Winner and still champion: VMEbus

Aug. 1, 1998
VME shows why it remains the leader in single-board computer architecture, while PC-MIP heats up the competition in mezzanine cards

VME shows why it remains the leader in single-board computer architecture, while PC-MIP heats up the competition in mezzanine cards

By John McHale

VMEbus practitioners continue to dominate military and aerospace single-board computer applications. They keep the use of VME backplane data buses and printed circuit cards on top by continually pushing the limit of VME`s performance, despite the promise of challengers such as CompactPCI.

Perhaps the central reason for VME`s longevity is its aptitude to absorb competing technologies such as Futurebus+ and CompactPCI to improve its own status, says Jerry Krasner, research editor at the Electronics Group of Miller Freeman Corp. in Wellesley, Mass.

VME continues to be the bus of choice, especially in the military, says Hubert Canvet, vice president of sales and marketing at Cetia in Cedex, France. In addition, PowerPC has emerged as the processor choice of VME users as they demand more and more functionality, he says.

Cetia engineers, for example, offer the VMPC4a-Dual CPU, a VME/PCI based single-board computer, providing multiprocessor capabilities in one VME slot. The dual-processor module takes advantage of two independent PowerPC 750 microprocessors running at 266 MHz or faster, sharing the same dynamic random access memory (DRAM) from 32 to 256 megabytes.

Military program managers like VME because the technology is stable, and has been so for 15 years, says Michael Stern, product manager of the PowerPC group at Radstone Technology in Towcester, England. Radstone`s rugged single-slot 6U PPC2 is part of the U.S. Navy`s Lightweight Hybrid Torpedo program, from Raytheon Electronic Systems Co. in Mukilteo, Wash.

The PPC2 comes with either the PowerPC 603e or PowerPC 604e microprocessor running at 100 MHz or the 133 MHz PowerPC 604. The PPC2 offers a 32-bit superscalar RISC processor, 64-bit external data bus, internal instructions and data cache, memory management unit and floating point unit, and a PMC expansion slot.

Current market numbers illustrate VME`s popularity with embedded systems designers. In 1997 VME`s share of the single-board computer market was about $670 million, while PCI`s share was $90 million, PC/104`s share was about $40 million, and CompactPCI was $10 million, says Miller Freeman`s Krasner.

One big advantage VME has over CompactPCI is the number of companies that produce VME, Krasner says. Where four companies make up 85 to 90 percent of the CompactPCI market, there are 25 to 27 companies that make up 70 percent of the VME market, enabling diversification and innovation without one large company driving the market, he says.

High-throughput VMEbus

VME designers met the challenge of CompactPCI by coming out with the VME320 backplane, says Ray Alderman, executive director of the VME International Trade Organization (VITA) in Scottsdale, Ariz. The VME320 technology enabled VMEbus systems to quadruple their performance and remain backward compatible to older VME equipment.

The VME320 star configuration was designed by Drew Berding at Arizona Digital in Scottsdale, Ariz., and by experts at Bustronics Corp. in Fremont, Calif. The VME320 design approach essentially made the backplane into a simple lumped capacitance instead of transmission line, Alderman says. This enables the rise times and fall times of the signals in the backplane to flow through the switching threshold without hanging or changing direction, which results in a fast signal and a fast protocol.

The VME320-based systems should be released at the end of this year, says Doug Patterson, technical marketing director for DY 4 Systems in Kanata, Ontario. DY 4`s DMV-176 single-board computer is part of the U.S. Navy`s AV-8B Harrier OSCAR (Open Systems Core Avionics Requirement) upgrade program from General Dynamics Information Systems (formerly Computing Devices) in Bloomington, Minn. Eventually Boeing avionics integrators will use OSCAR electronics on their F/A-18 Hornet jet fighter bomber.

The DMV-176 uses a PowerPC603e processor running at 200MHz with 12 megabytes of static random access memory (SRAM) or 64 megabytes of DRAM.

While embedded systems designers wait for VME320 products to become available, scientists are conversing with "the gods of physics" to accelerate VMEbus throughput to 533 megabytes per second, and even to 1,000 megabytes per second, Alderman says.

Making VME go faster is a transmission line problem; the only way to make the backplane go faster is to shorten up the transmission line, Alderman says. "But we can`t do that because we need a 21-slot chassis," he adds. "So we look for other ways like Drew Berding`s star configuration" and speeding up the current to overcome an unbalanced transmission line, Alderman says.

An unbalanced transmission line, which results when all the slots are not filled, can cause anomalies like reflections. These occur when the signal from a filled slot hits an empty slot and reflects back, creating noise and increasing current-slowing impedance.

Every backplane starts out with a certain amount of impedance measured in ohms, usually about 65, which prevents current from flowing through the transceiver, Alderman explains. Each time a slot in the backplane is filled it reduces the impedance eventually lowering it to about 25 ohms.

Scientists at Hybricon in Ayer Mass., and Tranu in Pforzheim-Buchenbronn, Germany, are working to increase bus speeds by lowering the impedance to 25 ohms. This setup speeds the current that flows through the transceiver to the transmission lines, thereby theoretically increasing the speed to as fast as 1,000 megabytes per second, Alderman explains.

"We don`t know if we can push it to 1,000 megabytes yet," Alderman continues. "We don`t know the sound barrier for pushing VME to a certain frequency. We have to find out the next wall. I think it will be 1,000 megabytes, but we still don`t know."

The scientists have to keep looking ahead because military customers want boards that are better, faster, and cheaper with more flexibility and more open standards, Patterson says.

VME is answering the demands for performance through the PowerPC microprocessor, says Jerry Gipper, vice president at Motorola Computer Group in Tempe, Ariz. The talk regarding VME 533 and VME 1000 is still in the idea stage and will be tough to design, he says. Tuning the VME320 already leaves little margin for error, Gipper says.

Motorola officials are marketing their PowerPC-based VME boards to military and aerospace systems designers, and point to a rich heritage in military designs. Motorola single-board computers are part of the U.S. Air Force F-16 with their MVME 162 single-board computer, based on the Motorola 68000 microprocessor. The MVME162 works with Ethernet, SCSI, and uses IndustryPack mezzanine modules.

The PowerPC features a host of advantages for embedded systems designers working on military and aerospace programs. "Our customers are looking for high-performance PowerPCs and very fast boot time," says Richard Jaenicke, vice president of marketing at Sky Computers in Chelmsford, Mass.

When they shop for single-board computers, designers all want the ability to insert new technology into their systems as it becomes available, says Clarence Peckham, president at SBS Embedded Computers, Inc. of Raleigh, N.C. SBS Embedded engineers offer the PROTEUS, a Pentium-based VMEbus PC/AT board featuring dual PCI mezzanine card (PMC) slots, processor speeds as fast as 300 MHz, 128 megabytes of EDO DRAM, and 72 megabytes of Flash memory, in one VMEbus slot.

Technology insertion is a question of low cost now versus high cost down the road when the technology is obsolete, Alderman says. The decision to use technology insertion depends on how much loss a company can swallow, he adds.

Technology insertion is the way to combat obsolescence in 20-year military programs, says Dick Copra, vice president at Vista Controls in Santa Clarita, Calif. Boards must have plug and play capability. Copra`s engineers offer the SCORE 603 single-board computer for navigation, fire control, and flight-control systems.

The device features a 603e PowerPC processor, containing 16 kilobytes of internal instruction and 16 kilobytes of internal data cache, running at 100 MHz or 133 MHz. The SCORE 603 also provides from eight megabytes to 64 megabytes of DRAM memory with error detection and correction.

"Parts need to be designed so you can throw them away in two years, other wise they become obsolete," Peckham says. The digital battlefield will demand upgradeable equipment, he says. Motorola engineers, on the other hand, design their boards for a five-to-10-year lifetime with technology insertion, Gipper says.

The PowerPC and Pentium are not the only microprocessors going into military and aerospace systems. The Sun SPARC also has its niche applications. "Our VME customers are looking not only for higher performance but high package density as well, says Bill Kehret president of Themis Computers in Fremont, Calif. The Themis SPARC-based 20MP single-board computer is part of the U.S. Navy`s Aegis Combat System, says Rick Studly director o the federal systems division at Themis.

The SPARC 20MP offers an enhanced VME64 interface, a fast 50 MHz MBus architecture, and VME driver compatibility with the entire range of SPARC processing technology. Themis combines the SPARC 20MP`s multiprocessor technology with memory expansion ranging from 64 to 512 megabytes, Ethernet, SCSI 2-FAST, two serial ports, keyboard/mouse port, a parallel port, audio port, and a high-performance VME64 interface.

Rugged boards

Increasing requirements for commercial off-the-shelf (COTS) components in military and aerospace electronic designs is ratcheting up the pressure on suppliers in several different ways. Among the most prominent issues are the apparently conflicting needs to reduce system costs and to ruggedize systems against the ravages of operating extremes in temperature, shock, vibration, and humidity.

Although reason tells most systems integrators that ruggedizing their designs against harsh conditions means an increase in cost, integrators and their suppliers today often must ruggedize at prices equal to or lower than what they have done in the past.

In the COTS world everyone is looking for cheaper products, Vista`s Copra, says. "They`re asking, `What can I get away with on the rugged issue?`," he says.

The need for inexpensive boards that can survive in harsh environments drives the rugged side of the market, Cetia`s Canvet says. For rugged environments Cetia engineers offer the Ruggedizer, a board-level heat sink designed to lower the overall operating temperature of the board, while adding mechanical stiffening and protection.

One of the biggest hassles for COTS companies, in addition to reconciling conflicts between ruggedization and price, involves the occasional need to deal with out-of-date military standards, says Peckham of SBS Embedded Computers. "Many of these standards date back to the 1960s," he adds. This, however, may be changing.

For many military applications where humans operate the devices and extreme temperatures do not exist, military leaders have relaxed the environmental constraints, says DY 4`s Patterson.

Earlier this year, for example, U.S. Air Force officials changed the temperature requirements for electronics aboard the Airborne Warning and Control System aircraft from the original -40 to 85 degrees Celsius range to 0 to 50 C to broaden their use of COTS equipment. Technicians at the Air Force Electronics Systems Center at Hanscom Air Force Base, Mass., determined that in 20 years of operation the aircraft operated in extreme temperatures so rarely that constraints were not necessary.

But in other mission-critical situations, the constraints remain, Patterson says. "With some applications you can`t mess with physics," Patterson adds. Experts from DY 4 and Systran Corp. in Dayton Ohio are working together to ruggedize Systran`s FibreXpress Fibre Channel interface boards. Systran leaders licensed their FibreXpress technology to DY 4, whose engineers will develop and sell rugged Fibre Channel interface boards in PMC, PCI, and 6U VME6U form factors.

"We look at this technology as eventually replacing, the MIL-STD-1553B data bus in new platforms," Patterson says.

The twin needs for ruggedness and affordability are pushing innovation in other directions as well. Engineers at Isothermal Systems Research in Clarkston, Wash., are looking to ruggedize commercial boards with spray liquid cooling. Isothermal officials claim their spray cooling system will increase power density, lower vibration, and lower weight in VME boards.

Isothermal`s cooling system uses the 3M liquid chemical called Fluorinert to cool the boards in a closed-loop system. Spray cooling removes heat 500 times more efficiently than air cooling, claim Isothermal officials. Conventional air-cooled systems are limited to a power density of about 1 watt per cubic inch, while spray cooling can handle more than 500 watts per cubic inch, they say.

The coolant eliminates the excess vibration of cold-plate cooling, says R.J. Baddeley, manager of government systems at Isothermal. Cold-plate cooling channels vibrations through the heat sink back to the board, unlike spray cooling devices where there is no structural path to transmit vibration, he explains.

"Liquid cooling is not something that Vista is doing, but we`re definitely keeping an eye on it," Copra says. If this approach proves successful, it might enable systems integrators to install commercial-grade boards in rugged applications, which could attract customers away from Vista, he points out.

Isothermal`s spray cooling is an unstable technology, claims Peckham of SBS Embedded Computers. "We prefer something with no moving parts with air blowing directly on to it," he says. "A pump could fail so we`ll have to wait and see."

The multiple pumps in Isothermal`s approach create single points of failure that could cause problems, adds Patterson of DY 4.

Liquid-cooling technology makes sense for critical applications, VITA`s Alderman says, because its closed-loop system prevents dirt or dust from getting in the enclosure. Systems will eventually go to it, he adds.


Although CompactPCI compares favorably with VME in price and off-the-shelf software support, critics point out that CompactPCI does not have the multiprocessing capability of VME, and does not support 21-card backplanes as VME does. Yet officials at the PCI Industrial Computer Manufacturers Group (PICMG) in Wakefield, Mass., are trying to change some of that. They are pushing a design that they claim enables CompactPCI to perform multiprocessing.

The plan calls for the Drawbridge 26550 bridge chip from Compaq Computer Corp. (formerly Digital Equipment Corp.) in Maynard, Mass., to connect two PCI buses, says Joe Pavlat, president of PICMG and strategic marketing director at Motorola`s Monterey Design Center (formerly Pro-Log Corp.) in Monterey, Calif.

The Drawbridge enables two separate buses - each with its own independent processor - to communicate data seamlessly back through the bridge in a high-availability multiprocessing system, Pavlat explains.

Yet critics of CompactPCI say bridges represent a slip-shod design approach that VME avoids. "Bridges are the AIDS virus in electronic form," VITA`s Alderman says. "I don`t care if it`s wrapped in a wet Hershey bar wrapper," bridges do not perform interrupt handling well, he claims. In the embedded systems community, Alderman and Pavlat are amiable antagonists.

The main problem with bridges is loose sequential consistency, Alderman says. This means that any bridge chip only allows one function to flow through a bridge at a time.

Pavlat counters that Alderman`s contentions are misleading. True, the drawbridge does add one clock cycle to each transaction, which comes to an extra 30 nanoseconds, Pavlat admits. But all backplanes are limited to one transaction at a time, he says.

CompactPCI is not only fast in time to market but also "rigidly flexible," claims Jim Medeiros, product marketing manager at Ziatech in San Luis Obispo, Calif. - rigid because its J1 and J2 connectors are strictly defined PCI interfaces, and flexible because the J3, J4, and J5 connectors work with different sub-busses and I/Os.

Ziatech engineers offer the ZT6500 3U CompactPCI, a Pentium-based single-board computer that runs at 133 to 200 MHz, and supports as much solid-state memory as 48 megabytes of DRAM and four megabytes of flash. A 256-kilobyte second-level cache module is available as an option. Other standard peripherals include 24 points of digital I/O, two serial ports, IEEE 1284 parallel port, keyboard controller, and real-time clock.

Medeiros points out that while 3U VME boards provide only half the performance of their 6U brethren, the 3U CompactPCI board maintains the same performance as its 6U version. The only drawback is that CompactPCI only brings the J1 and J2 connectors to the 3U level and loses connectors J3, J4, and J5.

PCI also benefits from microprocessors such as the PowerPC, Sparc, and Alpha, which all have the same PCI protocol, Pavlat says. "Compact PCI is processor agnostic, it serves all the processor gods," he adds.

CompactPCI has other advantages, points out Motorola`s Gipper. One, the market perceives CompactPCI as lower cost than VME; and two, CompactPCI is compatible with a wide variety of COTS software - particularly Windows-based software. Many people involved in desktop computer design believe PCI is too expensive, but it is still cheaper than VME, Pavlat says.

Although no CompactPCI products have replaced VME for existing systems yet, CompactPCI is winning over VME in lucrative new designs in telecommunications. Despite its cost advantages over VME, few, if any, new military systems designs are going with CompactPCI over VME, Pavlat says. CompactPCI not a big player in military because it has not proven that it can do multiprocessing and is not real time, Krasner says.

"Much of CompactPCI is hype," claims Ron Marcus, marketing communications manager at Synergy Microsystems in San Diego. CompactPCI is not even an official standard; it remains a specification used primarily for telecommunications, he says.

"They can`t ship enough CompactPCI to fill my trunk," Alderman quips. Prospective CompactPCI customers want to test the device for six to eight months before they make a decision on it, Alderman says. But after testing they find a problem with it and ask the manufacturer to fix it, then they take another six to eight months for more testing, he says. The devices never ship, Alderman says.

There are thousands of CompactPCI systems out there, Pavlat counters - at least 1,000 between Ziatech and Motorola alone, he adds.

Twilight of PCI?

One glaring disadvantage that CompactPCI has may be its reliance on Intel microprocessors. The discussion on PCI will be mute once in leaders of Intel Corp. of Santa Clara, Calif., releases their 64 bit Merced processor in 2000, Alderman says. The new device will run on a serial bus with no PCI interface, he says.

PCI filters out at high speeds, Alderman says, because the bus drives data in individual bits. As a result, not all bits arrive at the same time due to unequal transceivers, he says. "If bit one arrives before bit 2 and then bit 2 is read before bit 3, you`ll receive bad data," Alderman explains. The faster PCI runs the more these problems will occur, he claims.

The Merced may also spell the end for another powerful processor, the Alpha from Compaq, Alderman says. Right now at 64-bits, the Alpha is the fastest machine, but that will change, he says.

Compaq`s Alpha architecture is an advanced 64-bit RISC architecture designed with emphasis on speed, multiple instruction issue, multiple processors, and software migration from other operating systems.

The AlphaPC 164 Motherboard microprocessor is a superscalar implementation of the Alpha architecture that supports multiple operating systems. The board runs at speeds as fast as 500 MHz and has 128-bit or 256-bit data bus with 16 to 512 megabytes of DRAM.

Mezzanine boards

The next mezzanine on the market appears to be PC-MIP, a new mezzanine standard from SBS GreenSpring Modular I/O of Menlo Park, Calif., Motorola Computer Group, and Micro Electronik Neuremburg (MEN) GmbH of Germany.

The PC-MIP modules are a combination of the PCI bus and GreenSpring`s IndustryPack mezzanine modules, says Kim Rubin, vice president of SBS GreenSpring Computers.

Taking a step back from comments he made last fall touting PC-MIP as death of PMC, Rubin says his new mezzanine standard will compete not so much with PMC but with the silicon that goes on the board.

PC-MIP supports 4PQ 208 packages per module, has three 64-pin PCI connectors, and supports 300 lines of I/O per board per 6U host, Rubin says.

Six modules may mount on a 6U VME, 6U CompactPCI, or full-size desktop PCI slot board, including room for processors, bridge chips, and trace routing. Three modules fit on 3U boards or half-size desktop PCI cards.

PC-MIP will be less expensive than IndustryPack, but its market will not grow over the next five years, because the cheaper price will mean less volume, Kasner says. The device`s small size will also place it in low-end applications like the IndustryPack, serves, and may put PC-MIP at a competitive disadvantage with PMC.

Eventually PC-MIP will be conduction cooled and used in a specialized application for the military, Alderman says. The PC-MIP officials may even have to standardize it for rugged specifications at some point, he says.

PC-MIP`s business will also be hurt when the Merced and the serial bus technology hits the market, Alderman says. The technology`s PCI base will put it behind the Merced`s serial technology, but PC-MIP will continue to have a legacy customer base, he adds.

With its unique combination of PCI and IndustryPack there should be no shortage of opportunities for PC-MIP, Vista`s Copra says.

GreenSpring`s current mezzanine, IndustryPack, continues to be popular with small applications due to its small form factor. IP modules are applicable to systems with high I/O density and a diverse mix of analog, digital, and serial requirements with low slot space.

PMC wastes board real estate, Rubin says. IndustryPack, meanwhile, delivers more functionality per inch, he claims.

Engineers at GreenSpring and DY 4 have joined hands to bring the first conduction-cooled IndustryPack modules to the harsh-environment marketplace.

The new DY 4 IndustryPack products will be software compatible with SBS GreenSpring`s new VME64x-compliant VIPC664 quad carrier board and several selected GreenSpring IndustryPack modules, preserving customer investments in deployable system software, DY 4`s Patterson says.

"We`re seeing more PMC than IndustryPack at about a 10 to one rate," says Jeff Milrod, president of VME single-board digital signal processor designer Ixthos Inc. of Leesburg, Va. Because of its small form factor IndustryPack lends itself to low-end applications, Milrod says. Designers of high-end applications use PMC because they can load it up with electronics.

Milrod`s engineers produce the IXZPMC4, a digital signal processor for PCI bus boards containing at least one PMC slot. The device has four SHARC DSPs with 480 million floating point operations per second of performance, with a 32-bit, 33 MHz PCI bus, 80 megabytes per second of sustained PCI-SHARC throughput, and 16 megabits of Flash memory.

PMC and IndustryPack also compete with custom mezzanine cards. "It`s a make-versus-buy proposition," Rubin says. IndustryPacks are cheaper than in-house development and are faster to market, he says

"We build in house because we want higher density than PMC or IndustryPack," says Sky`s Jaenicke. Sky engineers have found that density with their Excalibur daughtercards.

The new device uses a custom memory controller and the 0.25-micron version of the PowerPC 604e microprocessor. Each of the four processors on the new Excalibur can sustain 667 megabytes per second of performance. The new Excalibur targets high-performance signal processing and imaging applications such as radar, sonar, and signals intelligence.

Another player in the PMC world is RAMiX in Chatsworth, Calif., whose engineers produce the PMC550 and PMC551 modules which include an integrated Intel i960 33 MHz microprocessor and PCI bridge, provisions for external interrupts to enable direct signaling of control events, direct-memory-access engines for efficient data transfer, and a local-time base.

Who`s doing what

Engineers at OR Computers in Fairfax, Va., offer the VR6 rugged 6U single-slot VMEbus board. It is available with a 233 MHz Pentium microprocessors as well as AMD K6 processors with 128 megabytes of DRAM. The VR6 includes PMC expansion on-board with a MIL-STD-1553 option.

Dynatem engineers in Mission Viejo, Calif., offer the DRC1 VME64 single-board computer which features the Intel Mobile Module and uses Pentium II (233 MHz and 266 MHz) or Pentium MMX (133 MHz to 266 MHz) processors, and is available in extended temperature versions with shock and vibration immunity.

Engineers at Synergy Microsystems, have designed the PEX3 PMC module carrier board for VMEbus systems. The board expands the total number of PMC modules on a single-board computer to four, enabling the addition of as much as 128 megabytes of flash memory to a system. The board also provides a high-speed secondary PCI bus for communication with several system boards. PCI supports 33 MHz, 64-bit PCI, for a maximum throughput of 264 megabytes per second between boards.

Experts at Omnibyte Corp. in West Chicago, Ill., offer the OB68K/VME1-M ruggedized single-board computer with components ranging from commercial- to extended-temperature commercial, to MIL STD 883B.

The REAL/STAR VME single-board computer from MODCOMP of Fort Lauderdale, Fla., comes with single or dual-Pentium processors. Complete VME systems with 3, 6, 10, 12, and 20 VME slots come in varied configurations with peripheral mounting and redundant power options.

Experts at General Micro Systems in Rancho Cucamonga, Calif., offer the V2P2 VME64 single-board computer with two Pentium II Deschutes processors running at 450 MHz, have 1 gigabyte of main memory, and a megabyte of L2 cache.

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The F/A-18 Horner jet fighter bomber will be upgraded as part of the OSCAR (Open Systems Core Avionics Requirement) program, which uses the DMV-176 single-board computer from DY 4.

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The PROTEUS, designed by engineers at Embedded Systems, is a Pentium-based VMEbus PC/AT board running at 300 MHz with 128 Mbytes of EDO DRAM.

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The expanded Excalibur daughtercard from Sky Computers is targeted at high-performance signal processing and imaging applications such as radar, sonar, and signal intelligence.

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The 68k MVME 162 single-board computer, designed by experts at Motorola Computer Group, is used in the U.S. Air Force F-16.

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The VMPC4a-Dual CPU from Cetia is a VME/PCI-based single-board computer, providing multiprocessor capabilities in a single VME slot with two independent PowerPC 750 microprocessors running at 266 MHz or faster.

PC/104: an alternative to VME in deeply embedded applications

PC/104 embedded computer modules, "which we invented in 1992," provide a compact modular building-block approach to incorporating PC hardware and software technologies into embedded systems, says Rick Lehrbaum, executive vice president and founder of Ampro Computers in San Jose, Calif. It is robust and rugged without the weight and size limitations for VME, making it ideal for embedded military applications, he says.

The standard PC bus form factor - 12.4 by 4.8 inches - and its associated card cages and backplanes are too bulky for most embedded control applications, Lehrbaum claims. PC/104, which comes in 3.6-by-3.8-inche stackable modules, is compatible with the PC bus, he adds

Systems engineers have designed PC/104 into military applications such as Global Positioning Systems and displays, Lehrbaum says.

Four corner-mounting holes in PC/104 cards enable designers to bolt the card in place, which make it resistant to shock and vibration. The cards also feature an extended operating temperature range of -40 to 85 degrees Celsius, he says.

Ampro`s Pentium-based PC/104 Little Board/P5I is running the central processing functions of the U.S. Army`s Soldier Portable On-system Repair Tool (SPORT), designed by engineers at Miltope Corp. in Hope Hull, Ala. The device is a 100/166 MHz Pentium processor with as much as 128 megabytes of onboard dynamic random access memory.

PC/104 does not need backplanes or card cages because the modules are self-stacking, says Matt Wray director of sales for Parvus Corp. in Salt Lake City. Each PC/104 module is stacked 0.6 inches apart.

The stacking of several modules in one location enables designers to make upgrades and temporarily add modules during a test or debug phase, Lehrbaum says.

The only problem with PC/104 is maintenance, says Jerry Krasner, research editor at the Electronics Group of Miller Freeman Corp. in Wellesley, Mass. If something fails in the middle of a stack of PC/104 boards, there is no way to get at it without removing all the cards, he points out.

While it may not be as sophisticated as VME, PC/104 makes sense because it is small, cheap, and works well in applications where VME is too large to fit, says Ray Alderman, executive director of the VME International Trade Organization in Scottsdale, Ariz.

PC/104 exemplifies commercial-off-the-shelf equipment (COTS), says Michael Stern, product manager of the PowerPC group at Radstone Technology in Towcester, England. It is rugged yet less expensive than building a custom device, he says.

Wray`s engineers at Parvus offer the Aircraft/Industrial PC/104 single-board computer. The device is part of the US Q113 radar and communications jammer for the U.S. Navy`s EA-6B electronic warfare aircraft. Engineers at Sanders Inc. in Hudson, N.H, designed the jammer.

Designers created PC/ 104-Plus in 1996 to take advantage of Intel`s Pentium technology, Lehrbaum says. Added to the original PC/104 form factor was a PCI bus, with a self-stacking 120-pin high-density connector from Samtec in New Albany, Ind., he explains. The new device operates at 132 megabytes per second - 26 times faster than PC/104, Lehrbaum adds.

The enhanced speed enables PC/104-Plus to be used for performance-intensive COTS applications that would otherwise be unduly burdened by the costs and bulk of a backplane and card cage approach like VME, Lehrbaum says.

Ampro engineers have teamed with experts at Motorola Computer Group in Tempe Ariz., to introduce EBX, a new form factor for compact high-performance embedded boards. The EBX format provides a standard mechanical design for embedded single-board computers, merging the expansion capability of PC/104-Plus and optional PCMCIA into a board measuring 5.75 inches by 8 inches. Some of the first EBX-compliant products include the Motorola MBX860 and the Ampro Little Board/P5i single-board computer.

"We see EBX as an excellent way for system designers to take advantage of the performance of PCI in embedded applications, while benefiting from multi-sourced off-the-shelf system options that minimize the need to re-invent the wheel," explains Jerry Gipper, vice president at Motorola Computer Group. "Typically, OEMs aren`t buying just chips anymore; they want complete solutions." - J.M.

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The Pentium-based PC/104 Little Board/P5I from Ampro Computers is running the central processing functions of the U.S. Army`s Soldier Portable On-system Repair Tool (SPORT), designed by engineers at Miltope Corp.

VxWorks leads in operating systems, with LynxOS and QNX hot on its tail

VxWorks continues to lead the way in operating systems for embedded single-board computers, but systems such as LynxOS and QNX are gaining ground with memory-protection technology.

VxWorks is the choice among embedded system designers because it has an intuitive programming model based on UNIX with POSIX compliance, says Bob Monkman, product marketing manager for VxWorks at Wind River Systems in Alameda, Calif.

"VxWorks is the clear winner in software," says Dick Copra, vice president at Vista Controls Corp., a VME single-board computer supplier in Valencia, Calif. It works with the PowerPC processor and Intel technology, he says.

Wind River`s VxWorks is the premier real-time operating system for large embedded applications, says Jerry Krasner research editor at the Electronics Group of Miller Freeman Corp. in Wellesley, Mass. It remains popular because real-time systems engineers inherently resist change; designers tend to stick with real-time systems that they understand and that have worked for them in the past, Krasner adds.

At the heart of the VxWorks run-time system is the Wind microkernel, which supports real-time features that include: fast multitasking, interrupt support, and preemptive and round-robin scheduling.

Wind River software engineers succeed because they have a commodity product with attractive tools, says William Weinberg director of technical marketing at Lynx Real-Time Systems in San Jose, Calif.

Although VxWorks can have very high performance, Weinberg claims, it lacks any real form of memory protection. What the Wind River system lacks in technology it makes up for in marketing, much like Redmond-Wash.-based Microsoft, he says.

Touting memory protection, designers at QNX in Ottawa, Ontario, and Lynx Real-Time Systems are challenging the hold of VxWorks on the embedded market

Engineers at Radstone Technology in Towcester, England, still go with VxWorks and LynxOS, which is not standard UNIX, but has a UNIX look and feel to it, says Michael Stern, product manager of the PowerPC group at Radstone. Lynx is easy to use, he says.

The LynxOS system ensures determinism by using kernel threads to reduce interrupt overhead by performing the bulk of asynchronous processing at the priority of the process that made the request.

LynxOS is currently supporting the required onboard processing for the U.S. Army`s Crusader field artillery system, designed by officials at United Defense LP in Minneapolis.

VxWorks is different from LynxOS because it is task-based while LynxOS is application based, Monkman says. Applications are made up of individual tasks or threads, and because VxWorks operates at the task level the continued switching between tasks enables greater determinism, which is "VxWorks` greatest advantage," he explains.

Unlike commercial operating systems such as Windows NT, real-time operating systems such as LynxOS, QNX, and VxWorks offer real-time determinism, he says.

When a fighter pilot is flying into combat, he does not want to spend twenty minutes trying to reboot NT, says Ray Alderman executive director of the VME International Trade Association in Scottsdale Ariz.

"By and large Windows NT does not make it into airplanes but works in a management function on ground systems," Monkman claims. It is not deterministic enough to make it into mission critical applications, he says.

QNX also has determinism with a memory protection technology that protects the applications, the drivers, and I/O devices during development and run time, says Mal Raddalgoda, director of corporate communications at QNX in Ottawa, Ontario. The only things the protection does not cover are basic operating system functions such as scheduling and interrupt handling, he says.

"We`ve developed an operating system with full memory protection and without any degradation in real-time performance," Raddalgoda claims. QNX also supports the PowerPC and MIPS microprocessor architectures, he says.

QNX officials offer two operating systems: QNX OS, and QNX/Neutrino. QNX OS is a real-time, extensible POSIX-certified operating system with a microkernel. QNX/Neutrino is a POSIX microkernel that can be scaled to a stand-alone system as small as 32 kilobytes or as large as 4G, with support for symmetric multiprocessing, enabling the same code base used in small embedded devices to be scaled up to large distributed networks.

QNX has memory protection but is not as POSIX oriented as LynxOS, Weinberg says. LynxOS has a more efficient use of overall memory, he claims.

Another player in the operating systems environment is the Solaris operating system from Sun Microsystems in Mountain View, Calif. Solaris is a high-availability clustering software for mission-critical and database computing and with the Solaris Global WebTone support provides uninterrupted use of mission critical resources.

Solaris works well in mission-critical situations because it is UNIX and POSIX based, says Rick Studly, director o the federal systems division at Themis Computer in Fremont, Calif. - J.M.

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