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Discussion Groups | Comp.Arch.Embedded | USB Remote wakeup

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USB Remote wakeup - Sandeeptssmg - 2009-12-07 00:32:00

Hi,
 I have a query on USB remote wakeup. While the device performs resume
signalling for ~1-15msec which wakes up the hub and inturn the host. 

What if there are multiple resume signalling's initiated from the device
when the hub/host is already up ?  

Will those consecutive resume signalling be ignored from host ?

Kindly let me know your valuable inputs.

Regards,
Sandeep	   
					
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Re: USB Remote wakeup - Arlet - 2009-12-07 01:57:00

On Sun, 06 Dec 2009 23:32:16 -0600, Sandeeptssmg wrote:

> Hi,
>  I have a query on USB remote wakeup. While the device performs resume
> signalling for ~1-15msec which wakes up the hub and inturn the host.
> 
> What if there are multiple resume signalling's initiated from the device
> when the hub/host is already up ?
> 
> Will those consecutive resume signalling be ignored from host ?

According to USB 2.0, section 7.1.7.7 Resume:

 A device with remote wakeup capability may not generate resume signaling
 unless the bus has been continuously in the Idle state for 5 ms (TWTRSM).
 This allows the hubs to get into their Suspend state and prepare for
 propagating resume signaling. The remote wakeup device must hold the
 resume signaling for at least 1 ms but for no more than 15 ms (TDRSMUP).
 At the end of this period, the device stops driving the bus (puts its
 drivers into the high-impedance state and does not drive the bus to the J
 state).

So, multiple resume signaling is not allowed.

The resume 'K' signaling from the device may interfere with data coming
from the hubs/host, and lead to errors.