PORTS Forum
Ports and Interfaces => USB => Topic started by: Renate on November 23, 2012, 10:24:20 am
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I know that I can write a driver/service/application to send reports/SET_FEATURE with any info I want from a Windows host to a USB device,
but I'd like to know if there are any OUTPUT reports or SET_FEATURE out of the standard Windows drivers that are useful.
For instance, the cap lock/num lock/scroll lock LEDs are easily accessible without doing anything on the host.
(This works in Windows/Unix.)
Is RTC in UTC available somehow?
How about current volume control level (especially since Windows does not support absolute levels on INPUT)?
How about some sort of machine or OS identification?
Any other sort of info that I could get for "free" would be appreciated.
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The main HID spec defines no Feature reports. Any Feature reports are likely defined in filter drivers that apply to specific device types. For example, I believe the keyboard reports work only on devices that identify themselves as system keyboards.
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SET_FEATURE is the obvious place to implement custom behavior based on host properties,
but I'm not really talking about that.
The keyboard LEDs are implemented as an output report.
Are any of the USB HID Usages supported as OUTPUT by the stock drivers out there?
That is, for instance, Consumer Controls : Volume as OUTPUT(data, var, abs)?
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One example:
http://msdn.microsoft.com/en-us/library/windows/hardware/jj128402%28v=vs.85%29.aspx
See also:
http://msdn.microsoft.com/en-us/library/windows/hardware/jj126194%28v=vs.85%29.aspx
I don't know of any structured documentation on what report items Windows supports for different device types.
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Even the screen brightness you cited in the first link is only INPUT.
It seems that most (all?) of the HID usages are like a TV remote control,
that is, you can go up or down but you never know where you are
(unless you have some other out-of-band feedback).
The only exception to this that I've seen is the system keyboard LED indicators.