s3c2440开发板gps模块

GPS模块

1. Gps模块引出四个管脚（1，2，3，5）分别为（Vcc，Tx，Rx，GND）只需要这四个管脚就可以了
2. 四个管脚接至Uart的serial port 2（挨着温度模块）
3. 模块接上天线（天线最好原装,使用桥梁Gps的天线发现不行）

备注：有可能出现无法读取到Gps数据，原因可能为管脚之间已经短路 

#include <stdio.h>
    #include <string.h>
    #include <stdlib.h>

    #include <fcntl.h> //文件控制定义
    #include <unistd.h> //Unix 标准函数定义
    #include <termios.h> //PPSIX 终端控制定义 //结构体termios,
    #include <errno.h> //错误号定义
    /* struct termios{
        unsigned short c_iflag; //输入模式标志
        unsigned short c_cflag; //控制模式标志
        unsigned short c_lflag; //本地模式标志
        unsigned char c_line; //控制协议
        unsigned char c_cc[NCCS] //控制字符
    } */

    static int g_nErrorCode = 0;

        char TestMode4[15] = //切换sirf至mode 4
           {0xA0, 0xA2,
            0x00, 0x07, // payload length
            0x96, // 150,switch operation mode
            0x1E ,0x54, // test mode 4
            0x00, 0x14, // SvID on simulator (21..) MUST match simulator
            0x00, 0x0A, // Period, tracking period 10 sec
            0x01, 0x15, // checksum --> (add all payload) % 0x07ff
            0xb0, 0xb3};
    unsigned char SwitchToSirf[] = //切回nmea协议命令
          { 0xa0, // KILL THIS BYTE
           0xa2,0x00,0x18, // start sequence and payload length
           0x81, // message ID dec 129, switch to NMEA
           0x02, // Mode
           0x01,0x01, // GGA
           0x00,0x01, // GLL
           0x01,0x01, // GSA
           0x05,0x01, // GSV
           0x01,0x01, // RMC
           0x00,0x01, // VTG
           0x00,0x01, // MSS
           0x00,0x01, // unused
           0x00,0x01, // ZDA
           0x00,0x01, // unused
           0x12,0xc0, // baudrate 4800
           0x01,0x67, // msg checksum
           0xb0,0xb3 // end sequence
          };

    //切换至sirf协议的nmea报文（两种报文对应波特率不同）
        char *SwitchToNMEA = "$PSRF100,0,57600,8,1,0*XX\r\n";
        char *SwitchToNMEA4800 = "$PSRF100,0,4800,8,1,0*XX\r\n";
        //char *pMsg;


    int GPS_Info_Process(char* info)
    {
        int dwCNOMean = 0;
        dwCNOMean=*((unsigned short*)&info[23]);
        printf("CNOMean = %d\n", dwCNOMean);
        return dwCNOMean;
    }


    static int GPS_DataReceive(int nProtocol)
    {


            struct termios options; //终端特性变量定义及初始化
            int fd, Rt, recv_len, fd_sel;
            //fd_set fd_gps, fd_sel;
            struct timeval tv; //定义超时控制结构
            fd_set fds; //文件描述符集合变量
            char buf[1024];
            int i, nReadIndex = 0, bHeaderOK = 0, nWriteIndex = 0;

            static char m_sMessage_ID46Buffer[60];

            const char acMessge2E[5] = { 0xa0, 0xa2, 0x00, 0x33, 0x2e }; // 2E Test Mode 3/4 - Message ID 46
            long nSeconds = time(NULL);
            printf("Start Time: %d\n", nSeconds);
            long nBegin;

            fd = open("/dev/tq2440_serial2", O_RDWR); //打开串口
            printf("Get fd: %d\n", fd);
            if (-1 == fd) // 不能打开串口一
            {
                   perror("Can't Open Port!\n");
                   g_nErrorCode = 1;
            }


            if (tcgetattr ( fd, &options) == -1) //获取当前设备方式
            {
                printf("Cannot get GPS configuration!\n");
                g_nErrorCode = 2;
                return 0;
            }
            cfsetispeed(&options,B4800); //设置输入为4800Bps
            cfsetospeed(&options,B4800); //设置输出为4800Bps
            options.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
            options.c_oflag &= ~OPOST;
            if (tcsetattr ( fd, TCSANOW, &options) == -1) //设置波特率
            {
                printf("Cannot set GPS configuration!\n");
                g_nErrorCode = 3;
                return 0;
            }



            tv.tv_sec = 5;
            tv.tv_usec = 0;

            FD_ZERO(&fds);
            FD_SET(fd, &fds);

        /*fd_sel = select(fd+1, &fds, NULL, NULL, &tv);
        if (fd_sel == 0)
        {
            printf("Select Failed!\n");
            g_nErrorCode = 4;
            return 0;
        }*/



        Rt = write(fd, SwitchToSirf, strlen(SwitchToSirf));

        if(Rt == -1)
        {
              printf("Switch to Sirf failed!\n");
              g_nErrorCode= 5 ;
              return 0;
        }
        printf("Switch OK\n");
        nBegin = time(NULL);
        while (time(NULL) - nBegin>1);


        Rt = write(fd, TestMode4, strlen(TestMode4));

        if(Rt == -1)
        {
              printf("Switch test mode 4 failed!\n");
              g_nErrorCode = 6;
              return 0;
        }
        printf("Mode 4 OK\n");
        nBegin = time(NULL);
        while (time(NULL) - nBegin>1);

        while(time(NULL) - nSeconds<35)
        {
            printf("Time: %d\n", time(NULL));
            if (FD_ISSET(fd, &fds))
            {
                printf("Data in\n");
                recv_len = read(fd, buf, 200);
                printf("%s\n", buf);
                printf("length: %d", recv_len);
                if (recv_len > 0)
                {
                    for (i = 0;i<recv_len;i++)
                    {
                        m_sMessage_ID46Buffer[i + nWriteIndex] = buf[i];
                    }
                    nWriteIndex += recv_len;

                    while (!bHeaderOK && (nReadIndex != nWriteIndex))
                    {
                        if (m_sMessage_ID46Buffer[nReadIndex] == acMessge2E[nReadIndex])
                        {
                            nReadIndex++;
                            if (nReadIndex == 5)
                                bHeaderOK = 1;
                        }
                        else {
                            for (i = 0;i<(nWriteIndex - nReadIndex + 1);i++)
                            {
                                m_sMessage_ID46Buffer[i] = m_sMessage_ID46Buffer[nReadIndex + i];
                            }
                            nReadIndex = 0;
                            nWriteIndex = i;
                            break;
                        }
                    }
                    if (nWriteIndex - 8 >= 0x33)
                    {
                        if (m_sMessage_ID46Buffer[58] != 0xB3 || m_sMessage_ID46Buffer[57] != 0xB0)
                        {
                            printf("Receiving Error gps data.\n");
                            g_nErrorCode = 7;
                            break;
                        }
                        else{
                            return GPS_Info_Process(m_sMessage_ID46Buffer) >= 43.5;
                        }
                    }
                }
            }
            printf("No data\n");
        }

        if(time(NULL) - nSeconds > 35) g_nErrorCode = 8; // timeout
        sleep(1);
        close(fd);
        return 0;
    }

    int main(int argc,char *argv[])
    {
        int nProtocol = 0;
        if (argc >= 1)
        {
            if (argv[1] == "nmea") {
                printf("Nmea Protocol\n");
                nProtocol = 1;
            }else if (argv[1] == "sirf"){
                printf("Sirf Protocol\n");
                nProtocol = 0;
            }
        }
        //nProtocol = 1;
        printf("---GPS Dump Test---\n");
        //printf("---GPS Dump Test: %s ---\n", GPS_DataReceive(nProtocol) ? "SUCCEEDED" : "FAILED");
        int GetGpsInfoSuccess=0;
        while(!GetGpsInfoSuccess){
            if(GPS_DataReceive(nProtocol)){
                GetGpsInfoSuccess=1;
                printf("Get Gps Info Success! \n\n");
            }
            sleep(5);
            printf("Sorry, Get Gps Info Failed! \n\n\n\n\n");
        }
        return g_nErrorCode;
    }