Linux 串口编程之GPS

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我是靠谱客的博主任性大白，这篇文章主要介绍Linux 串口编程之GPS，现在分享给大家，希望可以做个参考。

之前编写了一个读取GPS内容的代码，现将之贴出来。此代码中涉及到串口初始化、串口操作的打开、关闭、读写，还涉及到GPS相关协议的解析，如接收到的GPS数据如何处理，如何发送数据到GPS模块等。协议采用的是SIM68VB NMEA协议。

1、串口初始化代码如下：

此函数为设置串口属性如波特率、数据位、校验位、停止位，此函数将串口设置为非阻塞，在读串口时可采用I/O多路复用的机制。

例：configs ="115200,8,1,N" 115200代表波特率，8数据位，1停止位，N无校验

int SetNolockComCfg(int fd, char *configs)
{
   int uBaudRate, databits, stopbits;
   char parity;
   char temp[32];
   char *p1 = NULL, *p2 = NULL;
   int n = 0;
   unsigned int flag = 0;
   unsigned short Speed;
   int stats;
   struct termios options;

/* clear struct for new port settings */
bzero(&options, sizeof (struct termios));

   //波特率
   p1 = configs;
   p2 = strchr(p1, ',');
   n = p2 - p1;
   if (n) {
       strncpy(temp, p1, n);
       temp[n] = '';
       uBaudRate = atoi(temp);
   }
   else
       uBaudRate = COM_BAUDDEF;

   //数据位
   p1 = strchr(p2 + 1, ',');
   n = p1 - (p2 + 1);
   if (n) {
       strncpy(temp, p2 + 1, n);
       temp[n] = '';
       databits = atoi(temp);
   }
   else
       databits = COM_DABITSDEF;

   // 停止位
   p2 = strchr(p1 + 1, ',');
   n = p2 - (p1 + 1);
   if (n) {
       strncpy(temp, p1 + 1, n);
       temp[n] = '';
       stopbits = atoi(temp);
   }
   else
       stopbits = COM_STBITSDEF;

   //校验位
   if (p2 + 1 != NULL) {
       strcpy(temp, p2 + 1);
       parity = temp[0];
   }
   else {
       parity = COM_PARITYDEF;
   }

   //设置波特率
   switch (uBaudRate) {
   case 110:
       Speed = B110;
       break;

   case 300:
       Speed = B300;
       break;

   case 600:
       Speed = B600;
       break;

   case 1200:
       Speed = B1200;
       break;

   case 2400:
       Speed = B2400;
       break;

   case 4800:
       Speed = B4800;
       break;

   case 9600:
       Speed = B9600;
       break;

   case 19200:
       Speed = B19200;
       break;

   case 38400:
       Speed = B38400;
       break;

   case 57600:
       Speed = B57600;
       break;

   case 115200:
       Speed = B115200;
       break;

   case 230400:
       Speed = B230400;
       break;

   case 460800:
       Speed = B460800;
       break;

   case 921600:
       Speed = B921600;
       break;

   default:
       fprintf(stderr, "Unsupported data sizen");
       return -1;
   }

flag |= Speed;

   //设置数据位
   switch (databits) {
   case 5:
       flag |= CS5;
       break;

   case 6:
       flag |= CS6;
       break;

   case 7:
       flag |= CS7;
       break;

   case 8:
       flag |= CS8;
       break;

   default:
       fprintf(stderr, "Unsupported data sizen");
       return -1;

}

   //设置停止位
   switch (stopbits) {
   case 1:
       break;

   case 2:
       flag |= CSTOPB;
       break;

   default:
       fprintf(stderr, "Unsupported stop bitsn");
       return -1;

}

   //设置奇偶校验位
   switch (parity) {
   case 'n':
   case 'N':
       options.c_iflag = IGNPAR;
       break;

   case 'e':
   case 'E':
       flag |= PARENB;
       options.c_iflag = 0;
       break;

   case 'o':
   case 'O':
       flag |= PARENB | PARODD;
       options.c_iflag = 0;
       break;

   case 's':
   case 'S':
       flag |= PARENB | CMSPAR;
       options.c_iflag = 0;
       break;

   case 'm':
   case 'M':
       flag |= PARENB | PARODD | CMSPAR;
       options.c_iflag = 0;
       break;

   default:
       fprintf(stderr, "Unsupported parityn");
       return -1;

}

   options.c_cflag = flag | CREAD | CLOCAL;
   options.c_oflag = 0;
   options.c_lflag = 0;
   options.c_cc[VINTR] = 0;
   options.c_cc[VQUIT] = 0;
   options.c_cc[VERASE] = 0;
   options.c_cc[VKILL] = 0;
   options.c_cc[VEOF] = 4;
   // 100MS 串口等待接收(2S)
   options.c_cc[VTIME] = 0;
   options.c_cc[VMIN] = 0;
   options.c_cc[VSWTC] = 0;
   options.c_cc[VSTART] = 0;
   options.c_cc[VSTOP] = 0;
   options.c_cc[VSUSP] = 0;
   options.c_cc[VEOL] = 0;
   options.c_cc[VREPRINT] = 0;
   options.c_cc[VDISCARD] = 0;
   options.c_cc[VWERASE] = 0;
   options.c_cc[VLNEXT] = 0;
   options.c_cc[VEOL2] = 0;

//刷新输入输出缓冲
tcflush(fd, TCIOFLUSH);

//把设置真正写到串口中去
stats = tcsetattr(fd, TCSANOW, &options);

   if (stats != 0) {
       perror("tcsetattr fd1");
       return -1;

}

return 0;
}
2、GPS相关的数据定义在一个结构体中，如下

struct   stGPS {
   //位置信息有效性
   char   loca_state;
   //东西经
char   we;
   //经度位置
unsigned int   Longitude;
   //南北纬
char   ns;
   //纬度位置
unsigned int Latitude;
//海拔高度
   unsigned int Altitude;
   //距1970-1-1 0:0:0 的秒数
unsigned int Time;
};

3、获取GPS信息的函数如下

相关宏：
#define       GPGGA       "$GPGGA"   //GPS定位系统输出字符串的头部
#define       GPRMC       "$GPRMC"
#define       BDGGA       "$BDGGA"   //北斗定位系统输出字符串的头部
#define       BDRMC       "$BDRMC"

int GetBDGPSData(int   bdgps_fd, struct stGPS   *bdgps, int mode)
{
   int    ret;
   char   read_buf[512] = {0};
   char    *pGGA = NULL, *pRMC = NULL;
   char    gpstime[64] = {0};
   char   altitude[64] = {0};
   char   ns;    //纬度标识
   char   we;       //经度标识
   char   state;   //状态标识
   char   ns_data[16] = {0}; //纬度
   char   we_data[16] = {0};   //经度
   char    date[16] = {0};
   struct   tm    utc_time = {0};
   int    year;
   int    daytime;
   int    err_num;
   int       flag = 0;
   char    str1[10] = {0};
   char    str2[10] = {0};

   switch (mode){
       case   BD_MODE:
           memcpy(str1, BDGGA, sizeof(BDGGA));
           memcpy(str2, BDRMC, sizeof(BDRMC));
           break;
       case   GPS_MODE:
       default:
           memcpy(str1, GPGGA, sizeof(GPGGA));
           memcpy(str2, GPRMC, sizeof(GPRMC));
           break;
   }

   for(err_num=0; err_num<MAX_ERROR; err_num++){
       delay(0, 100);
       ret = read(bdgps_fd, read_buf, sizeof(read_buf));
       pGGA = strstr(read_buf,str1); //在字符串中查找字符串
       pRMC = strstr(read_buf,str2);
       if((ret>150) && pGGA && pRMC){
           flag = 1;
           break;
       }
   }
   if(!flag)
       return -1;

   printf("read num = %d nread_buf: %s n", ret, read_buf);

//根据需求我们需要采集到两次信息

   sscanf(pGGA, "%[^r]", pGGA); //解析字符串
   sscanf(pRMC, "%[^r]", pRMC);

//根据协议解析字符串
   sscanf(pGGA, "%*[^,],%*[^,],%*[^,],%*[^,],%*[^,],%*[^,],%*[^,],%*[^,],%*[^,],%[^,]",altitude);
   // 时间状态纬度 ns 经度 we
   sscanf(pRMC, "%*[^,],%[^,],%c, %[^,],%c,%[^,],%c,%*[^,],%*[^,],%[^,]",
                   gpstime, &state , ns_data, &ns, we_data, &we, date);
   year = atoi(date);
   daytime = atoi(gpstime);

   utc_time.tm_sec = daytime%100;
   utc_time.tm_min = daytime%10000/100 ;
   utc_time.tm_hour = daytime/10000;
   utc_time.tm_mday = year/10000;
   utc_time.tm_mon = year%10000/100;
   utc_time.tm_year = year%100 + 2000;

   bdgps->Longitude = atof(we_data) * 10000;
   bdgps->Latitude = atof(ns_data) * 10000;
   bdgps->loca_state = state;
   bdgps->Altitude   = atof(altitude) * 10000;
   bdgps->ns   = ns;
   bdgps->we   = we;
   bdgps->Time = mktime(&utc_time);

   return 0;
}

4、 main函数，采用select机制读取GPS串口的数据
int main()
{
   int       ret = 0;
   fd_set   readfs;
   int bdgps_fd, maxfd;
   int    err_num = 0;

struct   stGPS   bdgps = {0};
   struct timeval timeout={1, 0};

   bdgps_fd = open("/dev/ttyS1", O_RDWR);
   if(bdgps_fd < 0){
       perror("open ttyS1");
       return -1;
   }

   //设置为非阻塞
   ret = SetNolockComCfg(bdgps_fd, CONFIG);
   if(ret)
       return -1;

   while(1){
       FD_ZERO(&readfs);
       FD_SET(bdgps_fd, &readfs);
       maxfd = bdgps_fd + 1;
       ret = select(maxfd, &readfs, NULL, NULL, &timeout);
       if(ret < 0){
           perror("select"); //允许出错三次
           err_num++;
           if(err_num < MAX_ERROR)
               continue;
           else
               break;
       }
       err_num = 0;

       if(FD_ISSET(bdgps_fd, &readfs)){
           ret = GetBDGPSData(bdgps_fd, &bdgps, GPS_MODE);
           if(ret)
               continue;

           printf("bdgps->state: %c n",bdgps.loca_state);
           printf("bdgps->we: %c n",bdgps.we);
           printf("bdgps->Longitude:%d n",bdgps.Longitude);
           printf("bdgps->ns: %c n",bdgps.ns);
           printf("bdgps->Latitude: %d n",bdgps.Latitude);
           printf("bdgps->Altitude: %d n",bdgps.Altitude);
           printf("bdgps->Time:    %d n",bdgps.Time);
       }
usleep(50*1000);
   }
   close(bdgps_fd);

   return 0;

}