Basic question about UART RXCn flag (AVR)

Question

I got stuck in the interrupt part while learning AVR. Datasheet says about RXCn flag: "This flag bit is set when there are unread data in the receive buffer and cleared when the receive buffer is empty (i.e., does not contain any unread data)."

and there is an example about getting a characters with uart

while ( !(UCSRnA & (1<<RXCn)) );
/* Get and return received data from buffer */
return UDRn;

Will it wait here forever until the data comes from the Uart? And will mcu not be able to do any other work because of "while(1);"?

I know this method is polling and I also know that there is an interrupt method but will the mcu be locked because of this?

Answer 1

As @AterLux already said the program will halt until data is recived there are some other possibilities to catch the data nonblocking e.g.:

char uart_get(char *data)
{
  if (UCSRnA & (1<<RXCn) );
  {
    *data = UDRn;
    return 1;
  }
  
  return 0;
}

If no data has been received you will get 0 and can continue with the program. If you should use interrupt handling or polling depends on your problem. With interrupt handling you can use for example a circular buffer to save received data and use it if you need it. if you are still waiting for one value polling is also an oppertunity.