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SHB Express Brings PCI Express to MilCOTS Applications
Today's faster processors and chipsets have created a situation in which a
single-board computer can process data much faster than data can be delivered to it via the
backplane's PCI, PCI-X or ISA parallel communication buses. In some applications, this situation
creates a serious system bottleneck that calls for a faster data delivery methodology, and
PICMG and VITA member companies are developing new industry standards that utilize PCI Express
as the interface methodology between the processor board and system devices or option cards.
This article explains the new SHB Express (PICMG 1.3) industry standard and how this PCI Express
implementation can improve embedded computing system performance in military and aerospace
applications. There are always challenges associated with implementing any new technology, and
these are discussed along with alternative approaches to improving system performance. Several
new industry standards have been or are being developed that incorporate PCI Express and these
are summarized as well.
PCI Express In Brief
A common feature in all these new standards is the replacement of the
parallel bus interface between the processor board and backplane with the high-speed serial
links of PCI Express. A wealth of detailed information is available from a variety
of sources that explains the details of PCI Express technology, so this article focuses on the
PCI Express characteristics that are useful in embedded computing applications. PCI Express is
a high-speed, scaleable, fault tolerant serial communications interface developed by Intel and
endorsed by the PCI-SIG, PICMG and VITA. While PCI Express originally developed as a
component interconnect, the interface has properties that make it an ideal board- to board
data communication interface. PCI Express maintains the PCI/PCI-X addressing model to maximize
software reuse and system value, so it is not necessary to throw away any investment in operating
systems, application software, or device drivers. PCI Express-to-PCI/PCI-X bridge chip technology
enables older PCI/PCI-X option cards to co-exist in the same embedded system with newer PCI
Express cards.
New PCI Express video cards , plug-in option cards, and PMC modules are
becoming available that take advantage of the PCI Express interface. In a typical SHB
Express system, the PCI Express serial interface will provide at least a four-time data
throughput speed increase as compared to the fastest available parallel interface
found in a PICMG 1.0/1.2 system. The scalable nature of PCI Express allows an even faster
data throughput interface to be engineered for embedded computing systems.
SHB Express (PICMG 1.3) Overview
The ubiquitous PICMG 1.0 system has long been a mainstay in the embedded
computing industry because of its ability to support a large number of different
option cards and system peripherals while providing long MTBF, fast MTTR, long-life embedded
component support, and flexible system designs. SHB Express continues that legacy while providing
a faster system platform that maintains support for today's PCI/PCI-X option cards as well as
PCI Express cards. The SHB Express specification solves the bandwidth problem of PICMG 1.0
systems by providing a PCI Express interface between the SHB and the backplane. The specification
relieves data bottlenecks, maintains backward compatibility with PCI and PCI-X option cards,
provides additional power to the SHB Express edge connector, and offers advanced
features such as Intelligent Platform Management Interface (IPMI), Serial ATA, USB, and
Ethernet connections from the
PICMG 1.3 SHB's edge connectors
to the SHB Express-compatible
backplane. The SHB Express
specification replaces the PICMG
1.0 ISA/PCI bus combination with
PCI Express and/or PCI/PCI-X
interfaces to the backplane.
The SHB Express system host
board interfaces to PCI Express
peripherals on a backplane.
Multiple PCI Express links to the
backplane can operate at x1, x4,
x8, or x16, depending on the capabilities
of both the SHB and the
backplane. Edge connectors A
and B are the SHB's PCI Express
links to the backplane. Figure 1
shows the full-size PICMG 1.3
SHB card with all of the edge connectors
defined, and Figure 2
shows the half-size version.
Figure 3 shows an SHB
Express backplane. The SHB
Express standard supports both
PCI Express and PCI/PCI-X option
cards as well as I/O routed from
the system host board and the
backplane. These optional SHB
Express I/O routing features will
be useful in simplifying the system's
chassis and cable harness
design.
In summary, the SHB Express
specification improves embedded
computing efficiency, processing
speed and flexibility in
several key areas:
• It relieves data bottlenecks
caused by parallel bus communication
architectures.
• PCI Express-to-PCI/PCI-X bridge
chip technology maximizes system
design flexibility by maintaining
backward compatibility with
PCI and PCI-X option cards.
• System power delivery designs
are simplified by the additional
power delivery capability of the
SHB's edge connector C.
• It provides advanced system
diagnostics with the Intelligent
Platform Management Interface
(IPMI).
• The SHB Express specification
supports the optional routing of
USB and Ethernet from the system
host board's edge connector
C to the SHB Express-compatible
backplane.
There are always challenges,
pitfalls and alternatives to implementing
any new technology and
SHB Express is no exception.
However, most of the challenges
and pitfalls are due to the “newness”
of the specification and will
rapidly disappear. These issues are
listed in Table 1.
An SHB Express Military and
Aerospace Application
A good application for SHB
Express involves the tracking
and control of drone aircraft. This
is essentially a telemetry system involving
the processing of large amounts of location,
positioning and target data. The mobile base
station's embedded computing system
maintains communications with the aircraft
and handles large data downloads and
uploads.
The option cards handling these large
amounts of data often need to feed across
the backplane to the system host board. SHB
Express can significantly speed-up these data
transactions by quickly moving the data to
and from the option cards. The SHB Express
solution eliminates data bottlenecks caused
by extremely fast processors, large data
transfers, and slow parallel bus interfaces.
Other PCI Express Industry Standards
There are other solutions available that accomplish
the data throughput improvements
offered by SHB Express, either under development
or recently approved. These product solutions
come in variety of form factors including
those listed below:
3U CompactPCI Express: Currently in development,
this specification defines the optimum
PCI Express implementation for 3U
CompactPCI systems. Plans are being made to
develop a specification that leverages 3U
CompactPCI Express to define a 6U
CompactPCI Express specification.
PCI Express/Advanced Switching for
AdvancedTCA Systems (PICMG 3.4):
Developed in 2003, this specification defines the
PCI Express signals, guidelines and rules for
implementing PCI Express card usage in an
ATCA platform.
VITA 46: This specification is nearing final
approval and incorporates high-speed interfaces
and switch fabrics such as PCI Express
and Advanced Switching into 3U and 6U VME
platforms.
AMC.0/AMC.1: The AMC.1 specification is
nearing release and builds on the AMC.0 specification
by defining the implementation of PCI
Express and Advanced Switching on AMC.0
modules and on-carrier devices.
XMC Express/VITA 42: The goal of these
two specification groups is to create a unified
PCI Express implementation standard for
PMC/PrPMC mezzanine cards used in
CompactPCI and VMEbus systems.
COM Express: This PICMG industry standard
for computer-on-modules replaces the
PCI bus with PCI Express. It leverages ETX
and Plug-N-Run G3 mechanical specifications,
but is mostly a legacy-free implementation of
PCI Express in this embedded form factor.
Summary
PCI Express is indeed the “next big thing” in
embedded systems for MilCOTS applications.
PCI Express standards are being developed
and introduced for a wide variety of
processor boards used in various system
form factors, and the rate of introduction of
PCI Express - enabled boards will increase
throughout 2005. These new industry standards
are designed to maximize a seamless
transition to PCI Express technology in
embedded computing systems.
Trenton Technology, 2350 Centennial Dr.,
Gainesville, GA 30504; (770) 287-3100
www.trentontechnology.com.
About the Author
Jim Renehan is director of marketing for Trenton
Technology and has held various application
engineering and product management positions
in the industrial automation and embedded computing
industries. Trenton Technology is the
draft editor for the SHB Express specification,
and Renehan has been actively involved in
developing the specification. He holds a BS in
Industrial Education and Technology from Iowa
State University. He can be reached at
jrenehan@trentontechnology.com.
Brand or Product names are registered trademarks
or trademarks of their respective holders.
Copyright © 2005 Trenton Technology, Inc.
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