Epd.sleep(), machine.deepsleep() and partial updates: It's Possible!!!

[julien123123]

Hi,
First, thanks @phoreglad for writing that library!

I was looking for a way to save energy for a clock program that I am developing. I really wanted to be able to put my esp32 in deepsleep and not have to do a full update every time because it would be way too annoying. At first, I thought I had to rewrite parts of your library, and then I stumbled upon this article that suggested there was a simpler way.

As you may know, if I do a partial refresh after the display has been put to sleep, it will just put the new update over what was already on there. But, if I save the permanent buffer, aka 'epd._buffer_red', and I send it to the e-paper driver chip over SPI after a re-init after sending the command 'epd._send_command(0x26)', without sending the display update command, I can do my partial update as usual, and it will show the same way as if I never sent the display to sleep. If I want to send my esp32 to go into deep sleep in between updates, I can just send the last "permanent" buffer in a JSON file and load it on every wake up. (Yes, I totally broke the headers of the pico e-paper display to make it fit in a neat case with my esp32)

I thought it would be interesting for you to test and maybe add as a method. I wrote an example script for that, but I didn't know if it was useful to share it, as I'm using specific fonts with the Writer library.

[julien123123]

Here, I decided to make the demo file with annotations: https://gist.github.com/julien123123/9ec01d29f1dbf63ccfee3fc34e533984

It works with the contents of the examples folder of the library, and the file has to be main.py so that the deepsleep portion works.
Hope this helps someone!