MCUBOOT on nRF54L15: Can not FPROTECT region that big

[Fridtjof]

I'm working on a project for the nRF54L15. Until now I have not been using mcuboot, but since I added SB_CONFIG_BOOTLOADER_MCUBOOT=y to my sysbuild.conf, I get an error when building MCUBOOT:

error: static assertion failed: "Can not FPROTECT region that big"
   87 | #define BUILD_ASSERT(EXPR, MSG...) _Static_assert((EXPR), "" MSG)
      |                                    ^~~~~~~~~~~~~~

I found some old posts which recommended looking at partition manager and creating a pm_static, but partition manager was just deprecated so I want to use the device tree. How do I get rid of this build error?

[Fridtjof]

For whatever reason, the nRF54L-devices cannot FPROTECT more than 62kB. However, the standard size for the bootloader partition is 64kB. There are some .dtsi files in ncs which set the correct partition size, however, I don't know to make the build system include those.

I solved the issue by adding an overlay file to my project with the correct partitioning schema. In boards/nrf54l15dk_nrf54l15_partitions.overlay:

/delete-node/ &{/soc/rram-controller@5004b000/rram@0/partitions};

&cpuapp_rram {
	reg = <0x0 0x165000>;
	partitions{
		compatible = "fixed-partitions";
		#address-cells = <0x1>;
		#size-cells = <0x1>;
		boot_partition: partition@0 {
			label = "mcuboot";
			reg = <0x0 DT_SIZE_K(62)>;
		};
		slot0_partition: partition@10000 {
			label = "image-0";
			reg = <0x10000 0xa0000>;
		};
		slot1_partition: partition@b0000 {
			label = "image-1";
			reg = <0xb0000 0xa0000>;
		};
		storage_partition: partition@150000 {
			label = "storage";
			reg = <0x150000 0x15000>;
		};
	};
    // cpuflpr occupies 0x165000 - 0x17d000
};

Then including this file in cpuapp's and mcuboot's overlay files. In boards/nrf54l15dk_nrf54l15_cpuapp.overlay:

#include "nrf54l15dk_nrf54l15_partitions.overlay"

In sysbuild/mcuboot/boards/nrf54l15dk_nrf54l15_cpuapp.overlay:

#include "../../../boards/nrf54l15dk_nrf54l15_partitions.overlay"

When adding a sysbuild folder (which we must in order to add a device tree overlay to mcuboot), zephyr stops including the default mcuboot prj.conf. So I copied it and added it as sysbuild/mcuboot/prj.conf:

####################################################################
# Copied from $ZEPHYR_BASE/bootloader/mcuboot/boot/zephyr/prj.conf #
####################################################################

CONFIG_PM=n

CONFIG_MAIN_STACK_SIZE=10240

CONFIG_BOOT_SWAP_SAVE_ENCTLV=n
CONFIG_BOOT_ENCRYPT_IMAGE=n

CONFIG_BOOT_UPGRADE_ONLY=n
CONFIG_BOOT_BOOTSTRAP=n

### mbedTLS has its own heap
# CONFIG_HEAP_MEM_POOL_SIZE is not set

CONFIG_FLASH=y

### Various Zephyr boards enable features that we don't want.
# CONFIG_BT is not set
# CONFIG_I2C is not set

CONFIG_LOG=y
CONFIG_LOG_MODE_MINIMAL=y
### Ensure Zephyr logging changes don't use more resources
CONFIG_LOG_DEFAULT_LEVEL=0
### Use info log level by default
CONFIG_MCUBOOT_LOG_LEVEL_INF=y
### Decrease footprint by ~4 KB in comparison to CBPRINTF_COMPLETE=y
CONFIG_CBPRINTF_NANO=y
### Use picolibc to reduce flash usage
CONFIG_PICOLIBC=y
### Disable malloc arena because we don't need it
CONFIG_COMMON_LIBC_MALLOC_ARENA_SIZE=0

# NCS boot banner
CONFIG_NCS_APPLICATION_BOOT_BANNER_STRING="MCUboot"

Please tell me if this is a bad way to go.

[Fridtjof]

Actually this does not work. MCUBOOT does not seem to even boot

[Fridtjof]

I changed from using sysbuild/mcuboot/boards/nrf54l15dk_nrf54l15_cpuapp.overlay to sysbuild/mcuboot.overlay and deleted the sysbuild/mcuboot folder. This made the build system use mcuboot's default prj.conf, so the copied config file wasn't needed anymore.

But it still does not boot.

[Fridtjof]

I recreated the problem using the blinky sample. I also solved it. To recreate:

1. make a copy of blinky
2. in prj.conf, set CONFIG_MCUBOOT=y
3. create sysbuild.conf:
   

   SB_CONFIG_PARTITION_MANAGER=n
   SB_CONFIG_BOOTLOADER_MCUBOOT=y

Build with west build -b nrf54l15dk/nrf54l15/cpuapp --sysbuild and observe that the mcuboot build fails with the original error. Now, we fix this build error:

1. add boards/partitions.dtsi
   

   &boot_partition {
     reg = <0x0 DT_SIZE_K(62)>;
   };

2. add sysbuild/ folder and sysbuild/mcuboot.overlay
   

   #include "../boards/partition.dtsi"

Now The build will complete, but McuBoot will fail, and you can see the log over UART:

*** Booting MCUboot v2.3.0-dev-fce4dac2e629 ***
*** Using nRF Connect SDK v3.3.0-ba167d9f3db4 ***
*** Using Zephyr OS v4.3.99-fd9204a02d52 ***
I: Starting bootloader
I: Primary image: magic=unset, swap_type=0x1, copy_done=0x3, image_ok=0x3
I: Secondary image: magic=bad, swap_type=0x1, copy_done=0x2, image_ok=0x2
I: Boot source: none
I: Image index: 0, Swap type: none
E: Image in the primary slot is not valid!
E: Unable to find bootable image

The problem is that just by adding mcuboot.overlay, we have stopped the build system from including an important file, bootloader/mcuboot/boot/zephyr/app.overlay, which contains:

/ {
	chosen {
		zephyr,code-partition = &boot_partition;
	};
};

If you inspect our build/mcuboot/zephyr/zephyr.dts, you can see that zephyr,code-partition is set to &slot0_partition. If you add the above overlay code to sysbuild/mcuboot.overlay, the firmware successfully boots! Happy days!

Now my question is: Why? Is this a bug of some sort?

Edit: it seems like this solved the problem on blinky, but in my own larger project I'm still getting boot issues :(