MCUBOOT UART pin numbers

[rdolejs]

I have MCUBOOT working using the default UART pin numbers. I need to change the UART RX and TX pin numbers used by MCUBOOT for a custom application. I am able to change the UART pin numbers used in the application firmware by creating an overlay file and referencing the overlay file with a -DDTC_OVERLAY_FILE:STRING= argument in the extra CMake arguments in the VS Code build configuration.

I read the examples given on DevZone and created an overlay file for MCUBOOT.called mcuboot_dtc.overlay as shown below. This file is in a child_image directory.

&uart0_default {
    group1 {
        psels = <NRF_PSEL(UART_TX, 0, 0)>,
                <NRF_PSEL(UART_RTS, 0, 5)>;
    };
    group2 {
        psels = <NRF_PSEL(UART_RX, 0, 8)>,
                <NRF_PSEL(UART_CTS, 0, 7)>;
        bias-pull-up;
    };  
};

&uart0_sleep {
    group1 {
        psels = <NRF_PSEL(UART_TX, 0, 0)>,
                <NRF_PSEL(UART_RX, 0, 8)>,
                <NRF_PSEL(UART_RTS, 0, 5)>,
                <NRF_PSEL(UART_CTS, 0, 7)>;
        low-power-enable;
    };
};

I added lines to the CMakeLists.txt file to reference the overlay file.

cmake_minimum_required(VERSION 3.20.0)
find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
project(blinky)

set(mcuboot_DTC_OVERLAY_FILE
  ${CMAKE_CURRENT_SOURCE_DIR}/child_image/mcuboot_dtc.overlay
)

set(mcuboot_CONF_FILE
  ${CMAKE_CURRENT_SOURCE_DIR}/child_image/mcuboot.conf
)

target_sources(app PRIVATE src/main.c)

After these additions MCUBOOT is still using the default UART pin numbers. Is this the right approach? What could I missing?

Your help is appreciated.

Ray

[Vidar Berg]

Hello Ray,

mcuboot_DTC_OVERLAY_FILE and mcuboot_CONF_FILE must be set before find_package() and project() to be applied to the build. So, it should work if you move set() functions just below cmake_minimum_required(VERSION 3.20.0) line.

Another approach that does not involve changing cmakelist.txt is to use the naming convention described here: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/ug_multi_image.html#image-specific-variables. This will make the build system apply the configs and overlays to the mcuboot child image automatically.

Example of how you can apply board specific configurations to the mcuboot build:

├── child_image
│   └── mcuboot
│       └── boards
│           ├── nrf52840dk_nrf52840.conf
│           └── nrf52840dk_nrf52840.overlay

Best regards,

Vidar

[rdolejs]

Hi Vidar,

I tried the second approach and it worked. I left the mcuboot.conf file in the child_image directory and renamed mcuboot_dtc.overlay as nrf52840dk_nrf52840.overlay and placed it in the boards directory. The mcuboot uart pin numbers are now assigned correctly.

Thanks for your help,

Ray