The Raspberry Pi Foundation has confirmed it is working on a firmware update to resolve an unusual bug with its latest Raspberry Pi 4 Model B single-board computer: Running the device at high resolutions can, in particular circumstances and with particular cables and access points running at specific frequencies, knock out its ability to connect to Wi-Fi networks.
The issue first received some publicity courtesy of Enrico Zini, who discovered that the Raspberry Pi 4 boards being used to construct a digital signage system dubbed Himblick were dropping off the Wi-Fi network. A bit of testing later, and Zini found that the problem only occurred when running the boards at a 2560x1440 resolution; dropping to a lower display resolution resolved the issue immediately.
While Zini found the flaw occurred with the official Raspberry Pi micro-HDMI to HDMI Cable accessory, further testing carried out by the Raspberry Pi Foundation suggests that it's more likely to occur with cheaper HDMI cables with inadequate shielding — and then only with specific access points running on the 2.4GHz band and on Channel 1, 2, or 3.
"We're aware of the report, and have managed to reproduce the issue with one particular access point and (cheap) cable," confirms Raspberry Pi Foundation co-founder Eben Upton via email. "The original reporter seems to have been using the official cable, so that's a bit of a mystery.
"We're likely to ship a firmware update to address the issue in the next week or so. In the meantime, anyone who wants to use the 2560x1440 resolution, and who is experiencing this issue, should adjust their router to use 2.4GHz Channel 4 or above, or the 5GHz band."
The latter workaround pushes the radio frequency used for the Wi-Fi connection above the harmonics created by the HDMI output, and should get those affected by the issue back up and running while the Foundation works on a firmware fix.