Memory Low

The Cortex M3 based boards I’ve been playing around with are quite astounding, the MCUs they use as Systems-on-a-Chip have a very nice range of peripherals which really only leaves your imagination as a limit to what can be done. Being able to interface with off-the-shelf MMC cards for example, or talking to a simple LCD module is pretty neat.

The only major drawback is that those chips usually have very little RAM, even compared to the Newton ;) - eight to 64 kBytes are not exactly a lot. When using CoreForth as my experimental platform, it is therefore interesting to play around a bit with different memory management approaches. Forth itself usually likes to live in RAM since it is more powerful when self-modifying code can be used, but there are ways around this limitation.

When it comes to multitasking though (which is relatively trivial using a Cortex M3 since it pushes most registers onto the stack when an interrupt occurs), a traditional preemptive threading model is quite wasteful what comes to RAM as each thread needs a separate stack. But the revival of event based programming through Node.js led me to check local continuations , in other words, functions with multiple entry points. In this area, protothreads look particularly promising for an implementation in Forth!