This is vaguely related to Nettle, but may be of interest to some people on the list. I've tried to summarize how to implement ed25519 efficiently on low-end hardware, with MSP430 as a concrete example. Most of the tricks are used by Nettle's implementation as well.

Not sure if it would make any sense to try to port Nettle to such systems, but might be doable if there's interest in it. I would imagine that the need for good crypto on cheap devices is only going to increase in coming years.

See https://www.lysator.liu.se/~nisse/misc/ed25519-msp430.html.

Regards, /Niels