USB devices and processor C3 state at w2k

NTDEV
1

Problem: when our USB device is attached to a notebook running w2k,
processor never enters C3 power saving state. At XP and above the solution
is selective suspend but it doesn’t exists at w2k. I wonder is there is some
solution (software; physical device disconnect works but isn’t acceptable).

Till now we consider two imperfect solutions. First, simulate physical
disconnect. Firmware could detach device from USB on request from host. The
disadvantage is host software can’t access device until it decides to attach
back. Second, host software could disable part of USB stack. Unfortunately,
disabling device alone is insufficient, even USB Root Hub disable isn’t
enough. It is necessary to disable USB host controller (at least at XP when
selective suspend is disabled).

Is there something better? Note we use system supplied usbscan driver at w2k
but if own driver can solve it some way, it would be acceptable (despite of
very unhappy developer :).

Best regards,

Michal Vodicka
STMicroelectronics Design and Application s.r.o.
[michal.vodicka@st.com, http:://www.st.com]

2

See if this can help you:
http://support.microsoft.com/default.aspx?scid=KB;EN-US;Q297045&

Regards,
Dev

-----Original Message-----
From: Michal Vodicka [mailto:xxxxx@veridicom.cz.nospam]
Sent: Thursday, February 19, 2004 7:03 AM
To: Windows System Software Devs Interest List
Subject: [ntdev] USB devices and processor C3 state at w2k

Problem: when our USB device is attached to a notebook running w2k,
processor never enters C3 power saving state. At XP and above the solution
is selective suspend but it doesn’t exists at w2k. I wonder is there is some
solution (software; physical device disconnect works but isn’t acceptable).

Till now we consider two imperfect solutions. First, simulate physical
disconnect. Firmware could detach device from USB on request from host. The
disadvantage is host software can’t access device until it decides to attach
back. Second, host software could disable part of USB stack. Unfortunately,
disabling device alone is insufficient, even USB Root Hub disable isn’t
enough. It is necessary to disable USB host controller (at least at XP when
selective suspend is disabled).

Is there something better? Note we use system supplied usbscan driver at w2k
but if own driver can solve it some way, it would be acceptable (despite of
very unhappy developer :).

Best regards,

Michal Vodicka
STMicroelectronics Design and Application s.r.o.
[michal.vodicka@st.com, http:://www.st.com]

Questions? First check the Kernel Driver FAQ at
http://www.osronline.com/article.cfm?id=256

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3

> See if this can help you:

http:
>
It doesn’t seem to apply. If I understand it correctly, it solves problems
when no USB device is attached and laptop still can’t enter C3 state. This
is no problem in our case. Thanks anyway.

Best regards,

Michal Vodicka
STMicroelectronics Design and Application s.r.o.
[michal.vodicka@st.com, http:://www.st.com]</http:>