//----------------------------------------------------
//AUTHOR: lanyang123456
//DATE:2012-02-28
//----------------------------------------------------
内核版本2.6.18 或2.6.32 或 3.1.10
Linux内核源码中自带USB转串口驱动
目录为drivers/usb/serial,
一般情况下，系统将USB转串口驱动编译成内核模块，需要时自动加载到内核中。
将GPS设备(USB接口)插入到计算机中，系统自动识别设备,将USB转为串口，并输出信息。
命令行下查看，#dmesg
[ 909.159038] usb 2-4: new full speed USB device number 5 using ohci_hcd
[ 909.338158] usb 2-4: New USB device found, idVendor=067b, idProduct=2303
[ 909.338166] usb 2-4: New USB device strings: Mfr=0, Product=0, SerialNumber=0
[ 909.558764] USB Serial support registered for pl2303
[ 909.559656] pl2303 2-4:1.0: pl2303 converter detected
[ 909.594064] usb 2-4: pl2303 converter now attached to ttyUSB0
[ 909.594866] usbcore: registered new interface driver pl2303
[ 909.594872] pl2303: Prolific PL2303 USB to serial adaptor driver
#lsmod 可以查看新增加了模块,pl2303(GPS设备是pl2303芯片，大约多于70%的GPS设备是使用Prolific pl2303 driver这个驱动的。)
查看目录 /dev
通过命令ls -l /dev/ttyUSB0
crw-rw---- 1 root dialout 188,0……/dev/ttyUSB0
内核2.6.18系统下
直接通过ttyUSB0读GPS数据
程序如下
#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;
char buf[1024];
fd1 = open("/dev/ttyUSB0", O_RDWR);//打开串口
if (fd1 == -1)
exit(1);
nset1 = set_opt(fd1,4800, 8, 'N', 1);//设置串口属性
if (nset1 == -1)
exit(1);
while(1)
{
memset(buf,0,1024);
nread = read(fd1, buf, 1024);//读串口
if (nread > 0){
printf("\n GPS DATALen=%d\n",nread);
buf[nread] = '\0';
printf( "GPS %s\n", buf); //输出所读数据
}
sleep(2);//睡眠，等待数据多一点
}
close(fd1);
return 0;
}
一次读的结果如下
GPS DATALen=395
GPS $GPGGA,000531.979,0000.0000,N,00000.0000,E,0,00,50.0,0.0,M,0.0,M,0.0,0000*76
$GPGSA,A,1,,,,,,,,,,,,,50.0,50.0,50.0*05
$GPGSV,1,1,01,02,00,000,00*4A
$GPRMC,000531.979,V,0000.0000,N,00000.0000,E,,,270621,,*14
$GPVTG,,T,,M,,N,,K*4E
$GPGGA,000532.979,0000.0000,N,00000.0000,E,0,00,50.0,0.0,M,0.0,M,0.0,0000*75
$GPRMC,000532.979,V,0000.0000,N,00000.0000,E,,,270621,,*17
$GPVTG,,T,,M,,N,,K*4E
当在内核版本为2.6.32
运行程序，读到的数据长度为0
在3.1.10下
运行程序时，程序停在open函数这，不能往下运行
曾经怀疑是USB转串口驱动有问题，自己一琢磨，不是驱动的问题，内核版本越新，驱动更完善。所以考虑应用程序中，对串口操作函数的参数问题。
解决办法：
将open 函数改为
open(“/dev/ttyUSB0”,O_RDWR|O_NONBLOCK);
程序运行即可正常。
参考：
http://hi.baidu.com/%CD%FE%B5%C4%C9%FA%BB%EE/blog/item/5cae0e2749c7c71b8a82a135.html
http://linux.chinaunix.net/techdoc/develop/2007/11/15/972357.shtml
转载请注明出处。谢谢！