SDP3X.cpp

Go to the documentation of this file.

/****************************************************************************
 *
 *   Copyright (c) 2017 PX4 Development Team. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name PX4 nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/**
 * @file SDP3X.hpp
 *
 * Driver for Sensirion SDP3X Differential Pressure Sensor
 *
 */

#include "SDP3X.hpp"

int
SDP3X::probe()
{
    return !init_sdp3x();
}

int SDP3X::write_command(uint16_t command)
{
    uint8_t cmd[2];
    cmd[0] = static_cast<uint8_t>(command >> 8);
    cmd[1] = static_cast<uint8_t>(command & 0xff);
    return transfer(&cmd[0], 2, nullptr, 0);
}

bool
SDP3X::init_sdp3x()
{
    // step 1 - reset on broadcast
    uint16_t prev_addr = get_device_address();
    set_device_address(SDP3X_RESET_ADDR);
    uint8_t reset_cmd = SDP3X_RESET_CMD;
    int ret = transfer(&reset_cmd, 1, nullptr, 0);
    set_device_address(prev_addr);

    if (ret != PX4_OK) {
        perf_count(_comms_errors);
        return false;
    }

    // wait until sensor is ready
    px4_usleep(20000);

    // step 2 - configure
    ret = write_command(SDP3X_CONT_MEAS_AVG_MODE);

    if (ret != PX4_OK) {
        perf_count(_comms_errors);
        PX4_ERR("config failed");
        return false;
    }

    px4_usleep(10000);

    // step 3 - get scale
    uint8_t val[9];
    ret = transfer(nullptr, 0, &val[0], sizeof(val));

    if (ret != PX4_OK) {
        perf_count(_comms_errors);
        PX4_ERR("get scale failed");
        return false;
    }

    // Check the CRC
    if (!crc(&val[0], 2, val[2]) || !crc(&val[3], 2, val[5]) || !crc(&val[6], 2, val[8])) {
        perf_count(_comms_errors);
        return false;
    }

    _scale = (((uint16_t)val[6]) << 8) | val[7];

    switch (_scale) {
    case SDP3X_SCALE_PRESSURE_SDP31:
        _device_id.devid_s.devtype = DRV_DIFF_PRESS_DEVTYPE_SDP31;
        break;

    case SDP3X_SCALE_PRESSURE_SDP32:
        _device_id.devid_s.devtype = DRV_DIFF_PRESS_DEVTYPE_SDP32;
        break;

    case SDP3X_SCALE_PRESSURE_SDP33:
        _device_id.devid_s.devtype = DRV_DIFF_PRESS_DEVTYPE_SDP33;
        break;
    }

    return true;
}

int
SDP3X::collect()
{
    perf_begin(_sample_perf);

    // read 9 bytes from the sensor
    uint8_t val[6];
    int ret = transfer(nullptr, 0, &val[0], sizeof(val));

    if (ret != PX4_OK) {
        perf_count(_comms_errors);
        return ret;
    }

    // Check the CRC
    if (!crc(&val[0], 2, val[2]) || !crc(&val[3], 2, val[5])) {
        perf_count(_comms_errors);
        return EAGAIN;

    } else {
        ret = 0;
    }

    int16_t P = (((int16_t)val[0]) << 8) | val[1];
    int16_t temp = (((int16_t)val[3]) << 8) | val[4];

    float diff_press_pa_raw = static_cast<float>(P) / static_cast<float>(_scale);
    float temperature_c = temp / static_cast<float>(SDP3X_SCALE_TEMPERATURE);

    differential_pressure_s report;

    report.timestamp = hrt_absolute_time();
    report.error_count = perf_event_count(_comms_errors);
    report.temperature = temperature_c;
    report.differential_pressure_filtered_pa = _filter.apply(diff_press_pa_raw) - _diff_pres_offset;
    report.differential_pressure_raw_pa = diff_press_pa_raw - _diff_pres_offset;
    report.device_id = _device_id.devid;

    if (_airspeed_pub != nullptr && !(_pub_blocked)) {
        orb_publish(ORB_ID(differential_pressure), _airspeed_pub, &report);
    }

    ret = OK;

    perf_end(_sample_perf);

    return ret;
}

void
SDP3X::Run()
{
    int ret = PX4_ERROR;

    // measurement phase
    ret = collect();

    if (PX4_OK != ret) {
        _sensor_ok = false;
        DEVICE_DEBUG("measure error");
    }

    // schedule a fresh cycle call when the measurement is done
    ScheduleDelayed(CONVERSION_INTERVAL);
}

bool SDP3X::crc(const uint8_t data[], unsigned size, uint8_t checksum)
{
    uint8_t crc_value = 0xff;

    // calculate 8-bit checksum with polynomial 0x31 (x^8 + x^5 + x^4 + 1)
    for (unsigned i = 0; i < size; i++) {
        crc_value ^= (data[i]);

        for (int 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);
}