The driver IC is somewhat generic, so without knowledge of the specific settings and sequences used to make the display go you wont get anywhere with the datasheet, even with the best of intentions the permutations of possible settings are basically insurmountable.
Trust me when I say, that this is the most comprehensive and concise reference you could work from: https://github.com/pimoroni/inky-phat/blob/master/library/inkyphat/inky212x104.py
Note: While the data output stages look complex, they’re not so bad. I’d say you should ignore everything related to partial updates since they’re virtually useless (albeit you might think otherwise!).
These lines:
buf_red = numpy.packbits(numpy.where(region == RED, 1, 0)).tolist()
buf_black = numpy.packbits(numpy.where(region == BLACK, 1, 0)).tolist()
Are basically just finding every pixel that’s RED or BLACK, grabbing a 2d array with them set to 1 (on) or 0 (off) and then packing that into 8bit integers where each bit represents a pixel.
Note: the 8bit integers run along the shorter (104 pixel) axis of Inky pHAT. Each “column” (actually a row in Inky pHATs perspective) is 13 bytes wide, and the whole display is 212 columns.
I’m probably not explaining this well, but if you try and pack a 212x104 buffer into bytes without first rotating it you’re going to see really weird things on the display.
In the Python library the buffer starts off as a 212x104 2d array of ints, where each int can be wither WHITE, BLACK or RED. It’s then translated by the above into a 104x212 bit array, and packed into bytes.
In C, I’d probably store two buffers (one for RED, one for BLACK) of type uint8_t and have my set_pixel() method set or clear the correct bit so I didn’t have to do any transformation of the data.
What’s the SBC you’re using, by the way?