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ardupilot/libraries/AP_Airspeed/AP_Airspeed_SDP3X.cpp

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/*
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/>.
*/
/*
backend driver for airspeed from a I2C SDP3X sensor
with thanks to https://github.com/PX4/Firmware/blob/master/src/drivers/sdp3x_airspeed
*/
#include "AP_Airspeed_SDP3X.h"
#include <GCS_MAVLink/GCS.h>
#include <AP_Baro/AP_Baro.h>
#include <stdio.h>
#define SDP3X_SCALE_TEMPERATURE 200.0f
#define SDP3XD0_I2C_ADDR 0x21
#define SDP3XD1_I2C_ADDR 0x22
#define SDP3XD2_I2C_ADDR 0x23
#define SDP3X_CONT_MEAS_AVG_MODE 0x3615
#define SDP3X_CONT_MEAS_STOP 0x3FF9
#define SDP3X_SCALE_PRESSURE_SDP31 60
#define SDP3X_SCALE_PRESSURE_SDP32 240
#define SDP3X_SCALE_PRESSURE_SDP33 20
extern const AP_HAL::HAL &hal;
AP_Airspeed_SDP3X::AP_Airspeed_SDP3X(AP_Airspeed &_frontend, uint8_t _instance) :
AP_Airspeed_Backend(_frontend, _instance)
{
}
/*
send a 16 bit command code
*/
bool AP_Airspeed_SDP3X::_send_command(uint16_t cmd)
{
uint8_t b[2] {uint8_t(cmd >> 8), uint8_t(cmd & 0xFF)};
return _dev->transfer(b, 2, nullptr, 0);
}
// probe and initialise the sensor
bool AP_Airspeed_SDP3X::init()
{
const uint8_t addresses[3] = { SDP3XD0_I2C_ADDR,
SDP3XD1_I2C_ADDR,
SDP3XD2_I2C_ADDR
};
bool found = false;
bool ret = false;
for (uint8_t i=0; i<ARRAY_SIZE(addresses) && !found; i++) {
_dev = hal.i2c_mgr->get_device(get_bus(), addresses[i]);
if (!_dev) {
continue;
}
_dev->get_semaphore()->take_blocking();
// lots of retries during probe
_dev->set_retries(10);
// stop continuous average mode
if (!_send_command(SDP3X_CONT_MEAS_STOP)) {
_dev->get_semaphore()->give();
continue;
}
// these delays are needed for reliable operation
_dev->get_semaphore()->give();
hal.scheduler->delay_microseconds(20000);
_dev->get_semaphore()->take_blocking();
// start continuous average mode
if (!_send_command(SDP3X_CONT_MEAS_AVG_MODE)) {
_dev->get_semaphore()->give();
continue;
}
// these delays are needed for reliable operation
_dev->get_semaphore()->give();
hal.scheduler->delay_microseconds(20000);
_dev->get_semaphore()->take_blocking();
// step 3 - get scale
uint8_t val[9];
ret = _dev->transfer(nullptr, 0, &val[0], sizeof(val));
if (!ret) {
_dev->get_semaphore()->give();
continue;
}
// Check the CRC
if (!_crc(&val[0], 2, val[2]) || !_crc(&val[3], 2, val[5]) || !_crc(&val[6], 2, val[8])) {
_dev->get_semaphore()->give();
continue;
}
_scale = (((uint16_t)val[6]) << 8) | val[7];
_dev->get_semaphore()->give();
found = true;
char c = 'X';
switch (_scale) {
case SDP3X_SCALE_PRESSURE_SDP31:
c = '1';
break;
case SDP3X_SCALE_PRESSURE_SDP32:
c = '2';
break;
case SDP3X_SCALE_PRESSURE_SDP33:
c = '3';
break;
}
hal.console->printf("SDP3%c: Found on bus %u address 0x%02x scale=%u\n",
c, get_bus(), addresses[i], _scale);
}
if (!found) {
return false;
}
/*
this sensor uses zero offset and skips cal
*/
set_use_zero_offset();
set_skip_cal();
set_offset(0);
// drop to 2 retries for runtime
_dev->set_retries(2);
_dev->register_periodic_callback(20000,
FUNCTOR_BIND_MEMBER(&AP_Airspeed_SDP3X::_timer, void));
return true;
}
// read the values from the sensor. Called at 50Hz
void AP_Airspeed_SDP3X::_timer()
{
// read 6 bytes from the sensor
uint8_t val[6];
int ret = _dev->transfer(nullptr, 0, &val[0], sizeof(val));
uint32_t now = AP_HAL::millis();
if (!ret) {
if (now - _last_sample_time_ms > 200) {
// try and re-connect
_send_command(SDP3X_CONT_MEAS_AVG_MODE);
}
return;
}
// Check the CRC
if (!_crc(&val[0], 2, val[2]) || !_crc(&val[3], 2, val[5])) {
return;
}
int16_t P = (((int16_t)val[0]) << 8) | val[1];
int16_t temp = (((int16_t)val[3]) << 8) | val[4];
float diff_press_pa = float(P) / float(_scale);
float temperature = float(temp) / SDP3X_SCALE_TEMPERATURE;
WITH_SEMAPHORE(sem);
_press_sum += diff_press_pa;
_temp_sum += temperature;
_press_count++;
_temp_count++;
_last_sample_time_ms = now;
}
/*
correct pressure for barometric height
With thanks to:
https://github.com/PX4/Firmware/blob/master/Tools/models/sdp3x_pitot_model.py
*/
float AP_Airspeed_SDP3X::_correct_pressure(float press)
{
float sign = 1.0f;
// fix for tube order
AP_Airspeed::pitot_tube_order tube_order = get_tube_order();
switch (tube_order) {
case AP_Airspeed::PITOT_TUBE_ORDER_NEGATIVE:
press = -press;
sign = -1.0f;
break;
case AP_Airspeed::PITOT_TUBE_ORDER_POSITIVE:
break;
case AP_Airspeed::PITOT_TUBE_ORDER_AUTO:
default:
if (press < 0.0f) {
sign = -1.0f;
press = -press;
}
break;
}
if (press <= 0.0f) {
return 0.0f;
}
AP_Baro *baro = AP_Baro::get_singleton();
if (baro == nullptr) {
return press;
}
float temperature;
if (!get_temperature(temperature)) {
return press;
}
float rho_air = baro->get_pressure() / (ISA_GAS_CONSTANT * (temperature + C_TO_KELVIN));
/*
the constants in the code below come from a calibrated test of
the drotek pitot tube by Sensiron. They are specific to the droktek pitot tube
At 25m/s, the rough proportions of each pressure correction are:
- dp_pitot: 5%
- press_correction: 14%
- press: 81%
dp_tube has been removed from the Sensiron model as it is
insignificant (less than 0.02% over the supported speed ranges)
*/
// flow through sensor
float flow_SDP3X = (300.805f - 300.878f / (0.00344205f * (float)powf(press, 0.68698f) + 1.0f)) * 1.29f / rho_air;
if (flow_SDP3X < 0.0f) {
flow_SDP3X = 0.0f;
}
// diffential pressure through pitot tube
float dp_pitot = 28557670.0f * (1.0f - 1.0f / (1.0f + (float)powf((flow_SDP3X / 5027611.0f), 1.227924f)));
// uncorrected pressure
float press_uncorrected = (press + dp_pitot) / SSL_AIR_DENSITY;
// correction for speed at pitot-tube tip due to flow through sensor
float dv = 0.0331582f * flow_SDP3X;
// airspeed ratio
float ratio = get_airspeed_ratio();
// calculate equivalent pressure correction. This formula comes
// from turning the dv correction above into an equivalent
// pressure correction. We need to do this so the airspeed ratio
// calibrator can work, as it operates on pressure values
float press_correction = sq(sqrtf(press_uncorrected*ratio)+dv)/ratio - press_uncorrected;
return (press_uncorrected + press_correction) * sign;
}
// return the current differential_pressure in Pascal
bool AP_Airspeed_SDP3X::get_differential_pressure(float &pressure)
{
WITH_SEMAPHORE(sem);
if (AP_HAL::millis() - _last_sample_time_ms > 100) {
return false;
}
if (_press_count > 0) {
_press = _press_sum / _press_count;
_press_count = 0;
_press_sum = 0;
}
pressure = _correct_pressure(_press);
return true;
}
// return the current temperature in degrees C, if available
bool AP_Airspeed_SDP3X::get_temperature(float &temperature)
{
WITH_SEMAPHORE(sem);
if ((AP_HAL::millis() - _last_sample_time_ms) > 100) {
return false;
}
if (_temp_count > 0) {
_temp = _temp_sum / _temp_count;
_temp_count = 0;
_temp_sum = 0;
}
temperature = _temp;
return true;
}
/*
check CRC for a set of bytes
*/
bool AP_Airspeed_SDP3X::_crc(const uint8_t data[], uint8_t size, uint8_t checksum)
{
uint8_t crc_value = 0xff;
// calculate 8-bit checksum with polynomial 0x31 (x^8 + x^5 + x^4 + 1)
for (uint8_t i = 0; i < size; i++) {
crc_value ^= data[i];
for (uint8_t bit = 8; bit > 0; --bit) {
if (crc_value & 0x80) {
crc_value = (crc_value << 1) ^ 0x31;
} else {
crc_value = (crc_value << 1);
}
}
}
// verify checksum
return (crc_value == checksum);
}
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