用户空间使用i2c_dev
<!--[if !supportLists]-->第1章 <!--[endif]-->用户空间使用i2c_dev
对于注册的i2c适配器，用户空间也可以使用它们。在Linux内核代码文件/include/linux/i2c-dev.c中针对每个适配器生成一个主设备号为89的设备节点，实现了文件操作接口，用户空间可以通过i2c设备节点访问i2c适配器。适配器的编号从0开始，和适配器的设备节点的次设备号相同。
i2c适配器的设备节点是/dev/i2c-x，其中x是数字，代表适配器的编号。由于适配器编号是动态分配的（和注册次序有关），所以想了解哪一个适配器对应什么编号，可以查看/sys/class/i2c-dev/目录下的文件内容。
<!--[if !supportLists]-->1.1 <!--[endif]-->前期准备
为了在用户空间的程序当中操作i2c适配器，必须在程序中包含以下两句：
#include <linux/i2c-dev.h>
#include <linux/i2c.h>
这两个头文件中定义了之后需要用到的结构体和宏。
然后就可以打开设备节点了。但是打开哪一个呢？因为适配器的编号并不固定。为此我们在中端中运行以下命令：
[root@zlg /]# cat /sys/class/i2c-dev/i2c-0/name
PNX4008-I2C0
[root@zlg /]# cat /sys/class/i2c-dev/i2c-1/name
PNX4008-I2C1
[root@zlg /]# cat /sys/class/i2c-dev/i2c-2/name
USB-I2C
如果我们想打开第二个适配器，刚好它的编号是1，对应的设备节点是/dev/i2c-1。那么可以用下面的方法打开它：
int fd;
if ((fd = open(＂/dev/i2c-1＂,O_RDWR)) < 0) {
/* 错误处理 */
exit(1);
}
打开适配器对应的设备节点，i2c-dev为打开的线程建立一个i2c_client，但是这个i2c_client并不加到i2c_adapter的client链表当中。当用户关闭设备节点时，它自动被释放。
<!--[if !supportLists]-->1.2 <!--[endif]-->IOCTL控制
查看include/linux/i2c-dev.h文件，可以看到i2c-dev支持的IOCTL命令。如<!--[if supportFields]><span lang=EN-US><span style='mso-element:field-begin'></span> REF _Ref283302932 \h <span style='mso-element:field-separator'></span></span><![endif]-->程序清单 3.1<!--[if gte mso 9]><xml> <w:data>08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003200380033003300300032003900330032000000</w:data> </xml><![endif]--><!--[if supportFields]><span lang=EN-US><span style='mso-element:field-end'></span></span><![endif]-->所示。
程序清单 <!--[if supportFields]><span style='mso-bookmark:_Ref283302932'></span><span style='mso-element:field-begin'></span><span style='mso-bookmark:_Ref283302932'><span lang=EN-US><span style='mso-spacerun:yes'> </span>STYLEREF 1 \s <span style='mso-element:field-separator'></span></span></span><![endif]-->3<!--[if supportFields]><span style='mso-bookmark: _Ref283302932'></span><span style='mso-element:field-end'></span><![endif]-->.<!--[if supportFields]><span style='mso-bookmark:_Ref283302932'></span><span style='mso-element:field-begin'></span><span style='mso-bookmark:_Ref283302932'><span lang=EN-US> SEQ </span></span><span style='mso-bookmark:_Ref283302932'><span style='font-family:黑体;mso-ascii-font-family: Arial'>程序清单</span><span lang=EN-US> \* ARABIC \s 1 <span style='mso-element: field-separator'></span></span></span><![endif]-->1<!--[if supportFields]><span style='mso-bookmark:_Ref283302932'></span><span style='mso-element:field-end'></span><![endif]--> i2c-dev IOCTL命令
#define I2C_RETRIES 0x0701 /* 设置收不到ACK时的重试次数 */
#define I2C_TIMEOUT 0x0702 /* 设置超时时限的jiffies */
#define I2C_SLAVE 0x0703 /* 设置从机地址 */
#define I2C_SLAVE_FORCE 0x0706 /* 强制设置从机地址 */
#define I2C_TENBIT 0x0704 /* 选择地址位长:=0 for 7 bit , != 0 for 10 bit */
#define I2C_FUNCS 0x0705 /* 获取适配器支持的功能 */
#define I2C_RDWR 0x0707 /* Combined R/W transfer (one STOP only) */
#define I2C_PEC 0x0708 /* != 0 to use PEC with SMBus */
#define I2C_SMBUS 0x0720 /* SMBus transfer */
下面进行一一解释。
<!--[if !supportLists]-->1． <!--[endif]-->设置重试次数
ioctl(fd, I2C_RETRIES, m);
这句话设置适配器收不到ACK时重试的次数为m。默认的重试次数为1。
<!--[if !supportLists]-->2． <!--[endif]-->设置超时
ioctl(fd, I2C_TIMEOUT, m);
设置SMBus的超时时间为m，单位为jiffies。
<!--[if !supportLists]-->3． <!--[endif]-->设置从机地址
ioctl(fd, I2C_SLAVE, addr);
ioctl(fd, #define I2C_SLAVE_FORCE, addr);
在调用read()和write()函数之前必须设置从机地址。这两行都可以设置从机的地址，区别是第二行无论内核中是否已有驱动在使用这个地址都会成功，第一行则只在该地址空闲的情况下成功。由于i2c-dev创建的i2c_client不加入i2c_adapter的client列表，所以不能防止其它线程使用同一地址，也不能防止驱动模块占用同一地址。
<!--[if !supportLists]-->4． <!--[endif]-->设置地址模式
ioctl(file,I2C_TENBIT, select)
如果select不等于0选择10比特地址模式，如果等于0选择7比特模式，默认7比特。只有适配器支持I2C_FUNC_10BIT_ADDR，这个请求才是有效的。
<!--[if !supportLists]-->5． <!--[endif]-->获取适配器功能
ioctl(file,I2C_FUNCS,（unsigned long *）funcs)
获取的适配器功能保存在funcs中。各比特的含义如<!--[if supportFields]><span lang=EN-US style='mso-font-kerning:0pt'><span style='mso-element:field-begin'></span> REF _Ref283305554 \h <span style='mso-element:field-separator'></span></span><![endif]-->程序清单 3.2<!--[if gte mso 9]><xml> <w:data>08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003200380033003300300035003500350034000000</w:data> </xml><![endif]--><!--[if supportFields]><span lang=EN-US style='mso-font-kerning:0pt'><span style='mso-element:field-end'></span></span><![endif]-->所示。具体的含义可以参考<!--[if supportFields]><span lang=EN-US style='mso-font-kerning:0pt'><span style='mso-element:field-begin'></span> REF _Ref283456550 \r \h <span style='mso-element:field-separator'></span></span><![endif]-->第4章<!--[if gte mso 9]><xml> <w:data>08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003200380033003400350036003500350030000000</w:data> </xml><![endif]--><!--[if supportFields]><span lang=EN-US style='mso-font-kerning:0pt'><span style='mso-element:field-end'></span></span><![endif]-->。
程序清单 <!--[if supportFields]><span style='mso-bookmark:_Ref283305554'></span><span style='mso-element:field-begin'></span><span style='mso-bookmark:_Ref283305554'><span lang=EN-US><span style='mso-spacerun:yes'> </span>STYLEREF 1 \s <span style='mso-element:field-separator'></span></span></span><![endif]-->3<!--[if supportFields]><span style='mso-bookmark: _Ref283305554'></span><span style='mso-element:field-end'></span><![endif]-->.<!--[if supportFields]><span style='mso-bookmark:_Ref283305554'></span><span style='mso-element:field-begin'></span><span style='mso-bookmark:_Ref283305554'><span lang=EN-US> SEQ </span></span><span style='mso-bookmark:_Ref283305554'><span style='font-family:黑体;mso-ascii-font-family: Arial'>程序清单</span><span lang=EN-US> \* ARABIC \s 1 <span style='mso-element: field-separator'></span></span></span><![endif]-->2<!--[if supportFields]><span style='mso-bookmark:_Ref283305554'></span><span style='mso-element:field-end'></span><![endif]--> I2C FUNCTIONALILTY
/* include/linux/i2c.h */
#define I2C_FUNC_I2C 0x00000001
#define I2C_FUNC_10BIT_ADDR 0x00000002
#define I2C_FUNC_PROTOCOL_MANGLING 0x00000004 /*I2C_M_{REV_DIR_ADDR,NOSTART,..}*/
#define I2C_FUNC_SMBUS_PEC 0x00000008
#define I2C_FUNC_SMBUS_BLOCK_PROC_CALL 0x00008000 /* SMBus 2.0 */
#define I2C_FUNC_SMBUS_QUICK 0x00010000
#define I2C_FUNC_SMBUS_READ_BYTE 0x00020000
#define I2C_FUNC_SMBUS_WRITE_BYTE 0x00040000
#define I2C_FUNC_SMBUS_READ_BYTE_DATA 0x00080000
#define I2C_FUNC_SMBUS_WRITE_BYTE_DATA 0x00100000
#define I2C_FUNC_SMBUS_READ_WORD_DATA 0x00200000
#define I2C_FUNC_SMBUS_WRITE_WORD_DATA 0x00400000
#define I2C_FUNC_SMBUS_PROC_CALL 0x00800000
#define I2C_FUNC_SMBUS_READ_BLOCK_DATA 0x01000000
#define I2C_FUNC_SMBUS_WRITE_BLOCK_DATA 0x02000000
#define I2C_FUNC_SMBUS_READ_I2C_BLOCK 0x04000000 /* I2C-like block xfer */
#define I2C_FUNC_SMBUS_WRITE_I2C_BLOCK 0x08000000 /* w/ 1-byte reg. addr. */
#define I2C_FUNC_SMBUS_READ_I2C_BLOCK_2 0x10000000 /* I2C-like block xfer */
#define I2C_FUNC_SMBUS_WRITE_I2C_BLOCK_2 0x20000000 /* w/ 2-byte reg. addr. */
<!--[if !supportLists]-->6． <!--[endif]-->I2C层通信
ioctl(file,I2C_RDWR,(struct i2c_rdwr_ioctl_data *)msgset);
这一行代码可以使用I2C协议和设备进行通信。它进行连续的读写，中间没有间歇。只有当适配器支持I2C_FUNC_I2C此命令才有效。参数是一个指针，指向一个结构体，它的定义如<!--[if supportFields]><span lang=DE style='mso-ansi-language:DE'><span style='mso-element:field-begin'></span> REF _Ref283305956 \h <span style='mso-element:field-separator'></span></span><![endif]-->程序清单 3.3<!--[if gte mso 9]><xml> <w:data>08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003200380033003300300035003900350036000000</w:data> </xml><![endif]--><!--[if supportFields]><span lang=DE style='mso-ansi-language: DE'><span style='mso-element:field-end'></span></span><![endif]-->所示。其中i2c_msg的定义参考<!--[if supportFields]><span lang=EN-US><span style='mso-element:field-begin'></span> REF _Ref283227534 \h <span style='mso-element:field-separator'></span></span><![endif]-->程序清单 1.7<!--[if gte mso 9]><xml> <w:data>08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003200380033003200320037003500330034000000</w:data> </xml><![endif]--><!--[if supportFields]><span lang=EN-US><span style='mso-element:field-end'></span></span><![endif]-->。
程序清单 <!--[if supportFields]><span style='mso-bookmark:_Ref283305956'></span><span style='mso-element:field-begin'></span><span style='mso-bookmark:_Ref283305956'><span lang=EN-US><span style='mso-spacerun:yes'> </span>STYLEREF 1 \s <span style='mso-element:field-separator'></span></span></span><![endif]-->3<!--[if supportFields]><span style='mso-bookmark: _Ref283305956'></span><span style='mso-element:field-end'></span><![endif]-->.<!--[if supportFields]><span style='mso-bookmark:_Ref283305956'></span><span style='mso-element:field-begin'></span><span style='mso-bookmark:_Ref283305956'><span lang=EN-US> SEQ </span></span><span style='mso-bookmark:_Ref283305956'><span style='font-family:黑体;mso-ascii-font-family: Arial'>程序清单</span><span lang=EN-US> \* ARABIC \s 1 <span style='mso-element: field-separator'></span></span></span><![endif]-->3<!--[if supportFields]><span style='mso-bookmark:_Ref283305956'></span><span style='mso-element:field-end'></span><![endif]--> i2c_rdwr_ioctl_data
struct i2c_rdwr_ioctl_data {
struct i2c_msg __user *msgs; /* 指向i2c_msgs数组 */
__u32 nmsgs; /* 消息的个数 */
};
msgs[] 数组成员包含了指向各自缓冲区的指针。这个函数会根据是否在消息中的flags置位I2C_M_RD来对缓冲区进行读写。从机的地址以及是否使用10比特地址模式记录在每个消息中，忽略之前ioctl设置的结果。
<!--[if !supportLists]-->7． <!--[endif]-->设置SMBus PEC
ioctl(file,I2C_PEC,(long )select);
如果select不等于0选择SMBus PEC (packet error checking)，等于零则关闭这个功能，默认是关闭的。
这个命令只对SMBus传输有效。这个请求只在适配器支持I2C_FUNC_SMBUS_PEC时有效；如果不支持这个命令也是安全的，它不做任何工作。
<!--[if !supportLists]-->8． <!--[endif]-->SMBus通信
ioctl(file, I2C_SMBUS, (i2c_smbus_ioctl_data *)msgset);
这个函数和I2C_RDWR类似，参数的指针指向i2c_smbus_ioctl_data类型的变量，它的定义如<!--[if supportFields]><span lang=EN-US><span style='mso-element:field-begin'></span> REF _Ref283308161 \h <span style='mso-element:field-separator'></span></span><![endif]-->程序清单 3.4<!--[if gte mso 9]><xml> <w:data>08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003200380033003300300038003100360031000000</w:data> </xml><![endif]--><!--[if supportFields]><span lang=EN-US><span style='mso-element:field-end'></span></span><![endif]-->所示。如何填写i2c_smbus_ioctl_data的各个成员，参考<!--[if supportFields]><span lang=EN-US><span style='mso-element:field-begin'></span> REF _Ref283455290 \r \h <span style='mso-element:field-separator'></span></span><![endif]-->4.3<!--[if gte mso 9]><xml> <w:data>08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003200380033003400350035003200390030000000</w:data> </xml><![endif]--><!--[if supportFields]><span lang=EN-US><span style='mso-element:field-end'></span></span><![endif]-->节。
程序清单 <!--[if supportFields]><span style='mso-bookmark:_Ref283308161'></span><span style='mso-element:field-begin'></span><span style='mso-bookmark:_Ref283308161'><span lang=EN-US><span style='mso-spacerun:yes'> </span>STYLEREF 1 \s <span style='mso-element:field-separator'></span></span></span><![endif]-->3<!--[if supportFields]><span style='mso-bookmark: _Ref283308161'></span><span style='mso-element:field-end'></span><![endif]-->.<!--[if supportFields]><span style='mso-bookmark:_Ref283308161'></span><span style='mso-element:field-begin'></span><span style='mso-bookmark:_Ref283308161'><span lang=EN-US> SEQ </span></span><span style='mso-bookmark:_Ref283308161'><span style='font-family:黑体;mso-ascii-font-family: Arial'>程序清单</span><span lang=EN-US> \* ARABIC \s 1 <span style='mso-element: field-separator'></span></span></span><![endif]-->4<!--[if supportFields]><span style='mso-bookmark:_Ref283308161'></span><span style='mso-element:field-end'></span><![endif]--> i2c_smbus_ioctl_data
struct i2c_smbus_ioctl_data {
__u8 read_write;
__u8 command;
__u32 size;
union i2c_smbus_data __user *data;
};
<!--[if !supportLists]-->1.3 <!--[endif]-->i2c_dev使用例程
要想在用户空间使用i2c适配器，首先要如3.1<!--[if gte mso 9]><xml> <w:data>08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003200380033003300360034003500310038000000</w:data> </xml><![endif]-->节所示，选择某个适配器的设备节点打开，然后才能进行通信。
<!--[if !supportLists]-->1.3.1 <!--[endif]-->read()/write()
通信的方式有两种，一种是使用操作普通文件的接口read()和write()。这两个函数间接调用了i2c_master_recv和i2c_master_send。但是在使用之前需要使用I2C_SLAVE设置从机地址，设置可能失败，需要检查返回值。这种通信过程进行I2C层的通信，一次只能进行一个方向的传输。
下面的程序是ARM与E2PROM芯片通信的例子，如<!--[if supportFields]><span lang=EN-US><span style='mso-element:field-begin'></span> REF _Ref283651035 \h <span style='mso-element:field-separator'></span></span><![endif]-->程序清单 3.5<!--[if gte mso 9]><xml> <w:data>08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003200380033003600350031003000330035000000</w:data> </xml><![endif]--><!--[if supportFields]><span lang=EN-US><span style='mso-element:field-end'></span></span><![endif]-->所示。
程序清单 <!--[if supportFields]><span style='mso-bookmark:_Ref283651035'></span><span style='mso-element:field-begin'></span><span style='mso-bookmark:_Ref283651035'><span lang=EN-US><span style='mso-spacerun:yes'> </span>STYLEREF 1 \s <span style='mso-element:field-separator'></span></span></span><![endif]-->3<!--[if supportFields]><span style='mso-bookmark: _Ref283651035'></span><span style='mso-element:field-end'></span><![endif]-->.<!--[if supportFields]><span style='mso-bookmark:_Ref283651035'></span><span style='mso-element:field-begin'></span><span style='mso-bookmark:_Ref283651035'><span lang=EN-US> SEQ </span></span><span style='mso-bookmark:_Ref283651035'><span style='font-family:黑体;mso-ascii-font-family: Arial'>程序清单</span><span lang=EN-US> \* ARABIC \s 1 <span style='mso-element: field-separator'></span></span></span><![endif]-->5<!--[if supportFields]><span style='mso-bookmark:_Ref283651035'></span><span style='mso-element:field-end'></span><![endif]--> 使用read()/write()与i2c设备通信
#include <stdio.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <linux/i2c-dev.h>
#include <linux/i2c.h>
#define CHIP "/dev/i2c-0"
#define CHIP_ADDR 0x50
int main()
{
printf("hello, this is i2c tester\n");
int fd = open(CHIP, O_RDWR);
if (fd < 0) {
printf("open "CHIP"failed\n");
goto exit;
}
if (ioctl(fd, I2C_SLAVE_FORCE, CHIP_ADDR) < 0) { /* 设置芯片地址 */
printf("oictl:set slave address failed\n");
goto close;
}
struct i2c_msg msg;
unsigned char rddata;
unsigned char rdaddr[2] = {0, 0}; /* 将要读取的数据在芯片中的偏移量 */
unsigned char wrbuf[3] = {0, 0, 0x3c}; /* 要写的数据，头两字节为偏移量 */
printf("input a char you want to write to E2PROM\n");
wrbuf[2] = getchar();
printf("write return:%d, write data:%x\n", write(fd, wrbuf, 3), wrbuf[2]);
sleep(1);
printf("write address return: %d\n",write(fd, rdaddr, 2)); /* 读取之前首先设置读取的偏移量 */
printf("read data return:%d\n", read(fd, &rddata, 1));
printf("rddata: %c\n", rddata);
close:
close(fd);
exit:
return 0;
}
<!--[if !supportLists]-->1.3.2 <!--[endif]-->I2C_RDWR
还可以使用I2C_RDWR实现同样的功能，如<!--[if supportFields]><span lang=EN-US><span style='mso-element:field-begin'></span> REF _Ref283651333 \h <span style='mso-element:field-separator'></span></span><![endif]-->程序清单 3.6<!--[if gte mso 9]><xml> <w:data>08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003200380033003600350031003300330033000000</w:data> </xml><![endif]--><!--[if supportFields]><span lang=EN-US><span style='mso-element:field-end'></span></span><![endif]-->所示。此时ioctl返回的值为执行成功的消息数。
程序清单 <!--[if supportFields]><span style='mso-bookmark:_Ref283651333'></span><span style='mso-element:field-begin'></span><span style='mso-bookmark:_Ref283651333'><span lang=EN-US><span style='mso-spacerun:yes'> </span>STYLEREF 1 \s <span style='mso-element:field-separator'></span></span></span><![endif]-->3<!--[if supportFields]><span style='mso-bookmark: _Ref283651333'></span><span style='mso-element:field-end'></span><![endif]-->.<!--[if supportFields]><span style='mso-bookmark:_Ref283651333'></span><span style='mso-element:field-begin'></span><span style='mso-bookmark:_Ref283651333'><span lang=EN-US> SEQ </span></span><span style='mso-bookmark:_Ref283651333'><span style='font-family:黑体;mso-ascii-font-family: Arial'>程序清单</span><span lang=EN-US> \* ARABIC \s 1 <span style='mso-element: field-separator'></span></span></span><![endif]-->6<!--[if supportFields]><span style='mso-bookmark:_Ref283651333'></span><span style='mso-element:field-end'></span><![endif]--> 使用I2C_RDWR与I2C设备通信
#include <stdio.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <linux/i2c-dev.h>
#include <linux/i2c.h>
#define CHIP "/dev/i2c-0"
#define CHIP_ADDR 0x50
int main()
{
printf("hello, this is i2c tester\n");
int fd = open(CHIP, O_RDWR);
if (fd < 0) {
printf("open "CHIP"failed\n");
goto exit;
}
struct i2c_msg msg;
unsigned char rddata;
unsigned char rdaddr[2] = {0, 0};
unsigned char wrbuf[3] = {0, 0, 0x3c};
printf("input a char you want to write to E2PROM\n");
wrbuf[2] = getchar();
struct i2c_rdwr_ioctl_data ioctl_data;
struct i2c_msg msgs[2];
msgs[0].addr = CHIP_ADDR;
msgs[0].len = 3;
msgs[0].buf = wrbuf;
ioctl_data.nmsgs = 1;
ioctl_data.msgs = &msgs[0];
printf("ioctl write,return :%d\n", ioctl(fd, I2C_RDWR, &ioctl_data));
sleep(1);
msgs[0].addr = CHIP_ADDR;
msgs[0].len = 2;
msgs[0].buf = rdaddr;
msgs[1].addr = CHIP_ADDR;
msgs[1].flags |= I2C_M_RD;
msgs[1].len = 1;
msgs[1].buf = &rddata;
ioctl_data.nmsgs = 1;
ioctl_data.msgs = msgs;
printf("ioctl write address, return :%d\n", ioctl(fd, I2C_RDWR, &ioctl_data));
ioctl_data.msgs = &msgs[1];
printf("ioctl read, return :%d\n", ioctl(fd, I2C_RDWR, &ioctl_data));
printf("rddata: %c\n", rddata);
close:
close(fd);
exit:
return 0;
}