I just picked up a Waveshare 7.5" e-paper display + HAT. I’ve got it working using the provided demo implementation using Python, over SPI, but now thinking about writing a Scenic/Nerves driver for it. Before I jump in, has anyone tried this or anything similar already?

That sounds like a fun project! I haven’t done anything with e-ink displays yet. This one doesn’t seem to be available anymore, but is it kind of in line with what you’re thinking? http://www.pervasivedisplays.com/kits/mpicosys740

This one has promise with a built-in controller and uses SPI: https://www.waveshare.com/7.5inch-e-paper.htm. I can’t guarantee anything will work (you’ll have to do some trial and error, but that’s part of the fun!). There’s Raspberry Pi help in the wiki here https://www.waveshare.com/wiki/7.5inch_e-Paper_HAT#Working_with_Raspberry_Pi.

If it’s an SPI display, there are kernel drivers available for these displays so it might just work out of the box or you need to build a specific Nerves system (I just did that yesterday for a TFT SPI display). Driving it can either be trivial (boot Xorg, although on an e-ink display that’d be, err, “interesting”), doable (steal from my Uderzo project–the best solution of course ;-)), or pretty hard (drive the SPI display directly).

As far as I can tell, most people draw to the RPi’s videocore framebuffer and then copy each frame to SPI, which is what I ended up doing. The copy operation, after some setup, is two lines of code. I don’t think that it matters whether you have a TFT or an e-Ink display.