Embedded Computing Systems Evolve to CompactPCI Serial For High Performance
CompactPCI has served many industries well, but it’s time to consider CompactPCI Serial for today’s high-speed applications.
By Justin Moll, Vice President of Marketing, PICMG
For nearly 20 years, CompactPCI has been a highly successful architecture. Used with the PCIbus, it’s been utilized in telecom and datacom applications because of its high reliability, hot-swap, monitoring, and redundancy features. The PICMG architecture is also a staple in industrial automation, military, medical, test and measurement, and many other industries. CompactPCI even currently resides on another planet: It is the communication/control system on the Mars Rover. That mission was expected to only last three months, but the well-designed and durable Rover is still roving across the Red Planet, providing valuable data more than 13 years after it arrived on Mars. In today’s applications, CompactPCI is still favored for its reliability and consistency, and it enjoys particular favor in places like Japan. But today, many designers are making the shift to CompactPCI Serial to provide the next generation of bandwidth and support.
CompactPCI vs. CompactPCI Serial
CompactPCI is a bus-based architecture with data across a single path. CompactPCI Serial utilizes new AirMax serial connectors for differential pair routing. One could argue that the architecture should be called “CompactPCIe Serial,” but other serial fabrics, such as Ethernet, can be used as well. Star, Dual Star, and Mesh network configurations offer inherently higher reliability than bus architectures, and the data rates across serial connectors can go much higher. CompactPCI has a maximum data rate of 622Mb/s, while CompactPCI Serial can support PCIe Gen 3 lanes, four pairs of 10 Gigabit Ethernet (GbE) for 40G speeds per channel, and so on. (See Figure 1 for a performance comparison chart of the architectures.) CompactPCI Serial backplanes provide PCIe Gen 1, 2, and 3; USB 2.0 and 3.0; SATA 1, 2, 3; and 10GbE (Base-TX) to each slot at the same time. Their pin-out has dedicated pins for each of these busses, so they can all run at the same time.
Rugged and Ready
CompactPCI began to find use in many military applications in the late 1990s, and was a top choice for air- and conduction-cooled implementations. It was used in benign ground-based communications systems, as well as rugged systems in aircraft, naval vessels, and ground vehicles. The wedge-lock clamshells for conduction cooling provide further stability, and the modules meet MIL specs such as MIL-STD-810 and -901D for shock and vibration levels.
One minor drawback of legacy CompactPCI was that the male pins were on the backplane, which made it possible to inadvertently strike the backplane and cause the pins to bend. So, the AirMax VS® connectors in CompactPCI Serial utilize a wafer approach that protects both the male and female sides to provide higher reliability. (See Figure 2a for a close-up of the 2mm HM backplane connector in CompactPCI and Figure 2b for the AirMax VS connector in CompactPCI Serial.)
A large number of conduction-cooled boards are being used in rugged applications, particularly railway. CompactPCI Serial board vendors include MEN Micro, EKF, ADLINK, and Kontron. Backplane/chassis vendors include Pixus Technologies, Schroff, ELMA, Hartmann, and others.
CompactPCI Serial is already being used in some rugged and high-performance defense applications, including a conduction-cooled ATR with a 3U backplane and a supplementary internal fan for additional cooling. (See Figure 3.) It is much simpler and lower cost compared with other open-standard architectures.
CompactPCI Serial architecture is being used in many applications. In high-end industrial automation systems, it can be a conduit for control, communications, and real-time data analysis, among other functions. The transportation market frequently employs the rugged and high-reliability architecture in high-performance control systems for railway, communications, and dispatch designs, and is another large market for Compact PCI Serial.
Conduction-cooled versions provide several benefits. Without the need for a fan, the system consumes less space, has a longer life, can work in a fully enclosed environment, and provides higher reliability, and is ideal for use in rugged applications that often require MIL-grade shock, vibration, environmental, and EMI protection. (See Figure 4.)
The CompactPCI Serial for Space specification was recently ratified. The OneWeb program for over 900 satellites will use the new standard, and many CompactPCI Serial board and backplane/chassis vendors, including those mentioned above, are participating as well.
CompactPCI Serial vs. Open VPX
With so many highly ruggedized CompactPCI Serial boards and solutions, one might ask how the architecture compares to OpenVPX for mil/aero applications. OpenVPX is an excellent high-performance architecture with a very large installed base in defense programs. From a technical standpoint, the architectures are pretty close to being apples-to-apples. They share the same form factors (3U and 6U x 160mm), support the same serial fabric protocols (including PCIe Gen3 and 40GbE options), and are both easily and commonly ruggedized. Both also have shelf management provisions. But there are some differences.
First, OpenVPX has the benefit of sub-specifications that address specific needs in the defense market, such as special connectors for optical and RF requirements. However, these tend to be smaller, niche applications within the overall mil/aero market. From a marketing standpoint, OpenVPX has a big advantage with its recognizable brand name in the military market and large installed ecosystem.
The main advantages for CompactPCI Serial are a much lower cost and simpler interoperability. Estimates from various vendors indicate that CompactPCI Serial may be about 40% less expensive. This is due in part to a much lower cost connector solution and simpler (and thus lower cost) power supplies. CompactPCI Serial also uses just 6V, while OpenVPX can use up to six voltages. With CompactPCI Serial’s ecosystem and popularity growing, is it time for more mil/aero vendors to jump in? Time will tell.
The Future Looks Bright
CompactPCI has been around for 20 years, and is still being deployed in new applications today. For device designs that demand higher performance, CompactPCI Serial is ready to serve. Its higher-speed Airmax VS connectors and ability to evolve with more powerful processors and technologies give the architecture a long life expectancy. With an already large and steadily growing ecosystem, multiple vendors, and increasing brand awareness, the specification’s future looks bright.
Note: Special thanks to Pentair, Pixus, EKF, and MEN Micro for providing technical and marketing support on applications on CompactPCI Serial. For more information on CompactPCI Serial, a product directory, and application case studies, visit www.picmg.org