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| 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/faq.txt.
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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 SCSA)
- 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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