usb 1-1.1: new full-speed USB device number 5 using ehci-pci
usb 1-1.1: New USB device found, idVendor=067b, idProduct=2303
usb 1-1.1: New USB device strings: Mfr=1, Product=2, SerialNumber=0
usb 1-1.1: Product: USB-Serial Controller
usb 1-1.1: Manufacturer: Prolific Technology Inc.
usbcore: registered new interface driver usbserial
usbcore: registered new interface driver usbserial_generic
usbserial: USB Serial support registered for generic
usbcore: registered new interface driver pl2303
usbserial: USB Serial support registered for pl2303
usb 1-1.1: pl2303 converter now attached to ttyUSB0
[root@node3 vincent]# ls -l /dev/ttyUSB0
crw-rw---- 1 root dialout 188, 0 Dec 4 14:38 /dev/ttyUSB0
（连接上的话，下位机会每隔2秒发送一串数字，用windows笔记本进行过调试了，串口线什么的都没问题，但是放一台笔记本在哪里太麻烦了，也浪费一台电脑，刚好旁边有服务器，就插到服务器上去了，服务器的Linux内核的，可是插上去读不出任何数据）
已经显示连上了，波特率什么的也都设置好了，9600, 8, 'N', 1，但是不管用minicom还是网上找的的open，opt_set,read函数去读/dev/ttyUSB0，都读不到任何数据，把read返回值不为0，printf却什么都没有，按字符一个个%d的格式printf，全是0，请问是什么原因，我已经是root权限了。
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<unistd.h>
#include<termios.h>
#include<string.h>
int set_opt(int fd,int nSpeed, int nBits, char nEvent, int nStop)
{
struct termios newtio,oldtio;
if ( tcgetattr( fd,&oldtio) != 0) {
perror("SetupSerial 1");
return -1;
}
bzero( &newtio, sizeof( newtio ) );
newtio.c_cflag |= CLOCAL | CREAD;
newtio.c_cflag &= ~CSIZE;
switch( nBits )
{
case 7:
newtio.c_cflag |= CS7;
break;
case 8:
newtio.c_cflag |= CS8;
break;
}
switch( nEvent )
{
case 'O':
newtio.c_cflag |= PARENB;
newtio.c_cflag |= PARODD;
newtio.c_iflag |= (INPCK | ISTRIP);
break;
case 'E':
newtio.c_iflag |= (INPCK | ISTRIP);
newtio.c_cflag |= PARENB;
newtio.c_cflag &= ~PARODD;
break;
case 'N':
newtio.c_cflag &= ~PARENB;
break;
}
switch( nSpeed )
{
case 2400:
cfsetispeed(&newtio, B2400);
cfsetospeed(&newtio, B2400);
break;
case 4800:
cfsetispeed(&newtio, B4800);
cfsetospeed(&newtio, B4800);
break;
case 9600:
cfsetispeed(&newtio, B9600);
cfsetospeed(&newtio, B9600);
break;
case 115200:
cfsetispeed(&newtio, B115200);
cfsetospeed(&newtio, B115200);
break;
case 460800:
cfsetispeed(&newtio, B460800);
cfsetospeed(&newtio, B460800);
break;
default:
cfsetispeed(&newtio, B9600);
cfsetospeed(&newtio, B9600);
break;
}
if( nStop == 1 )
newtio.c_cflag &= ~CSTOPB;
else if ( nStop == 2 )
newtio.c_cflag |= CSTOPB;
newtio.c_cc[VTIME] = 0;//重要
newtio.c_cc[VMIN] = 100;//返回的最小值 重要
tcflush(fd,TCIFLUSH);
if((tcsetattr(fd,TCSANOW,&newtio))!=0)
{
perror("com set error");
return -1;
}
// printf("set done!\n\r");
return 0;
}
int main(void)
{
int fd1,nset1,nread;
FILE *fp;
char buf[1024];
//fp=fopen("buf.txt","w");
printf("opening ttyUSB0... ...\n");
fd1 = open("/dev/ttyUSB0",O_RDWR|O_NONBLOCK);//打开串口
if (fd1 == -1)
{
printf("fail to open /dev/ttyUSB0\n");
exit(1);
}
printf("success to open /dev/ttyUSB0\n");
printf("setting opt... ...\n");
nset1 = set_opt(fd1,9600, 8, 'N', 1);//设置串口属性
if (nset1 == -1)
{
printf("fail to set opt\n");
exit(1);
}
while (1)
{
memset(buf,0,1024);
nread = read(fd1, buf, 1024);//读串口
if (nread > 0){
printf("Len=%d\n",nread);
//printf("First=%d",buf[0]);
//printf(" Second=%d\n",buf[1]);
buf[nread] = 0;
printf(fp,"%s\n", buf); //输出所读数据
}
sleep(5);//睡眠，等待数据
}
close(fd1);
//fclose(fp);
return 0;
}
------解决思路----------------------
????????nread?=?read(fd1,?buf,?1024);//读串口
????????if?(nread?>?0){
????????????printf("Len=%d\n",nread);?
????????????//printf("First=%d",buf[0]);
????????????//printf("??Second=%d\n",buf[1]);
????????????buf[nread]?=?0;
????????????printf(fp,"%s\n",?buf);?//输出所读数据
????????}
nread返回的值是什么？