一、前言
上一篇博文記錄了使用wiringPi提供的串口驅動wiringSerial.c wiringSerial.h，並基於該驅動對串口進行簡單的通信，測試中發現該串口的驅動比較簡單，接收數據會存在分包的現象，另外一點是串口配置只提供了波特率參數配置，未提供其他如校驗、數據位和停止位驅動。這一片博文主要是對驅動進行修改。
二、修改驅動
wiringPi的驅動源碼可以在https://projects.drogon.net/raspberry-pi/wiringpi/中下載。找到wiringSerial.c 和 wiringSerial.h兩個文件，複製一份並重名命爲wiringSerial_Driver.c wiringSerial_Driver.h。以便於我們修改。
具體地，修改包括初始化函數、串口接收函數和串口發送函數。
2.1 初始化函數修改
可以同時初始化波特率、停止位、校驗位和數據位。參數gsfd爲全局定義的串口打開設備ID號，static int gsfd;
linux串口編程主要是對termios進行初始化，需要包含頭文件：#include <termios.h>
在Rpi3B中輸入：
man termios
可以查看termios的描述，具體不多講，看說明文檔即可，以下僅羅列部分：
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.
那麼具體的驅動可以改寫成一下內容：
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 ;
}
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 接收函數修改
實際測試時發現wiringSerial的接收函數serialDataAvail緩存大小隻有8字符，因此，超過8字符的數據將會分包，接收函數修改主要是對數據進行拼包，具體實現如下：
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 發送函數修改
發送函數基本和wiringSerial提供的驅動一致，只是將傳入的設備ID用全局變量替代，這樣在使用該函數時無需輸入串口的ID。具體修改如下：
void myserialDataSend(const char * ptr,int size)
{
while(size--)
{
serialPutchar(gsfd,*(ptr++));
}
}
三、編譯測試
對應的頭文件增加函數的聲明，編寫main.c測試文件：
#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);
}
}
}
}
編寫makefile，進行編譯並運行如下：
可以看到，數據以及拼包成功，說明驅動修改有效。