C/C++ is the most common IME, but Rust is coming along nicely. I'm working on a commercial firmware for ATSAMD21 using Rust, and have been finding it quite a n

C/C++ is the most common IME, but Rust is coming along nicely. I'm working on a commercial firmware for ATSAMD21 using Rust, and have been finding it quite a nice experience. The tooling is great, PACs and HALs are at least as good as the last time I used the Atmel-provided ones, it's really nice being able to just add a line to Cargo.toml to bring in a library rather than cribbing from a prior project or writing my own. That said, the Rust HAL for SAMD21 is certainly not complete; I'm working from a forked version of it, and have issued a few PRs to extend/fix it and other libraries. There are a few areas, DMA in particular, where the community hasn't quite decided on the right approach.