feat: add Epd7in3e based on e-ink Spectra6

[RitwikSaikia]

Implementation for 7.3inch_e-Paper_HAT_(E). which is based on e-Ink Spectra6 technology.

Tested on my personal display.

[RitwikSaikia]

What is required for this PR to be merged?

[dragazo]

Does this support full color? It looks like it just uses 6 colors unless I missed something. Also, it looks like some functions still have unimplemented!() placeholders, which will cause a firmware panic.

[ozwaldorf]

Does this support full color? It looks like it just uses 6 colors unless I missed something.

@dragazo The waveshare "full-color" displays are only using 6 colors. However, the colors are very vibrant so using dithering you can get a pretty decent looking image. But unfortunately it's not supporting full rgb.

[ozwaldorf]

Also having done some research into the board, it seems it doesn't support custom lut waveforms so the set_lut trait item wouldn't ever work for this display.

Similarly, there's no documentation from the manufacturer on how to send a partial or windowed update, so it seems only full buffer updates are possible

[ozwaldorf]

I have tested this using the ESP32-S3-PhotoFrame and can confirm the basic driver functionality is working as expected.

[ozwaldorf]

After reaching out to a few manufacturers producing this display, I managed to find a working implementation of partial refreshes! Additionally, I ported the sample into rust and successfully ran the partial refresh on the waveshare panel and driver.

The sample code is from the GoodDisplay variant, in the downloads section: https://www.good-display.com/product/533.html

Partial Update Implementation

Working for both GDEP073E01 or Waveshare Epd7in3e (Spectra 6e)

Command

0x83 (PTLW) - Partial Window command with 9 data bytes:

Byte	Description
0	X start MSB (bits 9:8)
1	X start LSB (bits 7:0)
2	X end MSB (bits 9:8)
3	X end LSB (bits 7:0)
4	Y start MSB (bits 9:8)
5	Y start LSB (bits 7:0)
6	Y end MSB (bits 9:8)
7	Y end LSB (bits 7:0)
8	0x01 (enable partial mode)

Coordinates are 10-bit values (max 1023). End coordinates are inclusive.

Sequence

1. Set partial window (0x83) with coordinates
2. Wait for BUSY
3. Send DTM (0x10) with pixel data for the region only
4. Wait for BUSY
5. Power on (0x04)
6. Wait for BUSY
7. Set booster (0x06) - same values as full refresh
8. Refresh (0x12, 0x00)
9. Wait for BUSY
10. Power off (0x02, 0x00)
11. Wait for BUSY

Notes

• X and width must be even (byte-aligned, 2 pixels per byte)
• Pixel format unchanged: 4bpp packed (same as full refresh)
• Buffer size = (width × height) / 2 bytes
• Uses same waveform as full refresh (no "fast partial" mode) - just updates smaller region
• Display must be initialized/awake before partial update