I2c dev

Linux i2c-dev驱动 用户空间操作示例

测试芯片为at24c16

打开i2c总线节点

file = open("/dev/i2c-0", O_RDWR);
if(file < 0){
    fprintf(stderr, "failed to open i2c bus\n");
    return -1;
}

设置器件地址

I2C_SLAVE_FORCE 表示即使该地址的i2c设备已经有驱动程序，也强制其可用

ret = ioctl(file, force?I2C_SLAVE_FORCE:I2C_SLAVE, 0x50);
if(ret < 0){
    fprintf(stderr, "failed to set slave addr\n");
    return -1;
}

EEPROM AT24C02

以EEPROM AT24C02字节写为例， 流程如下 S -> Daddr -> Waddr -> data -> T 起始 -> 器件地址 -> 目标地址 -> 数据 -> 结束 符合SMBus如下写序列

使用I2C_SMBUS_WRITE写2字节，详见于linux/i2c.h中

__s32 smbus_access(int file, char read_write, __u8 Waddr, int size, union i2c_smbus_data *data)
{
    struct i2c_smbus_ioctl_data msgs;

    msgs.read_write = read_write;
    msgs.command = Waddr;
    msgs.size = size;
    msgs.data = data;

    if(ioctl(file, I2C_SMBUS, &msgs) < 0){
        perror("error, failed to access smbus");
        return -errno;
    }

    return 0;
}

__s32 write_byte_data(int file, __u32 Waddr, __u32 value)
{
    union i2c_smbus_data data;
    data.byte = value;
    return smbus_access(file,I2C_SMBUS_WRITE, Waddr, I2C_SMBUS_BYTE_DATA, &data);
}

at24cxx每次写后需要max 10ms时间处理内部写循环

int waiting_write_cycle()
{
    int ret;
    struct timespec ts;
    /* waiting for at24cxx internal write cycle. 10ms max */
    ts.tv_sec =0;
    ts.tv_nsec = 10 * 1000 * 1000;
    ret = nanosleep(&ts, NULL);
    if(ret < 0){
        fprintf(stderr, "cannot sleep.\n");
        perror("ERRNO: ");
        return -errno;
    }

    return 0;
}

BH1750 光强传感器

以 BH1750 光强传感器为例

写命令

int bh1750_write_cmd(int fd, __u8 cmd)
{
    return smbus_access(fd, I2C_SMBUS_WRITE, cmd, I2C_SMBUS_BYTE, NULL);
}

读双字

int bh1750_read_word(int fd)
{
    union i2c_smbus_data data;
    struct i2c_smbus_ioctl_data msg;

    msg.read_write = I2C_SMBUS_READ;
    msg.size = I2C_SMBUS_WORD_DATA;
    msg.data = &data;

    if(ioctl(fd, I2C_SMBUS, &msg) < 0){
        perror("error, failed to access smbus");
        return -errno;
    }
    printf("raw data: %d\n", data.word);

    return data.word;
}

低分辨率模式光强转换 参考手册如下部分

可知，单次低分辨率模式下，直接将双字除以1.2即可

raw_data = bh1750_read_word(fd);

/* convert raw data to lux */
lux = raw_data / 1.2;
printf("lux: %f\n", lux);

包含如下头文件

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>

#include <linux/types.h>
#include <linux/i2c.h>
#include <linux/i2c-dev.h>

#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <time.h>