[opendtv] Re: USB 3.0
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Tue, 1 Jul 2008 18:19:28 -0400
Dan Grimes wrote:
> There are some distinct differences between IEEE 1394
> (a and b) and USB (1.0 and 2.0) that allow one to work
> for some applications and the other, not. For instance,
> IEEE 1394 allows video devices to directly stream DV and
> HDV encoded video straight to other devices or into
> computers. USB does not have the architecture to do this.
The most fundamental difference is that USB is a host/peripheral
interface, or master/slave if you will, and 1394 is not. USB uses a
polling protocol, where devices only speak when told to by the host,
whereas in 1394 any device can initate the connection. Both support
isochronous service, though.
So in any USB bus, a decision has to be made who the host is. In the
early days, when USB was 1.5 Mb/s max, used for mice and keyboards, that
made a lot of sense.
Thing is, some USB devices can now be configured to play either role.
Typically, for instance, PDAs can play either role, when connected to a
PC. So as speeds went up to 12 Mb/s, 480 Mb/s, and soon 4.8 Gb/s, the
expanded roles USB played made it less obvious who will end up being the
host.
The spec for 2.0 is available online.
http://www.usb.org/developers/docs/
Bert
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