linux iic驱动编程之数据传输函数

   linux在内核里面已经实现了iic总线的数据传输函数，作为一个初学者，可以初略的了解相关函数的实现，而没有必要深入的了解。具体的注释以及用法在内核代码的文件中有介绍。

最后一种iic数据传输函数以及相关结构体

struct i2c_msg {
__u16 addr; /* slave address */
__u16 flags;
#define I2C_M_TEN 0x0010/* this is a ten bit chip address */
#define I2C_M_RD 0x0001/* read data, from slave to master */
#define I2C_M_NOSTART 0x4000/* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_REV_DIR_ADDR 0x2000/* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_IGNORE_NAK 0x1000/* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_NO_RD_ACK 0x0800/* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_RECV_LEN 0x0400/* length will be first received byte */
__u16 len; /* msg length */
__u8 *buf; /* pointer to msg data */
};

我平时用的例子

u8 buf1[4] = { 0 };
u8 buf2[4] = { 0 };
struct i2c_msg msgs[] = {
{
.addr = client->addr,//0x38 从机地址
.flags = 0, //写
.len = 1,//要写的数据的长度
.buf = buf1, //要读取的从机里面哪一个寄存器的地址
},
{
.addr = client->addr, //从机地址
.flags = I2C_M_RD, // 要从机读取数据的宏定义
.len = 1,                        // 要读取数据的长度
.buf = buf2,                   //  从从机读出的数据存放在内核的缓存地址空间
},
};

i2c_transfer(client->adapter, msgs, 2);

调用内核函数，实现具体的读写操作

还有其他的函数 linux→Documentation→i2c→i2c-protocol里面有介绍

S     (1 bit) : Start bit  起始信号
P     (1 bit) : Stop bit  停止信号
Rd/Wr (1 bit) : Read/Write bit. Rd equals 1, Wr equals 0.  读写
A, NA (1 bit) : Accept and reverse accept bit.                    应答信号
Addr  (7 bits): I2C 7 bit address. Note that this can be expanded as usual to 
                get a 10 bit I2C address.    从机地址
Comm  (8 bits): Command byte, a data byte which often selects a register on
                the device.                       要读写的寄存器地址
Data  (8 bits): A plain data byte. Sometimes, I write DataLow, DataHigh
                for 16 bit data.                 要从从机读取或者写入的数据

SMBus Quick Command
===================


This sends a single bit to the device, at the place of the Rd/Wr bit.


A Addr Rd/Wr [A] P




SMBus Receive Byte:  i2c_smbus_read_byte()
==========================================


This reads a single byte from a device, without specifying a device
register. Some devices are so simple that this interface is enough; for
others, it is a shorthand if you want to read the same register as in
the previous SMBus command.


S Addr Rd [A] [Data] NA P




SMBus Send Byte:  i2c_smbus_write_byte()
========================================


This operation is the reverse of Receive Byte: it sends a single byte
to a device.  See Receive Byte for more information.


S Addr Wr [A] Data [A] P




SMBus Read Byte:  i2c_smbus_read_byte_data()
============================================


This reads a single byte from a device, from a designated register.
The register is specified through the Comm byte.


S Addr Wr [A] Comm [A] S Addr Rd [A] [Data] NA P




SMBus Read Word:  i2c_smbus_read_word_data()
============================================


This operation is very like Read Byte; again, data is read from a
device, from a designated register that is specified through the Comm
byte. But this time, the data is a complete word (16 bits).


S Addr Wr [A] Comm [A] S Addr Rd [A] [DataLow] A [DataHigh] NA P




SMBus Write Byte:  i2c_smbus_write_byte_data()
==============================================


This writes a single byte to a device, to a designated register. The
register is specified through the Comm byte. This is the opposite of
the Read Byte operation.


S Addr Wr [A] Comm [A] Data [A] P




SMBus Write Word:  i2c_smbus_write_word_data()
==============================================


This is the opposite of the Read Word operation. 16 bits
of data is written to a device, to the designated register that is
specified through the Comm byte. 


S Addr Wr [A] Comm [A] DataLow [A] DataHigh [A] P




SMBus Process Call:  i2c_smbus_process_call()
=============================================


This command selects a device register (through the Comm byte), sends
16 bits of data to it, and reads 16 bits of data in return.


S Addr Wr [A] Comm [A] DataLow [A] DataHigh [A] 
                             S Addr Rd [A] [DataLow] A [DataHigh] NA P




SMBus Block Read:  i2c_smbus_read_block_data()
==============================================


This command reads a block of up to 32 bytes from a device, from a 
designated register that is specified through the Comm byte. The amount
of data is specified by the device in the Count byte.


S Addr Wr [A] Comm [A] 
           S Addr Rd [A] [Count] A [Data] A [Data] A ... A [Data] NA P




SMBus Block Write:  i2c_smbus_write_block_data()
================================================


The opposite of the Block Read command, this writes up to 32 bytes to 
a device, to a designated register that is specified through the
Comm byte. The amount of data is specified in the Count byte.


S Addr Wr [A] Comm [A] Count [A] Data [A] Data [A] ... [A] Data [A] P




SMBus Block Write - Block Read Process Call
===========================================


SMBus Block Write - Block Read Process Call was introduced in
Revision 2.0 of the specification.


This command selects a device register (through the Comm byte), sends
1 to 31 bytes of data to it, and reads 1 to 31 bytes of data in return.


S Addr Wr [A] Comm [A] Count [A] Data [A] ...
                             S Addr Rd [A] [Count] A [Data] ... A P




SMBus Host Notify
=================


This command is sent from a SMBus device acting as a master to the
SMBus host acting as a slave.
It is the same form as Write Word, with the command code replaced by the
alerting device's address.


[S] [HostAddr] [Wr] A [DevAddr] A [DataLow] A [DataHigh] A [P]




Packet Error Checking (PEC)
===========================


Packet Error Checking was introduced in Revision 1.1 of the specification.


PEC adds a CRC-8 error-checking byte to transfers using it, immediately
before the terminating STOP.




Address Resolution Protocol (ARP)
=================================


The Address Resolution Protocol was introduced in Revision 2.0 of
the specification. It is a higher-layer protocol which uses the
messages above.


ARP adds device enumeration and dynamic address assignment to
the protocol. All ARP communications use slave address 0x61 and
require PEC checksums.




SMBus Alert
===========


SMBus Alert was introduced in Revision 1.0 of the specification.


The SMBus alert protocol allows several SMBus slave devices to share a
single interrupt pin on the SMBus master, while still allowing the master
to know which slave triggered the interrupt.


This is implemented the following way in the Linux kernel:
* I2C bus drivers which support SMBus alert should call
  i2c_setup_smbus_alert() to setup SMBus alert support.
* I2C drivers for devices which can trigger SMBus alerts should implement
  the optional alert() callback.




I2C Block Transactions
======================


The following I2C block transactions are supported by the
SMBus layer and are described here for completeness.
They are *NOT* defined by the SMBus specification.


I2C block transactions do not limit the number of bytes transferred
but the SMBus layer places a limit of 32 bytes.




I2C Block Read:  i2c_smbus_read_i2c_block_data()
================================================


This command reads a block of bytes from a device, from a 
designated register that is specified through the Comm byte.


S Addr Wr [A] Comm [A] 
           S Addr Rd [A] [Data] A [Data] A ... A [Data] NA P




I2C Block Read (2 Comm bytes)
=============================


This command reads a block of bytes from a device, from a 
designated register that is specified through the two Comm bytes.


S Addr Wr [A] Comm1 [A] Comm2 [A] 
           S Addr Rd [A] [Data] A [Data] A ... A [Data] NA P




I2C Block Write:  i2c_smbus_write_i2c_block_data()
==================================================


The opposite of the Block Read command, this writes bytes to 
a device, to a designated register that is specified through the
Comm byte. Note that command lengths of 0, 2, or more bytes are
supported as they are indistinguishable from data.


S Addr Wr [A] Comm [A] Data [A] Data [A] ... [A] Data [A] P