设备结构体i2c_client中addr的低8位表示设备地址。设备地址由读写位、器件类型和自定义地址组成，第7位是R/W位，0表示写，1表示读，所以I2C设备通常有两个地址，即读地址和写地址类型器件由中间4位组成，这是由半导体公司生产的时候就已经固化了。
自定义类型由低3位组成。由用户自己设置，通常的做法如EEPROM这些器件是由外部I芯片的3个引脚所组合电平决定的（A0,A1,A2）。A0,A1,A2 就是自定义的地址码。自定义的地址码只能表示8个地址，所以同一IIC总线上同一型号的芯片最多只能挂载8个。如果在两个不同IIC总线上挂接了两块类型和地址相同的芯片，那么这两块芯片的地址相同。这显然是地址冲突，解决的办法是为总线适配器指定一个ID号，那么新的芯片地址就由总线适配器的ID和设备地址组成
在做IIC总线实验的时候编译出现问题并且不能够匹配
WARNING: "i2c_del_driver" [/home/book/workspace/share/drivers/iic_drv/1th/at24cxx.ko] undefined!WARNING: "i2c_register_driver" [/home/book/workspace/share/drivers/iic_drv/1th/at24cxx.ko] undefined!
WARNING: "i2c_probe" [/home/book/workspace/share/drivers/iic_drv/1th/at24cxx.ko] undefined!
这是由于内核配置没有选上接口：
<*> I2C support --->
<*> I2C device interface (选上)
配置上接口口，编译时不会出现问题，可是新的问题出现了，不会自动匹配文件，解决方法如下
[ ] Autoselect pertinent helper modules (去掉)
<*> I2C bit-banging interfaces(选上)
<*> S3C2410 I2C Driver(选上)
<*> Tiny-USB adapter 选上)
*** Other I2C/SMBus bus drivers ***
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/jiffies.h>
#include <linux/i2c.h>
#include <linux/mutex.h>
#include <linux/fs.h>
#include <asm/uaccess.h> //copy_to_user
static unsigned short ignore[] = { I2C_CLIENT_END };
static unsigned short normal_addr[] = { 0x50, I2C_CLIENT_END }; /* 地址值是7位 */
/* 改为0x60的话, 由于不存在设备地址为0x60的设备, 所以at24cxx_detect不被调用 */
//地址是用的后7位
static unsigned short force_addr[] = {ANY_I2C_BUS, 0x60, I2C_CLIENT_END};
static unsigned short * forces[] = {force_addr, NULL};
static struct i2c_client_address_data addr_data = {
.normal_i2c = normal_addr, /* 要发出S信号和设备地址并得到ACK信号,才能确定存在这个设备 */
.probe = ignore,
.ignore = ignore,
//.forces = forces, /* 强制认为存在这个设备 */
};
static struct i2c_driver at24cxx_driver;
static int major;static struct class *cls;
struct i2c_client *at24cxx_client;
static ssize_t at24cxx_read(struct file *file, char __user *buf, size_t size, loff_t * offset)
{unsigned char address;
unsigned char data;
struct i2c_msg msg[2];
int ret;
/* address = buf[0]
* data = buf[1]
*/
if (size != 1)
return -EINVAL;
copy_from_user(&address, buf, 1);
/* 数据传输三要素: 源,目的,长度 */
/* 读AT24CXX时,要先把要读的存储空间的地址发给它 */
msg[0].addr = at24cxx_client->addr; /* 目的 */msg[0].buf = &address; /* 源 */
msg[0].len = 1; /* 地址=1 byte */
msg[0].flags = 0; /* 表示写 */
/* 然后启动读操作 */
msg[1].addr = at24cxx_client->addr; /* 源 */msg[1].buf = &data; /* 目的 */
msg[1].len = 1; /* 数据=1 byte */
msg[1].flags = I2C_M_RD; /* 表示读 */
ret = i2c_transfer(at24cxx_client->adapter, msg, 2);
if (ret == 2){
copy_to_user(buf, &data, 1);
return 1;
}
else
return -EIO;
}
static ssize_t at24cxx_write(struct file *file, const char __user *buf, size_t size, loff_t *offset)
{
unsigned char val[2];
struct i2c_msg msg[1];
int ret;
/* address = buf[0]
* data = buf[1]
*/
if (size != 2)
return -EINVAL;
copy_from_user(val, buf, 2);
/* 数据传输三要素: 源,目的,长度 */
msg[0].addr = at24cxx_client->addr; /* 目的 */
msg[0].buf = val; /* 源 */
msg[0].len = 2; /* 地址+数据=2 byte */
msg[0].flags = 0; /* 表示写 */
ret = i2c_transfer(at24cxx_client->adapter, msg, 1);
if (ret == 1)
return 2;
else
return -EIO;
}
static struct file_operations at24cxx_fops = {
.owner = THIS_MODULE,
.read = at24cxx_read,
.write = at24cxx_write,
};
static int at24cxx_detect(struct i2c_adapter *adapter, int address, int kind)
{
printk("at24cxx_detect\n");
/* 构构一个i2c_client结构体: 以后收改数据时会用到它 */
at24cxx_client = kzalloc(sizeof(struct i2c_client), GFP_KERNEL);
at24cxx_client->addr = address;//卸载驱动时候需要i2c_client
at24cxx_client->adapter = adapter;//设置才能调用at24cxx_detach
at24cxx_client->driver = &at24cxx_driver;
strcpy(at24cxx_client->name, "at24cxx");
i2c_attach_client(at24cxx_client);
major = register_chrdev(0, "at24cxx", &at24cxx_fops);
cls = class_create(THIS_MODULE, "at24cxx");
device_create(cls, NULL, MKDEV(major, 0), NULL, "at24cxx"); /* /dev/at24cxx */
return 0;
}
static int at24cxx_attach(struct i2c_adapter *adapter)
{
return i2c_probe(adapter, &addr_data, at24cxx_detect);
}
static int at24cxx_detach(struct i2c_client *client)
{
printk("at24cxx_detach\n");
device_destroy(cls, MKDEV(major, 0));
class_destroy(cls);
unregister_chrdev(major, "at24cxx");
i2c_detach_client(client);
kfree(i2c_get_clientdata(client));
return 0;
}
/* 1. 分配一个i2c_driver结构体 */
/* 2. 设置i2c_driver结构体 */
static struct i2c_driver at24cxx_driver = {
.driver = {
.name = "at24cxx",
},
.attach_adapter = at24cxx_attach,
.detach_client = at24cxx_detach,
};
static int at24cxx_init(void)
{i2c_add_driver(&at24cxx_driver);
return 0;
}
static void at24cxx_exit(void)
{
i2c_del_driver(&at24cxx_driver);
}
自我总结：
i2c_add_driver->
i2c_register_driver->
at24cxx_attach- >
i2c_probe ->
//如果检测到了这个设备的ID号，那么就调用at24cxx_detect
i2c_del_driver->
driver_unregister->
at24cxx_detach->
struct i2c_msg msg[1];//传输文件的消息结构体
i2c_transfer(at24cxx_client->adapter, msg, 1);//传输函数