树莓派UART串口编程--使用wiringPi库-C开发【2-修改驱动】

本文链接：https://blog.youkuaiyun.com/u010058695/article/details/100583943

一、前言

上一篇博文记录了使用wiringPi提供的串口驱动wiringSerial.c wiringSerial.h，并基于该驱动对串口进行简单的通信，测试中发现该串口的驱动比较简单，接收数据会存在分包的现象，另外一点是串口配置只提供了波特率参数配置，未提供其他如校验、数据位和停止位驱动。这一片博文主要是对驱动进行修改。

二、修改驱动

wiringPi的驱动源码可以在https://projects.drogon.net/raspberry-pi/wiringpi/中下载。找到wiringSerial.c 和 wiringSerial.h两个文件，复制一份并重名命为wiringSerial_Driver.c wiringSerial_Driver.h。以便于我们修改。

具体地，修改包括初始化函数、串口接收函数和串口发送函数。

2.1 初始化函数修改

可以同时初始化波特率、停止位、校验位和数据位。参数gsfd为全局定义的串口打开设备ID号，static int gsfd;

linux串口编程主要是对termios进行初始化，需要包含头文件：#include <termios.h>

在Rpi3B中输入：

man termios

可以查看termios的描述，具体不多讲，看说明文档即可，以下仅罗列部分：


NAME
       termios,  tcgetattr, tcsetattr, tcsendbreak, tcdrain, tcflush, tcflow, cfmakeraw, cfgetospeed, cfgetispeed, cfsetispeed, cfsetospeed, cfsetspeed - get
       and set terminal attributes, line control, get and set baud rate

SYNOPSIS
       #include <termios.h>
       #include <unistd.h>
       int tcgetattr(int fd, struct termios *termios_p);
       int tcsetattr(int fd, int optional_actions,
                     const struct termios *termios_p);
       int tcsendbreak(int fd, int duration);
       int tcdrain(int fd);
       int tcflush(int fd, int queue_selector);
       int tcflow(int fd, int action);
       void cfmakeraw(struct termios *termios_p);
       speed_t cfgetispeed(const struct termios *termios_p);
       speed_t cfgetospeed(const struct termios *termios_p);
       int cfsetispeed(struct termios *termios_p, speed_t speed);
       int cfsetospeed(struct termios *termios_p, speed_t speed);
       int cfsetspeed(struct termios *termios_p, speed_t speed);
   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
       cfsetspeed(), cfmakeraw(): _BSD_SOURCE

DESCRIPTION
       The termios functions describe a general terminal interface that is provided to control asynchronous communications ports.
   The termios structure
       Many of the functions described here have a termios_p argument that is a pointer to a termios structure.  This structure contains at least the follow‐
       ing members:
           tcflag_t c_iflag;      /* input modes */
           tcflag_t c_oflag;      /* output modes */
           tcflag_t c_cflag;      /* control modes */
           tcflag_t c_lflag;      /* local modes */
           cc_t     c_cc[NCCS];   /* special characters */
       The  values  that  may be assigned to these fields are described below.  In the case of the first four bit-mask fields, the definitions of some of the
       associated flags that may be set are exposed only if a specific feature test macro (see feature_test_macros(7))  is  defined,  as  noted  in  brackets
       ("[]").
       In  the  descriptions  below,  "not  in  POSIX"  means that the value is not specified in POSIX.1-2001, and "XSI" means that the value is specified in
       POSIX.1-2001 as part of the XSI extension.

那么具体的驱动可以改写成一下内容：

int myserialOpen (const char *device, const int baud, const int nbit, const char parity, const int nstop)
{
  struct termios options ;
  speed_t myBaud ;
  int     status;

  switch (baud)
  {
    case      50:	myBaud =      B50 ; break ;
    case      75:	myBaud =      B75 ; break ;
    case     110:	myBaud =     B110 ; break ;
    case     134:	myBaud =     B134 ; break ;
    case     150:	myBaud =     B150 ; break ;
    case     200:	myBaud =     B200 ; break ;
    case     300:	myBaud =     B300 ; break ;
    case     600:	myBaud =     B600 ; break ;
    case    1200:	myBaud =    B1200 ; break ;
    case    1800:	myBaud =    B1800 ; break ;
    case    2400:	myBaud =    B2400 ; break ;
    case    4800:	myBaud =    B4800 ; break ;
    case    9600:	myBaud =    B9600 ; break ;
    case   19200:	myBaud =   B19200 ; break ;
    case   38400:	myBaud =   B38400 ; break ;
    case   57600:	myBaud =   B57600 ; break ;
    case  115200:	myBaud =  B115200 ; break ;
    case  230400:	myBaud =  B230400 ; break ;
    case  460800:	myBaud =  B460800 ; break ;
    case  500000:	myBaud =  B500000 ; break ;
    case  576000:	myBaud =  B576000 ; break ;
    case  921600:	myBaud =  B921600 ; break ;
    case 1000000:	myBaud = B1000000 ; break ;
    case 1152000:	myBaud = B1152000 ; break ;
    case 1500000:	myBaud = B1500000 ; break ;
    case 2000000:	myBaud = B2000000 ; break ;
    case 2500000:	myBaud = B2500000 ; break ;
    case 3000000:	myBaud = B3000000 ; break ;
    case 3500000:	myBaud = B3500000 ; break ;
    case 4000000:	myBaud = B4000000 ; break ;

    default:
      return -2 ;
  }

  /* 有O_NONBLOCK 即为非阻塞方式，默认阻塞方式，等待vim vtime*/

  if ((gsfd = open (device, O_RDWR | O_NOCTTY | O_NDELAY | O_NONBLOCK)) == -1)
    return -1 ;

  fcntl (gsfd, F_SETFL, O_RDWR) ;

// Get and modify current options:

  tcgetattr (gsfd, &options) ;

    cfmakeraw   (&options) ;
    cfsetispeed (&options, myBaud) ;
    cfsetospeed (&options, myBaud) ;
    
    //data bit
    switch (nbit)
    {
        case 7: options.c_cflag &= ~CSIZE ; options.c_cflag |= CS7; break;
        case 8: options.c_cflag &= ~CSIZE ; options.c_cflag |= CS8; break;
        default:  options.c_cflag &= ~CSIZE ; options.c_cflag |= CS8; break;
    }
    //data parity
    switch(parity)  
    {
      case 'n':
      case 'N':
	      options.c_cflag &= ~PARENB ;
	      options.c_cflag &= ~INPCK;
	      break;
      case 'o':
      case 'O': 
	      options.c_cflag |= PARENB ;
	      options.c_cflag |= PARODD ;
	      options.c_cflag |= INPCK  ;
	      options.c_cflag |= ISTRIP	; 
	      break;
      case 'e':
      case 'E': 
	      options.c_cflag |= PARENB ;
	      options.c_cflag &= ~PARODD;
	      options.c_cflag |= INPCK 	;
	      options.c_cflag |= ISTRIP	;
	      break;
      default:
	      options.c_cflag &= ~PARENB ;
	      options.c_cflag &= ~INPCK;
	      break;
   }
   //data stopbits
    switch(nstop)
    {
      case 1: options.c_cflag &= ~CSTOPB ; break;
      case 2: options.c_cflag |= CSTOPB ;  break; 
      default: options.c_cflag &= ~CSTOPB ; break;    
    }

    options.c_cflag |= (CLOCAL | CREAD) ;
    options.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG) ;
    options.c_oflag &= ~OPOST ;

    options.c_cc [VMIN]  =   0 ;
    options.c_cc [VTIME] = 10 ;	// 0.5 seconds (100 deciseconds)

  tcsetattr (gsfd, TCSANOW, &options) ;

  ioctl (gsfd, TIOCMGET, &status);

  status |= TIOCM_DTR ;
  status |= TIOCM_RTS ;

  ioctl (gsfd, TIOCMSET, &status);

  usleep (10000) ;	// 10mS

  return gsfd ;
}

2.2 接收函数修改

提一下，Linux串口接收主要由阻塞和非阻塞接收两种方式，关于如何配置Linux串口驱动可以参考这篇博文：Linux 使用fcntl c_cc[VMIN] c_cc[CTIME]设置串口阻塞与非阻塞读取数据

实际测试时发现wiringSerial的接收函数serialDataAvail缓存大小只有8字符，因此，超过8字符的数据将会分包，接收函数修改主要是对数据进行拼包，具体实现如下：

int myserialDataRead( char *buf,  int * size)
{
  int size_i,i;
  i = 0;
  size_i = 0;
  while(1)
  {
  	i = read(gsfd, buf+size_i ,1024);
  	size_i += i;
  	if(i == 8)
  	{
  		
  	}
  	else if(i>0 && i <= 8)
  	{
  		*size = size_i;
  		return 0;
  	}
  	else
  	{
  		return -1;
  	}
  }
}

2.3 发送函数修改

发送函数基本和wiringSerial提供的驱动一致，只是将传入的设备ID用全局变量替代，这样在使用该函数时无需输入串口的ID。具体修改如下：

void myserialDataSend(const char * ptr,int size)
{
  while(size--)
  {
    serialPutchar(gsfd,*(ptr++));
  } 
}

三、编译测试

对应的头文件增加函数的声明，编写main.c测试文件：

#include<wiringPi.h>
#include"wiringSerial_Driver.h"
#include<stdio.h>
#include<string.h>

int main()
{
    int filedevid;
    int recbytenum;
    int rxflag;
    int i;
    char buf[1024];
    char bufprintf[1024];
    memset(buf,0,1024);
    memset(bufprintf,0,1024);
    wiringPiSetup();
    if((filedevid=myserialOpen("/dev/ttyAMA0",115200,8,'E',1))<0)
    {
        printf("/dev/ttyAMA0 Open Faild\r\n");
        return -1;
    }
    else
    {
        printf("/dev/ttyAMA0 Open with 115200,115200,8,'E',1, success\r\n");
        while(1)
        {
            rxflag = myserialDataRead(buf,&recbytenum);
            if(rxflag != -1)
            {
            	printf("Rpi3 uart rx %d byte: %s\r\n",recbytenum,buf);
                sprintf(bufprintf,"Rpi3 uart Tx %d byte: %s\r\n",recbytenum,buf);
                myserialDataSend(bufprintf, recbytenum);
            }
        }
    }
}

编写makefile，进行编译并运行如下：