Diff: main.cpp

Revision:

0:a9095d98a2b9

Child:

1:63a0fd33d5a5

diff -r 000000000000 -r a9095d98a2b9 main.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Fri Dec 18 02:44:01 2020 +0000
@@ -0,0 +1,183 @@
+#include "mbed.h"
+
+//NAV-
+
+DigitalOut myled(LED1);
+
+// serial port
+Serial pc(USBTX, USBRX); // tx, rx
+Serial ublox_ubx(p13,p14);//tx,rx
+
+const unsigned char UBX_HEADER[]        = { 0xB5, 0x62 };
+const unsigned char NAV_POSLLH_HEADER[] = { 0x01, 0x02 };
+const unsigned char NAV_STATUS_HEADER[] = { 0x01, 0x03 };
+
+enum _ubxMsgType {
+  MT_NONE,
+  MT_NAV_POSLLH,
+  MT_NAV_STATUS
+};
+
+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;
+};
+
+union UBXMessage {
+  NAV_POSLLH navPosllh;
+  NAV_STATUS navStatus;
+};
+
+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.
+int processGPS() {
+  static int fpos = 0;
+  static unsigned char checksum[2];
+  
+  static unsigned char currentMsgType = MT_NONE;
+  static int payloadSize = sizeof(UBXMessage);
+
+  while ( ublox_ubx.readable() ) {
+    
+    unsigned char c = ublox_ubx.getc();    
+    //Serial.write(c);
+    
+    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_POSLLH_HEADER) ) {
+          currentMsgType = MT_NAV_POSLLH;
+          payloadSize = sizeof(NAV_POSLLH);
+        }
+        else if ( compareMsgHeader(NAV_STATUS_HEADER) ) {
+          currentMsgType = MT_NAV_STATUS;
+          payloadSize = sizeof(NAV_STATUS);
+        }
+        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.
+          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;
+      }
+    }
+  }
+  return MT_NONE;
+}
+
+float latitude,longitude,height_float;
+int gps_Fix;
+
+/*--------------------------------------------*/
+int main() {
+    
+    //UART initialization
+    pc.baud(460800); //115.2 kbps
+    ublox_ubx.baud(460800); //115.2 kbps
+    
+    while(1) {
+        int msgType = processGPS();
+          if ( msgType == MT_NAV_POSLLH ) {
+             latitude=ubxMessage.navPosllh.lat/10000000.0f;
+             longitude=ubxMessage.navPosllh.lon/10000000.0f;
+             height_float=float(ubxMessage.navPosllh.height);
+             
+             pc.printf("latitude=%f,longitude=%f,height=%f\r\n",latitude,longitude,height_float);
+          }
+          else if ( msgType == MT_NAV_STATUS ) {
+              gps_Fix=int(ubxMessage.navStatus.gpsFix);
+              pc.printf("gps_Fix=%d\r\n",gps_Fix);
+              }
+        }
+  
+}