why i couldn't receive continuous data of GPS over UART?

[VPras]

Hi,

I am trying to get the NMEA data over UART and print it over another uart .But when i try read in loop after writing data to PC ,I'm not receiving any data. what could be the issue?

any ideas ??

[Trevor Jones]

just use this function to make the pointers the same

void clearRxBuffer(void) {

U1RxBufferPtrIN = U1RxBufSize - huart1.hdmarx->Instance->CNDTR;

U1RxBufferPtrOUT = U1RxBufferPtrIN;

}

then readable will return a zero, until a byte is received.

[T J]

actually, you should never clear the buffer.. just keep reading bytes from the circular DMA buffer like this:

I use this to check a frame... initialise haveGPSstringbytes = false;

if( ! haveGPSstringbytes){
                int length =  readableU1();       
                if (length >= 2)
                {
                    char firstByte =  peekRxU1(0);
                    char secondByte =  peekRxU1(1);
                
                    char readByte =  readU1();   // read and dump byte if not start of frame
               
                    if ((firstByte == '$') && (secondByte == 'G'))
                    {
                        GPSlength = 0;
                        haveGPSstringbytes = true;
                        GPSstring[GPSlength++] =  readByte; 
                    }
                }    
       }else{ 
         char readByte =  readU1();
         GPSstring[GPSlength++] =  readByte;
         
          //read in frame to end         
         // when you have a complete frame
          haveGPSstringbytes = false; //start new frame detector
          flagGPSFrameReceived = true;
        }

[VPras]

Thanks TJ,

code is working ,before i was using normal mode instead of circular mode.