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

转载：http://21cnbao.blog.51cto.com/109393/976137

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