No RX on UART

RE: No RX on UART

Susheel Nuguru — Thu, 08 Oct 2015 07:45:49 GMT

Good that you figured out the problem .. good luck.

RE: No RX on UART

Sergy — Wed, 07 Oct 2015 21:21:17 GMT

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.

RE: No RX on UART

Susheel Nuguru — Wed, 07 Oct 2015 09:35:12 GMT

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.

RE: No RX on UART

Sergy — Wed, 07 Oct 2015 09:09:40 GMT

Doesnt help, still getting error 1

I assume NRF_UART->RXDRDY is NRF_UART0->EVENTS_RXDRDY

RE: No RX on UART

Susheel Nuguru — Wed, 07 Oct 2015 08:50:44 GMT

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);
    }
   }

RE: No RX on UART

Sergy — Wed, 07 Oct 2015 08:32:41 GMT

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.

RE: No RX on UART

Sergy — Tue, 06 Oct 2015 20:07:21 GMT

Its indeed basic, so probably im doing something really wrong. The sequence that you described is correct. Currently i just have the lines connected to UART-USB interface on the PC, so I just see that nrf sends commands and GSM replies. I can make a picture on oscilloscope as well if that helps.

Please find photos attached. Measured at the same time from UART USB on PC and on oscilloscope.

RE: No RX on UART

Susheel Nuguru — Tue, 06 Oct 2015 19:04:08 GMT

I would like to see the TX and RX on a logic analyzer or some other line sniffer. Without softdevice what you are trying to do is quite basic and it should have worked.

You said that every 3 seconds the timer expires and if no reply from GSM is received, then nrf sends the command again. Can you please confirm that nrf sends command -> GSM module replies -> nrf does not get reply and times out ->nrf sends command again -> GSM replies.

If you can confirm this (how are you sniffing the TX and RX lines? can you put an image of it here?) then we know that atleast GSM module is not doing anything wrong and sending data with correct baudrate.

RE: No RX on UART

Sergy — Tue, 06 Oct 2015 11:35:33 GMT

Yes thats what I tried to do. The thing is that Im actually trying to actively read UART (using the simple UART method) and I have a timer to prevent hanging. So the timeout is set to 3 seconds, if i dont receive anything in 3 seconds I send a command again to GSM and try to read.

So you are saying i have to read the RX data, but there is nothing coming out of RX, basically I get stuck on this line:

while (NRF_UART0->EVENTS_RXDRDY != 1 && !gsmTimeout){};

I also make sure that GSM module is up and doesnt send anything at all before I clear UART, so it seems like UART cant recover from that problem and I dont understand why.

RE: No RX on UART

Susheel Nuguru — Tue, 06 Oct 2015 10:59:36 GMT

You can enable the interrupt when this error event occurs, and in the interrupt handler which is triggered by any error, you can recover the uart by

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

This will clear the error and uart is usable again. But if you have not read the RXD byte before GSM sends next character, then overrun error will occur agan. The above proposed way is brute force and does not handle specific errors uniquely, but is better than restarting the chip.

RE: No RX on UART

Sergy — Tue, 06 Oct 2015 09:24:29 GMT

Is there anything on nrf side that I could do to fix that? Can I reset UART somehow to recover from this? If I connect the output to a terminal on PC I dont see any extra data being sent, so i cant say that GSM does something wrong.

GSM might send a corrupted character when it reboots, but then afterwards it doesnt send anything unless it gets a request from nrf. But nrf seems unable to recover from erroneous state.

RE: No RX on UART

Susheel Nuguru — Tue, 06 Oct 2015 08:34:13 GMT

if you received 1101'b This means that you have got

overrun error. Which means that your RXD FIFO was full and yet there was new character received. Means your application is not reading bytes fast enough from uart. This happens if you transmit bytes from GSM larger than UART RX fifo size (6 bytes) and have not read anything from your nRF51 side.
Framing error. Your GSM module and nRF chip got out of sync as no valid stop bit was detected.
break condition detected.

error 2) and 3) occurred as the RX line was low for more than it should. you should check why your GSM module is sending such data!!

RE: No RX on UART

Sergy — Tue, 06 Oct 2015 08:16:47 GMT

Actually I just checked and I get 13 in ERRORSRC. How do I deal with it? It doesnt happen if after programming I completely power off the system and then turn it on again.

RE: No RX on UART

Susheel Nuguru — Tue, 06 Oct 2015 08:00:08 GMT

Hmm, have you checked if the nRF chip has generated any error like framing error or so? If you are not using softdevice, then this is the only explanation i can think of that there are some errors while receiving the data.

RE: No RX on UART

Sergy — Tue, 06 Oct 2015 07:50:42 GMT

Im not using SoftDevice as I wrote before, so no BLE communications and there is no other interrupts happening before the first UART communication completes.

RE: No RX on UART

Susheel Nuguru — Tue, 06 Oct 2015 05:29:42 GMT

UART needs HFCLK, not the Low frequency clock. Look at the image below from nRF51 Product Specification V3.1

There is not enough information for us to narrow down the problem. Is your nRF device having any BLE activity along with UART traffic? If so then without flowcontrol it is bound to miss packets.