Standards Update

Small Form Factor Special Interest Group Pushes Ambitious Standards Effort

Four new specifications set direction for industry future as new processor and I/O technologies emerge, driving down the size, cost and power consumption of high-performance modules


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The embedded board industry has recently experienced a rapid proliferation of standards for small form factor single board computers, I/O expansion modules and Computer-on-Module products as a result of the upcoming transition from legacy (ISA/PCI) expansion bus technologies to PCI Express and USB. Different groups of companies are meeting to prioritize legacy interfaces against new technologies whose role in embedded products may not yet be well understood. This inflection point in embedded computing provides an opportunity for new players with new and perhaps radical ideas to emerge on the embedded stage with an influence well beyond their size and history.

The Small Form Factor Special Interest Group (SFF-SIG) is one of those new players. Established in April 2008 by seven industry leaders, and now up to 18 members, the SFF-SIG is bringing new and fresh ideas to the embedded board marketplace. Unlike earlier trade groups that produced specifications for single board computers, the SFF-SIG is embracing a wide range of technologies critical to the embedded board marketplace, including single board computers, I/O modules, Computer-on-Modules and ruggedized mass storage.

The SIG’s first standards specification introduces a new interboard interface called Stackable Unified Module Interface Technology (SUMIT). This specification defines a connector and pin definition that enables I/O modules to be stacked on top of a single board computer. Unlike earlier stackable interfaces, SUMIT implements multiple bus technologies on a single, flexible, connector scheme that includes PCI Express, USB, LPC, I2C and SPI (Figure 1). Designers can choose to implement one or more of the expansion buses on their SBCs or I/O modules.

The SUMIT Specification, available on the SFF-SIG Web site at www.sff-sig-org, describes both a low-cost, single connector implementation providing a single x1 PCI Express lane along with three high-speed USB 2.0 channels, LPC bus, SPI/uWire and SMBus/I2C. A second connector may be added with one additional x1 PCI Express lane, one x4 PCI Express lane plus additional power, ground and control signals. The physical interface for SUMIT is provided by one or two high-speed, high-density Samtec QFS/QMS connectors with a 0.635 mm pin pitch. Use of this connector pre-qualifies SUMIT for Generation 2 PCI Express and USB 3.0 data rates of 5 GTran/s.

Pico ITXe

Again, unlike earlier specifications of this nature, SUMIT does not specify a board form factor. Indeed, the SUMIT I/O expansion interface may be built onto any of a wide range of industry standard board form factors, such as EPIC, EBX, PC/104, Mini-ITX and more. The small PCB space requirements of the SUMIT interface are combined with a desire to take advantage of the super high level of integration found among next-generation, ultra-low-power processor / chip set combinations such as Intel’s Atom and VIA’s Nano. As a result, the SFF-SIG is offering a new, ultra-small SBC form factor standard called Pico-ITXe. This tiny 72 x 100 mm board enables a new class of compact footprint embedded applications with stackable I/O expansion. Optimizing for ultra-low-power platforms leads to a short stack height of only 15.24 mm.

In another major break from the past, the Pico-ITXe specification does not specify a fixed location for the SUMIT expansion connectors. Since the location of the I/O module on such a small board has limited impact on overall system design, and since the routing of many hundreds of high-speed traces on a small PCB represents an enormous design challenge, flexibility in the module location makes the SBC much easier to design. The only requirement is that the I/O module not overhang the edge of the Pico-ITXe board and the relationship between the SUMIT connectors and expansion module mounting holes be maintained.

The Pico-ITXe Specification will show several examples of module placement (Figure 2), any of which constitutes an implementation that is compliant with the standard. In addition, the SFF-SIG will provide examples showing potential I/O module placement, using the SUMIT interface, on other industry standard form factor boards including EPIC and PC/104.

Such a small SBC form factor as Pico-ITXe mandates the definition of an ultra-small I/O expansion module. For use on Pico-ITXe SBCs (as well as any larger SUMIT-compliant SBC), the SFF-SIG has defined a new I/O module standard called Pico I/O. These stackable 60 x 72 mm boards can grab any of the bus interfaces available on the SUMIT interface while passing the remaining interfaces to the module above. Hence, Pico I/O could embrace a x1 or x4 PCI Express interface, LPC interface, USB interface, I2C, or SPI, or a combination of these. Both the Pico-ITXe and Pico I/O Specifications are slated for release to the public at the end of 2008. Draft versions are available now to SFF-SIG members.

Solid-State Storage

Small form factor boards, I/O expansion modules and a rigorous, multibus interface definition go a long way to providing all the tools for a small, next-generation embedded system design. However, they alone are not sufficient. Embedded systems need additional elements to be complete. One of those key elements is mass storage. The SFF-SIG is addressing the need for small, rugged mass storage for embedded systems via the MiniBlade Specification. Adapted from the SiliconDrive II Blade Specification originally created by Silicon Systems and Samtec, the MiniBlade Specification defines a connector, pin definition and module form factor for small, rugged removable subsystems such as mass storage and other I/O technologies. Unlike consumer-grade dongles and thumb drives, MiniBlade specifies a latching socket mechanism for increased resistance to shock and vibration (Figure 3).

Like commercial standards, the pin interface for MiniBlade is sufficiently flexible to enable I/O modules such as wireless interfaces, GPS and other I/O technologies. The creation of the final MiniBlade Specification is currently underway. Members of the SFF-SIG are invited to join the MiniBlade Working Group (MWG). The MiniBlade Specification should be published in the first quarter of 2009. Early drafts will be available to SIG members.


The last key specification to be included in this initial set from SFF-SIG addresses perhaps the most dominant trend within the embedded board space–Computer-on-Module products. There have been multiple attempts to create industry standards for COM modules that incorporate next-generation bus technologies. The bulk of these, however, are beset by issues that affect carrier board design ranging from a lack of interoperability among modules implementing the same standard to the need for custom BIOS development to support carrier board I/O.

While dozens of embedded OEMs have brute-forced their way through these issues, SFF-SIG believes that the time has come for a next-generation COM standard that learns from these mistakes and eliminates these issues through the inclusion of an appropriate mix of legacy and leading-edge signals. This new specification, designated Computer-On-Module Interconnect Technology (COMIT), is still in its formative stage with the COM Working Group at SFF-SIG. The concept, as initially outlined in the October 2008 issue of RTC, is to bring back to the module those devices which made implementation of earlier standards such a headache. These include:

• Two traditional serial ports to eliminate many if not all custom BIOS requirements

• The LPC bus to enable easy support of legacy (ISA) devices on the carrier board

• Ability of the module to operate on system power, generating all necessary voltages on the module

• Providing all necessary power planes and control signals to ensure a full ACPI implementation

Like the SUMIT specification described earlier, the COMIT Specification describes a connector and pin definition for Atom and Nano platforms, leaving the module form factor open. The COMIT interface can be implemented on any of the existing COM form factor standards such as ETX / XTX or any of the multitude of COM Express form factors. The single 240-pin COMIT connector (Figure 4) eliminates registration problems and supports multiple insertions. The connector is designed for the high signal speeds to be found in Generation 2 PCI Express, USB 3 and beyond. COMIT signals include:

• 3 PCI Express x1 lanes

• 1 PCI Express x4 lane

• 6 USB ports

• VGA + PnP

• Dual LVDS panel support (24-bit)

• SDVO (Serial Digital Video Out)

• 2 SATA channels

• HD AC’97 audio

• LPC Bus

• 8-bit SDIO

• 2 Serial UART ports

• SPI/uWire

• SMBus / I2C

• Power, Ground and various control signals

Manufacturers and system OEMs interested in participating in finalizing the definition of the COMIT Specification should contact the SIG. The first publication of the COMIT Specification is expected in the first quarter of 2009. A draft version will be available to SIG members late in 2008.

This ambitious plan–the release of four significant new industry standard specifications in its first year of existence–provides a resounding basis for continued growth of the SFF-SIG. For as systems shrink in size, and technology evolves to meet the needs of small form factor systems, additional areas need to be addressed. In addition to the requirements imposed by new processor / chipset solutions as well as new expansion bus architectures, the small form factor community would benefit from standards in the area of power supplies, cooling solutions, external graphics adapters, ruggedized RAM modules and many more.

A small number of dedicated individuals have driven the SIG to this point in time. Growth to the next level will require more effort from subject-matter experts. The SIG provides an excellent vehicle for suppliers to gather with their competitors and customers to define long-lived standards that will grow the market opportunity for everyone. Our industry, and the standards that drive it, are only as good as the standardization efforts made by the industry’s technology leaders. The SIG welcomes your membership, but more importantly, the contribution of your time, talent and resources to build sustainable, long-lived standards for the benefit of all. Contact the SFF-SIG at

Small Form Factor Special Interest Group