comport.c

一个串口通讯的c语言的例子

// 对串口的操作
#define ETX  0x03
#define STX  0x02

// 获得当前时间
long getCurrTime(){
	long currTime; 
	time( &currTime );
    //printf( "Time in seconds since UTC 1/1/70:\t%ld\n", currTime );
	return currTime;
}

//open a COM2 port :tty2a
int openPort(char *dev){
	int fd; /* File descriptor for the port */
	fd = open(dev, O_RDWR | O_NOCTTY | O_NDELAY);
	
	if (fd == -1){	// Could not open the port.
		printf("Unable to open %s port\n",dev);
		return -1;
	}
//	printf("Opened a serial port: %s\n",dev);
	return fd;
}

//close Port
void closePort(int fd){
	close(fd);
}

//read data from serial port and check data 
int readPort(int fd,unsigned char *buffer,int *length){
	int	i, n=0, len, timeout = 0;
	unsigned char lrc = '\x00';
	long currTime1,currTime2;
	*length = 0;

	currTime1 = getCurrTime();

	for (i=0;i<6;i++) {
		while (read(fd,&buffer[n],1) <= 0 ) {
//			printf("\nNot data\n" );
//			printf("i=[%02x]", i);
			currTime2 = getCurrTime();
//			printf("\ntime=%d-%d=%d\n",currTime2,currTime1,currTime2-currTime1);
			if( (currTime2-currTime1)>timeout){
//				printf("\nTime out=%d\n", currTime2-currTime1);
				return( 0 );
			}
		}
//		printf("[%02x]", buffer[n]);
		fflush(stdout);

		switch (i) {
			case 0:																// 启始位‘02’
				if (buffer[0] <> STX)					i--;
				else			n = 1;
				break;
			case 1:																// 长度（两位）
				len = 0;
			case 2:
				if (((buffer[n] & 0xf0) >> 4) > 9)		return -1;
				len = len * 10 + ((buffer[n] & 0xf0) >> 4);

				if ((buffer[n] & 0x0f) > 9)				return -1;
				len = len * 10 + (buffer[n] & 0x0f);

				lrc ^= buffer[n++];
				break;
			case 3:																// 数据
				lrc ^= buffer[n++];
				if (--len > 0)		i--;
				break;
			case 4:																// 停止位‘03’
				if (buffer[n] <> ETX)					return -1;
				lrc ^= buffer[n++];
				break;
			case 5:																// 校验和
				if (lrc != buffer[n++])					return -2;
				break;
		}
	}
	*length = n;
	return n ;
}

//write to serial port
void writePort(int fd,unsigned char *buffer,int len){
	int  k;

	for ( k = 0; k < len; k++) {
//		printf("[%02x]",buffer[k]);
		while ( write(fd, buffer + k, 1) != 1 );
	}
}

int setAttr(int fdread){
	struct termio comtty;
	
	if(ioctl(fdread,TCGETA,&comtty)){
		printf("\n[ERROR]: Get tty error\n" );
		return (-1);
	}

	comtty.c_iflag = 1;
	comtty.c_oflag = 0;
	comtty.c_cflag =(B9600|CS8|CREAD|HUPCL|CLOCAL);
	comtty.c_lflag = 0;
	comtty.c_cc[VMIN]=0;
	comtty.c_cc[VTIME]=1;

	if(ioctl(fdread,TCSETA,&comtty)==-1){
		printf("\n[ERROR]: Set tty error\n" );
		return (-1);
	}
}

int setNowait(int fd){
	struct termio term_attr;
	
	if(fd<0) return -1;
	
	if(ioctl(fd,TCGETA,&term_attr)<0)
		return -1;
	
	term_attr.c_cc[VMIN]=0;
	term_attr.c_cc[VTIME]=1;
	
	if(ioctl(fd,TCSETAW,&term_attr)<0)
		return -1;
	
	return 0;
}