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]

I use this method,

never miss abyte, make your buffer 1024bytes at least,

uint32_t U1RxBufferPtrIN =0;
uint32_t U1RxBufferPtrOUT =0;
void initUart1RxDMABuffer(void) {
 if (HAL_UART_Receive_DMA(&huart1, (uint8_t *)Usart1RxDMABuffer, U1RxBufSize) != HAL_OK)
 {
 sprintf(string, "initUart1RxDMABuffer Failed\n");
 puts1(string); 
 }
 else
 {
 sprintf(string, "initUart1RxDMABuffer OK!\n");
 puts1(string);
 }
}
char peekRxU1(int offset) {
 // offset of zero returns the next byte to be read
 int relativePtr = (U1RxBufferPtrOUT + offset) & (U1RxBufSize - 1); 
 char PeekRx = Usart1RxDMABuffer[relativePtr]; // just looking Don't increment pointer
return PeekRx;
}
char readU1(void) {
 char readByte = Usart1RxDMABuffer[U1RxBufferPtrOUT++];
 if (U1RxBufferPtrOUT >= U1RxBufSize) U1RxBufferPtrOUT = 0;
 return readByte;
}
char readableU1(void) {
 U1RxBufferPtrIN = U1RxBufSize - huart1.hdmarx->Instance->CNDTR;
 return U1RxBufferPtrIN - U1RxBufferPtrOUT;
} 
void clearRxBuffer(void) {
 U1RxBufferPtrIN = U1RxBufSize - huart1.hdmarx->Instance->CNDTR;
 U1RxBufferPtrOUT = U1RxBufferPtrIN;
}

[VPras]

Thanks Trevor,

Now i can able to get seamless data .now i wanted to clear the Usart1RxDMABuffer once it gets full and start filling the new data to that buffer.

is that possible without reinitialize again??

[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.