mpu9250_spi.cpp

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/**
 * @file mpu9250_spi.cpp
 *
 * Driver for the Invensense MPU9250 connected via SPI.
 *
 * @author Andrew Tridgell
 * @author Pat Hickey
 * @author David sidrane
 */

#include <drivers/device/spi.h>
#include "mpu9250.h"

#define DIR_READ            0x80
#define DIR_WRITE           0x00

/*
 * The MPU9250 can only handle high SPI bus speeds of 20Mhz on the sensor and
 * interrupt status registers. All other registers have a maximum 1MHz
 * SPI speed
 *
 * The Actual Value will be rounded down by the spi driver.
 * for a 168Mhz CPU this will be 10.5 Mhz and for a 180 Mhz CPU
 * it will be 11.250 Mhz
 */
#define MPU9250_LOW_SPI_BUS_SPEED   1000*1000
#define MPU9250_HIGH_SPI_BUS_SPEED  20*1000*1000

device::Device *MPU9250_SPI_interface(int bus, uint32_t cs);

class MPU9250_SPI : public device::SPI
{
public:
    MPU9250_SPI(int bus, uint32_t device);
    ~MPU9250_SPI() override = default;

    int read(unsigned address, void *data, unsigned count) override;
    int write(unsigned address, void *data, unsigned count) override;

protected:
    int probe() override;

private:

    /* Helper to set the desired speed and isolate the register on return */
    void set_bus_frequency(unsigned &reg_speed_reg_out);
};

device::Device *
MPU9250_SPI_interface(int bus, uint32_t cs)
{
    device::Device *interface = nullptr;

    interface = new MPU9250_SPI(bus, cs);

    return interface;
}

MPU9250_SPI::MPU9250_SPI(int bus, uint32_t device) :
    SPI("MPU9250", nullptr, bus, device, SPIDEV_MODE3, MPU9250_LOW_SPI_BUS_SPEED)
{
    _device_id.devid_s.devtype = DRV_ACC_DEVTYPE_MPU9250;
}

void
MPU9250_SPI::set_bus_frequency(unsigned &reg_speed)
{
    /* Set the desired speed */
    set_frequency(MPU9250_IS_HIGH_SPEED(reg_speed) ? MPU9250_HIGH_SPI_BUS_SPEED : MPU9250_LOW_SPI_BUS_SPEED);

    /* Isoolate the register on return */
    reg_speed = MPU9250_REG(reg_speed);
}

int
MPU9250_SPI::write(unsigned reg_speed, void *data, unsigned count)
{
    uint8_t cmd[2] {};

    if (sizeof(cmd) < (count + 1)) {
        return -EIO;
    }

    /* Set the desired speed and isolate the register */
    set_bus_frequency(reg_speed);

    cmd[0] = reg_speed | DIR_WRITE;
    cmd[1] = *(uint8_t *)data;

    return transfer(&cmd[0], &cmd[0], count + 1);
}

int
MPU9250_SPI::read(unsigned reg_speed, void *data, unsigned count)
{
    /* We want to avoid copying the data of MPUReport: So if the caller
     * supplies a buffer not MPUReport in size, it is assume to be a reg or reg 16 read
     * and we need to provied the buffer large enough for the callers data
     * and our command.
     */
    uint8_t cmd[3] {};

    uint8_t *pbuff  =  count < sizeof(MPUReport) ? cmd : (uint8_t *) data ;

    if (count < sizeof(MPUReport))  {
        /* add command */
        count++;
    }

    set_bus_frequency(reg_speed);

    /* Set command */
    pbuff[0] = reg_speed | DIR_READ ;

    /* Transfer the command and get the data */
    int ret = transfer(pbuff, pbuff, count);

    if (ret == OK && pbuff == &cmd[0]) {
        /* Adjust the count back */
        count--;

        /* Return the data */
        memcpy(data, &cmd[1], count);
    }

    return ret;
}

int
MPU9250_SPI::probe()
{
    uint8_t whoami = 0;

    int ret = read(MPUREG_WHOAMI, &whoami, 1);

    if (ret != OK) {
        return -EIO;
    }

    switch (whoami) {
    case MPU_WHOAMI_9250:
    case MPU_WHOAMI_6500:
        ret = 0;
        break;

    default:
        PX4_WARN("probe failed! %u", whoami);
        ret = -EIO;
    }

    return ret;
}