基于iic ds3231 linux驱动说明

基于I2C 实时时钟DS3231驱动说明：1Linux的I2C的整体架构Linux的i2c框架中各个部分的关系如图（1）所示：图（1）内核中i2c相关代码可以分为三个层次：●i2c框架：i2c.h和i2c-core.c为i2c框架的主体，提供了核心数据结构的定义、i2c适配器驱动和设备驱动的注册、注销管理，i2c通信方法上层的、与具体适配器无关的代码、检测设备地址的上层代码等；i2c-dev.c用于创建i2c适配器的/dev/i2c/%d设备节点，提供i2c设备访问方法等。

●i2c总线适配器驱动：定义描述具体i2c总线适配器的i2c_adapter数据结构、实现在具体i2c适配器上的i2c总线通信方法，并由i2c_algorithm数据结构进行描述。

●i2c设备驱动：定义描述具体设备的i2c_client和可能的私有数据结构、借助i2c框架的i2c_probe函数实现注册设备的attach_adapter方法、提供设备可能使用的地址范围、以及设备地址检测成功后创建i2c_client数据结构的回调函数。

2I2C驱动相关的数据结构I2C传送信息的数据结构体struct i2c_msg {__u16 addr; /* slave address */__u16 flags;#define I2C_M_TEN 0x10 /* we have a ten bit chip address */#define I2C_M_RD 0x01#define I2C_M_NOSTART 0x4000#define I2C_M_REV_DIR_ADDR 0x2000#define I2C_M_IGNORE_NAK 0x1000#define I2C_M_NO_RD_ACK 0x0800__u16 len; /* msg length */__u8 *buf; /* pointer to msg data */};其中addr 成员是指向器件的地址，flags 是读写标志位，len 是要发送的信息长度，*buf 是发送信息的数据指针，如果是读操作的buf是读到数据的指针。

I2C低层数据传输函数结构体struct i2c_algorithm {/* If an adapter algorithm can't do I2C-level access, set master_xferto NULL. If an adapter algorithm can do SMBus access, setsmbus_xfer. If set to NULL, the SMBus protocol is simulatedusing common I2C messages *//* master_xfer should return the number of messages successfullyprocessed, or a negative value on error */int (*master_xfer)(struct i2c_adapter *adap,struct i2c_msg *msgs,int num);int (*smbus_xfer) (struct i2c_adapter *adap, u16 addr,unsigned short flags, char read_write,u8 command, int size, union i2c_smbus_data * data);/* --- ioctl like call to set div. parameters. */int (*algo_control)(struct i2c_adapter *, unsigned int, unsigned long);/* To determine what the adapter supports */u32 (*functionality) (struct i2c_adapter *);};master_xfer 函数为I2C适配器提供数据传输函数，smbu_xfer 函数为subus协议函数，functionality 函数I2C适配器所支持的功能函数。

I2c 适配器数据结构体struct i2c_adapter {struct module *owner;unsigned int id;unsigned int class;const struct i2c_algorithm *algo; /* the algorithm to access the bus */void *algo_data;/* --- administration stuff. */int (*client_register)(struct i2c_client *);int (*client_unregister)(struct i2c_client *);/* data fields that are valid for all devices */u8 level; /* nesting level for lockdep */struct mutex bus_lock;struct mutex clist_lock;int timeout;int retries;struct device dev; /* the adapter device */struct class_device class_dev; /* the class device */int nr;struct list_head clients;struct list_head list;char name[I2C_NAME_SIZE];struct completion dev_released;struct completion class_dev_released;};适配器主要通过i2c_algorithm 结构体成员确定低层数据的传输方法，client_register 函数用来注册一个i2c_client设备，client_unregister 函数用来注销一个i2c_client 设备，bus_lock 总线互斥锁定义，I2C设备的描述结构体struct i2c_client {unsigned int flags; /* div., see below */unsigned short addr; /* chip address - NOTE: 7bit *//* addresses are stored in the *//* _LOWER_ 7 bits */struct i2c_adapter *adapter; /* the adapter we sit on */struct i2c_driver *driver;/* and our access routines */int usage_count; /* How many accesses currently *//* to the client */struct device dev; /* the device structure */struct list_head list;char name[I2C_NAME_SIZE];struct completion released;};addr 设备芯片的地址，adapter 指针指向设备所在的适配器结构体，driver指针指向所属的i2c驱动结构，dev 设备结体I2C 驱动结构体struct i2c_driver {int id;unsigned int class;/* Notifies the driver that a new bus has appeared. This routine* can be used by the driver to test if the bus meets its conditions* & seek for the presence of the chip(s) it supports. If found, it* registers the client(s) that are on the bus to the i2c admin. via* i2c_attach_client.*/int (*attach_adapter)(struct i2c_adapter *);int (*detach_adapter)(struct i2c_adapter *);/* tells the driver that a client is about to be deleted & gives it* the chance to remove its private data. Also, if the client struct* has been dynamically allocated by the driver in the function above,* it must be freed here.*/int (*detach_client)(struct i2c_client *);/* a ioctl like command that can be used to perform specific functions* with the device.*/int (*command)(struct i2c_client *client,unsigned int cmd, void *arg);struct device_driver driver;struct list_head list;};Attach_adapter 注册I2C设备引用的函数指针，detach_adapter 注销I2C设备引用的函数指针。

3引用到的I2C相关函数3.1. 用到的I2C驱动中各个函数的说明s tatic inline void *dev_get_drvdata(struct device *dev)返回设备私有数据的指针。

static inline void i2c_set_clientdata (struct i2c_client *dev, void *data)保存一个数据到设备的私有数据中。

int i2c_transfer(struct i2c_adapter * adap, struct i2c_msg *msgs, int num)I2C数据信息到设备中去，s32 i2c_smbus_write_byte_data(struct i2c_client *client, u8 command, u8 value)写一个值到指定位置。