在Android源碼樹中添加userspace I2C讀寫工具（i2c-util）

通過/dev/i2c-n節點，用戶可以在userspace直接訪問板上的i2c外設寄存器，主要是透過I2C_RDWR這個IO控制命令將i2c_msg數組傳遞給kernel去執行。下面的代碼可以完成這個功能：

#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目錄，上述源代碼存入android/external/i2c-util/i2c-util.c，編寫對應的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)

編譯Android後，上述工具會位於/system/bin目錄。在電路板上使用它：

/ #  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

本文出自 “宋寶華的博客” 博客，請務必保留此出處http://21cnbao.blog.51cto.com/109393/976137