EPD7in5 support

[str4d]

No description provided.

[str4d]

This seems to be about twice as slow to write to the screen as the Waveshare Python controller (specifically the July 10 2017 version, which is what I currently have hooked up to my screen), despite using the same panel settings.

[codecov-io]

Codecov Report

Merging #33 into master will increase coverage by 11.62%.
The diff coverage is 45.03%.

@@             Coverage Diff             @@
##           master      #33       +/-   ##
===========================================
+ Coverage   29.64%   41.26%   +11.62%     
===========================================
  Files           8       15        +7     
  Lines         533      853      +320     
===========================================
+ Hits          158      352      +194     
- Misses        375      501      +126

Impacted Files	Coverage Δ
src/epd7in5/command.rs	100% <100%> (ø)
src/epd7in5/graphics.rs	100% <100%> (ø)
src/epd7in5/mod.rs	4.59% <4.59%> (ø)
src/traits.rs	0% <0%> (ø)
src/interface.rs	0% <0%> (ø)
src/color.rs	84.84% <0%> (ø)
src/graphics.rs	95.14% <0%> (ø)
... and 1 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9390f9a...3bd62b3. Read the comment docs.

[str4d]

Measuring some drawing times (DATA_START_TRANSMISSION_1 + DISPLAY_REFRESH):

• Old Python driver: 24s
  • Buffer is 30720 bytes (= HEIGHT * WIDTH / 8)
  • Writes 4 data bytes per buffer byte
• Latest Python driver: 30s
  • Buffer is HEIGHT * WIDTH / 4 bytes
  • Writes 2 data bytes per buffer byte
• This Rust driver: 53s
  • Buffer is HEIGHT * WIDTH / 8 bytes
  • Writes 4 data bytes per buffer byte

[caemor]

The code looks good. Could you add the 7in5 display to the readme as well?

[caemor]

Measuring some drawing times (DATA_START_TRANSMISSION_1 + DISPLAY_REFRESH):

* Old Python driver: 24s
  
  * Buffer is 30720 bytes (`= HEIGHT * WIDTH / 8`)
  * Writes 4 data bytes per buffer byte

* Latest Python driver: 30s
  
  * Buffer is `HEIGHT * WIDTH / 4` bytes
  * Writes 2 data bytes per buffer byte

* This Rust driver: 53s
  
  * Buffer is `HEIGHT * WIDTH / 8` bytes
  * Writes 4 data bytes per buffer byte

You are using one of the raspberry pis?
Can you give me a link to the specific version you were using? I don't know why we are so much slower besides maybe doing some additional checks, but that shouldn't slow us down so much 🤔

[str4d]

Added to the readme.

Can you give me a link to the specific version you were using?

I'm using the Raspberry Pi Zero W.

[caemor]

Added a new issue for the performance tracking

[caemor]

@str4d do you remember if you used the same spi-frequency?