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Loadstone Secure Bootloader

Loadstone is a free and open secure bootloader for bare-metal and RTOS applications developed at Bluefruit Software. It's highly modular in order to enforce a small memory footprint (under 32kb with CRC image validation, and under 64kb with ECDSA image signing), easy to compile and port to different MCU architectures.

Loadstone rests atop the blue_hal crate, which is a collection of Rust hardware abstractions and drivers developed at Bluefruit.

A unique feature of Loadstone is its builder app. This graphical application allows you to define the collection of features and exact memory layout for your application, then trigger an automated Github Actions build. No tools or installation required, just navigate the GUI and get your final binary ready to flash!

Supported features

Loadstone currently supports:

  • Multiple image banks to store, copy, verify and boot firmware images. Image banks are fully configurable and flexible.
  • Support for an optional external flash chip.
  • Golden image rollbacks.
  • Automatic or app-triggered updates.
  • Image integrity guarantee via CRC check.
  • Image integrity and authenticity guarentees via ECDSA P256 signature verification (an image signing tool is provided under the tools/ directory.)
  • Serial communication for boot process reporting.
  • Serial recovery mode.
  • Indirect bootloader-app and app-bootloader communication.
  • Companion demo application with a feature-rich CLI to test all Loadstone features on target.

These features are modular and some of them may be available only for particular ports. At the moment, the port with the highest amount of support is the stm32f412 family.

Architecture

Loadstone is organized in an abstract, generic layer, and a port layer.

Ports exist under loadstone/src/ports/, and may be fully manually defined or depend on code generation. Those that depend on code generation require a configuration file generated in the loadstone_front application.

To know more about code generation and when/how to use it when expanding Loadstone, check out the documentation section for code generation.

Building

Building Loadstone requires embedding configuration in a LOADSTONE_CONFIG environment variable. It can be assigned an empty string, if you're just looking to run unit tests or to build Loadstone for a board that doesn't require code generation (one that you've defined manually under loadstone/src/ports.

# Run unit tests
LOADSTONE_CONFIG='' cargo test

# Building a codegen port
LOADSTONE_CONFIG=`cat my_stm32_config.ron` cargo b loadstone --features stm32f412

# Building a manual port
LOADSTONE_CONFIG='' cargo b loadstone --features my_manual_port