有关linux的i2c相关**有一下几篇，他们互相关联，应该一同看：
- i2c 驱动一：简介
- i2c 驱动二：devfs文件系统
- i2c 驱动三：自己实现设备和驱动分离
- i2c 驱动四：sysfs文件系统
- i2c 驱动五：gpio模拟i2c
1. 用 sysfs 实现 i2c，其实质是将 i2c 和 sysfs 结合起来，那首先来看看什么是 sysfs：【1】sysfs简介：sysfs 是基于内存的虚拟的文件系统，他的作用于 proc 相似，他的设计是吸取的 proc 中的很多教训，使之导出内核或其他的数据的方式更为统一
【2】此部分，有一个博客写的很好，在这里，暂时不做整理，直接点击跳转
【3】借助于 sysfs ，我们可以把要呈现的参数/数据以文件夹的形式呈现给用户，最直接的好处是你能够用命令行来读(cat)写(echo)参数/数据
【4】对sysfs中的函数，有一篇**写的很好，直接点击跳转
2. 说的再多，不如一个例子：由于手头上有个 mpu6050，所以，就以mpu6050为例，采用的传感器的小板子是 GY-521
目录结构：
.
├── dev
│ ├── Makefile
│ └── mpu6050_dev.c
└── dri
├── Makefile
└── mpu6050_dri.c
mpu6050_dev.c
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#include <linux/kernel.h> #include <linux/module.h> #include <linux/i2c.h> #include <linux/delay.h> MODULE_LICENSE(&quot;GPL&quot;); static struct i2c_client *mpu6050_clientp; static struct i2c_board_info mpu6050_i2c_devs = { .type = &quot;mpu6050&quot;, .addr = 0x68, /*I2C_BOARD_INFO(&quot;mpu6050&quot;, 0x50), //这个宏是上边两个变量赋值的替换*/ }; static int mpu6050_dev_init(void) { struct i2c_adapter *i2c_adap; //分配一个适配器的指针 printk(&quot;mpu6050_dev_init.\n&quot;); i2c_adap = i2c_get_adapter(0); //0 是 i2c 总线编号 mpu6050_clientp = i2c_new_device(i2c_adap, &mpu6050_i2c_devs); //只能添加一个 if (!mpu6050_clientp) printk(&quot;register i2c error!\n&quot;); i2c_put_adapter(i2c_adap); //释放 adapter return 0; } static void mpu6050_dev_exit(void) { printk(&quot;mpu6050_dev_exit.\n&quot;); i2c_unregister_device(mpu6050_clientp); } module_init(mpu6050_dev_init); module_exit(mpu6050_dev_exit);
Makefile
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ifeq ($(KERNELRELEASE),) #KERNELDIR ?= /lib/modules/$(shell uname -r)/build KERNELDIR ?= ~/wor_lip/linux-3.4.112 PWD := $(shell pwd) modules: $(MAKE) -C $(KERNELDIR) M=$(PWD) modules modules_install: $(MAKE) -C $(KERNELDIR) M=$(PWD) modules_install clean: rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions modules* Module* .PHONY: modules modules_install clean else obj-m := mpu6050_dev.o endif
mpu6050_dri.c
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#include <linux/kernel.h> #include <linux/module.h> #include <linux/i2c.h> #include <linux/delay.h> MODULE_LICENSE(&quot;GPL&quot;); #define SMPLRT_DIV 0x19 #define CONFIG 0x1A #define GYRO_CONFIG 0x1B #define ACCEL_CONFIG 0x1C #define ACCEL_XOUT_H 0x3B #define ACCEL_XOUT_L 0x3C #define ACCEL_YOUT_H 0x3D #define ACCEL_YOUT_L 0x3E #define ACCEL_ZOUT_H 0x3F #define ACCEL_ZOUT_L 0x40 #define TEMP_OUT_H 0x41 #define TEMP_OUT_L 0x42 #define GYRO_XOUT_H 0x43 #define GYRO_XOUT_L 0x44 #define GYRO_YOUT_H 0x45 #define GYRO_YOUT_L 0x46 #define GYRO_ZOUT_H 0x47 #define GYRO_ZOUT_L 0x48 #define PWR_MGMT_1 0x6B static struct kobject *example_kobj; struct i2c_client *glb_client; static int mpu6050_read_byte(struct i2c_client *client, unsigned char reg) { int ret; char txbuf[1] = { reg }; char rxbuf[1]; struct i2c_msg msg[] = { {client->addr, 0, 1, txbuf}, {client->addr, I2C_M_RD, 1, rxbuf} }; ret = i2c_transfer(client->adapter, msg, ARRAY_SIZE(msg)); if (ret < 0) { printk(&quot;ret = %d\n&quot;, ret); return ret; } return rxbuf[0]; } static int mpu6050_write_byte(struct i2c_client *client, unsigned char reg, unsigned char val) { char txbuf[2] = {reg, val}; struct i2c_msg msg[] = { {client->addr, 0, 2, txbuf}, }; i2c_transfer(client->adapter, msg, ARRAY_SIZE(msg)); return 0; } /* 读/sys/kernel/mpu6050_i2c文件下的文件时调用 */ static ssize_t foo_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf) /* buf是返回给用户空间的值 */ { unsigned short accel_x = 0, accel_y = 0, accel_z = 0; unsigned short gyro_x = 0, gyro_y = 0, gyro_z = 0; unsigned short temp = 0; mpu6050_write_byte(glb_client, PWR_MGMT_1, 0x00); mpu6050_write_byte(glb_client, SMPLRT_DIV, 0x07); mpu6050_write_byte(glb_client, CONFIG, 0x06); mpu6050_write_byte(glb_client, GYRO_CONFIG, 0x18); mpu6050_write_byte(glb_client, ACCEL_CONFIG, 0x01); mdelay(10); accel_x = mpu6050_read_byte(glb_client, ACCEL_XOUT_L); accel_x |= mpu6050_read_byte(glb_client, ACCEL_XOUT_H) << 8; accel_y = mpu6050_read_byte(glb_client, ACCEL_YOUT_L); accel_y |= mpu6050_read_byte(glb_client, ACCEL_YOUT_H) << 8; accel_z = mpu6050_read_byte(glb_client, ACCEL_ZOUT_L); accel_z |= mpu6050_read_byte(glb_client, ACCEL_ZOUT_H) << 8; printk(&quot;acceleration data: x = %04x, y = %04x, z = %04x\n&quot;, accel_x, accel_y, accel_z); gyro_x = mpu6050_read_byte(glb_client, GYRO_XOUT_L); gyro_x |= mpu6050_read_byte(glb_client, GYRO_XOUT_H) << 8; gyro_y = mpu6050_read_byte(glb_client, GYRO_YOUT_L); gyro_y |= mpu6050_read_byte(glb_client, GYRO_YOUT_H) << 8; gyro_z = mpu6050_read_byte(glb_client, GYRO_ZOUT_L); gyro_z |= mpu6050_read_byte(glb_client, GYRO_ZOUT_H) << 8; printk(&quot;gyroscope data: x = %04x, y = %04x, z = %04x\n&quot;, gyro_x, gyro_y, gyro_z); temp = mpu6050_read_byte(glb_client, TEMP_OUT_L); temp |= mpu6050_read_byte(glb_client, TEMP_OUT_H) << 8; printk(&quot;temperature data: %x\n&quot;, temp); return sprintf(buf, &quot;%x\n&quot;, temp); } /* 写/sys/kernel/mpu6050_i2c文件下的文件时调用 */ static ssize_t foo_store(struct kobject *kobj, struct kobj_attribute *attr, const char *buf, size_t count) { return 0; } static struct kobj_attribute foo_attribute = __ATTR(mpu6050_accelerationd, 0666, foo_show, foo_store); /* (文件名, 文件权限, 读这个文件时调用的函数, 写文件时调用时的函数) * 在/sys/kernel/mpu6050_i2c/下的文件 */ static struct kobj_attribute foo_attribute2 = __ATTR(mpu6050_gyroscope, 0666, foo_show, foo_store); static struct kobj_attribute foo_attribute3 = __ATTR(mpu6050_temperature, 0666, foo_show, foo_store); /* * 创建一个属性组,方便我们一次性的创建和删除 */ static struct attribute *attrs[] = { &foo_attribute.attr, &foo_attribute2.attr, &foo_attribute3.attr, NULL, /* 需要用NULL来表示属性列表的结束 */ }; /* * An unnamed attribute group will put all of the attributes directly in * the kobject directory. If we specify a name, a subdirectory will be * created for the attributes with the directory being the name of the * attribute group. */ static struct attribute_group attr_group = { .attrs = attrs, }; static int mpu6050_probe(struct i2c_client *client, const struct i2c_device_id *id) { int retval; glb_client = client; /* * 创建目录 /sys/kernel/mpu6050_i2c */ example_kobj = kobject_create_and_add(&quot;mpu6050_i2c&quot;, kernel_kobj); /* (kernel_kobj这个父文件夹下的叫mpu6050_i2c的文件夹) */ if (!example_kobj) return -ENOMEM; /* Create the files associated with this kobject */ retval = sysfs_create_group(example_kobj, &attr_group); if (retval) kobject_put(example_kobj); return 0; } static int mpu6050_remove(struct i2c_client *client) { /*struct bin_attribute *binp;*/ /*binp = i2c_get_clientdata(client);*/ /*sysfs_remove_bin_file(&client->dev.kobj, binp);*/ kobject_put(example_kobj); printk(&quot;driver removed.\n&quot;); return 0; } static const struct i2c_device_id mpu6050_id[] = { { &quot;mpu6050&quot;, 0 }, }; /*MODULE_DEVICE_TABLE(i2c, mpu6050_id);*/ static struct i2c_driver mpu6050_driver = { .driver = { .name = &quot;xx&quot;, //供模块匹配用 .owner = THIS_MODULE, }, .probe = mpu6050_probe, .remove = mpu6050_remove, .id_table = mpu6050_id, /* 用于I2C driver的probe函数调用 */ }; /*i2c_add_driver();*/ module_i2c_driver(mpu6050_driver);//简单方式，内核中是个宏，完成了模块的初始化和卸载
【1】当设备 和 驱动 匹配成功后，会在 /sys/kernel/ 下创建一个mpu6050_i2c 目录，里边有3个文件，如下图
<img id="aimg_awtDz" class="zoom" file="http://img.blog.csdn.net/20161108112220341" lazyloadthumb="1" border="0" alt="" />
【2】读传感器的值
<img id="aimg_WBCbo" class="zoom" file="http://img.blog.csdn.net/20161108112428201" lazyloadthumb="1" border="0" alt="" />
【3】很明显，程序中3个参数以文件夹的方式呈现给了用户，用户可以像操作文件的形式读写相应文件，在本程序中，我偷了个懒，读这3个参数执行了相同的函数，没有实现写的函数
【4】可以想到的是，程序中可以实现不同的读函数，实现单独的参数读取
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