Werner Almesberger wrote:
DING Changchang wrote:
I have tested two Y-cables Xiangfu bought:
http://downloads.qi-hardware.com/people/xiangfu/anelok/y-cable/Y-cable.JPG
http://downloads.qi-hardware.com/people/xiangfu/anelok/y-cable/Y-cable-with-chip.JPG
Great, thanks !
They both have the ID pin connected to GND in USB Micro B port as
the OTG host.
I love it ! As far as I can tell, it's totally against anything the
USB standards define, but it's just what works best for us :-)
The first one should meet all the needs:
Works fine when connecting usb keyboard/mouse/disk on the OTG slave
(the standard USB A female)
Perfect !
The power branch does deliver power to both slave and host, only
failing in charging a Nexus5. But it can charge a Nexus4 and power
up a RaspberryPi.
Excellent ! I think the reason that it sometimes works and sometimes
not is that some systems only draw power when something on the other
end of the cable tells them it's okay to do so (e.g., when they can
enumerate), while others just assume they can do it and go ahead.
The ones that try to be "nice" therefore don't charge / power while
the ones that don't pay attention to such things will just work.
USB OTG also specifies three more protocols (ADP, HNP, and SRP) that
can make life interesting. In particular, ADP (Attach Detection
Protocol) communicates over VBUS. So it would even work between the
power-only port and devices on the other ports. I guess that could
add an extra bit of unpredictability, too.
One problem is that the power branch has a Micro B female and is not
long enough. But we can connect it with a Micro B male to Standard A
male cable which is very easy to get:
Yes, that may be an option. Anelok needs a Full A to Micro B cable
anyway, so that combination may not be overly clumsy. As an added
benefit, it also solves the problem of having a sufficiently long
cable for power, since it's easy to get these cables in all kinds of
lengths.
The second one has a chip inside.
Oh, I didn't expect this. Are there any markings on the chip that
could tell us what it does ?
It cannot work properly when all three ends are in use.
Maybe the chip implements some of these fancy OTG protocols, e.g.,
HNP (Host Negotiation Protocol) which lets a B device become host,
just to get it wrong :)
Another cable Xiangfu ordered should arrive in a few days. I will
test it later.
Great ! Let's see what this does.
Thanks a lot ! This looks very good.
- Werner
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The third one has arrived but to my disappointment, it is nothing but a
USB HUB:
http://downloads.qi-hardware.com/people/xiangfu/anelok/y-cable/HUB.jpg
And about the chip on the second one:
http://downloads.qi-hardware.com/people/xiangfu/anelok/y-cable/Chip.jpg
I searched for the name, FC18XZ 436GA, but got no result. Sound like a
custom chip.
According to its instructions, this cable can be used in three modes:
- USB charging/SYNC mode: use full usb male and micro usb
- USB to USB extension mode: use full usb male and full usb female
- USB OTG mode: use full usb female and micro usb
When all three ports are in use, it is in USB charging/SYNC mode and
ignores the device connected to full usb female.
I tried cutting off the two data wires on the full usb female side but
that did not help either.
Anyway, the first Y-cable should be ok. We have ordered some more and
will ship some to you.
CC
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