You might be able to put something together using Raspup or Ultibo. IIRC, both should be able to run on all Pi models. Both are pretty lightweight, simple, and

You might be able to put something together using Raspup or Ultibo. IIRC, both should be able to run on all Pi models. Both are pretty lightweight, simple, and they could be a good base for building what you are looking for. Raspup is a Puppy Linux for Raspberry Pi. It uses Raspbian Buster as base. I haven't messed with I2C on my Pi, but if there are any userspace tools in Raspbian Buster's repo then you can use them on Raspup. The working upgrade path is the biggest annoyance here. Package management on Puppy in general is a pain for anything but simple install and removal. It seems like the Puppy community either doesn't upgrade or upgrades by installing the next Puppy version (which is usually fast). Ultibo is not Linux but a Free Pascal kernel that doesn't implement a complete OS. It is for using a Raspberry Pi board more like a microcontroller, but you can use it as a base for anything. For example, someone made a Z80 CP/M emulator that runs pretty fast. Besides the Free Pascal library, the tools here are pretty much what you write. This is probably the simplest option for a Pi that may be alright if you don't plan on using the full functionality of a Linux machine or you want to avoid the Linux kernel scheduler.