Saturday, May 28, 2022

xHCI

I've run into some (Windows) laptop display issues over the years, now that we're working with laptops more than desktops. Some rooting around has turned up the Device Manager. In it, under USB, the "eXtensible Host Controller Interface".

The Wiki page is actually... good here. It tells me that a laptop made up to December 2013 even if it has muh USB 3 will be on xHCI 1.0. That means USB 3 point zero. Laptops made up to early spring 2019 are xHCI 1.1 which handles USB 3.1. My main work laptop is (now) 1.2 / 3.2.

Why does this matter? Bandwidth - but not only bandwidth. It happens that bandwidth also includes display. "DisplayPort" must have the "Alt Mode". This only exists for USB 3.2, and not for all of them. ("Thunderbolt" is an Apple protocol, tho' compatible with Alt Mode.)

That is... an annoyance. USB 3 stood to do away with connecting all those ports to wires; just one docking-station was supposed to handle it. Well - not display. Better hope your laptop has HDMI.

The good news here for older laptops, is that you can daisychain additional monitors to the one you've HDMI'd. Those have to be the newer monitors however; they would chain each other over... sigh... USB 3 with Alt (== DP 1.4), or plain DP wires minimum-version 1.2.

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