Re: Wake on USB event

On 2/1/2025 1:22 AM, Sylvia Else wrote:

On 01-Feb-25 8:36 am, Don Y wrote:

On 1/31/2025 9:22 AM, Sylvia Else wrote:

It also seems like Windows only leaves USB ports powered up
during sleep *if* they were active while the machine was awake (?).

>
It appears to me that the device drives a 'K' state onto the data lines for between 1 and 15ms. The 'K' state is the opposite of the idle state.

>
Said another way, does the exchange contain "data" (a keystroke) or
is it purely for notification?

 On my reading of the spec, it just swaps the data line levels for a period, and then swaps them back. I wouldn't expect any data transfer, because USB devices do not spontaneously send data, they respond only when polled.

That is not contradictory to my observations.
The keyboard doesn't seem to generate any "bogus" keystrokes (like a
key being stuck).  I have made a crude attempt at verifying this by
creating a Notepad document with contents similar to:
..................
........X.........
..................
and positioned the cursor just after the 'X' with the 'X' highlighted as
"selected text"; the thinking being that any keystrokes will either cause
the X to be replaced, deleted or "moved", depending on their nature.
No change (with the good *or* bad keyboard).
If things are as you suggest, then the keyboard may be *continuously*
signalling for attention and Windows simply notes "no data" -- as if
this was a "spurious interrupt".
OTOH, if the PC was sleeping, it would be awakened to query the keyboard
and would THEN discover "no data", as above.  But, having been awakened,
it would be foolish to return to sleep (imagine the sort of loop this
could create).

I suspect it's going to come down to the voltage levels on the data+ and data- lines. Data+ should stay high (above 3V), and data- should stay low. Time to build that USB breakout box.

Yup.  I wanted a theory to pursue rather than just poking around and
hoping to stumble on something.  I'll have a look at the power distribution
*inside* the keyboard (as the working keyboard suggests what's coming
from the PC is "nominal" -- at least in the case of the mouse, keyboard
and other USB peripherals)
Thanks!