On 09/23/11 10:17, Alan Stern wrote: > On Fri, 23 Sep 2011, Steve Calfee wrote: > >> On 09/23/11 07:27, Alan Stern wrote: >>> On Thu, 22 Sep 2011, Iain Barker wrote: >>> >>>> Hi all, >>>> >>>> Is it possible to limit the maximum speed at which a USB 2.0 HUB will connect to USB devices? >>>> e.g. to make USB 2 devices connect at FULL_SPEED instead of HIGH_SPEED >>> >>> The only way to do this is to force the hub itself to connect at full >>> speed. There's no way to tell a hub to degrade just one of its ports. >>> If the hub is plugged directly into an EHCI controller and there's no >>> companion USB-1.1 controller (as is the case with Intel's >>> "rate-matching" hubs), there's no way to do it at all. >>> >> Hi Iain and Alan, >> >> Yes, there is a way to do it. Connect a FS only hub in front of the one >> you want to downshift. That will shift the entire downstream bus to FS only. > > That's what I said above: Force the hub itself to connect at full > speed. > > In this case it's not possible. The hub is built into the system; > there's no way to interpose another hub between it and the controller, > and even if there were, the EHCI controller wouldn't be able to > communicate with a full-speed-only hub. More and more we're seeing > systems that have only an EHCI controller with no companion > controllers; all communication has to take place through the built-in > hub. > Hi Alan, I see your point. However, how can this be true? How would you connect a mouse to that port? I don't know of any HS mice. An EHCI controller does not have to use a companion, it can have built in TT hardware (like the ARC/TRANSDIMENSION/chipidea/MIPS/... ehci core). That one can change speeds and not have a companion. If Iain has an external USB drive, it plugs in somewhere. If he plugs that into a FS hub, which is plugged into a USB port, then I think he will have the usb drive running at FS. Regards, Steve -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
