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Resources
CompactPCI
Frequently Asked Questions
- What
is the CompactPCI bus?
- CompactPCI is a very high performance industrial bus based on the standard
PCI electrical specification in rugged 3U or 6U Eurocard packaging. Unlike
its desktop cousin, the CompactPCI board uses a high quality 2 mm metric
pin and socket connector that meets IEC and Bellcore standards. CompactPCI
boards are inserted from the front of the chassis, and I/O can break out
either to the front or through the rear.
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- Where
does the CompactPCI specification come from?
- The CompactPCI effort was initiated in 1994 by Ziatech Corporation under
the auspices of the PCI Industrial Computer Manufacturer's group (PICMG).
The CompactPCI specification is the result of a concerted effort of the
CompactPCI subcommittee composed of the following companies: Digital Equipment,
GESPAC, I-Bus, Pro-Log, Teknor, Hybricon, and Ziatech.
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- What is
the PICMG?
- The PCI Industrial Computers Manufacturer's Group is a consortium of
more than 350 industrial computer product vendors. PICMG's charter is to
develop specifications for PCI-based systems and boards for use in industrial
computing applications. Member companies include industry leaders such
as IBM, Motorola, Texas Microsystems, HP, Compaq, Industrial Computer Source,
DEC, Force Computers, GESPAC, Pro-Log, Teknor and Ziatech. Membership in
PICMG is open to any organization or individual with a legitimate interest
in helping to extend the PCI standard in the industrial marketplace. The
PICMG can be contacted at (781) 224-1100.
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- What
other specifications has the PICMG issued?
- The first effort of the PICMG was to publish
a specification for passive backplane computers using both PC style (card
edge connector) ISA and PCI bus. This was completed in early 1995, and
is generally known as the "PCI-ISA
Passive Backplane" specification. The PICMG has also issued a specification
for PCI to PCI bridges which allow passive backplane computers to extend
the number of PCI slots. Both of these specifications are explained elsewhere
on this web site. The CompactPCI project began in 1994, with the first
formal specification approved in November of 1995.
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- What
applications are targeted by CompactPCI?
- CompactPCI is intended as an industrial bus for application in telecommunications,
computer telephony, real-time machine control, industrial automation, real-time
data acquisition, instrumentation, military systems or any other application
requiring high speed computing, modular and robust packaging design, and
long term manufacturer's support. Because of its extremely high bandwidth,
the CompactPCI bus is particularly well suited for many high speed data
communication applications such as servers, routers, converters and switches.
Although as yet incomplete, a hot swap feature has been planned for in
the CompactPCI specification which will be particularly well suited for
the telecommunication industry.
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- What
are the unique features and benefits of CompactPCI?
- Compared to standard desktop PCI, CompactPCI supports twice as many PCI
slots (8 versus 4) and offers a packaging scheme that is much better suited
for use in industrial applications. For example, Compact PCI cards are
designed for front loading and removal from a card cage. The cards are
firmly held in position by their connector, card guides on both sides,
and a face plate which solidly screws into the card cage. Cards are mounted
vertically allowing for natural or forced air convection for cooling. Finally,
the pin-and-socket connector of the CompactPCI card is significantly more
reliable and has better shock and vibration characteristics than the card
edge connector of the standard PCI cards. The power and signal pins on
the CompactPCI connector are staged so as to allow the specification in
the future to support hot swapping, a feature that is very important for
fault tolerant systems and which is not possible on standard PCI. Also,
6U CompactPCI supports 3 additional 2mm connectors with a total of 315
pins. These can be used for secondary buses (like SCSA or MVIP telephony
buses), bridges to other buses like VME or SCSI, or for user I/O. User
I/O can be routed out the back of a 6U card and out the back of the chassis,
a practice popular in the telecommunications industry.
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- Can
I have more than 8 slots in a CompactPCI system?
- Yes. Each CompactPCI bus is limited to eight
slots for electrical loading reasons. This can be easily expanded with
PCI-PCI bridge chips, available from a number of manufacturers. The bridge
chip acts as a sort of "super
buffer"
chip. Interrupts, plug-and-play information, and data are easily and generally
automatically transferred across the bridge. A bridge chip usually exacts
a one clock penalty ( generally about 30 nanoseconds) per transaction.
If the data transaction is a burst mode type - transferring hundreds or
thousands of bytes at a time - this overhead is extremely small. One advantage
of bridge chips is that each side of the bridge can be performing data
transfers to cards on its side of the bridge simultaneously.
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- What
processors can be implemented on CompactPCI?
- Although PCI has gained most of its recognition as a local bus for 80x86
based PCs, PCI is at the core of all modern microprocessor designs. PowerPC
and DEC's Alpha, for example, are supported with chip sets with PCI interfaces
and can be easily implemented on CompactPCI. In fact, CompactPCI is the
industrial bus that does the most justice to these very high performance
new chips, giving them a system bus with all the bandwidth that these chips
are capable of.
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- Are
CompactPCI products prone to early obsolescence?
- No. Unlike the desktop PC market which is driven by volume and fast changing
consumer demand, CompactPCI is driven by professional customers who value
product stability and long term availability. All major CompactPCI manufacturers
have at least 10 years of experience each serving the OEM marketplace and
have established reputations for protecting their customers from the dangers
of early obsolescence. This is achieved by a careful selection of components
and their suppliers, and even, in many cases, by stocking several years
worth of demand of key components.
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- What
are the software implications of PCI and CompactPCI?
- The PCI architecture, developed by Intel, has
been carefully planned to simplify the software integration of a peripheral
device. For example, all PCI or CompactPCI device have a set of 256 registers
which contain information on the device identity, as well as a great
deal of software programmable parameters such as address maps, or interrupt
types and levels. As a result, the system CPU can automatically detect
and identify a device on the bus and configure it without the need for
jumpers on the peripheral. PCI is a key element of the "Plug and Play" concept. CompactPCI
is truly a "systems level" bus, with configuration (plug and
play) and hardware abstraction layers. This permits a high level of software
portability, common in the desktop PC world but much more rare in embedded
systems.
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- What
are the system implications of CompactPCI?
- Every modern computer architecture has an internal PCI bus, whether or
not it supports PCI add-on slots (which it usually does). This is the case
for nearly all Pentium PCs, Alpha workstations, and PowerPC systems based
on the PREP or CHRP reference platform standard. CompactPCI makes it possible
to build any computer compliant with these hardware system designs. As
a result, CompactPCI systems can be built using standard components and
can run practically any operating system and thousands of application software
packages without modification.
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- Which
Operating Systems can CompactPCI computers run?
- Pentium based CompactPCI computers can run all operating systems that
have ever been ported to the PC, including MS-DOS, Windows 3.11, Windows
95, Windows NT, VxWorks, OS/2, SCO and BSD UNIX, LINUX, Novell Netware,
IntranetWare, OS-9000 and QNX. PowerPC based CompactPCI computers will
be able to run AIX, SOLARIS, Windows NT, Mac OS and OS-9.
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- Will
CompactPCI system run real-time operating systems well?
- The performance of CompactPCI is particularly well tuned to real-time
application, from machine control to machine vision, fast data acquisition
and data acquisition. Operating systems like OS-9, PSOS, VxWorks run very
well on CompactPCI hardware and will be instrumental in the expected success
of CompactPCI in these markets.
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- What
products are available on CompactPCI?
- CompactPCI Pentium and PentiumPro systems are available from a variety
of suppliers in a variety of packages. System level add-on function such
as 100 Mbit/s Ethernet, fast SCSI, accelerated VGA, image acquisition,
and analog and digital I/O, ATM, FireWire and FibreChannel communications,
motion control, and PMC and IndustryPack carriers are currently available.
Other companies have announced plans for PowerPC CPU boards, fast fiber
optics networks, image acquisition and processing, and a host of other
I/O.
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- What
other functions could benefit from CompactPCI?
- CompactPCI can benefit all applications requiring very high data transfer
rates. Data communication interfaces such as ATM and broadband ISDN are
good examples. In the field of high energy physics research, very fast
multi-channel data acquisition cards will benefit from CompactPCI. Many
of the most exciting applications are probably yet to be invented, but
if history is any indication, the sophistication of systems will increase
to use all available computing bandwidth that CompactPCI computers have
to offer.
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- What
about Hot Swap?
- The staged (multi-length) pins in the CompactPCI
connector cause some connections to be made before others when inserting
a card. The reverse occurs when a card is removed. This, in principle,
allows CompactPCI products to be hot swapped. This is a complex issue,
however, and significant efforts are underway by a number of PICMG member
companies to develop a quality solution. There are some significant obstacles
to be overcome. First, special circuitry must be developed so that a
board can be inserted and removed from a live, operating PCI bus. Second,
DC power to boards being hot swapped must generally be ramped up and
down to avoid "glitching"
the system's DC bus. Thirdly, applications software and operating systems
must be developed that recognize when a board is removed and another inserted.
This will be required to re-initialize complex I/O chips like graphics
adaptors or network interfaces. Despite these obstacles, however, hot swap
is a very desirable feature and a great deal of energy is being devoted
to developing viable techniques.
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- Are
CompactPCI products expensive?
- No. Even though they offer unprecedented performance, they are based
on broadly available silicon implementation produced in very high volume.
This high volume silicon has the highest performance/price ratio available
because of the economies of scale. Additionally, because the PCI bus is
not terminated, no external bus drivers are required to interface a PCI
peripheral. An Ethernet controller, for example, connects directly from
the leads of the controller chip on to the PCI connector. CompactPCI products
are typically priced below equivalent VME product but slightly above desktop
PCI products.
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- Where
can I learn more about PCI technology in general?
- There is a great deal of information on the web published by the PCI
SIG, which is the organization responsible for desktop PCI standards. You
can learn more about the SIG's activities by contacting www.pcisig.com. There
is a Frequently asked Questions section that can be reached at www.pcisig.com/support/faq/index.php3.
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- What
future developments are likely for CompactPCI?
- As of April 1996, several technical subcommittees have been formed to
expand the definition of the bus. They include:
- Hot Swap
- CompactPCI Bridging (more than 8 slots) - Recommended Practices
- VME-64 Extension (allows the construction of hybrid CompactPCI/VME
systems)
- TDM (Computer Telephony) Buses on P2 (including MVIP and SCS
- Also, a "Pin Registry" is being developed
to detail recommended practices for using the upper three connectors
on 6U boards for I/O. For example, PICMG has developed recommended practiced
for IndustryPack and PMC pinouts on the additional connectors.
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- How
can I get a copy of the CompactPCI Specification?
- You can get a copy by calling the PICMG at 781-246-9318. PICMG members
receive free copies of the specifications and updates. A short
form is available on this web site. You can get a membership
application by calling the same number.
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- Special Thanks to Cosma Pabouctsidis, GESPAC Corp., for these
FAQs Updated by Joe Pavlat, December, 1996
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