文章目录

1.i2c总线
- 1.1i2c总线驱动硬件知识复习
- 1.2i2c总线驱动框架结构
- 1.3i2c总线驱动的API
- 1.4i2c总线驱动的实例
2.i2c总线驱动
- 2.1si7006（sht20）设备树的编写
- - 2.1.1画出硬件连接图
  - 2.1.2找到控制器的设备树
  - 2.1.3编写自己的设备树
- 2.2i2c中相关的结构体
- 2.3封装数据发送数据的过程
- - 2.3.1消息的封装过程
  - 2.3.2消息的发送过程
- 2.4读取si7006串号和固件号实例
- 2.5读取si7006温湿度实例

1.i2c总线

1.1i2c总线驱动硬件知识复习

（1）i2c几根线？

scl:时钟线sda:数据线

（2）几种信号？

start:起始信号：scl为高电平的时候，sda从高到低的跳变stop:结束信号：scl为高电平的时候，sda从低到高的跳变ack:在第九个时钟周期的时候，sda总线是低电平就代表应答（master--->slave   slave ---->master）No ack:在第九个时钟周期的时候，sda总线持续高电平

（3）i2c读写时序

写时序：\*\*start+ (从机地址 7bit + 0(写) 1bit) + ack + 寄存器地址（8bit|16bit）+ack \*\***+data(8bit|16bit) + ack + stop**读时序：**start+ (从机地址 7bit + 0(写) 1bit) + ack + 寄存器地址（8bit|16bit）+ack ****start+ (从机地址 7bit + 1(读) 1bit) + ack + data(8bit 从机给主机) +NO ack+stop**

（4）i2c总线的特点

i2c是一个半双工,同步的，串行，具备应答机制的总线协议。

（5）i2c总线速率（控制器）

100K  低速    400K 全速   3.4M 高速

1.2i2c总线驱动框架结构

1.3i2c总线驱动的API

1.分配并初始化对象struct i2c_driver {int (*probe)(struct i2c_client *client, const struct i2c_device_id *id);int (*remove)(struct i2c_client *client);struct device_driver driver;//const struct i2c_device_id *id_table;}struct device_driver {const char       *name;const struct of_device_id *of_match_table;}//i2c的匹配方式只有两种：1.idtable，2.设备树
2.注册、注销#define i2c_add_driver(driver) i2c_register_driver(THIS_MODULE, driver)  //注册void i2c_del_driver(struct i2c_driver *driver); //注销
3.一键注册的函数module_i2c_driver(变量名);

1.4i2c总线驱动的实例

#include <linux/i2c.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/mod_devicetable.h>int myi2c_probe(struct i2c_client* client,const struct i2c_device_id* id)
{printk("%s:%d\n", __func__, __LINE__);return 0;
}
int myi2c_remove(struct i2c_client* client)
{printk("%s:%d\n", __func__, __LINE__);return 0;
}struct of_device_id oftable[] = {{.compatible = "hqyj,myi2c",},{}
};
MODULE_DEVICE_TABLE(of,oftable);struct i2c_driver myi2c = {.probe = myi2c_probe,.remove = myi2c_remove,.driver = {.name = "myi2c123456",.of_match_table = oftable,}
};
module_i2c_driver(myi2c);
MODULE_LICENSE("GPL");

2.i2c总线驱动

2.1si7006（sht20）设备树的编写

2.1.1画出硬件连接图

2.1.2找到控制器的设备树

stm32mp151.dtsi

i2c1: i2c@40012000 {compatible = "st,stm32mp15-i2c";  //和控制器匹配的名字reg = <0x40012000 0x400>;         //控制器的地址interrupt-names = "event", "error";interrupts-extended = <&exti 21 IRQ_TYPE_LEVEL_HIGH>,<&intc GIC_SPI 32 IRQ_TYPE_LEVEL_HIGH>;clocks = <&rcc I2C1_K>;resets = <&rcc I2C1_R>;#address-cells = <1>;#size-cells = <0>;     //修饰子节点 reg成员个数dmas = <&dmamux1 33 0x400 0x80000001>,<&dmamux1 34 0x400 0x80000001>;dma-names = "rx", "tx";power-domains = <&pd_core>;st,syscfg-fmp = <&syscfg 0x4 0x1>;wakeup-source;i2c-analog-filter;status = "disabled";  //控制器没有使能
};

2.1.3编写自己的设备树

参考：linux-5.10.61/Documentation/devicetree/bindings/i2c
&i2c1{pinctrl-names = "default", "sleep";pinctrl-0 = <&i2c1_pins_b>;       //管脚复用，工作状态                                                      pinctrl-1 = <&i2c1_sleep_pins_b>; //管脚复用，休眠状态i2c-scl-rising-time-ns = <100>;   //scl上升沿和下降沿的时间                                              i2c-scl-falling-time-ns = <7>;status = "okay";                  //使能控制器/delete-property/dmas;            //删除dma属性                                          /delete-property/dma-names;si7006@40{compatible = "hqyj,si7006";  //和设备驱动匹配的名字reg = <0x40>;                //从机地址};
};

2.2i2c中相关的结构体

i2c_client结构体：当驱动进入到probe函数之前，内核会创建i2c_client，

这个i2c_client是用来记录数据的。比如i2c_adapter（控制器驱动的对象）就

被存放到这个结构体中。后面在发消息的时候会用到这个i2c_adapter

https://www.totalphase.com/support/articles/200349176-7-bit-8-bit-and-10-bit-I2C-Slave-Addressing

struct i2c_client {unsigned short flags;     //i2c的标志位  I2C_M_TENunsigned short addr;        //从机地址char name[I2C_NAME_SIZE];  //设备的名struct i2c_adapter *adapter;//控制器的对象
};

i2c_msg结构体：i2c设备驱动和控制器驱动传输数据的时候是通过i2c_msg

结构体完成的。

//消息结构体
struct i2c_msg {__u16 addr;     //从机地址__u16 flags;    //读写标志位 0 写  1读__u16 len;     //消息的长度__u8 *buf;       //消息的首地址
};

2.3封装数据发送数据的过程

2.3.1消息的封装过程

有多少起始位就有多少消息，消息的长度是以字节表示的。

写的消息：

start+(slave addr 7bit 0 1bit)+ack+reg+ack+data+ack+stop

(slave addr 7bit 0 1bit)+reg+data

char wbuf[] = {reg,data};
struct i2c_msg w_msg = {.addr = client->addr,.flags = 0,.len = 2,.buf = wbuf,
};

读的消息：

start+(slave addr 7bit 0 1bit)+ack+reg+ack+

start+(slave addr 7bit 1 1bit)+ack+data+NO ack+stop

char rbuf[] = {reg};
unsigned char val;
struct i2c_msg r_msg[] = {[0] = {.addr = client->addr,.flags = 0,.len = 1,.buf = rbuf,},[1] = {.addr = client->addr,.flags = 1,.len = 1,.buf = &val,},
};

2.3.2消息的发送过程

int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
功能：发送消息
参数：@adap:控制器驱动对象的指针@msgs:消息的首地址@num:消息的个数
返回值：成功返回值等于num,否则就是失败

2.4读取si7006串号和固件号实例

si7006.h

#ifndef __SI7006_H__
#define __SI7006_H__#define GET_SERIAL  _IOR('j',0,int)
#define GET_FIRWARE  _IOR('j',1,int)#define SERIAL_ADDR 0xfcc9
#define FIRWARE_ADDR 0x84b8#endif

si7006.c

#include "si7006.h"
#include <linux/fs.h>
#include <linux/i2c.h>
#include <linux/init.h>
#include <linux/mod_devicetable.h>
#include <linux/module.h>
#include <linux/uaccess.h>
#include <linux/device.h>#define CNAME "si7006"
struct i2c_client* gclient;
int major;
const int count = 1;
struct class* cls;
struct device* dev;int i2c_read_serial_firware(unsigned short reg)
{int ret;unsigned char val;char r_buf[] = { reg >> 8, reg & 0xff };// 1.封装消息结构体struct i2c_msg r_msg[] = {[0] = {.addr = gclient->addr,.flags = 0,.len = 2,.buf = r_buf,},[1] = {.addr = gclient->addr,.flags = 1,.len = 1,.buf = &val,},};// 2.发送消息ret = i2c_transfer(gclient->adapter, r_msg, ARRAY_SIZE(r_msg));if (ret != ARRAY_SIZE(r_msg)) {printk("i2c read error\n");return -EAGAIN;}return val;
}
int si7006_open(struct inode* inode, struct file* file)
{return 0;
}
long si7006_ioctl(struct file* filp,unsigned int cmd, unsigned long arg)
{int data, ret;switch (cmd) {case GET_SERIAL:data = i2c_read_serial_firware(SERIAL_ADDR);if (data < 0) {printk("i2c read serial error\n");return data;}ret = copy_to_user((void*)arg, &data, sizeof(int));if (ret) {printk("copy data serial to user error\n");return -EIO;}break;case GET_FIRWARE:data = i2c_read_serial_firware(FIRWARE_ADDR);if (data < 0) {printk("i2c read firware error\n");return data;}ret = copy_to_user((void*)arg, &data, sizeof(int));if (ret) {printk("copy data firware to user error\n");return -EIO;}break;}return 0;
}
int si7006_close(struct inode* inode, struct file* file)
{return 0;
}
static struct file_operations fops = {.open = si7006_open,.unlocked_ioctl = si7006_ioctl,.release = si7006_close,
};int si7006_probe(struct i2c_client* client,const struct i2c_device_id* id)
{gclient = client;printk("%s:%d\n", __func__, __LINE__);// 1.注册字符设备驱动major = register_chrdev(0, CNAME, &fops);if (major < 0) {printk("register chrdev error\n");return -EAGAIN;}// 2.创建设备节点cls = class_create(THIS_MODULE, CNAME);if (IS_ERR(cls)) {printk("class create error\n");return PTR_ERR(cls);}dev = device_create(cls, NULL, MKDEV(major, 0), NULL, CNAME);if (IS_ERR(dev)) {printk("device create error\n");return PTR_ERR(dev);}return 0;
}
int si7006_remove(struct i2c_client* client)
{printk("%s:%d\n", __func__, __LINE__);device_destroy(cls, MKDEV(major, 0));class_destroy(cls);unregister_chrdev(major, CNAME);return 0;
}struct of_device_id oftable[] = {{.compatible = "hqyj,si7006",},{}
};
MODULE_DEVICE_TABLE(of, oftable);struct i2c_driver si7006 = {.probe = si7006_probe,.remove = si7006_remove,.driver = {.name = "si7006123456",.of_match_table = oftable,}
};
module_i2c_driver(si7006);
MODULE_LICENSE("GPL");

test.c

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include "si7006.h"int main(int argc, const char *argv[])
{int fd,serial,firware;if((fd = open("/dev/si7006",O_RDWR)) < 0){perror("open error");exit(EXIT_FAILURE);}ioctl(fd,GET_SERIAL,&serial);ioctl(fd,GET_FIRWARE,&firware);printf("serial = %#x,firware = %#x\n",serial,firware);close(fd);return 0;
}

2.5读取si7006温湿度实例