WIP: Add support for EPD 3in7

[Alexx-G]

Relates to #68

I've relied on driver implementation for STM32 and RPi.

[caemor]

Hey Alexx, how is your current status? greetings, Chris

[mangelajo]

I am preparing an updated PR for this display, as I recently got one looking for a fast-refresh display.

[mangelajo]

I am preparing an updated PR for this display, as I recently got one looking for a fast-refresh display.

Nice I got it working with the latest release. One of the issues seemed to be that the busy signal reading was inverted.

I have also verified that the Box::new(Displayxxx:default()) approach works, I'll document that in a separate PR too.

@caemor I guess that based on previous discussions the approach for 4-gray/1-gray is having 2 different versions of the display driver, right?

[peckpeck]

Is it of any use having a B/W only version ? Is it any faster ? If no a simple 4 gray implementation should be enough

[mangelajo]

I have posted the PR here https://github.com/caemor/epd-waveshare/pull/129

We could close this PR at this point, original authorship is retained in the commit

[mangelajo]

Is it of any use having a B/W only version ? Is it any faster ? If no a simple 4 gray implementation should be enough

Memory usage is half, for 4 grayscale it doesn't work in ESP32C3 as far as I checked.

I will do timing checks , and try to factor-out common parts across 4gray/BW.

[peckpeck]

i think esp32c3 has enough memory, but i understand the argument