为什么i2c_smbus函数不可用? (I2C –嵌入式Linux) [英] Why are i2c_smbus function not available? (I2C – Embedded Linux)

问题描述

在开发嵌入式Linux软件以在I2C总线上进行通信时，有很多关于使用 i2c_smbus _ 函数的参考.在软件项目中针对ARM8处理器在软件项目中引用了 i2c_smbus 之类的功能 i2c_smbus_read_word_data 时，例如在以下范围内未生成" i2c_smbus_read_word_data"之类的错误:编译.

There are many references to using i2c_smbus_ functions when developing embedded Linux software to communicate on the I2C bus. When i2c_smbus functions such as i2c_smbus_read_word_data are referenced in software project for ARM8 processor errors such as ‘i2c_smbus_read_word_data’ was not declared in this scope are generated at compile.

对以下头文件的调查表明，大多数 i2c_smbus 函数定义都不存在.

Investigation of the following header files indicate the absence of most i2c_smbus function definition.

• /usr/arm-linux-gnueabi/include/linux/i2c.h
• /usr/arm-linux-gnueabi/include/linux/i2c-dev.h

在以下参考文献中， i2c.h 文件已定义了所有i2c_smbus.

Also in that following reference i2c.h file has all the i2c_smbus defined.

该问题如何解决?

研究参考

1. 在Linux中从用户空间使用I2C
2. 来自Linux用户空间的I2C通信–第二部分
3. I2C开发人员界面

1. Using I2C from userspace in Linux
2. I2C Communication from Linux Userspace – Part II
3. I2C dev interface

推荐答案

因为您的应用程序使用了错误的头文件.

Because you are using a wrong header file for your application.

如果您在标头中的函数i2c_smbus_read_word_data()上看到extern，则该标头是您的内核的标头文件，而不是您的 application 的标头文件. Linux内核具有i2c_smbus_read_word_data()和其他i2c smbus函数供内部使用.但是它们是a)不是系统调用，或者b)无法从您的应用程序访问.

If you see an extern on the function i2c_smbus_read_word_data() in your header, it's a header file for your kernel, but not for your application. The Linux kernel has i2c_smbus_read_word_data() and other i2c smbus functions for its internal use. But they are a) not system calls, or b) not accessible from your application.

相反，请从lm-sensors中获取 i2c-tools 并进行安装.如果您使用的是Debian，只需

Instead, get i2c-tools from lm-sensors and install it. If you are using Debian, just

sudo apt-get install libi2c-dev

，并使用i2c_smbus_read_word_data()或它们提供的任何其他接口. i2c-dev是仅标头的程序包，这意味着没有库可链接.所有函数都是使用ioctl()定义的内联函数.

and use i2c_smbus_read_word_data() or any other interfaces they offer. i2c-dev is a header only package, meaning that there is no library to link to. All functions are inline functions defined using ioctl().

例如)

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_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;
        else
                return 0x0FFFF & data.word;
}

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