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平衡车、手机体感、旋翼无人机的平衡主要靠陀螺模组，MPU9250是一款常用的9轴姿态测量单元。MPU9250有两个内部时钟源，以及一个PLL。

时钟的选择需要综合平衡 时钟精度和功耗两个因素，所以从MPU9250的性能参数可以看到，一旦Gyro开启，功耗都是在mA级别，而加速度计和磁力计都是在uA级别的功耗。

电气元件：

电气接线图：

demo：

#include <stdio.h>
#include <string.h>
#include "pico/stdlib.h"
#include "hardware/spi.h"

#define PIN_MISO 4
#define PIN_CS   5
#define PIN_SCK  6
#define PIN_MOSI 7

#define SPI_PORT spi0
#define READ_BIT 0x80

static inline void cs_select() {
    asm volatile("nop \n nop \n nop");
    gpio_put(PIN_CS, 0);  // Active low
    asm volatile("nop \n nop \n nop");
}

static inline void cs_deselect() {
    asm volatile("nop \n nop \n nop");
    gpio_put(PIN_CS, 1);
    asm volatile("nop \n nop \n nop");
}

static void mpu9250_reset() {
    // Two byte reset. First byte register, second byte data
    // There are a load more options to set up the device in different ways that could be added here
    uint8_t buf[] = {0x6B, 0x00};
    cs_select();
    spi_write_blocking(SPI_PORT, buf, 2);
    cs_deselect();
}


static void read_registers(uint8_t reg, uint8_t *buf, uint16_t len) {

    reg |= READ_BIT;
    cs_select();
    spi_write_blocking(SPI_PORT, &reg, 1);
    sleep_ms(10);
    spi_read_blocking(SPI_PORT, 0, buf, len);
    cs_deselect();
    sleep_ms(10);
}


static void mpu9250_read_raw(int16_t accel[3], int16_t gyro[3], int16_t *temp) {
    uint8_t buffer[6];

    // Start reading acceleration registers from register 0x3B for 6 bytes
    read_registers(0x3B, buffer, 6);

    for (int i = 0; i < 3; i++) {
        accel[i] = (buffer[i * 2] << 8 | buffer[(i * 2) + 1]);
    }

    // Now gyro data from reg 0x43 for 6 bytes
    read_registers(0x43, buffer, 6);

    for (int i = 0; i < 3; i++) {
        gyro[i] = (buffer[i * 2] << 8 | buffer[(i * 2) + 1]);;
    }

    // Now temperature from reg 0x41 for 2 bytes
    read_registers(0x41, buffer, 2);

    *temp = buffer[0] << 8 | buffer[1];
}

int main() {
    stdio_init_all();

    printf("Hello, MPU9250! Reading raw data from registers via SPI...\n");

    // This example will use SPI0 at 0.5MHz.
    spi_init(SPI_PORT, 500 * 1000);
    gpio_set_function(PIN_MISO, GPIO_FUNC_SPI);
    gpio_set_function(PIN_SCK, GPIO_FUNC_SPI);
    gpio_set_function(PIN_MOSI, GPIO_FUNC_SPI);

    // Chip select is active-low, so we'll initialise it to a driven-high state
    gpio_init(PIN_CS);
    gpio_set_dir(PIN_CS, GPIO_OUT);
    gpio_put(PIN_CS, 1);

    mpu9250_reset();

    // See if SPI is working - interrograte the device for its I2C ID number, should be 0x71
    uint8_t id;
    read_registers(0x75, &id, 1);
    printf("I2C address is 0x%x\n", id);

    int16_t acceleration[3], gyro[3], temp;

    while (1) {
        mpu9250_read_raw(acceleration, gyro, &temp);

        // These are the raw numbers from the chip, so will need tweaking to be really useful.
        // See the datasheet for more information
        printf("Acc. X = %d, Y = %d, Z = %d\n", acceleration[0], acceleration[1], acceleration[2]);
        printf("Gyro. X = %d, Y = %d, Z = %d\n", gyro[0], gyro[1], gyro[2]);
        // Temperature is simple so use the datasheet calculation to get deg C.
        // Note this is chip temperature.
        printf("Temp. = %f\n", (temp / 340.0) + 36.53);

        sleep_ms(100);
    }

    return 0;
}

CMakeLists.txt:

add_executable(mpu9250_spi
        mpu9250_spi.c
        )

# Pull in our (to be renamed) simple get you started dependencies
target_link_libraries(mpu9250_spi pico_stdlib hardware_spi)

# create map/bin/hex file etc.
pico_add_extra_outputs(mpu9250_spi)

# add url via pico_set_program_url
example_auto_set_url(mpu9250_spi)