linux IIC子系统分析(七)——实例分析通过i2c-dev操作I2C设备

在前面的platform device和platform driver初始化中，我们已经实现了I2C总线驱动（adapter），但是我们的设备驱动还没有实现。如果我们现在要访问I2C设备（比如eeprom），我知道的有三总方法：

（一）i2c-dev操作I2C设备：不用添加设备驱动，用户直接在应用层完成对具体I2C 设备的驱动工作。

（二）sysfs操作I2C设备：需添加设备驱动，通过sys展示出来的文件操作设备（比如/sys/devices/platform/s3c2440-i2c/i2c-0/0-0050/eeprom）

（三）设备节点操作i2C设备：添加设备驱动，为设备驱动创建设备节点，从/dev访问I2C设备（比如/dev/eeprom）

AT24C02芯片在《linux IIC子系统分析(一)——AT24C02芯片简介》已介绍

下面以AT24C02为I2C设备实例，分别实现这三种方法。

用户要在应用程序的dev 目录下看到i2c设备节点，需要内核配置IIC选项：

I2C support-->

I2C device interface

选上该选项之后，内核将会把i2c-dev.c文件编译进内核，同时产生设备节点/dev/i2c/n，它代表一个可操作的适配器。如果不配置I2C device interface，将看不到节点/dev/i2c/n。

/*i2c_test.c
*/
#include <stdio.h>
#include <linux/types.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <errno.h>
//#include <linux/i2c-dev.h>
#define I2C_RETRIES 0x070
#define I2C_TIMEOUT 0x0702
#define I2C_RDWR 0x0707
/*********定义struct i2c_rdwr_ioctl_data和struct i2c_msg，要和内核一致*******/
struct i2c_msg
{unsigned short addr;unsigned short flags;  #define I2C_M_TEN 0x0010#define I2C_M_RD 0x0001unsigned short len;unsigned char *buf;
};
struct i2c_rdwr_ioctl_data
{struct i2c_msg *msgs;int nmsgs; /* nmsgs这个数量决定了有多少开始信号，对于“单开始时序”，取1*/
};int main()
{int fd,ret;struct i2c_rdwr_ioctl_data e2prom_data;fd=open("/dev/i2c/0",O_RDWR);if(fd<0){perror("open error");}e2prom_data.nmsgs=2; e2prom_data.msgs=(struct i2c_msg*)malloc(e2prom_data.nmsgs*sizeof(struct i2c_msg));if(!e2prom_data.msgs){perror("malloc error");exit(1);}ioctl(fd,I2C_TIMEOUT,1);ioctl(fd,I2C_RETRIES,2);/***write data to e2prom**/e2prom_data.nmsgs=1;(e2prom_data.msgs[0]).len=2; (e2prom_data.msgs[0]).addr=0x50;(e2prom_data.msgs[0]).flags=0; (e2prom_data.msgs[0]).buf=(unsigned char*)malloc(2);(e2prom_data.msgs[0]).buf[0]=0x10;(e2prom_data.msgs[0]).buf[1]=0x58;ret=ioctl(fd,I2C_RDWR,(unsigned long)&e2prom_data);if(ret<0){perror("ioctl error1");}sleep(1);/******read data from e2prom*******/e2prom_data.nmsgs=2;(e2prom_data.msgs[0]).len=1; (e2prom_data.msgs[0]).addr=0x50; (e2prom_data.msgs[0]).flags=0;//write(e2prom_data.msgs[0]).buf[0]=0x10;(e2prom_data.msgs[1]).len=1;(e2prom_data.msgs[1]).addr=0x50;(e2prom_data.msgs[1]).flags=I2C_M_RD;//read(e2prom_data.msgs[1]).buf=(unsigned char*)malloc(1);(e2prom_data.msgs[1]).buf[0]=0;ret=ioctl(fd,I2C_RDWR,(unsigned long)&e2prom_data);if(ret<0){perror("ioctl error2");}printf("buff[0]=%x\n",(e2prom_data.msgs[1]).buf[0]);close(fd);return 0;
}

经测试，可以正常输出：buff[0]=58

从上面的代码中可以看出来，用户直接在应用层通过适配器dev/i2c/0接口操作连接在I2C0总线上的设备。这种操作方式需要对I2C通讯总线以及I2C设备都非常熟悉才能够很好的操作，并且它的可移植性非常的差。对那些非常简单的I2C设备进行简单的操作可以使用这种方法。

上面代码是我自己写的一个测试程序。

如果要在应用层实现对EEPROM设备的所有操作接口函数，友善支臂有提供更好的应用程序。

以下代码为友善支臂提供，以供参考：

24cXX.h

/***************************************************************************copyright            : (C) by 2003-2004 Stefano Barbatoemail                : stefano@codesink.org$Id: 24cXX.h,v 1.6 2004/02/29 11:05:28 tat Exp $***************************************************************************//****************************************************************************                                                                         **   This program is free software; you can redistribute it and/or modify  **   it under the terms of the GNU General Public License as published by  **   the Free Software Foundation; either version 2 of the License, or     **   (at your option) any later version.                                   **                                                                         ****************************************************************************/
#ifndef _24CXX_H_
#define _24CXX_H_
#include <linux/i2c-dev.h>
#include <linux/i2c.h>#define EEPROM_TYPE_UNKNOWN 0
#define EEPROM_TYPE_8BIT_ADDR   1
#define EEPROM_TYPE_16BIT_ADDR  2struct eeprom
{char *dev;     // device file i.e. /dev/i2c-Nint addr; // i2c addressint fd;       // file descriptorint type;     // eeprom type
};/** opens the eeprom device at [dev_fqn] (i.e. /dev/i2c-N) whose address is* [addr] and set the eeprom_24c32 [e]*/
int eeprom_open(char *dev_fqn, int addr, int type, struct eeprom*);
/** closees the eeprom device [e] */
int eeprom_close(struct eeprom *e);
/** read and returns the eeprom byte at memory address [mem_addr] * Note: eeprom must have been selected by ioctl(fd,I2C_SLAVE,address) */
int eeprom_read_byte(struct eeprom* e, __u16 mem_addr);
/** read the current byte* Note: eeprom must have been selected by ioctl(fd,I2C_SLAVE,address) */
int eeprom_read_current_byte(struct eeprom *e);
/** writes [data] at memory address [mem_addr] * Note: eeprom must have been selected by ioctl(fd,I2C_SLAVE,address) */
int eeprom_write_byte(struct eeprom *e, __u16 mem_addr, __u8 data);#endif

24cXX.c

/***************************************************************************copyright            : (C) by 2003-2004 Stefano Barbatoemail                : stefano@codesink.org$Id: 24cXX.h,v 1.6 2004/02/29 11:05:28 tat Exp $***************************************************************************//****************************************************************************                                                                         **   This program is free software; you can redistribute it and/or modify  **   it under the terms of the GNU General Public License as published by  **   the Free Software Foundation; either version 2 of the License, or     **   (at your option) any later version.                                   **                                                                         ****************************************************************************/
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <linux/fs.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <errno.h>
#include <assert.h>
#include <string.h>
#include "24cXX.h"static inline __s32 i2c_smbus_access(int file, char read_write, __u8 command, int size, union i2c_smbus_data *data)
{struct i2c_smbus_ioctl_data args;args.read_write = read_write;args.command = command;args.size = size;args.data = data;return ioctl(file,I2C_SMBUS,&args);
}static inline __s32 i2c_smbus_write_quick(int file, __u8 value)
{return i2c_smbus_access(file,value,0,I2C_SMBUS_QUICK,NULL);
}static inline __s32 i2c_smbus_read_byte(int file)
{union i2c_smbus_data data;if (i2c_smbus_access(file,I2C_SMBUS_READ,0,I2C_SMBUS_BYTE,&data))return -1;elsereturn 0x0FF & data.byte;
}static inline __s32 i2c_smbus_write_byte(int file, __u8 value)
{return i2c_smbus_access(file,I2C_SMBUS_WRITE,value,I2C_SMBUS_BYTE,NULL);
}static inline __s32 i2c_smbus_read_byte_data(int file, __u8 command)
{union i2c_smbus_data data;if (i2c_smbus_access(file,I2C_SMBUS_READ,command,I2C_SMBUS_BYTE_DATA,&data))return -1;elsereturn 0x0FF & data.byte;
}static inline __s32 i2c_smbus_write_byte_data(int file, __u8 command, __u8 value)
{union i2c_smbus_data data;data.byte = value;return i2c_smbus_access(file,I2C_SMBUS_WRITE,command,I2C_SMBUS_BYTE_DATA, &data);
}static inline __s32 i2c_smbus_read_word_data(int file, __u8 command)
{union i2c_smbus_data data;if (i2c_smbus_access(file,I2C_SMBUS_READ,command,I2C_SMBUS_WORD_DATA,&data))return -1;elsereturn 0x0FFFF & data.word;
}static inline __s32 i2c_smbus_write_word_data(int file, __u8 command, __u16 value)
{union i2c_smbus_data data;data.word = value;return i2c_smbus_access(file,I2C_SMBUS_WRITE,command,I2C_SMBUS_WORD_DATA, &data);
}static inline __s32 i2c_smbus_process_call(int file, __u8 command, __u16 value)
{union i2c_smbus_data data;data.word = value;if (i2c_smbus_access(file,I2C_SMBUS_WRITE,command,I2C_SMBUS_PROC_CALL,&data))return -1;elsereturn 0x0FFFF & data.word;
}/* Returns the number of read bytes */
static inline __s32 i2c_smbus_read_block_data(int file, __u8 command, __u8 *values)
{union i2c_smbus_data data;int i;if (i2c_smbus_access(file,I2C_SMBUS_READ,command,I2C_SMBUS_BLOCK_DATA,&data))return -1;else {for (i = 1; i <= data.block[0]; i++)values[i-1] = data.block[i];return data.block[0];}
}static inline __s32 i2c_smbus_write_block_data(int file, __u8 command, __u8 length, __u8 *values)
{union i2c_smbus_data data;int i;if (length > 32)length = 32;for (i = 1; i <= length; i++)data.block[i] = values[i-1];data.block[0] = length;return i2c_smbus_access(file,I2C_SMBUS_WRITE,command,I2C_SMBUS_BLOCK_DATA, &data);
}/* Returns the number of read bytes */
static inline __s32 i2c_smbus_read_i2c_block_data(int file, __u8 command,__u8 *values)
{union i2c_smbus_data data;int i;if (i2c_smbus_access(file,I2C_SMBUS_READ,command,I2C_SMBUS_I2C_BLOCK_DATA,&data))return -1;else {for (i = 1; i <= data.block[0]; i++)values[i-1] = data.block[i];return data.block[0];}
}static inline __s32 i2c_smbus_write_i2c_block_data(int file, __u8 command,__u8 length, __u8 *values)
{union i2c_smbus_data data;int i;if (length > 32)length = 32;for (i = 1; i <= length; i++)data.block[i] = values[i-1];data.block[0] = length;return i2c_smbus_access(file,I2C_SMBUS_WRITE,command,I2C_SMBUS_I2C_BLOCK_DATA, &data);
}/* Returns the number of read bytes */
static inline __s32 i2c_smbus_block_process_call(int file, __u8 command,__u8 length, __u8 *values)
{union i2c_smbus_data data;int i;if (length > 32)length = 32;for (i = 1; i <= length; i++)data.block[i] = values[i-1];data.block[0] = length;if (i2c_smbus_access(file,I2C_SMBUS_WRITE,command,I2C_SMBUS_BLOCK_PROC_CALL,&data))return -1;else {for (i = 1; i <= data.block[0]; i++)values[i-1] = data.block[i];return data.block[0];}
}static int i2c_write_1b(struct eeprom *e, __u8 buf)
{int r;// we must simulate a plain I2C byte write with SMBus functionsr = i2c_smbus_write_byte(e->fd, buf);if(r < 0)fprintf(stderr, "Error i2c_write_1b: %s\n", strerror(errno));usleep(10);return r;
}static int i2c_write_2b(struct eeprom *e, __u8 buf[2])
{int r;// we must simulate a plain I2C byte write with SMBus functionsr = i2c_smbus_write_byte_data(e->fd, buf[0], buf[1]);if(r < 0)fprintf(stderr, "Error i2c_write_2b: %s\n", strerror(errno));usleep(10);return r;
}static int i2c_write_3b(struct eeprom *e, __u8 buf[3])
{int r;// we must simulate a plain I2C byte write with SMBus functions// the __u16 data field will be byte swapped by the SMBus protocolr = i2c_smbus_write_word_data(e->fd, buf[0], buf[2] << 8 | buf[1]);if(r < 0)fprintf(stderr, "Error i2c_write_3b: %s\n", strerror(errno));usleep(10);return r;
}#define CHECK_I2C_FUNC( var, label ) \do {     if(0 == (var & label)) { \fprintf(stderr, "\nError: " \#label " function is required. Program halted.\n\n"); \exit(1); } \} while(0);int eeprom_open(char *dev_fqn, int addr, int type, struct eeprom* e)
{int funcs, fd, r;e->fd = e->addr = 0;e->dev = 0;fd = open(dev_fqn, O_RDWR);if(fd <= 0){fprintf(stderr, "Error eeprom_open: %s\n", strerror(errno));return -1;}// get funcs listif((r = ioctl(fd, I2C_FUNCS, &funcs) < 0)){fprintf(stderr, "Error eeprom_open: %s\n", strerror(errno));return -1;}// check for req funcsCHECK_I2C_FUNC( funcs, I2C_FUNC_SMBUS_READ_BYTE );CHECK_I2C_FUNC( funcs, I2C_FUNC_SMBUS_WRITE_BYTE );CHECK_I2C_FUNC( funcs, I2C_FUNC_SMBUS_READ_BYTE_DATA );CHECK_I2C_FUNC( funcs, I2C_FUNC_SMBUS_WRITE_BYTE_DATA );CHECK_I2C_FUNC( funcs, I2C_FUNC_SMBUS_READ_WORD_DATA );CHECK_I2C_FUNC( funcs, I2C_FUNC_SMBUS_WRITE_WORD_DATA );// set working deviceif( ( r = ioctl(fd, I2C_SLAVE, addr)) < 0){fprintf(stderr, "Error eeprom_open: %s\n", strerror(errno));return -1;}e->fd = fd;e->addr = addr;e->dev = dev_fqn;e->type = type;return 0;
}int eeprom_close(struct eeprom *e)
{close(e->fd);e->fd = -1;e->dev = 0;e->type = EEPROM_TYPE_UNKNOWN;return 0;
}#if 0
int eeprom_24c32_write_byte(struct eeprom *e, __u16 mem_addr, __u8 data)
{__u8 buf[3] = { (mem_addr >> 8) & 0x00ff, mem_addr & 0x00ff, data };return i2c_write_3b(e, buf);
}int eeprom_24c32_read_current_byte(struct eeprom* e)
{ioctl(e->fd, BLKFLSBUF); // clear kernel read bufferreturn i2c_smbus_read_byte(e->fd);
}int eeprom_24c32_read_byte(struct eeprom* e, __u16 mem_addr)
{int r;ioctl(e->fd, BLKFLSBUF); // clear kernel read buffer__u8 buf[2] = { (mem_addr >> 8) & 0x0ff, mem_addr & 0x0ff };r = i2c_write_2b(e, buf);if (r < 0)return r;r = i2c_smbus_read_byte(e->fd);return r;
}
#endifint eeprom_read_current_byte(struct eeprom* e)
{ioctl(e->fd, BLKFLSBUF); // clear kernel read bufferreturn i2c_smbus_read_byte(e->fd);
}int eeprom_read_byte(struct eeprom* e, __u16 mem_addr)
{int r;ioctl(e->fd, BLKFLSBUF); // clear kernel read bufferif(e->type == EEPROM_TYPE_8BIT_ADDR){__u8 buf =  mem_addr & 0x0ff;r = i2c_write_1b(e, buf);} else if(e->type == EEPROM_TYPE_16BIT_ADDR) {__u8 buf[2] = { (mem_addr >> 8) & 0x0ff, mem_addr & 0x0ff };r = i2c_write_2b(e, buf);} else {fprintf(stderr, "ERR: unknown eeprom type\n");return -1;}if (r < 0)return r;r = i2c_smbus_read_byte(e->fd);return r;
}int eeprom_write_byte(struct eeprom *e, __u16 mem_addr, __u8 data)
{if(e->type == EEPROM_TYPE_8BIT_ADDR) {__u8 buf[2] = { mem_addr & 0x00ff, data };return i2c_write_2b(e, buf);} else if(e->type == EEPROM_TYPE_16BIT_ADDR) {__u8 buf[3] = { (mem_addr >> 8) & 0x00ff, mem_addr & 0x00ff, data };return i2c_write_3b(e, buf);} fprintf(stderr, "ERR: unknown eeprom type\n");return -1;
}

eeprog.c

/***************************************************************************copyright            : (C) by 2009 Guangzhou FriendlyaRM, in Chinaemail                : capbily@163.comwebsite      : http://www.arm9.net***************************************************************************/#include <stdio.h>
#include <fcntl.h>
#include <getopt.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include "24cXX.h"#define usage_if(a) do { do_usage_if( a , __LINE__); } while(0);
void do_usage_if(int b, int line)
{const static char *eeprog_usage = "I2C-24C08(256 bytes) Read/Write Program, ONLY FOR TEST!\n""FriendlyARM Computer Tech. 2009\n";if(!b)return;fprintf(stderr, "%s\n[line %d]\n", eeprog_usage, line);exit(1);
}#define die_if(a, msg) do { do_die_if( a , msg, __LINE__); } while(0);
void do_die_if(int b, char* msg, int line)
{if(!b)return;fprintf(stderr, "Error at line %d: %s\n", line, msg);fprintf(stderr, " sysmsg: %s\n", strerror(errno));exit(1);
}static int read_from_eeprom(struct eeprom *e, int addr, int size)
{int ch, i;for(i = 0; i < size; ++i, ++addr){die_if((ch = eeprom_read_byte(e, addr)) < 0, "read error");if( (i % 16) == 0 ) printf("\n %.4x|  ", addr);else if( (i % 8) == 0 ) printf("  ");printf("%.2x ", ch);fflush(stdout);}fprintf(stderr, "\n\n");return 0;
}static int write_to_eeprom(struct eeprom *e, int addr)
{int i;for(i=0, addr=0; i<256; i++, addr++){if( (i % 16) == 0 ) printf("\n %.4x|  ", addr);else if( (i % 8) == 0 ) printf("  ");printf("%.2x ", i);fflush(stdout);die_if(eeprom_write_byte(e, addr, i), "write error");}fprintf(stderr, "\n\n");return 0;
}int main(int argc, char** argv)
{struct eeprom e;int op;op = 0;usage_if(argc != 2 || argv[1][0] != '-' || argv[1][2] != '\0');op = argv[1][1];fprintf(stderr, "Open /dev/i2c/0 with 8bit mode\n");die_if(eeprom_open("/dev/i2c/0", 0x50, EEPROM_TYPE_8BIT_ADDR, &e) < 0, "unable to open eeprom device file ""(check that the file exists and that it's readable)");switch(op){case 'r':fprintf(stderr, "  Reading 256 bytes from 0x0\n");read_from_eeprom(&e, 0, 256);break;case 'w':fprintf(stderr, "  Writing 0x00-0xff into 24C08 \n");write_to_eeprom(&e, 0);break;default:usage_if(1);exit(1);}eeprom_close(&e);return 0;
}

Makefile

CFLAGS= -Wall -O2
CC=arm-linux-gcci2c: eeprog.o 24cXX.o$(CC) $(CFLAGS) -o i2c eeprog.o 24cXX.oclean: rm -f i2c 24cXX.o eeprog.o

说明：

1.分析的内核版本是linux2.6.32.2

2.开发板为友善之臂的mini2440, 用的是ARM9(S3C2440A)处理器

3.链接的IIC设备是EEPROM(AT24C02)

4.按照内核I2C子系统的注册顺序分析。

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