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0 pointshnarn7y ago0 comments

Also, isn't 3.0 fully backward compatible with 2.0? I imagine this would affect how critical people would classify support to be developed, if everything already works, just slower.

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3 comments · 1 top-level

floatboth7y ago· 2 in thread

It's backwards compatible on the device side (you can plug a 3.0 device into a 2.0 port and work at lower speed). But I really doubt that you can use an xHCI controller through EHCI drivers.

pgeorgi7y ago

> But I really doubt that you can use an xHCI controller through EHCI drivers.

Indeed, you can't. xHCI subsumes all USB operation and doesn't need companion controllers, but presents a _very_ different interface. That's different from the USB1/2 transition where USB2 was a separate controller that could take over the ports from a USB1 controller, giving them back if a USB1 device is attached.

Some boards/chipsets do that with EHCI and xHCI to support operating systems without xhci drivers, but that's getting rarer.

kqr7y ago

I'm fascinated this has worked so well in all operating systems I've used that I've never had reason to acquire this knowledge.

I'm simultaneously disappointed that this is not (as far as I can tell) widely known information. It sounds like the thing that may prevent you from going on goose chase if you ever need to debug it.

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