About USB device and interface descriptors
From: shahar (shahar_at_discussions.microsoft.com)
Date: 08/12/04
- Next message: shahar: "Re: safely eject USB memory stick"
- Previous message: shahar: "Re: when does a PDO become a PDO ?"
- Messages sorted by: [ date ] [ thread ]
Date: Wed, 11 Aug 2004 18:17:02 -0700
Hi,
To my understading device and interface descriptors contain a usb device
class type that recognizes the functions the device implements (audio,
storage, printer, etc.).
There are a few things I do not understand about the usb device class concept:
1) What is the purpose of the device class mentioned in the device
descriptor ? The class is mentioned in the interface descriptor and a device
may have many interfaces. Are there cases where the class in the device
descriptor is not 0xFF or 0x00 or the same as in the interface ?
2) Say a usb mass storage device reports an interface class of 0x03 (HID),
but it still reports "USB Mass Storage Device" in it's device description. Am
I right in guessing that the USBSTOR.SYS will still be loaded and a file
system will still be mounted regulary ? If so, what is the credebility of
this parameter if windows doesn't really care what is it's value ?
3) Isn't there a networking usb device class ? The Wi-Fi USB device I just
bought reports a interface class of 0xFE and subclass 0x01 which according to
the documentation is an infra-red device and the infra-red device I bought
reports 0xFF in the device class and 0x00 in the interface class (and 0x00 is
illegal to my understanding) ?
4) From my observation the compatible ID's a PDO for a USB device sometime
contain the class and sub class from the device descriptor and sometimes from
the interface descriptor. What is the algorithm for this decision ?
5) To my understanding when a device implements more than one interface the
PDO reports a USB\COMPOSITE compatible ID, yet the PDO for the bluetooth
adapter I bought does not report this ID. how can this be ?
I hope this is not too many questions in one shot...
Thank you
Shahar
- Next message: shahar: "Re: safely eject USB memory stick"
- Previous message: shahar: "Re: when does a PDO become a PDO ?"
- Messages sorted by: [ date ] [ thread ]
Relevant Pages
|
