d769e562c0
* Remove traits section now that we have embedded-hal-async and refer to it. * Explanation that embassy is multiple things. * Bootloader description image
37 lines
2.4 KiB
Plaintext
37 lines
2.4 KiB
Plaintext
= Bootloader
|
|
|
|
`embassy-boot` a lightweight bootloader supporting firmware application upgrades in a power-fail-safe way, with trial boots and rollbacks.
|
|
|
|
The bootloader can be used either as a library or be flashed directly if you are happy with the default configuration and capabilities.
|
|
|
|
By design, the bootloader does not provide any network capabilities. Networking capabilities for fetching new firmware can be provided by the user application, using the bootloader as a library for updating the firmware, or by using the bootloader as a library and adding this capability yourself.
|
|
|
|
The bootloader supports both internal and external flash by relying on the `embedded-storage` traits.
|
|
|
|
|
|
== Hardware support
|
|
|
|
The bootloader supports
|
|
|
|
* nRF52 with and without softdevice
|
|
* STM32 L4, WB, WL, L1, L0, F3, F7 and H7
|
|
|
|
In general, the bootloader works on any platform that implements the `embedded-storage` traits for its internal flash, but may require custom initialization code to work.
|
|
|
|
== Design
|
|
|
|
image::bootloader_flash.png[Bootloader flash layout]
|
|
|
|
The bootloader divides the storage into 4 main partitions, configurable when creating the bootloader
|
|
instance or via linker scripts:
|
|
|
|
* BOOTLOADER - Where the bootloader is placed. The bootloader itself consumes about 8kB of flash.
|
|
* ACTIVE - Where the main application is placed. The bootloader will attempt to load the application at the start of this partition. This partition is only written to by the bootloader.
|
|
* DFU - Where the application-to-be-swapped is placed. This partition is written to by the application.
|
|
* BOOTLOADER STATE - Where the bootloader stores the current state describing if the active and dfu partitions need to be swapped. When the new firmware has been written to the DFU partition, a flag is set to instruct the bootloader that the partitions should be swapped.
|
|
|
|
The partitions for ACTIVE (+BOOTLOADER), DFU and BOOTLOADER_STATE may be placed in separate flash. The page size used by the bootloader is determined by the lowest common multiple of the ACTIVE and DFU page sizes.
|
|
The BOOTLOADER_STATE partition must be big enough to store one word per page in the ACTIVE and DFU partitions combined.
|
|
|
|
The bootloader has a platform-agnostic part, which implements the power fail safe swapping algorithm given the boundaries set by the partitions. The platform-specific part is a minimal shim that provides additional functionality such as watchdogs or supporting the nRF52 softdevice.
|