在Android源码树中添加userspace I2C读写工具（i2c-util）

by @宋宝华Barry

通过/dev/i2c-n节点，用户可以在userspace直接访问板上的i2c外设寄存器，主要是透过I2C_RDWR这个IO控制命令将i2c_msg数组传递给kernel去执行。下面的代码可以完成这个功能：

#include <stdio.h>
#include <linux/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <errno.h>
#include <assert.h>
#include <string.h>
#include <linux/i2c.h>

/* This is the structure as used in the I2C_RDWR ioctl call */
struct i2c_rdwr_ioctl_data {
        struct i2c_msg __user *msgs;    /* pointers to i2c_msgs */
        __u32 nmsgs;                    /* number of i2c_msgs */
};

int i2c_read_reg(char *dev, unsigned char *buf, unsigned slave_address, unsigned reg_address, int len)
{
    struct i2c_rdwr_ioctl_data work_queue;
    unsigned char w_val = reg_address;
    int ret;

    int fd = open(dev, O_RDWR);
    if (!fd) {
        printf("Error on opening the device file\n");
        return 0;
    }

    work_queue.nmsgs = 2;
    work_queue.msgs = (struct i2c_msg*)malloc(work_queue.nmsgs *sizeof(struct
            i2c_msg));
    if (!work_queue.msgs) {
        printf("Memory alloc error\n");
        close(fd);
        return 0;
    }

    ioctl(fd, I2C_TIMEOUT, 2);
    ioctl(fd, I2C_RETRIES, 1);

    (work_queue.msgs[0]).len = 1;
    (work_queue.msgs[0]).addr = slave_address;
    (work_queue.msgs[0]).buf = &w_val;

    (work_queue.msgs[1]).len = len;
    (work_queue.msgs[1]).flags = I2C_M_RD;
    (work_queue.msgs[1]).addr = slave_address;
    (work_queue.msgs[1]).buf = buf;

    ret = ioctl(fd, I2C_RDWR, (unsigned long) &work_queue);
    if (ret < 0) {
        printf("Error during I2C_RDWR ioctl with error code: %d\n", ret);
        close(fd);
        free(work_queue.msgs);
        return 0;
    } else {
        printf("read salve:%02x reg:%02x\n", slave_address, reg_address);
        close(fd);
        free(work_queue.msgs);
        return len;
    }
}

int i2c_write_reg(char *dev, unsigned char *buf, unsigned slave_address, unsigned reg_address, int len)
{
    struct i2c_rdwr_ioctl_data work_queue;
    unsigned char w_val = reg_address;
    unsigned char w_buf[len+1];
    int ret;

    w_buf[0] = reg_address;

    int fd = open(dev, O_RDWR);
    if (!fd) {
        printf("Error on opening the device file\n");
        return 0;
    }

    work_queue.nmsgs = 1;
    work_queue.msgs = (struct i2c_msg*)malloc(work_queue.nmsgs *sizeof(struct
            i2c_msg));
    if (!work_queue.msgs) {
        printf("Memory alloc error\n");
        close(fd);
        return 0;
    }

    ioctl(fd, I2C_TIMEOUT, 2);
    ioctl(fd, I2C_RETRIES, 1);

    (work_queue.msgs[0]).len = 1 + len;
    (work_queue.msgs[0]).addr = slave_address;
    (work_queue.msgs[0]).buf = w_buf;

    memcpy(w_buf + 1, buf, len);

    ret = ioctl(fd, I2C_RDWR, (unsigned long) &work_queue);
    if (ret < 0) {
        printf("Error during I2C_RDWR ioctl with error code: %d\n", ret);
        close(fd);
        free(work_queue.msgs);
        return 0;
    } else {
        printf("write salve:%02x reg:%02x\n", slave_address, reg_address);
        close(fd);
        free(work_queue.msgs);
        return len;
    }
}

int main(int argc, char **argv)
{
    unsigned int fd;
    unsigned int slave_address, reg_address;
    unsigned r_w;
    unsigned w_val;
    unsigned char rw_val;

    if (argc < 5) {
        printf("Usage:\n%s /dev/i2c-x start_addr reg_addr rw[0|1] [write_val]\n", argv[0]);
        return 0;
    }

    fd = open(argv[1], O_RDWR);

    if (!fd) {
        printf("Error on opening the device file %s\n", argv[1]);
        return 0;
    }

    sscanf(argv[2], "%x", &slave_address);
    sscanf(argv[3], "%x", ®_address);
    sscanf(argv[4], "%d", &r_w);

    if (r_w == 0) {
        i2c_read_reg(argv[1], &rw_val, slave_address, reg_address, 1);
        printf("Read %s-%x reg %x, read value:%x\n", argv[1], slave_address, reg_address, rw_val);
    } else {
        if (argc < 6) {
            printf("Usage:\n%s /dev/i2c-x start_addr reg_addr r|w[0|1] [write_val]\n", argv[0]);
            return 0;
        }
        sscanf(argv[5], "%d", &w_val);
        if ((w_val & ~0xff) != 0)
            printf("Error on written value %s\n", argv[5]);

        rw_val = (unsigned char)w_val;
        i2c_write_reg(argv[1], &rw_val, slave_address, reg_address, 1);
    }

    return 0;
}

在android/external/新建i2c-util目录，上述源代码存入android/external/i2c-util/i2c-util.c，编写对应的Android.mk:

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)

LOCAL_MODULE_TAGS := optional

LOCAL_MODULE := i2c-util

LOCAL_SRC_FILES += \
    i2c-util.c \

include $(BUILD_EXECUTABLE)

编译Android后，上述工具会位于/system/bin目录。在电路板上使用它：

/ #  i2c-rw /dev/i2c-2 0x38 0x1 0
read salve:38 reg:01 value:12
/ #
/ #  i2c-rw /dev/i2c-2 0x38 0x2 0
read salve:38 reg:02 value:81