Displayio column & row commands are 16 bit (need 8 bit too)

[rdagger]

I wrote a CircuitPython displayio driver for the SSD1351 OLED 128x128 display. I confirmed the init sequence works by manually sending SPI commands to the display using the FourWire.send() method. However, none of the displayio commands work.

A closer look with a scope shows that displayio sends 16 bit values when it calls set_column and set_row. The SSD1351 expects 8 bit values for column and row.

Would it be possible to add a command_byte_length parameter to the displayio.display class constructor? It could default to 2 for 16 bit displays such as the ILI9341 and the user could pass 1 for 8 bit displays like the SSD1351.

[makermelissa]

@rdagger I noticed there's a comment in CircuitPython with this issue with a "To Do" next to it, so let's leave this open. However, I was able to get a working driver without this change for the SSD1351. As of right now the PR hasn't been merged yet, but you can download it off my repo until it has.

[rdagger]

@makermelissa I tested the SSD1351 driver and the example that you linked above and it doesn't work yet. I don't see how it could until the changes to set_column & set_row byte length are added?

Maybe I'm misunderstanding your post or maybe you have a different revision of the SSD1351? I'm using a generic SSD1351, but the Adafruit SSD1351 datasheet also shows a single byte for column/row start and a single byte for column/row end (page 36, section 10.1.1 & 10.1.2).

[dhalbert]

Could be 4.0.0 milestone or could be 4.x, depending on whether this appears to be necessary.

[makermelissa]

Thanks for testing @rdagger. It must have been the CircuitPython PR I prepared for this. I'll test it with the PR again.

[makermelissa]

Oh, I didn't address your comment @dhalbert. I'd say it should remain a milestone since it's necessary for displayio to work on certain displays.

@rdagger I swear it was working last night, but it's not working for me anymore, so now I'm trying to figure out what I did so I can duplicate. :)

[rdagger]

Seems like it will be difficult for the displayio.display class to maintain compatibility across all the different LCD displays. I took a look at writing a driver for an older Adafruit ST7565 display. Instead of a set_column command it has set_column_upper and set_column_lower commands. Instead of set_row it has set_page (The display is broken into 8 horizontal pages which are numbered from the center 0 to 3 and 7 to 4).

[deshipu]

Fortunately there is a very limited number of different displays in use in there, and all the new ones follow the MIPI standard, so we could either hard-code the weird ones or simply completely leave them out.

[makermelissa]

In certain cases such as this display, I think there is enough flexibility to get it working. I had it displaying the other night, but must not have unplugged the display before testing Beta 5, so something was still properly initialized when I tested. I do know it works under the right conditions though.

[makermelissa]

Ok, I figured it out. I was using && instead of & for bitwise and. Once I fixed that it worked beautifully. Submitted PR so hopefully we'll get that up and running pretty soon.