mirror of https://github.com/ArduPilot/ardupilot
144 lines
3.8 KiB
C++
144 lines
3.8 KiB
C++
/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
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/*
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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/*
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backend driver for airspeed from a I2C MS4525D0 sensor
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*/
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#include "AP_Airspeed_I2C.h"
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#include <AP_Common/AP_Common.h>
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#include <AP_HAL/AP_HAL.h>
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#include <AP_Math/AP_Math.h>
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extern const AP_HAL::HAL &hal;
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#define I2C_ADDRESS_MS4525DO 0x28
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// probe and initialise the sensor
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bool AP_Airspeed_I2C::init()
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{
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// get pointer to i2c bus semaphore
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AP_HAL::Semaphore* i2c_sem = hal.i2c->get_semaphore();
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// take i2c bus sempahore
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if (!i2c_sem->take(200)) {
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return false;
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}
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_measure();
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hal.scheduler->delay(10);
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_collect();
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i2c_sem->give();
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if (_last_sample_time_ms != 0) {
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hal.scheduler->register_timer_process(FUNCTOR_BIND_MEMBER(&AP_Airspeed_I2C::_timer, void));
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return true;
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}
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return false;
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}
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// start a measurement
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void AP_Airspeed_I2C::_measure()
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{
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_measurement_started_ms = 0;
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if (hal.i2c->writeRegisters(I2C_ADDRESS_MS4525DO, 0, 0, NULL) == 0) {
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_measurement_started_ms = AP_HAL::millis();
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}
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}
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// read the values from the sensor
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void AP_Airspeed_I2C::_collect()
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{
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uint8_t data[4];
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_measurement_started_ms = 0;
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if (hal.i2c->read(I2C_ADDRESS_MS4525DO, 4, data) != 0) {
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return;
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}
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uint8_t status = data[0] & 0xC0;
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if (status == 2 || status == 3) {
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return;
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}
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int16_t dp_raw, dT_raw;
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dp_raw = (data[0] << 8) + data[1];
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dp_raw = 0x3FFF & dp_raw;
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dT_raw = (data[2] << 8) + data[3];
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dT_raw = (0xFFE0 & dT_raw) >> 5;
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const float P_min = -1.0f;
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const float P_max = 1.0f;
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const float PSI_to_Pa = 6894.757f;
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/*
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this equation is an inversion of the equation in the
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pressure transfer function figure on page 4 of the datasheet
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We negate the result so that positive differential pressures
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are generated when the bottom port is used as the static
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port on the pitot and top port is used as the dynamic port
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*/
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float diff_press_PSI = -((dp_raw - 0.1f*16383) * (P_max-P_min)/(0.8f*16383) + P_min);
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_pressure = diff_press_PSI * PSI_to_Pa;
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_temperature = ((200.0f * dT_raw) / 2047) - 50;
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_last_sample_time_ms = AP_HAL::millis();
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}
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// 1kHz timer
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void AP_Airspeed_I2C::_timer()
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{
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AP_HAL::Semaphore* i2c_sem = hal.i2c->get_semaphore();
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if (!i2c_sem->take_nonblocking()) {
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return;
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}
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if (_measurement_started_ms == 0) {
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_measure();
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i2c_sem->give();
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return;
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}
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if ((AP_HAL::millis() - _measurement_started_ms) > 10) {
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_collect();
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// start a new measurement
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_measure();
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}
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i2c_sem->give();
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}
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// return the current differential_pressure in Pascal
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bool AP_Airspeed_I2C::get_differential_pressure(float &pressure)
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{
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if ((AP_HAL::millis() - _last_sample_time_ms) > 100) {
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return false;
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}
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pressure = _pressure;
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return true;
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}
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// return the current temperature in degrees C, if available
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bool AP_Airspeed_I2C::get_temperature(float &temperature)
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{
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if ((AP_HAL::millis() - _last_sample_time_ms) > 100) {
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return false;
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}
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temperature = _temperature;
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return true;
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}
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