Some UART registers don't change after changing in .overlay

Question

I ran into a problem that some parameters that I change in the device tree are not applied.

For example:
The resulting zephyr.dts file contains this setting:

uart0: uart@8000 {
	compatible = "nordic,nrf-uarte";
	reg = < 0x8000 0x1000 >;
	interrupts = < 0x8 0x1 >;
	status = "okay";
	label = "UART_0";
	current-speed = < 0x1c200 >;
	tx-pin = < 0x5 >;
	rx-pin = < 0x6 >;
};

in <devicetree_unfixed.h> these settings are also updated. I am interested in Tx Rx pins.

#define DT_N_S_soc_S_peripheral_40000000_S_uart_8000_P_tx_pin 5
#define DT_N_S_soc_S_peripheral_40000000_S_uart_8000_P_rx_pin 6

But when these values are to be written to registers, the register value remains the same. (file nrf_uarte.h)

This happens at the initialization stage of running main.

Why does it work like this? What can block writing to these registers?

I use nRF Connect SDK v1.3.0

Håkon Alseth · Accepted Answer

Hi, 
 
 I'm glad to hear that it worked! 
 The SPM is the secure part of the multi-image build process: 
 http://developer.nordicsemi.com/nRF_Connect_SDK/doc/1.3.0/nrf/ug_multi_image.html 
 
 And the SPM module documentation is available here: 
 http://developer.nordicsemi.com/nRF_Connect_SDK/doc/1.3.0/nrf/include/spm.html?highlight=spm 
 
 By adding the lines to your cmakelists.txt, you can now configure spm, overlay, and mcuboot specific to your wanted configuration (even when doing multi-image builds). Note that if you want this in other projects, you will need to append those lines to the cmakelists.txt project file there as well. 
 
 Kind regards, 
 Håkon

Some UART registers don't change after changing in .overlay

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