[ltp] T400 does not enter C4/C6 sleep state with USB devices connected

[Pedro Ribeiro]

On 22 February 2010 17:13, Richard Neill <rn214@hermes.cam.ac.uk> wrote:
>
>
> Pedro Ribeiro wrote:
>>
>> However, its behaviour is really strange.
>> If I plug it in directly into a USB port in the laptop I get this:
>>
>> usb 3-1: new low speed USB device using uhci_hcd and address 3
>> usb 3-1: New USB device found, idVendor=046d, idProduct=c01d
>> usb 3-1: New USB device strings: Mfr=1, Product=2, SerialNumber=0
>> usb 3-1: Product: USB-PS/2 Optical Mouse
>> usb 3-1: Manufacturer: Logitech
>>
>>
>> But if I plug it in the mini dock, I get this:
>>
>> usb 1-5.3: new low speed USB device using ehci_hcd and address 16
>> usb 1-5.3: New USB device found, idVendor=046d, idProduct=c01d
>> usb 1-5.3: New USB device strings: Mfr=1, Product=2, SerialNumber=0
>> usb 1-5.3: Product: USB-PS/2 Optical Mouse
>> usb 1-5.3: Manufacturer: Logitech
>>
>
> I suspect what is going on is that the mini-dock contains a USB2 hub. This
> contains a "transaction translator" which sort-of converts USB1 devices into
> USB2 devices, as far as the laptop is concerned.
>
> From the laptop's perspective, the mouse-via-hub is still the same device
> that it was before, but the laptop only has to handle the USB2 protocol over
> the bus to the hub. This protocol runs much faster than USB1, and has
> support for power-management.
>
> Richard
> --
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>

That would make some sense, but the mouse still gets detected as a low
speed usb device - USB 1.1 I guess. So there is some kind of
passthrough here...

Pedro