USB being upgraded for robust 12Mbit/sec connections, other features...........
techweb.cmp.com
Posted: 9:00 p.m. EST, 2/11/98
Drafters prepare 'cleaned up' spec for USB
By Rick Boyd-Merritt
NEW YORK -- The Universal Serial Bus is about to get a spring cleaning.
A USB 1.1 specification is in the works, aimed at making this
12-Mbit-per-second connection for computer and consumer-electronic
devices more robust and mature.
"It's basically a cleaning up of the spec, avoiding ambiguity and clarifying
some things which might be subject to interpretation," said Steve Whalley,
chairman of the USB Implementers Forum and a program manager for
USB at Intel Corp.
The first draft of USB 1.1 is out now to members of the ad hoc consortium
of companies responsible for developing the spec. Members include
Compaq, Digital Equipment, IBM, Intel, Microsoft and Nortel. Details of
the new spec may be discussed at the Intel Developers Forum Feb. 17,
though a full release will not be ready until midyear. Developers had
originally hoped their work would be ready for release at the Windows
Hardware Engineering Conference in April.
After the expected June release, silicon makers will have 12 months to
comply with the new spec. Any existing USB device would still be
compatible with USB 1.1 devices, and developers expect host controllers
to only require new software drivers to support the standard, although the
spec contains new recommendations for host controllers. USB hub chips,
however, will have to go through a silicon revision to be 1.1-compatible.
"There's a substantial rewrite of the chapter on USB hubs," said one
developer of the spec who asked not to be named. "A lot of issues are in
areas such
as power management, tighter timings to speed up the process of
enumerating devices on the bus, and defining more boundary conditions.
There is also some elimination of work done in hub hardware that can now
be pushed to the software stack."
In the power-management area, USB 1.1 tries to address the many kinds
of system "wake up" events that a device may encounter. To address this
issue, some suspend and resume modes have been changed.
Another part of the spec is a new "interrupt out" feature that allows a host
controller to send occasional data to a USB device with a guarantee that
the data will be delivered in a bounded amount of time. The feature serves
a set of devices-such as joysticks that offer force feedback-that don't
require multimedia streaming but do have occasional priority demands.
Much of the new spec addresses ways to eliminate relatively rare error
conditions or multiple error conditions that might occur simultaneously. "We
have not run into any situations where the bus doesn't do what people want
it to do, but we have seen some boundary conditions where the spec
doesn't guarantee everything will work as it should in some worst-case
scenarios," said the USB developer. "The number of times all these error
conditions will cascade at once is very rare, but we want to deal with them
as part of making the bus more robust and mature."
This marks the first revision of the USB spec since it was rolled out at
Comdex/Fall in 1995 and formally ratified in January 1996. Given that the
bus is just now hitting its stride in acceptance, developers are keen to
ensure USB 1.1 offers full backward compatibility. Dataquest estimates as
many as 37 million USB connections shipped in 1997, representing as
much as a 50 percent penetration rate on desktop PCs. It forecasts that 99
million USB-enabled devices could ship this year.
"With things like USB, we are trying to get off the incremental-upgrade
treadmill that PCs have been on and not force engineers to go back and
reinvent a bus every 18 months," said the USB developer. "The goal is we
don't break anything that is out there." |
