CompactPCI—Present and Future
Joe Pavlat, Director, MCG & President PCI Industrial Computer Manufacturers Group
(PICMG)
Introduction
From its rather humble origins as a high speed video bus, the Peripheral Component
Interconnect (PCI) bus has become the universal bus for virtually all high performance
microprocessors. It is used as an interconnect between boards in a system, as a method
of hooking chips together on a board, and as a micro-architecture within chips. It is the
core of both PowerPC architectures and Intel Pentium/Pentium II architectures. Today,
most high performance peripheral chips use the PCI interface.
The continued success of the PCI bus is a direct result of its dominance in the desktop
PC marketplace. The competition in that market is intense, requiring ever higher
performance at ever lower prices. The resulting wealth of high performance, low cost
silicon and software is attractive to the embedded computer marketplace as well. While
the performance/price ratio of desktop technology makes it appealing for embedded
applications, the packaging and short product lifetimes typical of the commercial market
leave a lot to be desired. Embedded computers must work in extremes of temperature,
shock, and vibration. They generally need to be modular with a wide range of available
industrial and communications interfaces. In "mission critical" applications they must
offer redundant capability and/or be very quick to repair —often without turning off the
power.
It is with these requirements in mind that the CompactPCI standard was developed.
Utilizing rugged Eurocard packaging, CompactPCI offers a passive backplane for high
reliability, vertical card orientation for good cooling, gas tight high density pin-and-socket
connectors, and metal front panels that screw securely in place. CompactPCI was
developed by members of the PCI Industrial Computer Manufacturers Group
(PICMG), a consortium of suppliers to the industrial computer and telecommunications markets.
Since its inception in 1994, PICMG has grown to 400 members in North America and
has branches in Europe, Japan, and China.
The robust nature and high performance of CompactPCI is making it attractive to
developers of telecom and telephony equipment at a time when they are moving away
from a vertically oriented, "make-everything-in-house" mindset towards outsourcing.
Faster, Smarter
In today’s competitive and global marketplace equipment suppliers must work faster and
they must work smarter. Market windows for new and innovative products are
shrinking, and with them product development schedules and budgets. Progressive corporate
mangers are focusing more on core competencies and outsourcing much of what was
previously designed and built in-house.
This trend towards outsourcing is dramatically changing the product development
process in the telecom industry. Hardware design costs are often dwarfed by software
development expenses. The doctrine of re-use of existing hardware and software is
becoming essential to rapid and cost effective new product introduction.
Project managers are adopting a philosophy of "build what you must and buy what you
can." Embedded computers and microprocessors are common in virtually all electronic
equipment today and there is a rapidly growing trend away from designing boards and
systems in-house and towards buying standard, off-the-shelf or customized product from
embedded computer specialists.
Outsourcing embedded computer technologies like CompactPCI provides benefits
beyond shorter product development cycles and reduced engineering expense.
Designing with modern high performance microprocessors requires considerable
expertise on high frequency design and simulation. The technology is evolving rapidly,
and 1,000 megahertz processors are on the horizon. The knowledge required to design
with today’s high speed parts is considerable and is highly specialized. As a result, more
and more equipment designers are turning to commercially available CompactPCI
products.
CompactPCI Focuses on Telecom and Telephony
The development of the CompactPCI standard was heavily influenced by the needs of
the telecommunications market. In addition to high performance, ruggedness, and
modularity, telecom equipment builders have additional requirements not easily met by
any other platform.
Telecom customers demand that their equipment be very reliable, and acceptable
downtimes are measured in seconds or minutes per year. While making circuitry very
reliable through conservative design, the use of good components, and good
manufacturing is essential, boards do eventually fail. In order to repair a system fast,
boards must be able to be removed and inserted with a minimum of chassis and cable
disassembly. CompactPCI’s Eurocard mechanics are a good foundation for this, as
boards load and unload from the front of the chassis using a simple manual
injector/ejector mechanism. Changing a board without changing all of the fixed cabling to
that board is also possible with CompactPCI, because the standard defines a method
for routing I/O signals from a plug-in card through the backplane and out the rear of the
chassis via a small rear panel transition card. The method used is defined by the IEEE
1101.10 and 1101.11 specifications. This allows a plug-in card to be removed without
disturbing the I/O wiring to the chassis.
Hot Swap
Although CompactPCI cards are relatively quick to replace, the entire system must
usually be turned off before a card is inserted or removed. During this time, valuable data
can be lost and service interrupted. Also, today’s complex operating systems often take
minutes to boot up when the system is turned back on, and this adds to the time the
system is unavailable.
How can the downtime be minimized when a card is swapped? Easy—just do it with the
power on. While the concept of "hot swapping" cards isn’t new to the telecom world,
solutions have always been vendor specific and proprietary. There has never been an
industry-accepted way of doing this. At least, not until now.
The CompactPCI Hot Swap Specification (PICMG 2.1) defines a standard method for
inserting and extracting boards from a live system. Physical, electrical and software
interconnect methods are defined. The spec defines a range of hot swap capability, from
simple systems where an operator must inform the system via console operation exactly
what card is to be removed to fully automatic mechanisms permitting remote diagnostics
and repair. The latter is important to the wireless and cellular world, where the equipment
is often physically located in a remote location like a mountaintop. While the Hot Swap
spec currently defines the process only for I/O boards and not for CPU’s, is a significant
step forward for the industry and is the basis for most CompactPCI design wins in the
telecom industry. Figure 1 shows a CompactPCI chassis, the Motorola CPX2208, that
is Hot Swap ready and also incorporates rear panel I/O. |
