Dave Ferguson responded to your earlier question about bandwidth and
bulk pipes. As he said, if you don't have a pending read or write on
a given, non-periodic pipe, the controller will not issue any
requests to that endpoint. It will, as Dave said, have to follow
some data structures in memory for that endpoint to find out that
there is nothing pending....
I'm afraid we need more detail in what you are seeing. What do you
mean by "robs the other open interface from bandwidth"? Is it that
you don't get the same amount of packets per microframe? What other
traffic is on the bus? What does a bus trace show?
--
Fernando Urbina
USB Technology Team
Apple Computer, Inc.
On Jun 12, 2005, at 5:54 PM, Juan Pertierra wrote:
Could someone shed some light on how the USB bandwidth is allocated
in Mac OS X given a device with a specific number of
configurations, interfaces/config, endpoints/interface? It seems
that even if an end point within an interface is not being used,
the system allocates bandwidth for it thus slowing everything down
a bit. However, I have also noticed that even if a configuration
has 2 interfaces and one of the interfaces is not opened, it still
robs the other open interface from bandwidth, and this doesn't make
sense to me. If I modify my device to have two configurations,
such that I can switch between the two, will this guarantee that
bandwidth is allocated only for the interfaces for the
configuration in effect?
What is also puzzling is that I am using BULK endpoints, and to the
best of my knowledge the bandwidth should be use on a first-come-
first-serve basis, so if I don't use a BULK endpoint I don't see
why it should rob bandwidth from the other endpoint, but that
definitely is the case.
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