File content as of revision 0:91d5f51f73e2:

//=========================================================
//GNSS logger with ublox-NEO7M 
//MPU board:  mbed LPC1768
//GNSS module: ublox-NEO7M
//2021/04/26  A.Toda
//========================================================
#include "mbed.h"

//=========================================================
//Port Setting
Serial pc(USBTX, USBRX); // tx, rx
SPI spi(p11, p12, p13);  // mosi, miso, sclk
DigitalOut CS(p15);      // NEO-7MのCSピン

//=========================================================
//受信したメッセージから抽出したい情報
float latitude,longitude,height_float;  //緯度、経度、高度
int gps_Fix; // GPSの測位状態この値が3ならば3D Fix状態である
float velN_float,velE_float,velD_float; // NED座標系に置ける速度

//=========================================================
//UBXデータを処理したかどうかのフラグ
int flag_posllh,flag_velned;

//=========================================================
//処理時間計測の為のタイマー
Timer processing_timer;

//=========================================================
//処理時間
int processed_time,processed_time_before,processed_time_after;

//=========================================================
//Ticker
Ticker timer1; //
Ticker timer2; //

//=========================================================
//Logging variables
float imu_mesurement_freq = 400; //Hz
float gnss_mesurement_freq = 5;  //theta_update_freq;

float imu_interval = 1.0f/imu_mesurement_freq;   //sec
float gnss_interval = 1.0f/gnss_mesurement_freq; //sec

//=========================================================
//Header char
const unsigned char UBX_HEADER[]        = { 0xB5, 0x62 };
const unsigned char NAV_POSLLH_HEADER[] = { 0x01, 0x02 };
const unsigned char NAV_STATUS_HEADER[] = { 0x01, 0x03 };

const unsigned char NAV_VELNED_HEADER[] = { 0x01, 0x12 };

enum _ubxMsgType {
  MT_NONE,
  MT_NAV_POSLLH,
  MT_NAV_STATUS,
  MT_NAV_VELNED
};

//=========================================================
//メッセージの構造体
struct NAV_POSLLH {
  unsigned char cls;
  unsigned char id;
  unsigned short len;
  unsigned long iTOW;
  long lon;
  long lat;
  long height;
  long hMSL;
  unsigned long hAcc;
  unsigned long vAcc;
};

struct NAV_STATUS {
  unsigned char cls;
  unsigned char id;
  unsigned short len;
  unsigned long iTOW;
  unsigned char gpsFix;
  char flags;
  char fixStat;
  char flags2;
  unsigned long ttff;
  unsigned long msss;
};

struct NAV_VELNED  {
  unsigned char cls;
  unsigned char id;
  unsigned short len;
  unsigned long iTOW;
  signed long velN;
  signed long velE;
  signed long velD;
  unsigned long speed;
  unsigned long gSpeed;
  signed long heading;
  unsigned long sAcc;
  unsigned long cAcc;
    
};

//=========================================================
//受信したメッセージを格納する為の共用体
union UBXMessage {
  NAV_VELNED navVelned;//payload size is 36bytes
  NAV_POSLLH navPosllh;//payload size is 28bytes
  NAV_STATUS navStatus;//payload size is 16bytes
};

UBXMessage ubxMessage;

// The last two bytes of the message is a checksum value, used to confirm that the received payload is valid.
// The procedure used to calculate this is given as pseudo-code in the uBlox manual.
void calcChecksum(unsigned char* CK, int msgSize) {
  memset(CK, 0, 2);
  for (int i = 0; i < msgSize; i++) {
    CK[0] += ((unsigned char*)(&ubxMessage))[i];
    CK[1] += CK[0];
  }
}

//=========================================================
// Compares the first two bytes of the ubxMessage struct with a specific message header.
// Returns true if the two bytes match.
bool compareMsgHeader(const unsigned char* msgHeader) {
  unsigned char* ptr = (unsigned char*)(&ubxMessage);
  return ptr[0] == msgHeader[0] && ptr[1] == msgHeader[1];
}

//=========================================================
// Reads in bytes from the GPS module and checks to see if a valid message has been constructed.
// Returns the type of the message found if successful, or MT_NONE if no message was found.
// After a successful return the contents of the ubxMessage union will be valid, for the 
// message type that was found. Note that further calls to this function can invalidate the
// message content, so you must use the obtained values before calling this function again.
void processGPS() {
  
  static int fpos = 0;
  static unsigned char checksum[2];
  
  static unsigned char currentMsgType = MT_NONE;
  static int payloadSize = sizeof(UBXMessage);
  
  CS = 0;  //SPIによる読み出しを開始
  
  processed_time_before = processing_timer.read_us();// captureing prossing time
  
  /*
  NEO-7Mに(0xFF)を送って、取得した情報を1byteずつ以下の
  for文で確認する。
  
  */
  for(int buff_counter=1;buff_counter<50;buff_counter++){  
    
    unsigned char c = spi.write(0xFF); 
    
    if ( fpos < 2 ) {
      // For the first two bytes we are simply looking for a match with the UBX header bytes (0xB5,0x62)
      if ( c == UBX_HEADER[fpos] )
        fpos++;
      else
        fpos = 0; // Reset to beginning state.
    }
    else {
      // If we come here then fpos >= 2, which means we have found a match with the UBX_HEADER
      // and we are now reading in the bytes that make up the payload.
      
      // Place the incoming byte into the ubxMessage struct. The position is fpos-2 because
      // the struct does not include the initial two-byte header (UBX_HEADER).
      if ( (fpos-2) < payloadSize )
        ((unsigned char*)(&ubxMessage))[fpos-2] = c;


      fpos++;
      
      if ( fpos == 4 ) {
        // We have just received the second byte of the message type header, 
        // so now we can check to see what kind of message it is.
        
        if ( compareMsgHeader(NAV_VELNED_HEADER) ) {
          currentMsgType = MT_NAV_VELNED;
          payloadSize = sizeof(NAV_VELNED);
          
        }
        else if ( compareMsgHeader(NAV_STATUS_HEADER) ) {
          currentMsgType = MT_NAV_STATUS;
          payloadSize = sizeof(NAV_STATUS);
        }
        
        else if ( compareMsgHeader(NAV_POSLLH_HEADER) ) {
          currentMsgType = MT_NAV_POSLLH;
          payloadSize = sizeof(NAV_POSLLH);
          
        }
        
        else {
          // unknown message type, bail
          fpos = 0;
          continue;
        }
      }

      if ( fpos == (payloadSize+2) ) {
        // All payload bytes have now been received, so we can calculate the 
        // expected checksum value to compare with the next two incoming bytes.
        calcChecksum(checksum, payloadSize);
      }
      else if ( fpos == (payloadSize+3) ) {
        // First byte after the payload, ie. first byte of the checksum.
        // Does it match the first byte of the checksum we calculated?
        if ( c != checksum[0] ) {
          // Checksum doesn't match, reset to beginning state and try again.
          fpos = 0; 
        }
      }
      else if ( fpos == (payloadSize+4) ) {
        // Second byte after the payload, ie. second byte of the checksum.
        // Does it match the second byte of the checksum we calculated?
        fpos = 0; // We will reset the state regardless of whether the checksum matches.
        if ( c == checksum[1] ) {
          // Checksum matches, we have a valid message.
          if(currentMsgType==MT_NAV_POSLLH){
             latitude=ubxMessage.navPosllh.lat/10000000.0f;
             longitude=ubxMessage.navPosllh.lon/10000000.0f;
             height_float=float(ubxMessage.navPosllh.height);
             
             flag_posllh=1;//位置情報を読み取った合図としてフラグを立てる
              }
          else if(currentMsgType==MT_NAV_VELNED){
              velN_float=float(ubxMessage.navVelned.velN);
              velE_float=float(ubxMessage.navVelned.velE);
              velD_float=float(ubxMessage.navVelned.velD);
              
              flag_velned=1;//速度情報を読み取った合図としてフラグを立てる
              
              }
          else if(currentMsgType==MT_NAV_STATUS){
              
              }
          
          //return currentMsgType; 
        }
      }
      else if ( fpos > (payloadSize+4) ) {
        // We have now read more bytes than both the expected payload and checksum 
        // together, so something went wrong. Reset to beginning state and try again.
        fpos = 0;
      }
    }
  }
  
  CS = 1;  //SPIによる読み出しを終了させる
  

  //processGPS()の処理に必要な時間の計測
  //複数のメッセージを読み取る、つまりこの関数をメッセージの数だけwhile内で読み出すとき、
  //この関数の処理時間(processed_time)として保存されるのは
  //最後に呼び出されたprocessGPSの処理時間となる。
   processed_time_after = processing_timer.read_us();// captureing prossing time
   processed_time=processed_time_after-processed_time_before;
   
}

void imu_mesurement()
{
}

void ublox_logging()
{
    //detach the rotary imu mesurement
    timer1.detach();

    for(int message_number=0; message_number<3;message_number++){
        processGPS();
    }
        
    //位置と速度情報を読み取った場合
    if((flag_posllh==1)&&(flag_velned==1)){
        /*Teratermでロギングする用の表示*/
        pc.printf("%f,%f,%f,%f,%f,%f\r\n",latitude,longitude,height_float,velN_float,velE_float,velD_float);
        /*計測ではなくデバッグ用の表示*/
        //pc.printf("latitude=%f,longitude=%f,height=%f\r\n",latitude,longitude,height_float);
        //pc.printf("velN=%f,velE=%f,velD=%f\r\n",velN_float,velE_float,velD_float);
        //pc.printf("processed_time(us)=%d\r\n",processed_time);
            
        /*processGPSの処理時間の表示*/
        //pc.printf("processed_time_before(us)=%d\r\n",(processed_time_before));
        //pc.printf("processed_time_after(us)=%d\r\n",(processed_time_after));
            
        /*フラグを0に戻す*/
        flag_posllh=0;
        flag_velned=0;
            
    }else{}
        
    //attach a timer for imu mesurement (400 Hz)
    timer1.attach(&imu_mesurement, imu_interval);
}


/*--------------------------------------------*/
int main() {
    
    //UART initialization
    pc.baud(460800); //115.2 kbps
    
    //フラグのリセット
    flag_posllh=0;
    flag_velned=0;
    
    //-------------------------------------------  
    //Timer
    //-------------------------------------------  
    //timer1: imu mesurement, 400 Hz
    timer1.attach(&imu_mesurement, imu_interval);
    //timer2: GNSS mesurement, 5 Hz
    timer2.attach(&ublox_logging, gnss_interval);
    
    processing_timer.start();//timer starts
    
    while(1) {
        
        //        
        }//while
  
}