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Make displayio more flexible to support more controllers (like the one in Waveshare 1.54inch e-Paper V2) #7560

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dquadros opened this issue Feb 9, 2023 · 3 comments · Fixed by #7891
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Make displayio more flexible to support more controllers (like the one in Waveshare 1.54inch e-Paper V2) #7560

dquadros opened this issue Feb 9, 2023 · 3 comments · Fixed by #7891
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@tannewt
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displayio enhancement
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8.x.x

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@dquadros
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dquadros commented Feb 9, 2023

At the moment displayio makes many assumptions on the format of the display controller commands, limiting the controllers it can support.

In my particular case I tried to create a driver for the Waveshare 1.54inch e-Paper V2 display (datasheet). While the display has a 200x200 pixels resolution, the row addressing commands (0x45 and 0x4F) use a two byte, LSB first, parameter for the row. Function displayio_display_core_set_region_to_update() (at displayio_core.c) assumes a one byte parameter for self->ram_height less than 256 and a two byte (MSB first) parameter for self->ram_height greater than 255.

To support this controller there is a need of a more flexible way to specify the format of row addressing commands (or a way to override this in the python code, which would probably have performance issues).
@tannewt
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tannewt commented Feb 9, 2023

It looks like this display is using an SSD1681: https://www.good-display.com/product/208.html

We have a CircuitPython driver for it here: https://github.com/adafruit/Adafruit_CircuitPython_SSD1681/blob/main/adafruit_ssd1681.py

The main trick is that you can set ram width >256 but then say this display is only 200 wide. That'll use the two byte form but only compute 200 pixels wide.

@tannewt tannewt closed this as completed Feb 9, 2023
@dquadros
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dquadros commented Feb 9, 2023

It looks like this display is using an SSD1681: https://www.good-display.com/product/208.html

We have a CircuitPython driver for it here: https://github.com/adafruit/Adafruit_CircuitPython_SSD1681/blob/main/adafruit_ssd1681.py

The main trick is that you can set ram width >256 but then say this display is only 200 wide. That'll use the two byte form but only compute 200 pixels wide.

I actually tried that before opening this issue... It does not work because the byte order for the row is different. In display_core.c we have:

if (self->ram_height < 0x100) { data[data_length++] = y1; data[data_length++] = y2; } else { data[data_length++] = y1 >> 8; data[data_length++] = y1 & 0xff; data[data_length++] = y2 >> 8; data[data_length++] = y2 & 0xff; }

The display datasheet (and the manufacture's example code) shows:

image

Anyway, thanks for the fast reply!

@tannewt tannewt reopened this Feb 9, 2023
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tannewt commented Feb 9, 2023

Ah ok. @makermelissa wrote that driver and can let us know why it is that way. We could add a flag for byte order if needed.

@dhalbert dhalbert added this to the 8.x.x milestone Feb 17, 2023
@dhalbert dhalbert assigned dhalbert and tannewt and unassigned dhalbert Apr 14, 2023
@tannewt tannewt mentioned this issue Apr 21, 2023
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dhalbert pushed a commit that referenced this issue Apr 26, 2023
@tannewt
Add address_little_endian for displayio
7089ea4 
Add address_little_endian for epaper displays with little endian
(low byte first) addresses.

Also clears allocated display and display bus memory so it has a
known state. The acep member wasn't always set so it varied
accidentally.

Fixes #7560. May fix #7778. Fixes #5119.
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Add address_little_endian and fix display memory reuse tannewt/circuitpython
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