If it has SPI support throw in a w3 line nic and use Rust with Smoltcp.

You could implement a simple http over serial line and then front with nginx. No TCP necessary at all. Or throw an esp32 on it, and use its tcp stack.

> and use Rust

The page mentions gcc nor clang, so chances are high the “Full C compiler” is home-grown.

If so, there probably is work to do to built a Rust compiler for it.