Re: Should the USB device to go into suspend when the USB host is suspended?


Sivaraj wrote:

Hi,

Arlet wrote:

Sivaraj wrote:
Can anybody please share your views on this?

Sivaraj wrote:
Hello,

Is it necessary/MUST for the USB device to go into suspend when the USB
host is suspended, provided that the device is Remote-Wakeup Enabled?
What the spec says?

Don't top-post. Have some patience (24 hours is a good time to wait).
Make sure you provide necessary details for the answer. For example,
what "host" and what "spec" are you talking about ?

Host -> PC
Spec -> USB spec

I am sorry for the top-post, i am new to this. Also i needed the answer
in quick time, i will correct myself when i post in future.. Thanks for
all your responses. Then the spec doesn't hav the info i am looking.
Actually I am testing a scenario where I am suspending the host PC and
observing the behavior of the attached USB device. I want to know this:

When I suspend the host the USB bus will be suspeneded, So if any
connected USB device will not get the bus power during this period, in
this case, what should be state of the device, should the state be
suspended or normal?

As far as a USB device is concerned, it must go into suspend mode when
it detects "suspend signalling" on the bus, and stay active at any
other time.

When a host goes into suspend mode, this is a completely unrelated
event, which just happens to use the same word. A host in suspend (or
any other power save state), has 3 options as far as the USB bus is
concerned:

1) let it stay awake
2) let it go to USB suspend
3) remove power

In the second case, the devices will still be able to receive power
from the USB bus, but at a much reduced current (2.5mA max for devices
supporting remote wakeup).

In the third case, the device will be reset and reconfigured when power
is restored, even when it is self-powered.

What the host does with the USB bus depends on the OS, hardware, and/or
user settings. If you're using Windows, you can probably find
information regarding power management on the microsoft.com site.

.

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