On Sun, 15 Nov 2009, Alan Stern wrote:
On Sun, 15 Nov 2009, Theodore Kilgore wrote:
That doesn't explain why the old code worked with OHCI but not UHCI.
We may never know the answer.
No, it does not explain. But I am somehow less curious about that than I
was 12 hours ago. What about you? Feel that way, too?
No, I am just as curious as before. Maybe more so, knowing it has
become even less likely that I will ever learn the answer. It's
frustrating.
I see your point. And it is a very valid one. So, actually, I should
probably re-state what I said. What I really meant was, there is no longer
an emergency. Now it is merely a matter of piqued curiosity. That in
itself is a sufficient motivation for further research, of course.
One of the things which would obviously help would be, if Pixart Imaging,
which apparently was the source of the sensor chips in these cameras,
would cooperate with us. It would actually be nice to know what some of
the commands sent down to the camera are really supposed to be doing. We
have figured out an amazing portion of those things, but there is still a
lot that nobody knows, who does not have access to the SDK for the
cameras. I wonder if someone like Greg has enough clout to be able to go
and talk to companies like this, and at least get them to engage in a
two-way conversation. Not that their engineers necessarily know
themselves, of course, what they are doing and why. They really may not. I
will only say that I have seen enough to know that the people who write
the OEM drivers for lots of cheap consumer hardware can't do any better
than to put their pants on one leg at a time, just like the rest of us.
One possible explanation: UHCI always carries out its periodic
transfers at the beginning of each frame. OHCI doesn't, or least, it
doesn't have to. Now there's no good reason why this should make any
difference to the cameras, but perhaps it does anyway.
Interesting. Perhaps it does matter to the camera. The camera does, after
all, have to have the data ready to serve up at the right time in the
cycle. And if it doesn't, then no data.
If you are really interested in trying to look more deeply into this, then
why not?
Theodore Kilgore
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