Military Embedded Systems Spring 2005 Volume 1 Number 1

Industry Analysis
MILITARY EMBEDDED SYSTEMS Resource Guide
VMEbus technology and its life cycle
By Jerry Gipper
Life cycle longevity is one of the
key attributes of VMEbus that
contributes to its popularity in
defense programs needing highend
embedded computing solutions.
Suppliers of VMEbus technology have
listened well to their users. Over the years,
significant improvements have been made
to the performance and capabilities of this
technology. The industry suppliers have
developed a technology roadmap that preserves
backward compatibility of today’s
solutions with those of the past. Utilizing
a VME life cycle model is generally good
life-cycle planning practice. The VME
Standards Organization continues to battle
the pros and cons of new technology and
backwards compatibility. They have made
reasonable accommodations where possible
giving suppliers alternatives to move
forward with leading-edge technology at a
pace that suites their target markets.
The original VMEbus specification
(VME32) started out as a definition for a
parallel computer bus supporting 24-bit
addressing and 16-bit data paths with
expansion capability to 32-bit addressing
and 32-bit data paths. The theoretical
maximum performance of the bus was
40 MBps and it was considered exceptional
if a product could hit 20 MBps. The first
generations of products took several years
before they started pushing the capability
envelope of the original specification.
VMEbus enhancements
Enhancements were later proposed and
adopted that pushed the capability to support
64-bit data paths (commonly referred
to as VME64) and raised the theoretical
throughput bandwidth to 80 MBps. To
fully use the enhancements required that
a new VME connector be implemented,
this connector was cleverly designed so
that VME64 products can be completely
compatible with the original VME32 generations.
Recently, the VMEbus specification was
enhanced once again to VME 2eSST, that
extends performance by adding a two
edge, source synchronizing data transfer
capability that allows sustained data transfers
in excess of 300 MBps. VME 2eSST
is totally backwards compatible with
existing connectors and backplanes. The
secret sauce is in new incident wave bus
transceivers that allow older backplanes
to handle the high speed waveforms. The
original VME32 specification had enough
foresight to provide for VME 2eSST type
capabilities without redefining the original
bus protocols. Most importantly, this
means that software does not have to be
rewritten to use the new protocols.
Concepts exist that could take the parallel
VMEbus to over 500 MBps while maintaining
that ever important backwards
compatibility. VMEbus technology has
also embraced the movement to serial
switch fabric solutions. These solutions
are not necessarily a new concept but they
are gaining new acceptance as they have
become more practical and have shown
tremendous ability to provide scalable
high bandwidth.
Ethernet is now one of the most common
fabric solutions. The VME technology
family has several alternatives to choose
from that use Ethernet. VITA 31, which
adds Gigabit Ethernet on VME64 backplanes
via a previously defined P0 connector,
is the first generation of switch
fabric solutions implemented in VMEbus
backplanes. VITA 31 works with the existing
VME32, VME64, and VME2eSST
configurations.
VME Switched Serial (VXS) combines
the event driven parallel VMEbus with
enhancements to support switch fabrics
over a new P0 connection. VXS maintains
backward compatibility with existing
backplanes that do not have a conflicting
P0 scheme. Several fabric protocols are
mapped out for VXS including 10 Gigabit
Ethernet, PCI Express, Serial RapidIO,
and InfiniBand. VME’s parallel bus architecture
provides bus control and maintenance
data, handling everything from
single byte transactions to 300+ MBps
block data transfers. Combining this in
various ways with the emerging switch
fabric technologies for multi-point,
high-speed data transfers creates choices
for all types of embedded computing
designs.
All of these enhancements to the VMEbus
technology have been evolutionary in
nature, carefully specified to maximize
backwards compatibility, extend the technology
life cycle of VMEbus, and most
importantly, preserve years of investments
made by users of VME technology.
Additional work continues to extend
the capabilities of VME technology even
further.
Migration planning
But what can suppliers do to allow development
programs to take advantage of the
work done by the standards developers?
Since most embedded computing applications
have a long life, system designers
and integrators need to be sure that their
supplier will be capable of manufacturing
computing platforms, whose form,
fit, and function does not change without
warning, for a period of several years.
The industry goal should be to have useful
life cycles in excess of 10 years. Products
should be planned to handle changes and
part obsolescence to allow production to
continue for a minimum of 10 years. To
do this, I propose a concept of what I call
a virtual product life cycle. An individual
product should go through no more than
three major revisions over this 10-year
life span. These revisions should be timed
to optimize design and manufacturing
changes as well as parts obsolescence.
How would this work? Revision A is
planned as the first release of the product
and should be available for approximately
three years (see Figure 1). At the
end of year two, release the second version,
revision B. There would be approximately
a one year overlap of these two
revisions (A and B). These versions
should have consistent features and exter-
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