We use multiple configurations on our device, I think it might
illustrate how it may be useful.
Our USB device send a very large amount of information over USB to
the computer, using IN endpoints.
However, we need to configure the device by sending a little
information from the computer using OUT endpoints.
If we just have one configuration with both the setup OUT endpoints
and the data acquisition IN endpoints, the mac will allocate USB
bandwidth by dividing it among all the endpoints, yielding a lower
available bandwidth for the important data acuiqisition IN
endpoints,while allocating way too much bandwidth to the setup OUT
endpoints which are only used briefly.
Therefor, we have a configuration for setup, and another
configuration for actual operation. This causes the mac to allocate
full bandwidth to the IN endpoints when the data acquisition
configuration is selected.
Hope this helps,
Juan
--------------------------------
Juan P. Pertierra
Chief Engineer
Reel Stream LLC
Ph: (765) 807-2509
Fax: (765) 807-5060
email@hidden
--------------------------------
On Feb 16, 2006, at 4:03 PM, Dan Smith wrote:
We have some version 0.001 firmware running on a Cypress EZ-USB FX2LP
prototyping system. I'm trying to write Mac OS X code to talk to
it. I'm
following the sample code in USB Device Interface Guide,
2005-11-09, fairly
slavishly.
I was encountering some very weird semi-reproducible problems. What I
eventually found was that these problems were associated with my
attempts to
configure the device, a la Listing 2-5. If I simply omitted this step,
everything works perfectly.
So, our firmware engineer is saying, "I haven't paid much attention
to that.
I've assumed that the Cypress-provided code was taking care of it
automatically
but now I'm not so sure."
The question I have is this. Our device is only going to have one
configuration, and it's going to be vendor-specific. As a matter of
good
practice, if you know that a device with device ID so-and-so,
product ID
so-and-so has only one configuration, would you bother to go
through the
configuration steps anyway, or would you skip them?
Second, neither the Cypress book nor "USB Complete" explains very
clearly just
what would be some real-world examples of multiple configurations,
or how they
would be used. What are some real-world examples? Do end user
typically select
a configuration in some utility? Does a system typically configure
the USB
device as soon as it's connected, or does it get switched from one
to another
while it's running, or what? What are they for, and how are they
typically used?
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