USB multipleclass enumeration

Nov 08, 2007 3 Replies
J

Hi Group-



I was wondering if the USB standard allows for a physical device to enumerate as more device connection. I tried searching for the answer using Google and I come up empty.



Does anyone know?



For example, let's say I have a test and measurement device that will use USBTMC but I also want to be able to communicate with it on a non-USBTMC bulk endpoint for the purposes of receiving streaming binary data from the device. My vision is a USBTMC compliant device with an out-of-band channel for supplemental purposes. I think the concept is valid but I just don't know if the concept will fit in with USB standard.



If it's possible, can anyone point me to any examples?



Thanks, John Speth


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J

I'd like to correct my question that had a typo:

I was wondering if the USB standard allows for a physical device to enumerate as more THAN ONE device connection.

Sorry about that.

John Speth

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S

se

the

Hi John,

USB protocol allows you to report several logical functions on one physical device. This is called a composite device (this is what you should google if you want more info on how to do it, or straighter:

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the full USB2.0 specification is public and free, have a look at chapter 9).

The main problem, as my experience goes, is whether the drivers on the host will behave nicely enough to share the access to you device. On some project for my employeer, I have noticed it's sometimes not the case... unfortunately.

For example, I have an all-in-one copier/scanner/printer. When I connect it to my laptop, it advertises one function for the printer, and one function for the scanner (and maybe one for the integrated memory card reader)

Cheers,

St=E9phane

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C

A lot of USB audio devices create multiple (>2) devices, for example.

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