On Sat, 14 Nov 2009, Alan Stern wrote:
On Sat, 14 Nov 2009, Theodore Kilgore wrote:
Now, what is happening is that all of the supported cameras work
beautifully when hooked to a machine which is using OHCI. Most of them
also work beautifully when hooked up to a machine which is using UHCI. But
the CIF type 1 cameras fail to work properly if hooked to a machine
running UHCI. They are detected correctly, and apparently are initialized
correctly (I have looked at a bit of dmesg output, usbmon output and such,
by now) but when they are asked to emit a stream across the isochronous
endpoint the stream is not forthcoming.
I have tested now on six machines, as I said. Three of them are OHCI
type machines, and all of the cameras run. Three of them are UHCI type
machines, and the CIF type 1 cameras do not run. Of course, the problem
could be local to the driver code itself. But with a consistent pattern
like that one does begin to wonder.
It could be a matter of insufficient power. Maybe the OHCI controllers
provide more bus current than the UHCI controllers do. Are the failing
cameras bus-powered? (Also, have you tried connecting the cameras to
the UHCI controller through a powered hub?)
If that's not the case, perhaps you could post a pair of usbmon traces
for the same camera, showing how it works with one controller but not
with another.
Alan Stern
Hi,
Opening up this old thread again. To review:
The original problem has been solved, in that a missing command made the
cameras in question to work on both kinds of controllers. So there is no
crisis.
But the natural question arose, that just what is happening here, and
nobody knows, and several people were curious.
Alan Stern suggested that the use of a USB analyser might help to track
down the mystery. So I went and got one. I have not had time to do more
than to hook it up and to verify that it works, because the semester is
just ending here. I will be free by next week, having then completed the
semester's grading for my classes. And, having spent my institution's
money for the USB analyser, I intend to pursue the matter to some kind of
conclusion.
This message is to let anyone know, who is interested in the results of
the experimentation and who might have a good suggestion or two about
what to look for.
Theodore Kilgore
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