MCUBOOT bootloader upgrade OTA

[A Maq]

Using following settings:

IDE : VS Code (NRF connect plug-in)

Programmer : Stm32Cube programmer

Stlink Debugger 

OS: Zephyr 

MCU: Stm32u5 series 

 Modem: Sierra wireless

I'm trying to upgrade MCUboot ( Zephyr's) bootloader using FOTA .

I can upgrade application firmware however couldn't find any documentation or information about upgrade for MCUBOOT bootloader on stm32 chips.

Can anyone please suggest what can be potential solution for MCUBOOT bootloader upgrade over the air on STM32 chip or are there any specific changes required in MCUboot from zephyr to make it work with STM32?

Do I need another bootloader immutable to upgrade mcuboot bootloader if yes where to find that on Stm32 resources?

[Sarra.S]

Hello @A Maq, 

As described in building and using MCUBoot with Zephyr; in paragraph signing the application, 

"In order to upgrade to an image (or even boot it, if MCUBOOT_VALIDATE_PRIMARY_SLOT is enabled), the images must be signed. To make development easier, MCUboot is distributed with some example keys. It is important to stress that these should never be used for production, since the private key is publicly available in this repository. See below on how to make your own signatures.

Images can be signed with the scripts/imgtool.py script. It is best to look at samples/zephyr/Makefile for examples on how to use this."

[A Maq]

@Sarra.S thanks for your response. I have all the FOTA working using the MCUboot bootloader and FOTA libraries. Now what I am trying to do is upgrade bootloader image itself using FOTA not the firmware image(that is already working). In NRF(Nordic chips)devices they use two stage bootloader for the bootloader upgrade out of them first bootloader is immutable (fixed will not upgrade) the second bootloader is upgradeable using the first one.

I was wondering in STM32 do we have the same kind of mechanism for upgrading the bootloader image using FOTA or that is different. If it is different is there any documentation which I can refer to? if now then where can I get the first stage bootloader(immutable) for STM32u575

Something like shown in below image is the NRF chips mechanism for upgrading the bootloader image.

[A Maq]

@Sarra.S 

Haven't heard back from you that. Any thoughts on the question after more details shared ?

I did come across immutable bootloader which is in system memory. Is that what is required as first stage bootloader to upgrade second bootloader ( MCUboot from zephyr)?