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

[Yury Morgunov]

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

[Yury Morgunov]

As I found out, we cannot change these registers when uart is on.
It turns out that when the program starts. Before running main.
uart0 is already included and, accordingly, no initialization occurs.
Why is this happening?

[Håkon Alseth]

Hi,

 

Its the SPM configuration that overrides your wanted configuration.

Could you try the sequence described here?

https://devzone.nordicsemi.com/f/nordic-q-a/60471/nrf9160-psm-current-consumption-test-problem/245872#245872

 

then re-generate your project, and it should also override the spm image.

 

You can also create a file "spm.conf" which disables serial (CONFIG_SERIAL=n)

 

Kind regards,

Håkon

[Yury Morgunov]

Thanks for the answer!
Do I understand correctly that by describing the spm.conf file I am setting up the SPM functionality?
Those. it turns out that SPM configures its peripherals (for example uart 0) and therefore my configuration described in the device tree is not applied?

How can I then find out what is using and overriding SPM?
I have the same problem with uart1.

I just tried adding the spm.conf file next to prj.conf. CMakeLists hasn't changed yet.
Added to it:
CONFIG_SERIAL = n

But I did not see any changes, uart0 continues to work on pins 29 and 28.

[Yury Morgunov]

Oh no, sorry. Adding spm.conf file helped! I forgot to clear flash on nrf9160.
This is good, it would be great to learn more about how SPM works. I used to think that its functionality is limited to memory protection.

Is there any simple description of how it works, what and how it uses and how it can be customized?

[Håkon Alseth]

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