There’s now an interpreter in wasmtime called Pulley. It’s an optimizing interpreter based on Cranelift, which generates interpreter opcodes which are more efficient to traverse than directly interpreting the Wasm binary.

I have run wasmtime on the esp32 microcontrollers with plenty of ram to spare, but I don’t have a measurement handy.

Wasmtime has many capabilities that wasmi does not, and therefore has more optional dependencies, but the required set of dependencies has been portable to every platform I've targeted so far. If anything does present a concrete issue we are eager to address it. For example, you could file an issue on target-lexicon describing how to reproduce your issue.

Wasmtime's epoch system was designed specifically to have a much, much lower performance impact than fuel metering, at the cost of being nondeterministic. Since different embeddings have different needs there, wasmtime provides both mechanisms. Turning epochs on should be trivial if your system provides any sort of concurrency: https://github.com/bytecodealliance/wasmtime/blob/main/examp...

Not sure how to help with this much information but I've built and run wasmtime on some pretty squalid architectures (xtensa and riscv32 microcontrollers among others) but the right collection of features might not be obvious. We can help you find the right configuration on the Bytecode Alliance zulip or the wasmtime issue tracker if you need it.

All of the C primitives there implemented in (unsafe) Rust, but we built that example for an audience that already had some platform elements in C. We'll try to improve the example so that both integrating with C, and using pure Rust, are covered.