What does "USB selective suspend" mean?

Question

In Windows 7, Power Options->USB Settings->USB selective suspend setting, what does "USB selective suspend" mean?  Also, given that there is only one setting, why does it say "USB Settings" instead of "USB Setting"?

Answer 1

A USB device driver can send a message to windows telling it to idle the device.  This puts the device in a low-power state (the suspend state).  When a USB device is suspended, windows does not wait for it to respond before entering a sleep or hibernate mode.  If you disable this feature, the system will simply return a failure to the driver when the driver attempts to enter suspend state.  If the driver complies with Microsoft guidelines, it will simply retry the idle request at every expiration of its idle timer.

Answer 2

Another confusing answer, god give me strength.

Answer 3

Why would a USB device driver send a message to Windows telling it to idle the device? Could a mouse or keyboard have such functionality? Would having this USB selective suspend enabled allow the keyboard or mouse to freeze up by going into a suspended state? I'm looking at this because I'm troubleshooting problems involving the freezing of both my keyboard and mouse at irregular intervals.

In USB, there is such a thing as a "composite device" which means different devices (simple example, webcam with a microphone) exist on the same physical device.  These have separate drivers.  Let's say you have two functions, A & B.  Function A is idle, and wants to be a good citizen and power down to save power so it issues a selective suspend.  But Function B is still in active use.  Since these functions are on the same physical device, there needs to be a mechanism for all functions to say they want to power down and when there is consensus, the device is suspended.

I hope this contributes to the conversation.

Answer 4

I googled, it got me here

Answer 5

_Kelter thanks for the explanation... now can I ask for a prediction? 

I'm having problems with Win 7 (Ultra 64) waking up from sleep, similar to lots of queries here, MS support, and the web.  After finding out how to generate a "Power Efficiency Diagnostics Report" I see multiple errors of "USB Suspend:USB Device not Entering Suspend".  Somewhere in my researching this, I found a suggestion that worked for everyone who tried it, which was to go into Device Manager>USB Controllers> and then select the first item (in my case it's "Generic USB Hub") open its Properties>Power Management and then DESELECT "Allow the computer to turn off this device..."  and then the suggestion was to do this for EVERY USB device in the list.(!!!)

So here's the question, do you think that going to Power Options->USB Settings->USB selective suspend and then DISABLING it would have the same effect as what was described above?

A similar effect but not the same.  Any newly attached device, as well any devices switched to another port will not receive this setting.  Issues start to happen when the usb port or hub is going into a lowered power state and one of the devices doesn't report as its compatible or not at all will fail to work when the port or usb is set back to a normal state.  You will then be seeing hardware errors for that device.  This is why people choose to disable any usb suspending, its not needed on my desktop machine, but it might be crucial for laptop users on the batt.