A Rust port of avrth, a Scheme implementation of Forth for the AVR microcontroller family, which in turn is based on AmForth.
If you want a production-ready Forth implementation for AVR microcontrollers, you are advised to use AmForth -- it comes with documentation, a community, and is well-maintained.
This knock-off (and the original Scheme knock-off) tries to improve upon AmForth mainly by including a Forth VM that can run on the host system, but mimics the target VM as closely as possible.
This should allow you (eventually, see feature list at the bottom) to:
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Do some prototyping and testing without actually needing a microcontroller.
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Flash only the minimal runtime required to the target, leaving out the compiler and REPL, thus minimizing flash usage.
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Avoid overwriting the original boot loader on the Arduino platform. AmForth requires you to overwrite the boot loader, as only code running in the boot loader area can write to the flash memory. Avrth gives you the option of compiling a complete image on the host, which can be flashed just like you would when using C, leaving the bootloader area alone.
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Avrth aims to eventually implement a "mixed-mode" operation, where a part of the code runs on the host and part of it runs on the target, allowing prototyping on the host, while still being able to invoke code on the target seamlessly. Once you are satisfied with the newly-written code, you should be able to transfer it to the target.
Beside these directly user-facing benefits, having the option of executing on the host also allows for some implementation-level benefits:
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Non-primitive words in Avrth can be written in Forth, instead of AmForth's approach of "Assembler-that-is-really-Forth". The Avrth implementation contains a basic reader and compiler implemented in Rust which understands enough Forth syntax to read and compile the words constituting the actual Forth REPL.
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The Scheme implementation of Avrth includes an AVR assembler, so you don't need Wine and the proprietary assembler required to build AmForth. The Rust port does not yet include an assembler (nor any target-specific code), but the intention is to include one, perhaps even supporting the same syntax as the proprietary assembler needed to build AmForth, so the assembly code used in AmForth can be re-used directly.
This is the list of features working (or mostly-working ;-) in the Scheme implementation, and their current status in the Rust port:
- Host VM
- Minimal reader and compiler for bootstrapping
- Reader and compiler implemented in Forth
- Enhanced host-only development support (e.g.
require) - Assembler for AVR
- Compilation to ELF images
- Mixed-mode operation