linux下已经集成了iic驱动，我想拿eeprom读写操作来做个应用试试（代码如下）。
算法：“先定义一个字符串，写进去，读出来，看一下是不是成功写入”

但是发现走到ioctl就会返回-1，是怎么回事啊？ 请用过linux下IIC的兄弟进来帮忙指点一下，跪谢


#define EEPROM_SLAVE_ADD    0xA0

int main(void)
{
        int ret1 = 0;
        int ret2 = 0;
        int r = 0;
        char null_buf[8]={'A', 'B', 'C', 'D', 'E', 'F', 'G', 0};
        char outbuf[8]={'Z','Z','Z','Z', 0,0,0,0};

        int fd = open("/dev/i2c/0",O_RDWR);    //can read and write
        printf("open(/dev/i2c/0) return:(%d) \n", fd);
        if (fd == -1)
        {
                printf("can't open device /dev/i2c/0. \n");
                exit(1);
        }

        if( ( r = ioctl(fd, I2C_SLAVE_FORCE, EEPROM_SLAVE_ADD)) < 0)
        //这里的命令字换成I2C_SLAVE也是返回-1
        {
               printf("ioctl failed.r:(%d).\n", r);
               return -1;
        }


        ret1 = write(fd,null_buf,8);
        printf("write returned.ret1:(%d). \n", ret1);
        if( !ret1 )
         {
                     printf("write failed.ret1:(%d). \n", ret1);
                     exit(1);
         }

        ret2 = read(fd,outbuf,8);
        printf("read returned.ret2:(%d). \n", ret2);
        if( !ret2 )
         {
                     printf("read failed.ret2:(%d). \n", ret2);
                     exit(1);
         }

      printf("outbuf: %s\n", outbuf);
      close(fd);
}

友善之臂已经提供了操作i2d的编程示例.
http://www.arm9.net/download-linux-examples.asp

26672624兄弟：不能用文件系统接口来访问么？

看清楚代码, 还真不知道在Linux中不通过设备文件如何访问设备.:

int eeprom_open(char *dev_fqn, int addr, int type, struct eeprom* e)
{
    int funcs, fd, r;
    e->fd = e->addr = 0;
    e->dev = 0;
    
    fd = open(dev_fqn, O_RDWR);
    if(fd <= 0)
    {
        fprintf(stderr, "Error eeprom_open: %s\n", strerror(errno));
        return -1;
    }

    // get funcs list
    if((r = ioctl(fd, I2C_FUNCS, &funcs) < 0))
    {
        fprintf(stderr, "Error eeprom_open: %s\n", strerror(errno));
        return -1;
    }

    
    // check for req funcs
    CHECK_I2C_FUNC( funcs, I2C_FUNC_SMBUS_READ_BYTE );
    CHECK_I2C_FUNC( funcs, I2C_FUNC_SMBUS_WRITE_BYTE );
    CHECK_I2C_FUNC( funcs, I2C_FUNC_SMBUS_READ_BYTE_DATA );
    CHECK_I2C_FUNC( funcs, I2C_FUNC_SMBUS_WRITE_BYTE_DATA );
    CHECK_I2C_FUNC( funcs, I2C_FUNC_SMBUS_READ_WORD_DATA );
    CHECK_I2C_FUNC( funcs, I2C_FUNC_SMBUS_WRITE_WORD_DATA );

    // set working device
    if( ( r = ioctl(fd, I2C_SLAVE, addr)) < 0)
    {
        fprintf(stderr, "Error eeprom_open: %s\n", strerror(errno));
        return -1;
    }
    e->fd = fd;
    e->addr = addr;
    e->dev = dev_fqn;
    e->type = type;
    return 0;
}

引用第2楼riyan于2009-08-07 15:19发表的  :
26672624兄弟：不能用文件系统接口来访问么？

友善之臂提供的例子里用的就是文件系统接口(open, ioctl, ...);
你的程序的问题在于设定的I2C Slave地址不对，根据i2c的spec, i2c 设备的地址为7bit或10bit。mini2440上的AT24C08的地址为0x50

多谢kasim。slaveadd换成0x50之后确实可以读出数据了。
另外有个问题，slaveadd设置成功之后，怎么设置在eeprom中操作的起始地址？比如我想从eeprom的第10个字节开始写入

为什么不看看write()系统调用的用法？

器件的地址不是0xa0吗   按照电路板原理图A0A1A2接地  器件前四位固有地址1010  那么加起来写操作就是0xa0  ？  读操作就是0xa1？