Author Topic: Class Specific Requests interface routing confusion...  (Read 65 times)

anotherstevest

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Class Specific Requests interface routing confusion...
« on: November 08, 2018, 05:31:48 pm »
I'm still jumping around the USB Complete (5th) and maybe I've just jumped over it... (or I'm just being thick which also happens...)  But from the perspective of the device firmware, how does it know to which interface-specific code/instance is appropriate to handle the Class Specific Requests it receives on EP0.  I'm thinking, for example, of a composite device with multiple Virtual Com ports which have class specific codes for setting control line state - all of which, it appears, come in to EP0 without referencing an interface number...  What have I missed?  Is the interface number buried in the data somewhere?  My Beagle Total Data Center decodes enough to find DTR and RTS but nothing else...

Thanks for the insight (here and in the book).

Steve.


Jan Axelson

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Re: Class Specific Requests interface routing confusion...
« Reply #1 on: November 08, 2018, 06:33:27 pm »
In USB class specifications, the definitions for class-specific requests typically assign wIndex as the target interface number.

anotherstevest

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Re: Class Specific Requests interface routing confusion...
« Reply #2 on: November 09, 2018, 12:42:51 pm »
Many thanks!  It's as straight forward as I thought it should be...

Jan Axelson

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Re: Class Specific Requests interface routing confusion...
« Reply #3 on: November 09, 2018, 09:50:16 pm »
Straightforward maybe, but not obvious!