nrf_serial_rx_drain not clearing overrun error (?)

[Pete W]

Hi,

I'm using nrf_serial to configure and then read data from a GPS engine, but I am getting unrecoverable OVERRUN errors on start-up if the GPS device is sending data when I try to configure the serial port. I was hoping that I could just call the nrf_serial_rx_drain(xxx) function in my serial_event_handler to reset the buffer read and write pointers, but this has no effect, and the OVERRUN error appears on every subsequent character. Th only way I can get round it is by staging the initalisation as follows:

1. Initialise the serial port for TX only by setting the RX pin to NRF_UART_PSEL_DISCONNECTED.

2. Send a command to the GPS to switch off all messages.

3. Re-initialise the serial port to enable RX

4. Send a command to the GPS to enable the required messages.

but this is clunky and I still have to insert a short delay between each step to prevent the overruns.

Am I using nrf_serial_rx_drain(xxx) incorrectly, or misunderstood its function ?

Thanks

[ovrebekk]

Hi Pete

I asked one of the developers to have a look and see if the issue seems familiar. 

In the mean time another potential workaround is to configure the UART with the RX on a different pin, one that is not used for anything else and can be pulled high by enabling the internal pullup resistor. 

Then after the nrf_serial library is successfully configured you can change the RX pin to the correct one, either by writing to the PSEL.RXD register directly, or by adding a function to the nrf_serial library that allows you to reassign the pin without doing a full re-initialization (probably a more reliable solution). 

Best regards
Torbjørn

[Krzysztof Chruscinski]

Hi,

couple of questions. Are you using UART or UARTE underneath? What device are you using and which SDK? Are you using flow control?

If you are not using flow control (and don't plan to use it) I would recommend to check nrf_libuarte_async library for UARTE. It is capable of reliably receiving data of any length. nrf_serial stops and starts reception between every byte so it is possible to hit framing error if interrupt is not handled on time.

[Pete W]

Thanks for the tip. I might give that a try.

[ovrebekk]

Hi

Do you mean my tip or that of Krzysztof?

I would also suggest giving the nrf_libuarte_async driver a go, as it is more optimized for these asynchronous use cases. It might solve your issue without requiring a lot of workarounds. 

Best regards
Torbjørn

[Pete W]

Hi, sorry for the slow response - I thought I had replied to you. I'm using the nRF52840 and SDK15.3, and UARTE, with no flow control. I did try the libuarte_async library, and although I got the example working I had trouble integrating the ble stack and rest of my application - I couldn't set up sdk_config.h to get everything to compile. I'm not having any other issues with the nrf_serial library so I'll stick with that for now but will give libuarte_async another look when I get a chance.

Regards

Pete