33 lines
2.1 KiB
Plaintext
33 lines
2.1 KiB
Plaintext
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= Bootloader
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`embassy-boot` a lightweight bootloader supporting firmware application upgrades in a power-fail-safe way, with trial boots and rollbacks.
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The bootloader can be used either as a library or be flashed directly if you are happy with the default configuration and capabilities.
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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.
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The bootloader supports both internal and external flash by relying on the `embedded-storage` traits.
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== Hardware support
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The bootloader supports
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* nRF52 with and without softdevice
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* STM32 L4, WB, WL, L1 and L0
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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.
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== Design
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The bootloader divides the storage into 4 main partitions, configured by a linker script:
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* BOOTLOADER - Where the bootloader is placed. The bootloader itself consumes about 8kB of flash.
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* 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.
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* DFU - Where the application-to-be-swapped is placed. This partition is written to by the application.
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* 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.
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The partitions for ACTIVE (+BOOTLOADER), DFU and BOOTLOADER_STATE may be placed in separate flash, but they have to support compatible page sizes.
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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.
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