Seeing this has given me renewed determination to actually make progress on my WS2812 RGB LED Pocket CHIP project. Original plan was to use a 3.3V/8MHz Arduino Pro Mini in the back of the Pocket CHIP that could be programmed direct from the CHIP (which has 3.3V logic) but it turns out that making the 5V logic WS2812 work with a 3.3V logic Arduino has issues & the header at the top of the Pocket CHIP doesn't actually expose the connections you need to program the Arduino directly anyway.
I think what I'm going to do now is have either a 5V/16MHz Arduino Pro Mini or an Arduino Nano in the back of the case to control the LEDs, then have a couple of GPIO pins connected between the Arduino & the CHIP via the header at the top of the Pocket CHIP to toggle different patterns. Still a very overcomplicated way of doing it, but that's half the fun
I got started last night by working out how to get an Arduino to read the state of the Pocket CHIP's GPIO pins - had an issue with reliability until I remembered I'd need to tie the 5V & GND rails of the two devices together & then it worked fine