在QT210 LDD的Android源码树中添加I2C读写工具（i2c-util）

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QT210 LDD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  

QT210 LDD S5PV210平台地址系： http://item.taobao.com/item.htm?id=13261044573