No RX on UART

[Sergy]

Hi,

I'm using 51822 to control GSM module via UART (57600, no flow control). My device is USB and battery powered. After I program the chip I HAVE to disconnect all the power in order to start system clean and have it working. If I don't completely remove power on start nrf will send commands to GSM module, GSM module will recognize them and send a reply to nrf, but nrf won't get anything on RX (I'm using simple UART without interrupt and without softdevice).

What could it be? I also don't use 32khz xtal, so it synthesises clock from hf crystal.

[Sergy]

I do understand why I get initial error 13 - its because when GSM reboots it pulls RX line low. But then after that I clear the error and UART should just work, but it doesnt for some reason. I keep getting error 1 (overrun) and I cant recover from it.

[Susheel Nuguru]

uint32_t error;
       if(NRF_UART->EVENTS_ERROR !=0)
       {
            NRF_UART->EVENTS_ERROR = 0;
            error = NRF_UART->ERRORSRC;
            NRF_UART->ERRORSRC = error;

// flush the RX FIFO by reading and ignoring them

 

   while (NRF_UART->EVENTS_RXDRDY != 0) 
    { 
        error = NRF_UART->RXD; 
        NRF_UART->EVENTS_RXDRDY = 0;
        //Give a moment for more data in FIFO to move into RXD register
        nrf_delay_ms(1);
    }
   }

[Sergy]

Doesnt help, still getting error 1

I assume NRF_UART->RXDRDY is NRF_UART0->EVENTS_RXDRDY

[Susheel Nuguru]

Yes sorry, it was EVENTS_RXDRDY , dont remember the format from top of my head sometimes. I fixed my previous comment.

What is the size of the command that GSM is sending? should be definitely more than 6 bytes. Can you change the baudrate on both sides to very low say 4800 and see if that helps. If that does not help, then i need the line sniff data/image or some code to look into.

[Sergy]

Thanks for being so patient with me. Your previous answer actually does solve the problem, there was a bug in how I handled timer for timing out the readout from UART.