NRF5340: How to configure P0.02 and P0.03 (NFCT) as GPIO?

[bubune]

Hello,

We are working with the nRF5340DK using nRF Connect SDK v2.9.1.
Our firmware targets the nrf5340dk_nrf5340_cpuapp_ns board.

We would like to use P0.02 and P0.03 as GPIOs, specifically as UART2 RX and TX.
From what I have read (for example, here: nRF5340: best way to configure P0.02 (NFCT) as GPIO with TFM ), it seems that no special configuration is required—these pins should be usable as UART pins by simply configuring them in the device tree.

However, while I can successfully configure and use other pins as UART, when I assign P0.02 and P0.03, I am not able to send or receive any data.

Is there any additional configuration required to use these two pins as UART?

Regards,
Bruno

[Menon]

Hello,

You need to use a devicetree overlay to configure the NFCT pins as GPIOs. Please try the following overlay file:

&uicr {
nfct-pins-as-gpios;
};

See this devzone case as a reference.

Kind Regards,

Abhijith

[bubune]

Hello Abhijith,

Thanks for your quick reply. 

As explained in the link in my previous post, the symbol uicr is not known in the nrf5340dk_nrf5340_cpuapp_ns target.

I've already tried this solution before, but here is the compile log output:

Found devicetree overlay: /Users/nono/Documents/git/firmware/app.overlay
devicetree error: /Users/Nono/Documents/git/firmware/app.overlay:23 (column 1): parse error: undefined node label 'uicr'
CMake Error at /Users/Nono/Documents/git/firmware/zephyr/cmake/modules/dts.cmake:295 (execute_process):
  execute_process failed command indexes:

    1: "Child return code: 1"

Regards,

Bruno

[bubune]

In addition, when I read the NFCPINS UICR register (0x00FF8028), I get the value 0xFFFFFFFE:

nrfjprog --memrd 0x00FF8028
0x00FF8028: FFFFFFFE

which is the expected value for configuring the pins as GPIO instead of NFC.

I don't knwon what I miss.

Regards,

Bruno

[Turbo J]

bubune said:

these pins should be usable as UART pins by simply configuring them in the device tree.

The backside printing on my NRF5340DK implies otherwise - it shows a not connected (NC) component between the pin header and the GPIO on the NRF chip. Its only connected to the NRF antenna inputs.

No idea if that changed between board revisions, this board here is the version before they changed the debugger chip to an NRF variant.

[Menon]

Hello,

The nrfprog --memrd value you shared confirms that the pins are configured as GPIOs (see this page). So, this might not be the issue you are seeing.

Kind Regards,

Abhijith