Overview

This folder contains a simple bootloader called "riotboot". A header with metadata of length RIOTBOOT_HDR_LEN precedes the RIOT firmware. The header contains "RIOT" as a magic number to recognize a RIOT firmware image, a checksum, and the version of the RIOT firmware APP_VER. This bootloader verifies the checksum of the header which is located at an offset (ROM_OFFSET) with respect to the ROM_START_ADDR defined by the CPU, just after the space allocated for riotboot.

In case of multiple firmware slots, the bootloader iterates through valid headers and boots the newest image.

riotboot consists of:

• This application which serves as minimal bootloader,
• the module "riotboot_hdr" used to recognize RIOT firmware which riotboot can boot,
• the module "riotboot_slot" used to manage the partitions (slots) with a RIOT header attached to them,
• a tool in dist/tools/riotboot_gen_hdr for header generation,
• several make targets to glue everything together.

Concept

riotboot expects the flash to be formatted in slots: at the CPU_FLASH_BASE address resides the bootloader, which is followed by a slot 0 containing a RIOT firmware image. If present, a second firmware image (in slot 1) starts just afterwards.

The bootloader and a RIOT firmware in slot 0 are depicted below:

|------------------------------- FLASH -------------------------------------|
|----- RIOTBOOT_LEN ----|----------- RIOTBOOT_SLOT_SIZE (slot 0) -----------|
                        |----- RIOTBOOT_HDR_LEN ------|
 ---------------------------------------------------------------------------
|        riotboot       | riotboot_hdr_t + filler (0) |   RIOT firmware     |
 ---------------------------------------------------------------------------

Please note that RIOTBOOT_HDR_LEN depends on the architecture of the MCU, since it needs to be aligned to 256B. This is fixed regardless of sizeof(riotboot_hdr_t)

Also note that, if no slot is available with a valid checksum, no image will be booted and the bootloader will enter while(1); endless loop.

Requirements

Try to compile and run tests/riotboot:

$ BOARD= make -C tests/riotboot flash test

If the test succeeds, your board is supported. Else you can try to port riotboot to your board (see the below porting guide).

When building the bootloader, the global define RIOTBOOT is available. You can use this define to skip certain parts in board_init() (or cpu_init()) that should not be executed during boot. Note that this define is different from MODULE_RIOTBOOT, which is also defined when building an application that utilizes riotboot.

Single Slot

Just compile your application with FEATURES_REQUIRED += riotboot. The header is generated automatically according to your APP_VER, which can be optionally set (current system time in seconds since 1970 (epoch) by default) in your makefile.

Flashing example

If your application is using the riotboot feature, the usual targets (all, flash, flash-only) will automatically compile and/or flash both the bootloader and slot0, while ensuring that slot 1 is invalidated so slot 0 will be booted.

The image can also be flashed using riotboot/flash which also flashes the bootloader. Below a concrete example:

BOARD=samr21-xpro FEATURES_REQUIRED+=riotboot APP_VER=$(date +%s) make -C examples/hello-world riotboot/flash-combined-slot0

The above compiles a hello world binary and a bootloader, then flashes the combined binary comprising of: bootloader + slot 0 header + slot 0 image. If booted, the device will execute the Hello-World image.

A comprehensive test is available at tests/riotboot (also see below).

Multi-Slot

When several slots are available, the bootloader iterates through valid headers and boots the newest image (which has the greater VERSION)

Dedicated make targets are available to build and flash several slots:

• riotboot/slot1: Builds a firmware in ELF and binary format with an offset at the end of slot 0;
• riotboot/flash-slot1: builds and flashes a firmware for slot 1;
• riotboot/flash-extended-slot0 builds + flashes slot 0 and erases (zeroes) the metadata of slot 1 (invalidating it);
• riotboot builds both slot 0 and 1.

In particular, if one wants to be sure to boot a particular image, using the target riotboot/flash-extended-slot0 is the way to go (resulting in only slot 0 being valid, thus being booted). This is done automatically by make flash if the riotboot feature is used.

Testing riotboot

See tests/riotboot/README.md.

Quick riotboot porting guide

Your board/cpu is not supported yet? Try to port riotboot!

Porting to a board based on an Arm Cortex-M0+/3/4/7/22/33 MCU

Extending riotboot to support another board with a Cortex-M0+/3/4/7/22/33 microcontroller is rather straightforward. You need to:

• Provide the variables ROM_START_ADDR and ROM_LEN as well as RAM_LEN and RAM_START_ADDR.
• Adapt the linker scripts for your cpu to pass the test tests/cortexm_common_ldscript. This test ensures that the linker script supports building firmware's with a rom offset and specific sized firmware's.
• Make the startup code board_init(), cpu_init idempotent, i.e. whether you execute it once, or twice, it works all the same. The global define RIOTBOOT can be useful here. (e.g. cpu/efm32/cpu.c)
• Make sure (and adapt if needed) that the flasher script can:
  • flash a .bin
  • flash at a specified offset
  • flash without performing mass erase, only erase flash sections to be written e.g.: makefiles/tools/edbg.inc.mk
• Declare FEATURES_PROVIDED += riotboot for the target BOARD.
• Make sure that RIOTBOOT_LEN size is such that the remainder of the flash can be divided by the number slots while staying FLASHPAGE_SIZE aligned. e.g: cpu/nrf52/Makefile.include
• Check other specific BOARD/CPU flash alignment requirements (e.g.: kinetis vector table must be naturally aligned to the power of two, see cpu/kinetis/Makefile.include)

Porting to a board based on other types of MCUs

For other MCU architectures the following extra requirements must be fulfilled:

• Provide the functions defined in the header sys/include/riotboot/slot.h, in particular riotboot_slot_jump(unsigned slot) which will allow jumping from the bootloader to another slot/application.
• Adapt the linker script so that it supports building firmware's with a rom offset and a defined firmware size. To get an idea look at cpu/cortexm_common/Makefile.include

Additional remarks:

• If your are in Big-Endian, you may need to further adapt some part of the code.