_temperature() * 0.2f);
hal.scheduler->delay(100);
}
_ground_pressure.set_and_save(ground_pressure);
_ground_temperature.set_and_save(ground_temperature);
}
/**
update the barometer calibration
this updates the baro ground calibration to the current values. It
can be used before arming to keep the baro well calibrated
*/
void AP_Baro::update_calibration()
{
_ground_pressure.set(get_pressure());
_ground_temperature.set(get_temperature());
}
// return current altitude estimate relative to time that calibrate()
// was called. Returns altitude in meters
// note that this relies on read() being called regularly to get new data
float AP_Baro::get_altitude(void)
{
float scaling, temp;
if (_last_altitude_t == _last_update) {
// no new information
return _altitude + _alt_offset;
}
#if defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)
// on AVR use a less exact, but faster, calculation
scaling = (float)_ground_pressure / (float)get_pressure();
temp = ((float)_ground_temperature) + 273.15f;
_altitude = logf(scaling) * temp * 29.271267f;
#else
// on faster CPUs use a more exact calculation
scaling = (float)get_pressure() / (float)_ground_pressure;
temp = ((float)_ground_temperature) + 273.15f;
// This is an exact calculation that is within +-2.5m of the standard atmosphere tables
// in the troposphere (up to 11,000 m amsl).
_altitude = 153.8462f * temp * (1.0f - expf(0.190259f * logf(scaling)));
#endif
_last_altitude_t = _last_update;
// ensure the climb rate filter is updated
_climb_rate_filter.update(_altitude, _last_update);
return _altitude + _alt_offset;
}
// return current scale factor that converts from equivalent to true airspeed
// valid for altitudes up to 10km AMSL
// assumes standard atmosphere lapse rate
float AP_Baro::get_EAS2TAS(void)
{
if ((fabs(_altitude - _last_altitude_EAS2TAS) < 100.0f) && (_EAS2TAS != 0.0f)) {
// not enough change to require re-calculating
return _EAS2TAS;
}
float tempK = ((float)_ground_temperature) + 273.15f - 0.0065f * _altitude;
_EAS2TAS = safe_sqrt(1.225f / ((float)get_pressure() / (287.26f * tempK)));
_last_altitude_EAS2TAS = _altitude;
return _EAS2TAS;
}
// return current climb_rate estimeate relative to time that calibrate()
// was called. Returns climb rate in meters/s, positive means up
// note that this relies on read() being called regularly to get new data
float AP_Baro::get_climb_rate(void)
{
// we use a 7 point derivative filter on the climb rate. This seems
// to produce somewhat reasonable results on real hardware
return _climb_rate_filter.slope() * 1.0e3f;
}