I'm looking at these long series of pushes and pops [1]. You have 26 general-purpose registers plus X, Y, Z. I wonder if it would be possible to have e.g. only 4 threads and have dedicated registers for each thread, avoiding the need to store/load all of them on each context switch. This would reduce the overhead and might make this a bit more usable in the real world.

I mean, this is certainly possible when writing assembly. But I wonder if you can convince avr-gcc to do it. To have it limit its use of registers for a part of the compiled C code.

A similar problem appears with interrupt handlers in C [2]. avr-gcc is smart enough to only push/pop registers in a handler that were actually clobbered in the code. But if you call a function pointer from an interrupt handler, it will always push/pop entire CPU state since it will assume that the code the pointer points to will potentially clobber everything. This significantly increases interrupt latency.

[1] https://github.com/TurkeyMcMac/avr_threads/blob/master/avrt....

[2] https://www.avrfreaks.net/forum/calling-function-pointers-is...