The Raspberry Pi Kernel  sometimes updates firmware, which can which can break the Frame Buffer Copy mechanism. In this particular case, it only seems to affect the Raspberry Pi 4. The issue appears as a garbled screen that looks like static.

To check your kernel version, run the following command:

dpkg -l raspberrypi-kernel

You should see output similar to the following. If the kernel version is later than 1:1.20210527, then the following fix should work.

We have a script that is able to set the kernel version to the kernel version prior to it breaking. To "pin" the kernel version to an older version prior to it breaking, you'll need to run a few commands. You can either SSH into the Pi or hook up an HDMI cable, though the display may appear small.

Once you'd at a command prompt, run the following commands. Note that the 1: prefix in the version number is on purpose because of the way that pinning was recently changed.

cd ~
sudo sh 1:1.20210527-1

After it finishes, reboot the Pi.

Once the Pi is back up, the display may appear inverted. To fix this, just run the Adafruit PiTFT script again and reboot a second time.

You can check the new kernel version by running the dpkg command again:

dpkg -l raspberrypi-kernel

This time, your version should be 1:1.20210527-1.

BrainCraft Audio Driver Reinstall

If your display is a BrainCraft HAT and you have pinned your kernel, you should be running a kernel version of around 5.10. You can check this by typing uname -r.

If you pinned to an older version that uses a kernel of 5.4, you may need to reinstall the audio drivers at this point to get sound working. Be sure to follow the BrainCraft HAT Audio Setup instructions for a kernel version around 5.4 when reinstalling.

Unpinning the Kernel

To unpin the kernel, just delete the file /etc/apt/preferences.d/99-adafruit-pin-kernel and update the Pi with the following commands:

sudo apt update
sudo apt upgrade

This guide was first published on Jun 25, 2020. It was last updated on Jun 25, 2020.

This page (Kernel Module Troubleshooting) was last updated on Oct 13, 2021.

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