APP_UART_COMMUNICATION_ERROR when interfacing with external MCU

[Clonimmus74]

Hi,

I use the peripheral ble_app_uart with nRF52832 (Murata module). The nRF52832 is connected to another MCU, STM32L476, via UART.

P0.5 - RTS

P0.6 - TX

P0.7 - CTS

P0.8 - RX

The connections to the MCU are correct.

I constantly get the APP_UART_COMMUNICATION_ERROR (immediately) when running the application (running on pca10040 eval board doesn't cause the error).

I tried running the STM32L4 MCU and stop it in the beginning of the code right after clock and GPIO initialization, after I release the nRF52832 reset line, 

then I started the debug session of the nRF52832 and the error persisted.

The error code is 4 (BREAK in ERRORSRC register).

If I change the baud rate to 9600 the error code changes to 12.

If I disconnect the UART TX pin of the STM32L4 (connected to P0.8 in the  nRF52832, configured as UART RX) the error doesn't occur.

I must add that my code, at this stage, doesn't send anything on that line, and it is pulled up (I tried without pulling the pin but got the same results).

I use the latest SDK V15.0.0, with IAR v8.22

Any ideas?

Thanks

[MartinBL]

Hi,

1. What Murata module is it?
2. Is it so that you get errors even though the STM isn't sending any data?
3. Have you also connected the two devices to common ground?
4. Are they using the same (or equal) supply voltage?
5. Not that it matters much at this point maybe, but error 4 is a framing error isn't it? Error 12 would indicate both a framing and break error. 

[Clonimmus74]

Fixed !

The BLE UART RX pin was shorted to Gnd (due to wire soldered to a resistor connected to it in order to see the line in oscilloscope).

MartinBL regardless you raised good points:

1. MBN52832

2. Yes

3. Yes

4. Yes

5. As far as I understand

I still don't understand why every UART error causes a system reset. How can I prevent it and instead address the error and move on?

[MartinBL]

Hi,

I'm glad you fixed it.

Most of the functions in the SDK return an error or success code. You will also see that these codes are often checked with a macro called APP_ERROR_CHECK(). Depending on your compiler optimization level and preprocessor symbols, this macro either resets your device on an error or, if you debug like this, you will be sent to an error handler where you can get info about what went wrong. 

 

[Clonimmus74]

So in release mode I can't use APP_ERROR_CHECK since it will reset the device. I will have to handle every error separately. Am I right?