Y-cable and USB-OTG: mutually exclusive

Werner Almesberger werner at openmoko.org
Wed Apr 30 20:15:42 CEST 2008

Joachim Steiger wrote:
> - i really like my mini-usb. (for mechanical, practical and spread in
> the real world)

Me too. Of course, if the market really switches to micro-USB, the
scenario may be very different in a few months. If only Nokia use
micro-USB, we'll be of course happier with mini.

We may be able to design for one, and change our minds later. The
problem here is mainly the case. Apparently, it's fiendishly
expensive and time-consuming to make the molds, but some changes
can apparently be accommodated without too much pain.

> - the N8xx series is the only device i know i were near which does OTG
> as far as i know.

I don't know enough about OTG to tell whether it's actually good or bad.
Of course, if it becomes popular, we'd look rather silly with our own

> * i would rather like A due to the more widespread of cables and
> devices, but its propably too big

Yeah, I'd have to dig quite deep into my gadgets box to actually
find something that does mini-A.

> * put a single 2-positions switch below the battery flap to switch this
>  whole port to jtag.

That's where your proposal gets a bit messy. It means that we couldn't
have JTAG/serial console and host mode. So if anything blows up there,
we're blind. Not the end of the world (after all, we survive quite well
on the PC, without having all these niceties), but unpleasant.

> please let me know what you think

The host vs. JTAG/console exclusion aside, it has a nice ring to it.

One bit that may be troublesome is the USB switch, though. USB is very
finicky about line impedance, reflections, an all that, so making a
switch that doesn't distort the signal too much may be difficult to

- Werner

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