Read NMEA Data via UART STM32

[MSchmutz]

Hello

I am currently working on a microcontroller project I am building a GPS tachometer which transfers the NMEA data of the GNSS 4 Click Module from Mikroe via UART to my STM32L052K6T6 and outputs it to a display

I have so far UART initialized with the BAUD rate and so on my question is now how can I read the NMEA data correctly from the USART1->DRD (data register) so that I can store a readable string in a variable and output it to a display

I have as far as the data register is stored in a char this is correct ? how can I read the NMEA data from it ? I am still a beginner in this topic...

Below you can see my code, which I already have

I would be very grateful for any help :D

void USART1_IRQHandler(void) 

{

   char data;

   //check if we are here because of RXNE interrupt

   if ((USART1->ISR & USART_ISR_RXNE) == USART_ISR_RXNE) //if RX is not empty (Received character ?)

   {

     data = (uint8_t)USART1->RDR;           //Receive data, clear flag 

     while (!(USART1->ISR & USART_ISR_TC));

     // ... make your stuff with the received byte(s)

     USART1->ICR = USART_ICR_TCCF; // Clear TC flag

     USART1->CR1 = USART_CR1_TCIE; // Enable TC interrupt

     lcdWriteNumberPos(2, 9, "%.2f", data);

     lcdWriteStringPos(2, 12, "km/h");

   }

   //check if we are here because of TXEIE interrupt

   if (USART1->ISR & USART_ISR_TXE)  //if TX is not empty

   {

   //handle transmit completion here

   } 

 }

[TDK]

So you're able to receive individual characters? You need to set up a buffer which you can then process when you receive the ending characters (CRLF). And don't start storing into the buffer until a starting character ($) is received. The buffer should track how many characters are currently stored.

[Tesla DeLorean]

You probably don't have time to take excursions to write to the lcd in the handler, you have only a single byte time.

Here's a more complete example I posted for the F746I-DISCO

https://community.st.com/s/contentdocument/0690X000008B85YQAS

[Bill Dempsey]

Just curious why you used this construct in your code vs "while(1)" as you did in the other functions

void _sys_exit(int return_code)
{
label:  goto label;  /* endless loop */
}

[MSchmutz]

Hi Clive thank you for your help

I now have another question, how do I get the GPVTG Sentence without the other?

[Jorgie]

Hi Tesla,

I've tried to follow the link you provided, but as the thread is so old it has disappeared.

Any chance you could let me know what that linked contained?

Regards

Sean

[Tesla DeLorean]

https://github.com/cturvey/RandomNinjaChef/blob/main/f746g_disco_gps.c

[Jorgie]

Thank you. I now have this working on an STM32L053