ZEPboot - A work in progress - expect rough edges

Overview

ZEPboot is a secure bootloader for 32-bit MCUs. ZEPboot defines a common infrastructure for the bootloader, system flash layout on microcontroller systems, and provides a secure bootloader that enables easy software upgrade.

Many idea's that are used in the implementation are coming from MCUboot, a similar bootloader for 32-bit MCUs.

ZEPboot is developed on top of the zephyr RTOS.

Documentation

Project documentation is located in the docs folder.

Testing the bootloader with nrfjprog

Testing the bootloader with nrfjprog on nrf51/nrf52 devices requires 6 steps:

Step 1: Compile and program the bootloader

west build -d build_zepboot -s zepboot/bootloader/ -b nrf52_pca10040 -t flash

REMARK: The configuration file creates a bootloader with logging enabled, this creates a bootloader of about 22Kb. With logging disabled this size reduces to about 14.5Kb.

Step 2: Compile a test program (e.g. hello_world)

Creating a program for ZEPboot requires the following additions to prf.conf (nrf52_pca10040, image running from slot 0):

CONFIG_FLASH_LOAD_OFFSET=0xc200
CONFIG_FLASH_LOAD_SIZE=0x32000

or (nrf52_pca10040, image running from slot 1):

CONFIG_FLASH_LOAD_OFFSET=0x3e200
CONFIG_FLASH_LOAD_SIZE=0x32000

west build -s zephyr/samples/hello_world/ -b nrf52_pca10040

Step 3: Sign and encrypt the test program:

./scripts/imgtool.py sign -io 0x200 -ss 0x32000 -a 8 -v 0.0.1 -sk root-ec256.pem -ek boot-ec256.pem build/zephyr/zephyr.hex build/signed.hex

Step 4: Adapt the signed.hex file and load it

In case a image for execution from slot 1 has been generated, this image can be loaded using nrfjprog:

nrfjprog --program build/signed.hex --sectorerase

In case the created hex file was generated for slot 0 it is required to adapt the starting address to upload it to slot 1 using nrfjprog (for nrf52_pca10040):

objcopy --change-addresses 0x32000 build/signed.hex build/signedoff.hex

Upload the new signedoff.hex using nrfjprog:

nrfjprog --program build/signedoff.hex --sectorerase

Step 5: Write the swap command

Remark: the command has to be written in reverse order

nrfjprog --memwr 0x6f000 --val 0xE2000011 --verify

Step 6: Hit reset