ms5611_i2c.cpp

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/**
 * @file ms5611_i2c.cpp
 *
 * I2C interface for MS5611
 */

#include "ms5611.h"

#define MS5611_ADDRESS_1        0x76    /* address select pins pulled high (PX4FMU series v1.6+) */
#define MS5611_ADDRESS_2        0x77    /* address select pins pulled low (PX4FMU prototypes) */



device::Device *MS5611_i2c_interface(ms5611::prom_u &prom_buf);

class MS5611_I2C : public device::I2C
{
public:
    MS5611_I2C(uint8_t bus, ms5611::prom_u &prom_buf);
    virtual ~MS5611_I2C() = default;

    virtual int read(unsigned offset, void *data, unsigned count);
    virtual int ioctl(unsigned operation, unsigned &arg);

protected:
    virtual int probe();

private:
    ms5611::prom_u  &_prom;

    int     _probe_address(uint8_t address);

    /**
     * Send a reset command to the MS5611.
     *
     * This is required after any bus reset.
     */
    int     _reset();

    /**
     * Send a measure command to the MS5611.
     *
     * @param addr      Which address to use for the measure operation.
     */
    int     _measure(unsigned addr);

    /**
     * Read the MS5611 PROM
     *
     * @return      PX4_OK if the PROM reads successfully.
     */
    int     _read_prom();

};

device::Device *
MS5611_i2c_interface(ms5611::prom_u &prom_buf, uint8_t busnum)
{
    return new MS5611_I2C(busnum, prom_buf);
}

MS5611_I2C::MS5611_I2C(uint8_t bus, ms5611::prom_u &prom) :
    I2C("MS5611_I2C", nullptr, bus, 0, 400000),
    _prom(prom)
{
}

int
MS5611_I2C::read(unsigned offset, void *data, unsigned count)
{
    union _cvt {
        uint8_t b[4];
        uint32_t w;
    } *cvt = (_cvt *)data;
    uint8_t buf[3];

    /* read the most recent measurement */
    uint8_t cmd = 0;
    int ret = transfer(&cmd, 1, &buf[0], 3);

    if (ret == PX4_OK) {
        /* fetch the raw value */
        cvt->b[0] = buf[2];
        cvt->b[1] = buf[1];
        cvt->b[2] = buf[0];
        cvt->b[3] = 0;
    }

    return ret;
}

int
MS5611_I2C::ioctl(unsigned operation, unsigned &arg)
{
    int ret;

    switch (operation) {
    case IOCTL_RESET:
        ret = _reset();
        break;

    case IOCTL_MEASURE:
        ret = _measure(arg);
        break;

    default:
        ret = EINVAL;
    }

    return ret;
}

int
MS5611_I2C::probe()
{
    _retries = 10;

    if ((PX4_OK == _probe_address(MS5611_ADDRESS_1)) ||
        (PX4_OK == _probe_address(MS5611_ADDRESS_2))) {
        /*
         * Disable retries; we may enable them selectively in some cases,
         * but the device gets confused if we retry some of the commands.
         */
        _retries = 0;
        return PX4_OK;
    }

    return -EIO;
}

int
MS5611_I2C::_probe_address(uint8_t address)
{
    /* select the address we are going to try */
    set_device_address(address);

    /* send reset command */
    if (PX4_OK != _reset()) {
        return -EIO;
    }

    /* read PROM */
    if (PX4_OK != _read_prom()) {
        return -EIO;
    }

    return PX4_OK;
}

int
MS5611_I2C::_reset()
{
    unsigned    old_retrycount = _retries;
    uint8_t     cmd = ADDR_RESET_CMD;
    int     result;

    /* bump the retry count */
    _retries = 10;
    result = transfer(&cmd, 1, nullptr, 0);
    _retries = old_retrycount;

    return result;
}

int
MS5611_I2C::_measure(unsigned addr)
{
    /*
     * Disable retries on this command; we can't know whether failure
     * means the device did or did not see the command.
     */
    _retries = 0;

    uint8_t cmd = addr;
    return transfer(&cmd, 1, nullptr, 0);
}

int
MS5611_I2C::_read_prom()
{
    uint8_t     prom_buf[2];
    union {
        uint8_t     b[2];
        uint16_t    w;
    } cvt;

    /*
     * Wait for PROM contents to be in the device (2.8 ms) in the case we are
     * called immediately after reset.
     */
    px4_usleep(3000);

    uint8_t last_val = 0;
    bool bits_stuck = true;

    /* read and convert PROM words */
    for (int i = 0; i < 8; i++) {
        uint8_t cmd = ADDR_PROM_SETUP + (i * 2);

        if (PX4_OK != transfer(&cmd, 1, &prom_buf[0], 2)) {
            break;
        }

        /* check if all bytes are zero */
        if (i == 0) {
            /* initialize to first byte read */
            last_val = prom_buf[0];
        }

        if (prom_buf[0] != last_val || prom_buf[1] != last_val) {
            bits_stuck = false;
        }

        /* assemble 16 bit value and convert from big endian (sensor) to little endian (MCU) */
        cvt.b[0] = prom_buf[1];
        cvt.b[1] = prom_buf[0];
        _prom.c[i] = cvt.w;
    }

    /* calculate CRC and return success/failure accordingly */
    return (ms5611::crc4(&_prom.c[0]) && !bits_stuck) ? PX4_OK : -EIO;
}