An Interview with PICMG President and Chairman Joe Pavlat

From small to large, PICMG evolves COM Express, CompactPCI, AdvancedTCA and MicroTCA.

In the embedded space there are three primary open standards organizations: PC/104 Consortium, VITA and PICMG. Of the three, PICMG has perhaps had the most activity over the past twelve months since it’s so closely tied to the commercial market’s technology whims and endless product introductions. There have been updates to COM Express, CompactPCI, AdvancedTCA (it’s now officially ok to call it "ATCA") and MicroTCA. An interview with PICMG’s president and chairman—and my personal friend—Joe Pavlat reveals the details going on in three major spec areas.

Going Back 20 Years
PICMG began in 1994 and continues to evolve with technology trends. In the last year alone, the IEEE has finished off the 40G Ethernet spec, Intel has refreshed the Atom product line to the Silvermont architecture and won SoC smartphone designs, Cisco now forecasts M2M node growth on the same charts as smartphones and tablets, the move to serial interfaces like PCIe Gen 2/3 continues unabated, USB 3.0 is commonplace, and board vendors keep introducing newer, faster, denser versions of AMD- , ARM-, Freescale- and Intel-based single board computers (SBCs). Hundreds of companies participate in PICMG to stay abreast of and exert some control over all this change.

Says Pavlat: "Our membership started to decline a bit after the 2008 financial collapse, but PICMG is still profitable and we’re picking up new members again." Membership now stands at about 200 companies, with some of the biggest names in the tech world listed on the PICMG website. The organization focuses on three core technology areas, which the membership continues to develop (Table 1): the smallest form factor is COM Express; the middle size is CompactPCI and now CompactPCI Serial; and the largest is ATCA, MicroTCA, Advanced Mezzanine Card (AMC), or what PICMG calls collectively "xTCA." Of all the tech trends, says Pavlat, the move to serial interfaces is providing the most change in PICMG’s specs.

Core Specification Name

Variant Names


COM Express


PICMG’s small form factor computer-on-module (COM) card that plugs onto customizable baseboards or can be used standalone. Allows evolving the CPU and chipset on the COM without changing system I/O baseboard.


CompactPCI, cPCI, CompactPCI Serial, CompactPCI Express

3U, 6U sizes; CompactPCI Serial converts parallel interfaces to serial; CompactPCI Express evolves PXI to the serial realm with pins for instrumentation clocks and triggers.

xTCA AdvancedTCA, ATCA, AMC, MicroTCA Full size server, data center and line card with Advanced Mezzanine Card (AMC) daughterboards. Versions of AMC become MicroTCA when inserted in special chassis.

Table 1: PICMG’s three core form factor categories.

COM Express Version 2.1
Pavlat believes COM Express is "probably the second most popular small form factor behind PC/104,” having dozens to hundreds of vendors offering COM Express versions. There are over 700 products listed on the PICMG Product Listings section of the website. When first created, COM Express took a much different tack from PC/104: it sought to abstract all of the nuances of high-speed signaling from the user. By putting the CPU and chipset on the mezzanine (computer-on-module) card, the end user "didn’t need to worry about high-speed interfaces, trace impedances, buried vias or any of those details," says Pavlat. The COM vendor worried about that; all the user need to do was design the baseboard to interface to relays, serial lines or other system-level I/O.

Because COM Express users are not willing to pay for features they don’t need, the PICMG spec COM.0 defines seven different pin-out types. Type 1 and Type 10 modules have a single 220-pin connector (A-B), whereas Types 2 through 6 use a pair of 220 pin connectors (A-B, C-D) for a total of 440 pins. The details are shown in Table 2, taken from the COM.0 PICMG specification. For the sharp-eyed reader, Types 7-9 are reserved for the future. COM Express boards can also come in various sizes called Mini, Compact, Basic and Extended.

Table 2: COM Express pin-out types. Type 1 is the least functional with the smallest amount of I/O. (Courtesy: PICMG COM.0 specification.)

Table 2 also shows the market trend from parallel interfaces to serial ones, and PICMG felt the need to revise the COM Express specification COM.0 (1995) to Version 2.1 in May 2012. According to Pavlat: "There were about 15 companies actively participating in defining the serial interfaces and modifications to COM Express. Of note were ADLINK, Radisys, Kontron, Congatec, PFU Systems and GE Intelligent Platforms, though there were others." The changes made to COM Express are too numerous to list here, but the design trend towards rich multimedia and high-res video interfaces played a strong role in the redesign. There’s now extensive video port support for VGA, LVDS, SDVO, DP, eDP, DVI and HDMI terminal drivers plus a x16 PCI Express Graphics (PEG) port to carrier board graphics controller.

The changes include: migrating AC97 audio to high-definition audio; the SDVO interface is no longer muxed with the PEG port but available now via a digital display interface port in Types 6 and 10; there are more PCIe lanes added throughout; rarely used 12V pins were "reclaimed" for new serial functions; IDE and PCI ports were dropped or diminished for PCIe and SATA; and LVDS ports were added, some of which share pins with optional CAN bus signals.

All in all, a comprehensive update of the original 1995 spec was performed to evolve COM Express with the changes in serial interfaces, IC vendor chipsets and end user requirements. It’s interesting to note what COM Express doesn’t do. According to PICMG’s Pavlat: "Unlike VME, which intentionally maintains backward compatibility because of its customer base requirements, it doesn’t always make sense for COM Express to be backward compatible." The market wants forward momentum, and PICMG is delivering it with major changes to the COM Express specification to Version 2.1.

As well, PICMG members are in the process of overhauling the "COM Express Carrier Design Guide," a textbook-like document describing how best to build a baseboard. Released in 2009 as Revision 1, a new version is due out soon to map the I/O changes brought about in Version 2.1 of COM.0 (Figure 1).

Figure 1: PICMG’s COM Express Carrier Design Guide is due for a refresh soon because of all the changes in the COM Express spec that added higher speed serial interfaces. (Courtesy: PIGMG).

CompactPCI Goes Serial and Express
Ethernet just goes faster and faster. From 10Mbps up to 40Gbps, we’ve been discussing the "serialization" of Ethernet applied to COM Express. But it was on an open standard CompactPCI variant called PICMG 2.16 that in 2000 facilitated the first switched backplane using plain vanilla Ethernet. It was released during the so-called "fabric wars" when, according to Pavlat, "Ethernet was number one then, it’s number one now, and it just keeps getting faster and faster."

The original CompactPCI spec is nearly twenty years old, was released in 1995, used the then-new parallel PCI bus, and was based on the familiar (and well-accepted) 3U/6U Eurocard standard. Unlike its quasi-competitor VME which is also based on the Eurocard, it wasn’t aimed at the military market and was "much cheaper than VME." Successful in commercial markets galore, "cPCI"—as it is sometimes called—actually did find its way into mil/aero/defense/space applications because the 3U size meshed perfectly in smaller 1/2 ATR (short) avionics boxes and had ample I/O on the multi-row connector.

According to PICMG’s Pavlat, the newest Mars Rovers Curiosity is controlled by CompactPCI. The two Rover Computational Element (RCE) cards are radiation-hardened PowerPC 3U cPCI modules built by BAE. Pavlat says that BAE claims that about 70 percent of satellite missions today use CompactPCI.

PCI Express was added to CompactPCI in 2005, but driven by National Instruments, a Revision 2 version of the CompactPCI Express specification was released in April 2013. The new spec quadruples the bandwidth to 5 Gbps transfer rate and 8 Gbps transfer on PCIe. Interface- and product-level interoperability was given careful consideration because unlike the COM Express market, instrumentation customers do care about backward compatibility and maintaining legacy systems. Besides performance improvements, Rev 2 clears the way for modern revisions and I/O updates to the (non-PICMG) complementary test and instrumentation specification called PXI. CompactPCI Express Rev 2 "has parallel interfaces, like the old CompactPCI, some serial interfaces like the newer CompactPCI Serial, but extra pins and functions for instrumentation users like clocks and triggers," says Pavlat.

In Europe, MEN Mikro Elektronik pushed forward a new specification called CompactPCI Serial in 2011 which replaces parallel interfaces with high-speed serial: SATA, PCI Express and Ethernet on the backplane. Driven by MEN’s customers in the transportation and industrial control markets, "It really gives CompactPCI a mid-life kicker," says Pavlat, "and depending upon how you build the backplane, you can use old CompactPCI cards as peripherals if you want, or build the system entirely out of CompactPCI Serial cards."

Figure 2: JPL’s Mars Rover Curiosity uses dual CompactPCI boards designed by BAE Systems. (Courtesy: PICMG, NASA, and JPL.)

All totaled, says Pavlat and a press release issued by PICMG in April 2013, the market for all things CompactPCI "represents well over $400 million in annual revenues," making CompactPCI one of PICMG’s most successful specifications.

AdvancedTCA : HA and Hot Swap Spawn MicroTCA
PICMG’s third major specification series is xTCA which includes AdvancedTCA (ATCA), Advanced Mezzanine Card (AMC) and MicroTCA. The AdvancedTCA market, according to Pavlat, is somewhere between $1.5B-2.5B per year, primarily driven by the telcos in applications ranging from central office switches to cellular base station backhaul equipment. Conceived in 2001 by a collection of telco companies looking to focus on their software IP instead of building proprietary hardware that added no value, "ATCA is our most successful specification to date," says Pavlat, "because it had the most direct customer input. It’s been a huge success." The requirements documents that drove ATCA came from companies such as Alcatel, Lucent, Nortel, Motorola and more.

Technically, the most important feature of ATCA is the high-availability, managed architecture that makes sure if something fails, another entity takes over. In fact, the extensive infrastructure—enabled by infrastructure standards such as IPMI—monitors fan speeds, voltages, currents, temperatures and is capable of predicting the failure of a fan, for example, weeks before it fails. "With over 30 years of mostly proprietary HA experience," asserts Pavlat, "the telcos knew what they wanted and needed…" Part of that architecture required a bladed architecture that could evolve with changing processor standards such as Intel Xeons and packet processors, but also included a hot-swappable, HA mezzanine card with I/O tailored to each system requirement.

The result was the Advanced Mezzanine Card (AMC), which spawned its own card standard called PICMG MicroTCA (or µTCA for short). Ratified in 2006, the specification MTCA.0 is going on eight years old and has itself spawned four subsidiary specifications (Table 3). Small and compact, AMC cards plug into a backplane that forms an HA, hot-swappable system " that gets close to the two-level maintenance holy grail in military and defense applications," chuckles Pavlat.

Table 3: MicroTCA, a rugged offshoot of PICMG’s Advanced Mezzanine Cards, has multiple specifications. The appeal of MicroTCA is the high-availability, hot-swappable compact architecture and backplane. (Courtesy: PICMG.)



Joe Pavlat has been designing embedded computer systems for 36 years and has held senior management positions in both engineering and marketing. Since 1995 he has been president and chairman of the PCI Industrial Computer Manufacturers Group (PICMG). He was directly involved in the development of both the CompactPCI® and AdvancedTCA® standards. He does not use Facebook.

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