This is something that perplexed me a few years ago with Flash Forth on a PIC18/PIC24/Arduino Uno. I was using the Python serial emulator S-Term because it is simple in the source code and worked. I really wanted a way to load more structured Words into the FF dictionary with bookmarks in a way that made sense structurally. That lead to a desire to execute code from the uC on the host system, but I never wrapped my head around how to do this in practice.

As a random simple example, let's say I set up an interrupt based on the internal temperature sensor of the PIC18. Once triggered the uC must call a Python script on the host system and this script defines a new FF word on the uC by defining the Word in the interpreter.

How do you connect these dots to make this work at the simplest 'hello world' level? I tried modifying S-Term at one point, but I didn't get anywhere useful with my efforts.