Link Power Management (LPM) support and testing RRS feed

  • Question

  • Hello:

    I got a couple of questions relating to Link Power Management (LPM) as below:

    1/ Is LPM supported in Windows 7 that has USB 3.0 HCI (i.e. xHCI) with hw support for LPM. Assumed that device is either USB 2.0 or USB 3.0 with hw support for LPM. I am looking for a yes or no answer here. If yes, then what specific test jobs in the latest HCK 2.1 specifically test this ? If no, and this is only for Windows 8/8.1, why not? since Windows 7 is going to be around for at least another year or so.

    2/ This is related to the above question. I need to know the HCK 2.1 test jobs that specifically test LPM for Windows 8.1 and Windows 7 (if the answer above is yes)

    3/ What is the difference between LPM (hw solution), and the current USB selective suspend/resume (sw solution) other than one is hw based and the older one is sw based. Do they mutually exclusively exist? How does LPM trigger? Is this strictly via "Power Management" tab under device properties? (a/ Allow the computer to turn off this device to save power, b/ "Allow this device to wake the computer").

    The difference is that if both Host Controller and Device support LPM via hw/fw, then LPM will kick in. Else if hw does not support, then the old traditional sw based will be used?

    4/ While testing, I observe the below and it does look like a bug to me.

    I test with Windows 8.1, Dell Precision M4600 which has Renesas USB 3.0 xHCI (0.96 spec). The laptop also has Intel EHCI on it.

    The "Remote Wake Up" feature, "Allow this devivce to wake the computer" does not work when attached to one of the EHCI port. However, it does work when attach to one of the xHCI port.

    The difference between the Intell EHCI and Renesas xHCI is that the xHCI expose the Root Hub port directly to the attached device where the EHCI does not but rather via an intermediate generic hub ports.

    The issue here is the backward compatibilty of this feature is now broken, the "Power Management" feature no longer work when device attached to EHCI where it always been working on Windows 7. Can someone on the Microsoft team comment on this?




    Monday, June 9, 2014 9:04 PM