I made progress on my custom firmware for the nuphy air60!

I setup a sdcc-based toolchain and produced working firmware that initializes all the base peripherals: sys-clock, watchdog, ldo, uart.

This allows me to run my own code and jump back into the ISP bootloader making it a fairly ergonomic dev setup.

Read more: https://carlossless.io/nuphy-air-60-part-2/
Code: https://github.com/carlossless/sh68f90a-experiments