Problems with UARTE on nRF52832

[A1exey]

Hi. We are using nRF52832 and we have problem with UARTE. SoftDevice version - S132 5.0.0, SDK version - 14.2.0.
Our application uses nRF and Mbed Serial to communicate with the GSM module using UART protocol with RTS/CTS flow control and sometimes reception errors occur, such as missing or incorrect bytes. Worth noticing: this errors occur only when there is BLE scan running at same time.
With digital analyzer we saw that there is no interference on pins and data transmits to nRF correctly, but sometimes nRF doesn't set RTS pin high after receiving next byte and apparently doesn't generate ENDRX event, which causes data corruption:

Our first hypothesis was that UART interruppt handling takes too much time due to the high priority interrupts from SoftDevice. So we modified implementation of Mbed Serial to work with a larger DMA buffer (DMA buffer is now flushed after a certain timeout after receiving last byte from the modem. The number of bytes received is counted using PPI and TIMER). But reception errors still occur. After connecting RXRDY event to pin toggle task, we can see that sometimes nRF doesn't generate RXRDY events properly:

Do you have any idea why this could happen?

[Dmitry]

Hi,

it's likely that errors are occuring due to oscillator switching (HFINT<->HFXO). Try to call sd_clock_hfclk_request() to force CPU work from HFXO all the time.

[A1exey]

Thanks for the reply! I tried this solution but unfortunately it didn't help, errors still occur.

[Kenneth]

I am not familiar with the mbed serial, but it could be interesting to find if there is an error triggered and which one:
https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.nrf52832.ps.v1.1/uarte.html#register.ERRORSRC

This error is likely handled by the UART interrupt handler, so you may need to set a breakpint to catch it. Also, how the serial library will handle this error would be interesting to look at, for instance does it just stop the UART, in that case you may need to init the library again. 

Personally I would recommend checking out the libuarte example and library if possible:
https://infocenter.nordicsemi.com/topic/sdk_nrf5_v17.0.2/libuarte_example.html
https://infocenter.nordicsemi.com/topic/sdk_nrf5_v17.0.2/lib_libuarte.html

Best regards,
Kenneth

[A1exey]

I read the value of the ERRORSRC register immediately after receiveing the error and saw that it contains a framing error bit (according to the documentation, this means: "A valid stop bit is not detected on the serial data input after all bits in a character have been received."). But the signal from modem looks good on digital analyzer:

Level toggling on channel 10 corresponds to RXRDY events. In this example, events stop generating correctly after the fourth byte.

Kenneth said:

Also, how the serial library will handle this error would be interesting to look at

There is no error handling in the code, so the only result of this error is data corruption.

Kenneth said:

Personally I would recommend checking out the libuarte example and library if possible

Thanks, I will check it later.

[Kenneth]

I suspect that UART RX is started in the middle of an UART byte, this would trigger a framing error.

Best regards,
Kenneth