AP_Baro: Adding a new LPS25H Barometer driver

The following is a Barometer sensor driver for the LPS25H Barometer that
is integrated in the 96Boards STM32 Sensor mezzanine board.
the update includes the .cpp and .h files of the driver as well as the
updates required in AP_Baro.cpp.

libraries/AP_Baro/AP_Baro.cpp

@@ -34,6 +34,7 @@
 #include "AP_Baro_HIL.h"
 #include "AP_Baro_KellerLD.h"
 #include "AP_Baro_MS5611.h"
+#include "AP_Baro_LPS25H.h"
 #include "AP_Baro_qflight.h"
 #include "AP_Baro_QURT.h"
 #if HAL_WITH_UAVCAN
@@ -479,6 +480,9 @@ void AP_Baro::init(void)
 #elif HAL_BARO_DEFAULT == HAL_BARO_QURT
     drivers[0] = new AP_Baro_QURT(*this);
     _num_drivers = 1;
+#elif HAL_BARO_DEFAULT == HAL_BARO_LPS25H
+	ADD_BACKEND(AP_Baro_LPS25H::probe(*this,
+                                      std::move(hal.i2c_mgr->get_device(HAL_BARO_LPS25H_I2C_BUS, HAL_BARO_LPS25H_I2C_ADDR))));
 #endif
 
     // can optionally have baro on I2C too

libraries/AP_Baro/AP_Baro_LPS25H.cpp

@@ -0,0 +1,136 @@
+/*
+   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/>.
+ */
+#include "AP_Baro_LPS25H.h"
+
+#include <unistd.h>
+#include <utility>
+#include <stdio.h>
+extern const AP_HAL::HAL &hal;
+
+
+#define LPS25H_ID            	  0xBD
+#define LPS25H_REG_ID		      0x0F
+#define LPS25H_CTRL_REG1_ADDR     0x20
+#define LPS25H_CTRL_REG2_ADDR     0x21
+#define LPS25H_CTRL_REG3_ADDR     0x22
+#define LPS25H_CTRL_REG4_ADDR     0x23
+#define LPS25H_FIFO_CTRL          0x2E
+#define LPS25H_TEMP_OUT_ADDR      0xAB	//Regsiter address is 0x2B in 2's compliment.
+#define PRESS_OUT_XL_ADDR		  0xA8	//Regsiter address is 0x28 in 2's compliment.
+//putting 1 in the MSB of those two registers turns on Auto increment for faster reading.
+
+AP_Baro_LPS25H::AP_Baro_LPS25H(AP_Baro &baro, AP_HAL::OwnPtr<AP_HAL::Device> dev)
+    : AP_Baro_Backend(baro)
+    , _dev(std::move(dev))
+{
+}
+
+AP_Baro_Backend *AP_Baro_LPS25H::probe(AP_Baro &baro,
+                                       AP_HAL::OwnPtr<AP_HAL::Device> dev)
+{
+    if (!dev) {
+        return nullptr;
+    }
+    AP_Baro_LPS25H *sensor = new AP_Baro_LPS25H(baro, std::move(dev));
+    if (!sensor || !sensor->_init()) {
+        delete sensor;
+        return nullptr;
+    }
+    return sensor;
+}
+
+bool AP_Baro_LPS25H::_init()
+{
+    if (!_dev || !_dev->get_semaphore()->take(HAL_SEMAPHORE_BLOCK_FOREVER)) {
+        return false;
+    }
+    _has_sample = false;
+
+    _dev->set_speed(AP_HAL::Device::SPEED_HIGH);
+
+    uint8_t whoami;
+    if (!_dev->read_registers(LPS25H_REG_ID, &whoami, 1)  ||
+        whoami != LPS25H_ID) {
+        // not a LPS25H
+        _dev->get_semaphore()->give();
+        return false;
+    }
+
+    //init control registers.
+    _dev->write_register(LPS25H_CTRL_REG1_ADDR,0x00); // turn off for config
+    _dev->write_register(LPS25H_CTRL_REG2_ADDR,0x00); //FIFO Disabled
+    _dev->write_register(LPS25H_FIFO_CTRL, 0x01);
+    _dev->write_register(LPS25H_CTRL_REG1_ADDR,0xc0);
+
+    _instance = _frontend.register_sensor();
+
+    _dev->get_semaphore()->give();
+
+    // request 25Hz update (maximum refresh Rate according to datasheet)
+    _dev->register_periodic_callback(40 * AP_USEC_PER_MSEC, FUNCTOR_BIND_MEMBER(&AP_Baro_LPS25H::_timer, void));
+
+    return true;
+}
+
+
+
+//  acumulate a new sensor reading
+void AP_Baro_LPS25H::_timer(void)
+{
+    _update_temperature();
+    _update_pressure();
+    _has_sample = true;
+}
+
+// transfer data to the frontend
+void AP_Baro_LPS25H::update(void)
+{
+    if (_sem->take_nonblocking()) {
+        if (!_has_sample) {
+            _sem->give();
+            return;
+        }
+
+        _copy_to_frontend(_instance, _pressure, _temperature);
+        _has_sample = false;
+        _sem->give();
+    }
+}
+
+// calculate temperature
+void AP_Baro_LPS25H::_update_temperature(void)
+{
+    uint8_t pu8[2];
+    _dev->read_registers(LPS25H_TEMP_OUT_ADDR, pu8, 2);
+    int16_t Temp_Reg_s16 = (uint16_t)(pu8[1]<<8) | pu8[0];
+    if (_sem->take_nonblocking()) {
+        _temperature=((float)(Temp_Reg_s16/480)+42.5);
+        _sem->give();
+    }
+
+}
+
+// calculate pressure
+void AP_Baro_LPS25H::_update_pressure(void)
+{
+    uint8_t pressure[3];
+    _dev->read_registers(PRESS_OUT_XL_ADDR, pressure, 3);
+    int32_t Pressure_Reg_s32 = ((uint32_t)pressure[2]<<16)|((uint32_t)pressure[1]<<8)|(uint32_t)pressure[0];
+    int32_t Pressure_mb = Pressure_Reg_s32 / 4096; // scale
+    if (_sem->take_nonblocking()) {
+        _pressure=Pressure_mb;
+        _sem->give();
+    }
+}

libraries/AP_Baro/AP_Baro_LPS25H.h

@@ -0,0 +1,37 @@
+#pragma once
+
+#include <AP_HAL/AP_HAL.h>
+#include <AP_HAL/Device.h>
+#include <AP_HAL/utility/OwnPtr.h>
+
+#include "AP_Baro_Backend.h"
+
+#define HAL_BARO_LPS25H_I2C_BUS 0
+#define HAL_BARO_LPS25H_I2C_ADDR 0x5D
+
+
+class AP_Baro_LPS25H : public AP_Baro_Backend
+{
+public:
+    AP_Baro_LPS25H(AP_Baro &baro, AP_HAL::OwnPtr<AP_HAL::Device> dev);
+
+    /* AP_Baro public interface: */
+    void update();
+
+    static AP_Baro_Backend *probe(AP_Baro &baro, AP_HAL::OwnPtr<AP_HAL::Device> dev);
+
+private:
+    virtual ~AP_Baro_LPS25H(void) {};
+
+    bool _init(void);
+    void _timer(void);
+    void _update_temperature(void);
+    void _update_pressure(void);
+
+    AP_HAL::OwnPtr<AP_HAL::Device> _dev;
+
+    bool _has_sample;
+    uint8_t _instance;
+    float _pressure;
+    float _temperature;
+};