面试被问到IIC，总结。

Linux3.5内核中，IIC。

 1 i2c_add_driver
 2     i2c_register_driver
 3         a. at24cxx_driver放入i2c_bus_type的drv链表
 4            并且从dev链表里取出能匹配的i2c_client并调用probe
 5         driver_register
 6             
 7         
 8         b. 对于每一个适配器，调用__process_new_driver
 9            对于每一个适配器，调用它的函数确定address_list里的设备是否存在
10            如果存在，再调用detect进一步确定、设置，然后i2c_new_device
11         /* Walk the adapters that are already present */
12         i2c_for_each_dev(driver, __process_new_driver);
13             __process_new_driver
14                 i2c_do_add_adapter
15                     /* Detect supported devices on that bus, and instantiate them */
16                     i2c_detect(adap, driver);
17                         for (i = 0; address_list[i] != I2C_CLIENT_END; i += 1) {
18                             err = i2c_detect_address(temp_client, driver);
19                                         /* 判断这个设备是否存在：简单的发出S信号确定有ACK */
20                                         if (!i2c_default_probe(adapter, addr))
21                                             return 0;
22                                         
23                                         memset(&info, 0, sizeof(struct i2c_board_info));
24                                         info.addr = addr;    
25                                         
26                                         // 设置info.type
27                                         err = driver->detect(temp_client, &info);
28                     
29                                         i2c_new_device

使用读写IIC器件的函数接口：

/**
*I2c_Master_发送-在主传输模式下发出单个I2c消息
*@客户端：从设备的句柄
*@buf：将写入从系统的数据
*@计数：要写入的字节数，必须小于64K，因为msg.len是u16
*返回负的errno，或者返回写入的字节数。
*/

/**
 * i2c_master_send - issue a single I2C message in master transmit mode
 * @client: Handle to slave device
 * @buf: Data that will be written to the slave
 * @count: How many bytes to write, must be less than 64k since msg.len is u16
 *
 * Returns negative errno, or else the number of bytes written.
 */
int i2c_master_send(const struct i2c_client *client, const char *buf, int count)
{
    int ret;
    struct i2c_adapter *adap = client->adapter;
    struct i2c_msg msg;

    msg.addr = client->addr;
    msg.flags = client->flags & I2C_M_TEN;
    msg.len = count;
    msg.buf = (char *)buf;

    ret = i2c_transfer(adap, &msg, 1);

    /*
     * If everything went ok (i.e. 1 msg transmitted), return #bytes
     * transmitted, else error code.
     */
    return (ret == 1) ? count : ret;
}

/**
*I2c_Master_Recv-在主接收模式下发出单个I2c消息
*@客户端：从设备的句柄
*@buf：从从属服务器读取数据的存储位置
*@计数：要读取的字节数，必须小于64K，因为msg.len是u16
*返回负的errno，否则返回读取的字节数。
*/

/**
 * i2c_master_recv - issue a single I2C message in master receive mode
 * @client: Handle to slave device
 * @buf: Where to store data read from slave
 * @count: How many bytes to read, must be less than 64k since msg.len is u16
 *
 * Returns negative errno, or else the number of bytes read.
 */
int i2c_master_recv(const struct i2c_client *client, char *buf, int count)
{
    struct i2c_adapter *adap = client->adapter;
    struct i2c_msg msg;
    int ret;

    msg.addr = client->addr;
    msg.flags = client->flags & I2C_M_TEN;
    msg.flags |= I2C_M_RD;
    msg.len = count;
    msg.buf = buf;

    ret = i2c_transfer(adap, &msg, 1);

    /*
     * If everything went ok (i.e. 1 msg received), return #bytes received,
     * else error code.
     */
    return (ret == 1) ? count : ret;
}

面试被问到IIC，总结。

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