by LiAnLab.org / 宋宝华
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
本文转自 21cnbao 51CTO博客，原文链接：http://blog.51cto.com/21cnbao/976137
，如需转载请自行联系原作者
