我试着从LIS3DH加速度计上得到读数，我得到了随机数

Question

我有LIS3DH加速度计与i2c连接，当我运行脚本时，它应该打印出x，y，z值，我得到的是随机数。

我在C++中使用i2c和smbus库，它们是Linux的一部分。

这是加速度计的(datasheet)https://cdn-shop.adafruit.com/datasheets/LIS3DH.pdf。

我试过更改收款机的地址。

我尝试了__s16而不是__s32。

我不确定我是不是错过了一些应该在阅读之前发生的事情。我不知道是否还需要写其他登记簿。我有点不清楚到底是怎么回事，函数底部有从寄存器返回的位数和值。我想学习。

extern "C" {
    #include <linux/i2c-dev.h>
    #include <i2c/smbus.h>
}
#include <sys/ioctl.h>
#include <fcntl.h>    /* For O_RDWR */
#include <unistd.h> 
#include <iostream>
using namespace std;

int file;
int adapter_nr = 1;
const char* filename = "/dev/i2c-8";
int initialize_mpu(int file);
__s32 high;
__s32 low;
__s32 value;
int read_raw_data(int file, __u8 addr);

int main() {
    file = open(filename, O_RDWR);
    if (file < 0) {
        exit(1);
    }
    int addr = 0x18;

    if (ioctl(file, I2C_SLAVE, addr) < 0) {
         exit(1);
    }

    __u8 res;

    __s32 accel_x;
    __s32 accel_y;
    __s32 accel_z;
    
    __s32 accel_x_register_high = 0x29;
    __s32 accel_y_register_high = 0x2B;
    __s32 accel_z_register_high = 0x2D;
    
    char buf[10];
    
    res = i2c_smbus_write_byte_data(file, addr, 0);

    if (res < 0) {
      /* ERROR HANDLING: i2c transaction failed */
    } else {
      /* res contains the read word */
    }
    
    buf[1] = 0x02;
    buf[2] = 0x03;
    if (write(file, buf, 3) != 3) {
      /* ERROR HANDLING: i2c transaction failed */
    }
    initialize_mpu(file);

    while (1) {
        
        accel_x = read_raw_data(file, accel_x_register_high) / 131.0;
        accel_y = read_raw_data(file, accel_y_register_high) / 131.0;
        accel_z = read_raw_data(file, accel_z_register_high) / 131.0;

        cout << accel_x <<" " << accel_y << " " << accel_z << " " << endl;

        usleep(100000);
    }
}


int initialize_mpu(int file) {
    i2c_smbus_write_byte_data(file, 0x20, 0xA7); //Write A7h into CTRL_REG1;      // Turn on the sensor, enable X, Y, Z axes with ODR = 100Hz normal mode.
    i2c_smbus_write_byte_data(file, 0x21, 0x09); //Write 09h into CTRL_REG2;      // High-pass filter (HPF) enabled
    i2c_smbus_write_byte_data(file, 0x22, 0x40); //Write 40h into CTRL_REG3;      // ACC AOI1 interrupt signal is routed to INT1 pin.
    i2c_smbus_write_byte_data(file, 0x23, 0x00); //Write 00h into CTRL_REG4;      // Full Scale = +/-2 g
    i2c_smbus_write_byte_data(file, 0x24, 0x08); //Write 08h into CTRL_REG5;      // Default value is 00 for no latching. Interrupt signals on INT1 pin is not latched.
    // configurations for wakeup and motionless detection
    i2c_smbus_write_byte_data(file, 0x32, 0x10); //Write 10h into INT1_THS;          // Threshold (THS) = 16LSBs * 15.625mg/LSB = 250mg.
    i2c_smbus_write_byte_data(file, 0x33, 0x00); //Write 00h into INT1_DURATION;     // Duration = 1LSBs * (1/10Hz) = 0.1s.
    //readRegister();  //Dummy read to force the HP filter to set reference acceleration/tilt value
    i2c_smbus_write_byte_data(file, 0x30, 0x2A); //Write 2Ah into INT1_CFG;          // Enable XLIE, YLIE, ZLIE interrupt generation, OR logic.
}


// Read the data of two 8-bit registers and compile into one 16-bit value
// register_address is the first (high) register, register_address-1 is the low register
// E.g., if the two registers contain the 8-bit values 0x01 and 0x02, this
// function returns the value 0x0102
int read_raw_data(int file, __u8 register_address) {
    high = i2c_smbus_read_byte_data(file, register_address);
    low = i2c_smbus_read_byte_data(file, register_address-1);
 
    value = (high << 8 | low);
 
    // This converts it from an unsigned 0-63355 value
    // to a signed value between -32769 and 32768
     if (value > 32768)
         value = value - 65536;
 
    return value;
}

Answer 1

我使用的initialize_mpu注册地址错误。

在这个数据表的某个地方有一些配置选项。我申请了一份，现在我拿到了读数。

extern "C" {
    #include <linux/i2c-dev.h>
    #include <i2c/smbus.h>
}
#include <sys/ioctl.h>
#include <fcntl.h>    /* For O_RDWR */
#include <unistd.h> 
#include <iostream>
using namespace std;

int file;
int adapter_nr = 1;
const char* filename = "/dev/i2c-8";
int initialize_mpu(int file);

__s32 high;
__s32 low;
__s32 value;

int read_raw_data(int file, __u8 addr);

int main() {
    file = open(filename, O_RDWR);
    if (file < 0) {
        exit(1);
    }
    int addr = 0x18;

    if (ioctl(file, I2C_SLAVE, addr) < 0) {
         exit(1);
    }

    __u8 res;

//     __s32 whoami;
    __s32 accel_x2;
    __s32 accel_x;
    __s32 accel_y;
    __s32 accel_z;
    
    __s32 accel_x_register_high = 0x29;
    __s32 accel_y_register_high = 0x2B;
    __s32 accel_z_register_high = 0x2D;
    
    res = i2c_smbus_write_byte_data(file, addr, 0);

    if (res < 0) {
      /* ERROR HANDLING: i2c transaction failed */
    } else {
      /* res contains the read word */
    }


               
    initialize_mpu(file);
    
    
    

    while (1) {

        accel_x = read_raw_data(file, accel_x_register_high) / 133.0;
        accel_y = read_raw_data(file, accel_y_register_high) / 133.0;
        accel_z = read_raw_data(file, accel_z_register_high) / 133.0;

        cout << accel_x <<" " << accel_y << " " << accel_z << " " << endl;

        usleep(150000);
    }
}


int initialize_mpu(int file) {
    i2c_smbus_write_byte_data(file, 0x20, 0x57);
    i2c_smbus_write_byte_data(file, 0x21, 0x00);
    i2c_smbus_write_byte_data(file, 0x22, 0x40);
    i2c_smbus_write_byte_data(file, 0x23, 0x00);
    i2c_smbus_write_byte_data(file, 0x24, 0x08);
    i2c_smbus_write_byte_data(file, 0x32, 0x10);
    i2c_smbus_write_byte_data(file, 0x33, 0x00);
    i2c_smbus_write_byte_data(file, 0x30, 0x0A);
}

// Read the data of two 8-bit registers and compile into one 16-bit value
// register_address is the first (high) register, register_address-1 is the low register
// E.g., if the two registers contain the 8-bit values 0x01 and 0x02, this
// function returns the value 0x0102
int read_raw_data(int file, __u8 register_address) {
    high = i2c_smbus_read_byte_data(file, register_address);
    low = i2c_smbus_read_byte_data(file, register_address-1);
 
    value = (high << 8 | low);
 
//     This converts it from an unsigned 0-63355 value
//     to a signed value between -32769 and 32768
     if (value > 32768)
         value = value - 65536);
 
    return value;
}