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

by @宋宝华Barry

原文地址，请尊重作者的版权等信息！

http://blog.youkuaiyun.com/21cnbao/article/details/7919055

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：
[cpp] view plaincopy
#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:
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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：
[plain] view plaincopy
/ #  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