On Thu, 2019-02-28 at 17:02 +0000, Junge, Terry wrote: > This could also be a parser error. In the HID specification section 6.2.2.8 it > states that the last declared Usage Page is applied to Usages when the Main > item is encountered. > > "If the bSize field = 1 or 2 then the Usage is interpreted as an unsigned > value > that selects a Usage ID on the currently defined Usage Page. When the parser > encounters a main item it concatenates the last declared Usage Page with a > Usage to form a complete usage value. Extended usages can be used to > override the currently defined Usage Page for individual usages." >
Hi Terry, thanks for the comment.
Just for the record the paragraph I cited on my patch is the following:
6.2.2.7 Global Items
[...]
Usage Page: Unsigned integer specifying the current Usage Page. Since a
usage are 32 bit values, Usage Page items can be used to conserve space
in a report descriptor by setting the high order 16 bits of a
subsequent usages. Any usage that follows which is defines* 16 bits or
less is interpreted as a Usage ID and concatenated with the Usage Page
to form a 32 bit Usage.
* This is a spec errata, I belive it should say "defined"
As you can see they use the word "follows" which in my opinion contradicts the
paragraph you pointed out. That said I may be wrong, I'm not too good at
reading specs :).
I checked the HID parser and it's indeed written assuming local items are
preceded by a Usage Page. I'd be glad to fix it there, but it would be nice to
have the mantainer's opinion on the matter first.
Regards,
Nicolas
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