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Bits&Bytes-0x03

· 2 min read
Ray Bello

IMU Configuration​

Sequence​

Added a step to select the internal 8Mhz oscillator as the clock source

// Set MPU9250 Clock Source to use the X Gyro for reference, which is slightly better than the default internal clock source.
// +-----+-----+-----+-----+-----+-----+-----+-----+
// |  7  |  6  |  5  |  4  |  3  |  2  |  1  |  0  |
// +-----+-----+-----+-----+-----+-----+-----+-----+
// |     |     |     |     |     |   CLKSEL[2:0]   |
// +-----+-----+-----+-----+-----+-----+-----+-----+
uint8_t buf[2] = {MPU9250_RA_PWR_MGMT_1, MPU9250_CLOCK_PLL_XGYRO};
i2c_write_blocking(i2c_default, this->i2c_addr, buf, 2, false);
#if defined IMU_VERBOSE_CONFIG
    printf("[IMU][CONFIG] wrote %d to MPU9250_RA_PWR_MGMT_1:%d\n", buf[1], MPU9250_RA_PWR_MGMT_1);
#endif
sleep_ms(DELAY_BETWEEN_WR_MS);

Added full scale range sensitivity selection for both accelerometer and gyroscope. 

// Set Gyro full scale range
// +-----+-----+-----+-----+-----+-----+-----+-----+
// |  7  |  6  |  5  |  4  |  3  |  2  |  1  |  0  |
// +-----+-----+-----+-----+-----+-----+-----+-----+
// |     |     |     |FS_SEL[1:0]|     |     |     |
// +-----+-----+-----+-----+-----+-----+-----+-----+
buf[0] = MPU9250_GYRO_CONFIG;
buf[1] = (uint8_t)setting.gyro_fs_sel << 3;
i2c_write_blocking(i2c_default, this->i2c_addr, buf, 2, false);
#if defined IMU_VERBOSE_CONFIG
    printf("[IMU][CONFIG] wrote %d to MPU9250_GYRO_CONFIG:%d\n", buf[1], MPU9250_GYRO_CONFIG);
#endif
sleep_ms(DELAY_BETWEEN_WR_MS);

// Set Accel full scale range
// +-----+-----+-----+-----+-----+-----+-----+-----+
// |  7  |  6  |  5  |  4  |  3  |  2  |  1  |  0  |
// +-----+-----+-----+-----+-----+-----+-----+-----+
// |     |     |     |AFS_SEL[1:0]|    |     |     |
// +-----+-----+-----+-----+-----+-----+-----+-----+
buf[0] = MPU9250_ACCEL_CONFIG;
buf[1] = (uint8_t)setting.accel_fs_sel << 3;
i2c_write_blocking(i2c_default, this->i2c_addr, buf, 2, false);
#if defined IMU_VERBOSE_CONFIG
    printf("[IMU][CONFIG] wrote %d to MPU9250_ACCEL_CONFIG:%d\n", buf[1], MPU9250_ACCEL_CONFIG);
#endif
sleep_ms(DELAY_BETWEEN_WR_MS);

Validating Sequence​

[IMU][CONFIG] wrote 1 to MPU9250_RA_PWR_MGMT_1:107
[IMU][CONFIG] wrote 0 to MPU9250_GYRO_CONFIG:27         // GYRO_250DPS
[IMU][CONFIG] wrote 0 to MPU9250_ACCEL_CONFIG:28        // ACCEL_2G

Tasks contd.​

MPU9250 IMU Driver​

  • Done: Implement full scale range and gyro sensitivity selection, currently using default settings.
  • Done: Add hardware reset & calibration sequence

Attitude Estimation​

  • Done: Refactor the existing attitude estimation algorithm with modularity/flexibility in mind.

Defines Used​

#define DELAY_BETWEEN_WR_MS         50        // Delay between I2C writes during configuration
#define MPU9250_GYRO_CONFIG         0x1B      // Gyro FS_SEL address
#define MPU9250_ACCEL_CONFIG        0x1C      // Accel AFS_SEL address
#define MPU9250_CLOCK_PLL_XGYRO 0x01        // Xgyro pll clock 
#define MPU9250_RA_PWR_MGMT_1   0x6B      // Power management register 1 address