On Thursday 11 November 2004 16:10, Rudolf Ladyzhenskii wrote:
> USB OTG is not a software extension of existing ptotocol,
> it is effectively difefrent standard alltogether.
Not so. It's the OTG "Supplement" to USB 2.0 ... an OTG
device is a "dual role" device with hardware and software
support for the Host role, the Peripheral role, and some
additions that kick in before (and between!) those roles.
OTG just builds on top of the existing USB 2.0 stack. ALL
of that stack; many operating systems only support one
role, so adding support for the other role can seem to
be almost "a different standard" (though it isn't).
> You really should read some books on USB then you will see the difference.
Or better yet, some of the short papers (and webpages) from
vendors like Philips and Cypress, and the specs at USB-IF.
Also some of the slide presentations at www.usb.org from
the relevant developers' conference.
Whereas earlier that day, Alan Stern enscribed:
> > Most host controllers are not designed to operate as slaves, and it's
> > impossible to make them do so. As just one example, a slave is not
> > supposed to supply power to the Vbus line but a master is.
The OTG way to say that is that only the A-device supplies
power ... regardless of whether it's acting in host/master
or peripheral/slave role.
> > On the other hand, there is the USB OTG ("On The Go") specification, which
> > provides a way for a device to act as either a host or a slave. Two OTG
> > devices can be connected to each other using a symmetrical cable
OTG cables are no more symmetrical than normal USB cables;
the A and B ends are different.
> > and they
> > will be able to communicate (and transfer files, for example).
Like to print the pictues, or synchronize appointments/contacts,
network to whatever, and so on.
> > Almost no
> > Linux computers have OTG hardware, however, and standard hardware does not
> > support OTG.
PCs and workstations aren't candidates for OTG,
if that's what you mean by "standard hardware".
Reference platforms for quite a few modern ARM
systems support OTG ... and Linux, though not
necessarily at the same time yet! That's
"standard hardware" for anyone developing new
Linux based products.
OTG is early in its lifecycle, and not many
folk have designed products to use it yet.
That takes time.
- Dave
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