开发板下完成基于IIC协议的AHT20温湿度采集，Linux 开发板下读取数据

初始化等没有做，只写了读与写，能够正常读取数据

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#include 
#include 
#include 
#define AHT20_DEVICE_ADDR 0x38
#define DEFAULT_I2C_BUS "/dev/i2c-0"
// CRC校验类型：CRC8/MAXIM
//多项式：X8+X5+X4+1
// Poly：0011 0001  0x31
//高位放到后面就变成 1000 1100 0x8c
// C现实代码：
uint8_t Calc_CRC8(uint8_t *message, uint8_t Num)
{
    uint8_t i;
    uint8_t byte;
    uint8_t crc = 0xFF;
    for (byte = 0; byte < Num; byte++)
    {
        crc ^= (message[byte]);
        for (i = 8; i > 0; --i)
        {
            if (crc & 0x80)
                crc = (crc << 1) ^ 0x31;
            else
                crc = (crc << 1);
        }
    }
    return crc;
}
/*****************************************************************************
  i2c写函数，参数1：设备号，参数2：从设备地址,参数3：要写入的数据缓冲区，参数4：写入数据大小
******************************************************************************/
int i2c_write(int fd, unsigned char device_addr, unsigned char *buff, int ByteNo)
{
    struct i2c_rdwr_ioctl_data msg_rdwr;
    struct i2c_msg i2cmsg;
    int i;

    unsigned char sendbuf[15] = {0};
    memset(sendbuf, 0, 15);
    memcpy(sendbuf, buff, ByteNo);

    printf("write_buffer:=");
    for (i = 0; i < ByteNo; i++)
        printf("%.2X ", sendbuf[i]);
    printf("\r\n");
    printf(" i2c_write ByteNo:=[%d],device_addr:=[%.2X]\n", ByteNo, device_addr);
    printf("\r\n");
    msg_rdwr.msgs = &i2cmsg;
    msg_rdwr.nmsgs = 1;

    i2cmsg.addr = device_addr;
    i2cmsg.flags = 0; // write
    i2cmsg.len = ByteNo;
    i2cmsg.buf = sendbuf;

    if ((i = ioctl(fd, I2C_RDWR, &msg_rdwr)) < 0)
    {
        perror("ioctl()");
        fprintf(stderr, "ioctl returned %d\n", i);
        return -1;
    }

    return 0;
}
/*****************************************************************************
  i2c读函数，参数1：设备号，参数2：从设备地址,参数3：读取数据缓冲区，参数4：读取数据大小
******************************************************************************/
int i2c_read(int fd, unsigned char device_addr, unsigned char *buff, int ByteNo)
{
    struct i2c_rdwr_ioctl_data msg_rdwr;
    struct i2c_msg i2cmsg;
    int i;

    printf("i2c_read  ByteNo:=[%d],device_addr:[%.2X]\n", ByteNo, device_addr);
    printf("\r\n");

    msg_rdwr.msgs = &i2cmsg;
    msg_rdwr.nmsgs = 1;
    i2cmsg.addr = device_addr;
    i2cmsg.flags = I2C_M_RD; // read
    i2cmsg.len = ByteNo;
    i2cmsg.buf = buff;

    if ((i = ioctl(fd, I2C_RDWR, &msg_rdwr)) < 0)
    {
        perror("ioctl()");
        fprintf(stderr, "ioctl returned %d\n", i);
        return -1;
    }

    return 0;
}
int show_data(unsigned char *readbuf)
{
    unsigned char AHT20_OutData[10];
    uint32_t H1, T1;
    int i;

    u_int16_t w_SetCrc1 = Calc_CRC8((uint8_t *)readbuf, 6);
    printf("检查crc值为= %.2X; \n", w_SetCrc1);
    printf("read_buffer:=");
    for (i = 0; i < 7; i++)
        printf("%.2X ", readbuf[i]);
    printf("\r\n");
    if ((readbuf[0] & 0x68) == 0x08)
    {
        H1 = readbuf[1];

        H1 = (H1 << 8) | readbuf[2];
        H1 = (H1 << 8) | readbuf[3];
        H1 = H1 >> 4;

        H1 = (H1 * 1000) / 1024 / 1024;

        T1 = readbuf[3];
        T1 = T1 & 0x0000000F;
        T1 = (T1 << 8) | readbuf[4];
        T1 = (T1 << 8) | readbuf[5];

        T1 = (T1 * 2000) / 1024 / 1024 - 500;

        AHT20_OutData[0] = (H1 >> 8) & 0x000000FF;
        AHT20_OutData[1] = H1 & 0x000000FF;

        AHT20_OutData[2] = (T1 >> 8) & 0x000000FF;
        AHT20_OutData[3] = T1 & 0x000000FF;
    }
    else
    {
        AHT20_OutData[0] = 0xFF;
        AHT20_OutData[1] = 0xFF;

        AHT20_OutData[2] = 0xFF;
        AHT20_OutData[3] = 0xFF;
        printf("读取失败.......................................................");
    }
 
    int t = T1 / 10;
    int t1 = T1 % 10;
    float Temp = (float)(t + t1 * 0.1);
    int h = H1 / 10;
    int h1 = H1 % 10;
    float Humi = (float)(h + h1 * 0.1);

    printf("温度:[%.1f],湿度:[%.1f]\r\n", Temp, Humi);
    printf("\r\n");
    return 0;
}
int main(int argc, char **argv)
{
    printf("----start---------\n");
    int i;
    unsigned char writebuf[3] = {0xAC, 0x33, 0x00};
    unsigned char readbuf[7];

    int fd = open(DEFAULT_I2C_BUS, O_RDWR);

    if (fd < 0)
    {
        printf("open failed/n");
        return -1;
    }

    while (1)
    {
        memset(readbuf, 0, sizeof(readbuf));
        i2c_write(fd, AHT20_DEVICE_ADDR, writebuf, 3);
        usleep(100 * 1000); // 休眠一秒
        i2c_read(fd, AHT20_DEVICE_ADDR, readbuf, 7);
        show_data(readbuf);
        usleep(2000 * 1000); // 休眠一秒
    }
    close(fd);
    return 0;
}

运行效果：