Pi Zero DFRobot 2.8" USB Display glitches


#1

Hi all, hopefully someone can chime in and point me in the right direction.

I’ve been trying to get the DFRobot USB display working on my Pi Zero and am getting mixed results. Using the handy install script I’ve been able to get it working, sort of. I’m able to display both the console and the desktop by following the respective guides but I’m experiencing horrible screen tearing and other display glitches. Text rendering over itself, random green/red lines cutting across the screen, in the case of the desktop everything is flickering around all over the place.

I expect this is some sort of resolution problem but I haven’t been able to do anything that has any real (positive or negative) impact.

In config.txt I have:

  • Forced console size with framebuffer_width=320 & framebuffer_height=240.
  • Tried the following:
    hdmi_group=2
    hdmi_mode=87
    hdmi_cvt=320 240 60 1 0 0 0
  • disable_overscan=1

Below is a photo of what I’m experiencing. This is basically a fresh install of raspbian with the kernel downgraded to 4.4.38, I’d consider this the source of the issue but I’m experiencing the same problem with a raspi a+. Any ideas?!??!


#2

First off, I’m not sure what’s going on here! But I’ve pushed a 4.4.50+ kernel module for you to try:https://github.com/pimoroni/rp_usbdisplay

As far as I understand, none of the /boot/config.txt settings will have any bearing whatsoever on the USB display- unless you’re using fbcopy or similar to try and copy the Pi’s internal framebuffer to the USB display?


#3

Yes I suspected config changes weren’t doing anything but worth a try.

I’ll give the new kernel a try when I get home, maybe I was just unlucky!


#4

Just to update; I’ve powered up and was just about to update/upgrade etc when it appears the previous glitches were gone. I’ve not changed anything…

Using nano and opening up a text file like the screenshot before shows no problems whatsoever. Good that it’s fixed itself, if not slightly worrying…


#5

Is this the classic “turned it off and on again”, my best guess for it going wrong was maybe you were using FBCopy and it was out of phase with the screen update, so it was copying half of one frame and half of another, but even so that doesn’t look like the effect that would be produced in such a case.

T’was weird!


#6

Hmm I’m not so sure, many a reboot was made and the problem persisted. Regardless it seems to be fine though, although still major problems loading the desktop (not that you’d want to do that I guess). Turns out the display isn’t suitable for my needs anyway but handy to have working!