Troubleshooting • jwz's flappy gpio problems

jwz is having all sorts of trouble with headless Raspberry Pi 4 Model Bs having unstable GPIO.

Quoting in full from jwz: GPIO madness:

Dear Lazyweb, riddle me this:

1. Boot Pi with HDMI monitor attached: works fine.
2. Boot without monitor: all GPIO inputs "flap" about once a second.
3. Plug in monitor: 10 seconds later, inputs start behaving normally.
4. Unplug monitor: remains good. Until reboot.

WTF?

Raspberry Pi 4 Model B Rev 1.5, Debian GNU/Linux 12 (bookworm) 12.11. Two different Pis, same behavior.

I guess I don't care why it wants a monitor so badly, so I tried to fake it out and convince it that one is there. Are are all of my config.txt changes:

Code:

#dtoverlay=vc4-kms-v3ddtoverlay=vc4-kms-v3d,noaudiomax_framebuffers=2[all]dtoverlay=disable-wifidtoverlay=disable-btframebuffer_width=1280framebuffer_height=720hdmi_force_hotplug=1hdmi_drive=2core_freq_min=500core_freq=500

I tried adding this to commandline.txt, didn't help: video=HDMI-A-1:1920x1080M@60

Many people have suggested fixes in the comments, but nothing seems to fix the unstable GPIO. What has been tried and found not to work:

• display_auto_detect=0;
• hdmi_force_hotplug;
• a dummy HDMI plug isn't going to work with the particular hardware configuration.

What system software could be affecting GPIO operation, but only while truly headless?

Statistics: Posted by scruss — Mon Jan 19, 2026 5:53 pm — Replies 2 — Views 49

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