linux下串口读写问题 read 一次读不全
我要在本机(linux)串口上进行读写，一开始时发送接收都正常，但是我用windos下的“串口调试助手”发送给我的程序时必须要加上回车换行，否则read函数不返回，后来google了一下，又添加了2条语句设置串口（代码在下面说明），现在收数据可以不用加回车换行了，但是每次read返回的数据都不完整，比如我发了20个字符，read先是读取了8个字符到缓冲区，然后又读取剩下的字符。有没有什么办法可以一次读取全部的，或者可以判断数据还没有收完，接着read，直到结束.
int speed_arr[] = { B38400, B19200, B9600, B4800, B2400, B1200, B300,
B38400, B19200, B9600, B4800, B2400, B1200, B300,};
int name_arr[] = {38400, 19200, 9600, 4800, 2400, 1200, 300, 38400,
19200, 9600, 4800, 2400, 1200, 300,};
/**
*@brief Set Serial Port BitRate
*@param fd Type : int The File Description of Serial Port
*@param speed Type : int Serial Speed
*@return void
*/
void set_speed(int fd, int speed)
{
int i;
int status;
struct termios Opt;
tcgetattr(fd, &Opt);
for( i=0; i < (sizeof(speed_arr) / sizeof(int)); i++ )
{
if (speed == name_arr[i])
{
tcflush(fd, TCIOFLUSH);
cfsetispeed(&Opt, speed_arr[i]);
cfsetospeed(&Opt, speed_arr[i]);
status = tcsetattr(fd, TCSANOW, &Opt);
if (status != 0)
{
perror( "tcsetattr fd ");
return;
}
tcflush(fd,TCIOFLUSH);
}
}
}
/**
*@brief Set Serial Port Databits, Stopbits and Parity.
*@param fd Type: int The File Description of Serial Port
*@param databits Type: int Databits 7 or 8
*@param stopbits Type: int Stopbits 1 or 2
*@param parity Type: int Parity Type: n,N,e,E,o,O,s,S
*/
int set_Parity(int fd,int databits,int stopbits,int parity)
{
struct termios options;
if ( tcgetattr( fd,&options) != 0)
{
perror( "SetupSerial 1 ");
return(-1);
}
options.c_cflag &= ~CSIZE;
switch (databits) /*Set Datebits*/
{
case 7:
options.c_cflag |= CS7;
break;
case 8:
options.c_cflag |= CS8;
break;
default:
fprintf(stderr, "Unsupported data size\n ");
return(-1);
}
switch (parity) /*Set Parity*/
{
case 'n ':
case 'N ':
options.c_cflag &= ~PARENB; /* Clear parity enable */
options.c_iflag &= ~INPCK; /* Enable parity checking */
break;
case 'o ':
case 'O ':
options.c_cflag |= (PARODD | PARENB); /* Odd Checking*/
options.c_iflag |= INPCK; /* Disnable parity checking */
break;
case 'e ':
case 'E ':
options.c_cflag |= PARENB; /* Enable parity */
options.c_cflag &= ~PARODD; /* Even Checking*/
options.c_iflag |= INPCK; /* Disnable parity checking */
break;
case 'S ':
case 's ': /*as no parity*/
options.c_cflag &= ~PARENB;
options.c_cflag &= ~CSTOPB;
break;
default:
fprintf(stderr, "Unsupported parity\n ");
return(-1);
}
switch (stopbits) /*Set Stobits*/
{
case 1:
options.c_cflag &= ~CSTOPB;
break;
case 2:
options.c_cflag |= CSTOPB;
break;
default:
fprintf(stderr, "Unsupported stop bits\n ");
return(-1);
}
/* Set input parity option */
if (parity != 'n ')
options.c_iflag |= INPCK;
/*以下两句添加后发送方可以不加回车换行，但是read读取不完整*/
options.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG); /*Input*/
options.c_oflag &= ~OPOST; /*Output*/
tcflush(fd,TCIFLUSH);
options.c_cc[VTIME] = 150; /* Timeout in 15 seconds*/
options.c_cc[VMIN] = 0; /* Update the options and do it NOW */
if (tcsetattr(fd,TCSANOW,&options) != 0)
{
perror( "SetupSerial 3 ");
return(-1);
}
return(0);
}
int main (int argc, char *argv[])
{
char buffer[512]= " ";
int ser_fd = open( "/dev/ttyS1 ",O_RDWR | O_NOCTTY);
if ( -1 == ser_fd)
{
perror( "Cannot Open Serial Port ");
return(-1);
}
set_speed(ser_fd,19200);
if ( -1 == set_Parity(ser_fd,7,1, 'E ') )
{
printf( "Set Parity Error\n ");
close(ser_fd);
exit (-1);
}
while( 1 )
{
nread = read( ser_fd, buffer, sizeof(buffer));
if ( nread < 0 )
perror( "read from Serial Port Error:\n ");
}
}
[解决办法]
int qstatus;
ioctl(ser_fd, FIONREAD, &qstatus);
看qstatus的值,其值为串口缓冲内有多少数据可多.
你可用先判断数据够不够你要的在去读.
[解决办法]
/*//////////////////////////////////////////////////////////////////////////////
Function: CSerial
Description: Constructor of class CSerial
Calls: ---
Called By: ---
Input: ---
Output: ---
Return: ---
Others: public
//////////////////////////////////////////////////////////////////////////////*/
CSerial::CSerial ( void )
{
m_cDataBit = 8;
m_cParityBit = 0;
m_cStopBit = 1;
m_cFlow = 0;
m_hCom = -1;
}
/*//////////////////////////////////////////////////////////////////////////////
Function: ~CSerial
Description: Destructor of class CSerial
Calls: ---
Called By: ---
Input: ---
Output: ---
Return: ---
Others: public
//////////////////////////////////////////////////////////////////////////////*/
CSerial::~CSerial ( void )
{
if ( m_hCom != -1 )
close(m_hCom);
}
/*//////////////////////////////////////////////////////////////////////////////
Function: Initial
Description: 串口初始化
Calls: ---
Called By: ---
Input: tty: 串口号 0~n 代表串口1~n+1
baut: 波特率 如B9600, 参数为系统定义的常量
Output: ---
Return: true: 初始化成功 false:失败
Others: public
//////////////////////////////////////////////////////////////////////////////*/
bool CSerial::Initial ( int tty, int baut )
{
termios termios_old, termios_new;
if ( m_hCom != -1 )
close(m_hCom);
sprintf ( m_sTTY, "/dev/ttyS%d ", tty );
//打开串口
//O_NOCTTY: 通知系统，该程序不想成为此端口的“控制终端”。
// 如果不设，则任何输入（如键盘的中断信号）都会影响程序的运行
//O_NODELAY: 该程序不关注DCD信号线所处的状态，即不管对端设备是在运行还是挂起。
// 若不设置，则程序会被置为睡眠状态，直到DCD信号低为止(可能无流控制时无效)
m_hCom = open ( m_sTTY, O_RDWR | O_NOCTTY | O_NDELAY );
if ( m_hCom == -1 )
return false;
m_nBaut = baut;
bzero(&termios_old, sizeof(termios_old));
bzero(&termios_new, sizeof(termios_new));
cfmakeraw(&termios_new);
tcgetattr(m_hCom, &termios_old);//get the serial port attributions
//------------设置端口属性----------------
//baudrates
cfsetispeed(&termios_new, m_nBaut); //填入串口输入端的波特率
cfsetospeed(&termios_new, m_nBaut); //填入串口输出端的波特率
termios_new.c_cflag |= CLOCAL; //控制模式，保证程序不会成为端口的占有者
termios_new.c_cflag |= CREAD;//控制模式，使能端口读取输入的数据
// 控制模式，flow control
switch(m_cFlow)
{
case 1:
termios_new.c_cflag |= CRTSCTS; //hardware flow control
break;
case 2:
termios_new.c_iflag |= IXON | IXOFF |IXANY; //software flow control
break;
default:
termios_new.c_cflag &= ~CRTSCTS; //no flow control
break;
}
//控制模式，data bits
termios_new.c_cflag &= ~CSIZE; //控制模式，屏蔽字符大小位
switch(m_cDataBit)
{
case 5:
termios_new.c_cflag |= CS5;
case 6:
termios_new.c_cflag |= CS6;
case 7:
termios_new.c_cflag |= CS7;
default:
termios_new.c_cflag |= CS8;
}
//控制模式 parity check
switch(m_cParityBit)
{
case 1:
termios_new.c_cflag |= PARENB; //odd check
termios_new.c_cflag &= ~PARODD;
break;
case 2:
termios_new.c_cflag |= PARENB; //even check
termios_new.c_cflag |= PARODD;
break;
default:
termios_new.c_cflag &= ~PARENB; //no parity check
break;
}
//控制模式，stop bits
switch ( m_cStopBit )
{
case 2:
termios_new.c_cflag |= CSTOPB; //2 stop bits
break;
default:
termios_new.c_cflag &= ~CSTOPB; //1 stop bits
break;
}
//other attributions default
termios_new.c_oflag &= ~OPOST;//输出模式，原始数据输出
termios_new.c_cc[VMIN] = 1;//控制字符, 所要读取字符的最小数量
termios_new.c_cc[VTIME] = 1;//控制字符, 读取第一个字符的等待时间unit: (1/10)second
tcflush(m_hCom, TCIFLUSH);//溢出的数据可以接收，但不读
tcsetattr(m_hCom, TCSANOW, &termios_new);//设置新属性，TCSANOW：所有改变立即生效tcgetattr(fdcom, &termios_old);
return true;
}
/*//////////////////////////////////////////////////////////////////////////////
Function: Cleanup
Description: 串口清理
Calls: ---
Called By: ---
Input: ---
Output: ---
Return: ---
Others: public
//////////////////////////////////////////////////////////////////////////////*/
void CSerial::Cleanup ( void )
{
if ( m_hCom != -1 )
close(m_hCom);
}
/*//////////////////////////////////////////////////////////////////////////////
Function: Send
Description: 通过串口向外发N个字节
Calls: ---
Called By: ---
Input: data: 发送字节首地址
datalen: 发送字节长度
Output: ---
Return: -1: 发送失败 > 0:已经发送的字节
Others: public
//////////////////////////////////////////////////////////////////////////////*/
int CSerial::Send ( char *data, int datalen )
{
if ( m_hCom == -1 ) //串口未被打开
return -1;
int len = 0;
len = write( m_hCom, data, datalen);//实际写入的长度
if(len == datalen)
{
return len;
}
else
{
tcflush(m_hCom, TCOFLUSH);
return -1;
}
}
/*//////////////////////////////////////////////////////////////////////////////
Function: Receive
Description: 从串口读入N个字节
Calls: ---
Called By: ---
Input: data: 读入字节首地址
datalen: 发送字节长度
timeout: 超时时间,单位秒 <0 时代表无限期等待
Output: ---
Return: -1: 读入失败 > 0:已经读入的字节
Others: public, timeout默认-1
//////////////////////////////////////////////////////////////////////////////*/
int CSerial::Receive ( char *data, int datalen, int timeout )
{
int readlen, fs_sel;
fd_setfs_read;
struct timeval tv_timeout;
if ( m_hCom == -1 ) //串口未被打开
return -1;
FD_ZERO(&fs_read);
FD_SET(m_hCom, &fs_read);
if ( timeout > 0 )
{
tv_timeout.tv_sec = timeout; //time out : unit sec
tv_timeout.tv_usec = 0;
fs_sel = select( m_hCom+1, &fs_read, NULL, NULL, &tv_timeout);
}
else//死等
{
fs_sel = select( m_hCom+1, &fs_read, NULL, NULL, NULL );
}
if(fs_sel)
{
readlen = read(m_hCom, data, datalen);
return readlen;
}
else
{
return(-1);
}
return readlen;
}
