mcuboot_opensource

Overview

The mcuboot_opensource is a second stage bootloader based on MCUBoot project. It is primarily meant to be used together with OTA (over-the-air) update examples to demonstrate functionality of application self-upgrade.

Flash memory layout

Flash memory is divided into multiple regions to allocate space for bootloader, main application and application update:

  • MCUBoot partition (reserved for bootloader itself, starts at the beginning of the FLASH memory)

  • Primary application partition (active application image)

  • Secondary application partition (candidate application - place to download OTA image to be used for update)

The partitioning is defined by definitions in flash_partitioning.h header file. The MCUBoot partition starts at the very beginning of the FLASH memory and spans up to BOOT_FLASH_ACT_APP. The primary partition occupies range starting from BOOT_FLASH_ACT_APP up to BOOT_FLASH_CAND_APP. The secondary partition starts at BOOT_FLASH_CAND_APP and it is automatically assigned the same size as the primary one. The rest of the memory may be used by the application for arbitrary purposes.

Important notice: should you need to change the partitioning please make sure to update also the header file used by the OTA application! If the partitioning information used by the bootloader and the application is not in sync, it may lead to malfunction of boot/OTA process or to upredictable behavior.

Flash remapping functionality

The default upgrade mechanism in MCUBoot is the SWAP algorithm. There are several NXP processors which support flash remapping functionality that can be used to speed up the OTA update process and minimize the flash wear. Flash remapping feature is used for zero-copy image swapping without the need of any data moving operations. This results in the fastest update operation possible. There are several platforms that support this mechanism. Mostly based on their external memory FlexSPI controller (eg. RT1060, RW612…). Platforms like MCX N9 also implement this mechanism for their internal flash memory.

The boards with such processors have example projects configured to use this feature. This is achieved by using MCUboot’s DIRECT-XIP mechanism and by activating flash remapping when needed - image is still built to run from primary slot. Keep in mind that DIRECT-XIP mode loads image with the highest version (no rollback support).

IMPORTANT NOTE: Signed application images directly programmed into flash memory by a programmer require additional “–pad –confirm” parameter for imgtool. This parameter adds additional trailer to the signed image and is required by bootloader direct-xip process (see MCUBoot documentation for more information). Signed images used in OTA process do not require “-pad” parameter.

List of boards with projects supporting flash remapping function:

  • MIMXRT1040-EVK

  • MIMXRT1060-EVK

  • MIMXRT1060-EVKB

  • MIMXRT1060-EVKC

  • MIMXRT1064-EVK

  • MIMXRT1160-EVK

  • MIMXRT1170-EVK

  • MIMXRT1170-EVKB

  • RD-RW612-BGA

  • RD-RW612-QFN

  • FRDM-RW612

  • EVK-MIMXRT595

  • EVK-MIMXRT685

  • MIMXRT685-AUD-EVK

  • MCX-N9XX-EVK

  • MCX-N5XX-EVK

  • FRDM-MCXN947

Encrypted XIP support

For more information please see mcuboot_encrypted_xip.md (in mcuboot_opensource/ext/nxp_encrypted_xip)

This extension of MCUboot functionality can be evaluated by enabling define CONFIG_ENCRYPT_XIP_EXT_ENABLE in sblconfig.h

List of boards with projects supporting encrypted XIP:

  • MIMXRT1020-EVK (BEE)

  • MIMXRT1040-EVK (BEE)

  • IMXRT1050-EVKB (BEE)

  • MIMXRT1060-EVK (BEE)

  • MIMXRT1060-EVKB (BEE)

  • MIMXRT1060-EVKC (BEE)

  • MIMXRT1064-EVK (BEE)

  • RDRW612BGA (IPED)

  • FRDMRW612 (IPED)

Signing the application image

MCUBoot expects signed application image in specific format to be present in the primary partition. The very same image format is also used for OTA updates.

A dedicated tool (imgtool) is used to generate application image in the desired format. It is implemented as a Python script which can be found in the SDK package in middleware/mcuboot_opensource/scripts folder.

Alternatively the tool can be installed by the Python package manager:

pip install imgtool

Please note that imgtool version installed by the Python package manager is not guaranteed to be compatible with MCUBoot present in you SDK package.

The mcuboot_opensource SDK project comes with its set of private-public keys. The key pair is stored in the keys subdirectory (e.g. boards/[board]/mcuboot_opensource/keys). The public key is already pre-configured in the source code of MCUBoot in a form of an array initializer.

To sign an application binary, imgtool must be provided with respective private key and a set of parameters as in the following example:

imgtool sign --key sign-rsa2048-priv.pem
             --align 4
             --header-size 0x400
             --pad-header
             --slot-size 0x200000
             --max-sectors 800
             --version "1.0"
             app_binary.bin
             app_binary_SIGNED.bin

NOTE that other boards may require different parameters - check their readme file.

The parameters used in the example above are tested with out-of-the-box configuration of MCUBoot and OTA examples in the SDK package. However, some of them may depend on the application or board setup and thus may need to be modified. See the MCUBoot documentation for the meaning of the parameters and align them with your project setup if necessary. https://docs.mcuboot.com/imgtool.html

Using MCUXpresso Secure Provisioning Tool for MCUBoot image signing

MCUXpresso Secure Provisioning Tool from verion 9 supports automation for MCUBoot image signing. Using this tool it’s possible to setup the device for entire boot chain in a few steps.

Prepare the Demo

  1. Connect a USB cable between the PC host and the OpenSDA(or USB to Serial) USB port on the target board.

  2. Open a serial terminal on PC for OpenSDA serial(or USB to Serial) device with these settings:

    • 115200 baud rate

    • 8 data bits

    • No parity

    • One stop bit

    • No flow control

    • line ending set for LF (‘\n’)

  3. Build project and program it to the target board.

  4. Either press the reset button on your board or launch the debugger in your IDE to begin running the demo.

Running the demo

When the demo runs successfully, the terminal will display the following:

hello sbl.
Bootloader Version 1.0.0

Further messages printed to the terminal depend on the content of the FLASH memory. In case there was no application programmed so far (i.e. the FLASH was blank), similar text as the following would be printed:

Primary image: magic=unset, swap_type=0x1, copy_done=0x3, image_ok=0x3
Secondary image: magic=unset, swap_type=0x1, copy_done=0x3, image_ok=0x3
Boot source: none
Swap type: none
erasing trailer; fa_id=2
Unable to find bootable image

At this point the bootloader is in place, resident in the FLASH memory. You may stop debuger, switch to an OTA example and follow the relevant readme located in example’s directory.

Supported Boards