Advent of Code, but on the ATSAMD21G18, specifically an Arduino Nano 33 IoT, which I had in a drawer.

After I did all of last year's AoC in under one second, I wasn't really sure what to do this year. I'll probably be busier than last year as well, so I don't expect to actually finish in December (or at all). Instead I figured it would be a fun to add some additional constraints and see how far I can get, and maybe learn something along the way.

I've been doing more and more embedded Rust over the last two years, but I still feel out of my element compared to "regular" Rust.

So this is Rust, but without the std and alloc libraries, which means no String or Vec or any kind of dynamically-sized, heap-allocated data structures.

At first I was actually considering the Arduino Uno and its ATmega328p, but 32 kB of program space is tricky if I want to include the input in the binary via include_str!() (though I could drip-feed it in via serial), and 2 kB of memory will be prohibitively small.

Instead I'm using the more powerful SAMD21. Processing speed probably isn't too bad at 48 MHz, and 256 kB of program memory should be fine as well. We will see how far 32 kB of memory get me, that's only 4,096 u64s, minus the working stack.

For obvious reasons I will only run one day at a time.

So far, yes. I use the Arduino serial console to grab the results, which are printed on a loop.

Grab a bunch of dependencies:

• rustup
• arduino-cli
• just

arduino-cli core install arduino:samd
cargo install cargo-binutils
rustup component add llvm-tools-preview
rustup target add thumbv6m-none-eabi

Make sure to place your puzzle inputs in the inputs directory.

Build and flash with:

just build day-01
just upload /dev/tty.usbmodem123

The name of the serial port will vary based on the current phase of the moon. Mine is either 101 or 1101.