Raspberry Pi 4 WiFi stops working at 2560 x 1440 screen resolution
This is part of a series of post on the design and technical steps of creating Himblick, a digital signage box based on the Raspberry Pi 4.
One full day of crazy debugging, and the result is that if the Raspberry Pi 4 outputs HDMI at a resolution of 2560×1440, the WiFi stops working.
Any lower resolution we tried, from 2048×1080 down, does not show this problem.
We did not try any resolution above 2560×1440, for lack of a monitor that would do it.
We reproduced this:
on both microHDMI outputs
with two different cables: one with a microHDMI to HDMI dongle adapter; one direct microHDMI to HDMI. The latter is the one I bought in the Raspberry Pi Store in Cambridge together with one of the Pi 4 units.
with three different RaspberryPi units
with 4 different power supplies: one rated at 2A, one rated at 3A, one rated at 3A bought in the Raspberry Pi shop in Cambridge, and a laptop USB-C charger
with stock Raspbian Buster Lite
with stock Raspbian Buster
killing every process in the system, starting the network manually with wpa_supplicant and dhclient, and starting X manually with sudo X
with two different SD cards
connected to an AP some meters away, and connected to a phone hotspot next to the Raspberry PI
This post seem to have become quite popular, so to be clear, the intention is to document the issue that we spent a whole day chasing so that others won’t have to.
It’s been fantastic to see how this has made the rounds and resulted in actual RF measurements being made, and better pinpointing of the issue than we could ever have achieved.
I greatly admire Raspberry Pi’s work. Thanks to them we get to have an affordable standard platform with a wide use base, which over time gets extremely well known, and as such can be a very well mapped ground to build on.