A personal experiment to try and get this display working. I think it was successful but one of my displays sometimes don't want to update. I don't know why. Could be this code, so beware! There comes no warranty with this software.
Everything is hardcoded, pin configuration and target chip. But there are no dependencies (except avr-gcc).
I'm still putting it out here in case someone could get something out of it.
The MCU in the picture is a Atmel ATMEGA328P and the EInk display says WFT0213CZ16 LW on the back. I think that would be the HTEW0213Z16 on this official page and I think it's also the product enlisted here.
If you run this code unmodified, it should display the contents of
hello.png on the screen as shown in picture above.
I've used the official data sheet. When that one was unclear, I looked at the stm32 example code for some inspiration. This took me 1 day. Things like this should really not be that hard!
It was surprisingly hard to find a working startup sequence. I couldn't get the official AVR HelTec code to work.