New Standards Divide Interfaces and Form Factors

By Ellen Konieczny

Compared to the legacy standards bodies in the embedded space, the Small Form Factor Special Interest Group (SFF-SIG) is practically a newborn. It takes a correspondingly fresh approach by creating board-to-board interconnect standards without specifying a board form factor. With the proliferation of bus technologies, the SIG realized that numerous central-processing-unit (CPU) form factors could offer identical expansion interfaces. Such an approach is welcome in the “smaller is better” culture that dominates most of today’s embedded market. Yet it also raises questions about the impact that such a change will have on designers and integrators and the embedded market in general.

The SFF-SIG (www.sff-sig.org) published three standards documents in its first year, although the second and third standards leverage the work done for the first standard— Stackable Unified Module Interface Technology (SUMIT). SUMIT has garnered a lot of attention because multiple buses appear on either one or two connectors. As a result, a designer can build a one-connector or two-connector system. Although this effort was largely driven by PCI Express, there’s also LPC for legacy-type systems for products that were originally done for the ISA bus as well as USB. There are four USB interfaces on this connector system as well as SPI and I2C.

Computer On Module Interface Technology (COMIT) takes many of the same ground rules used in SUMIT, but puts them onto a single connector for a COM interface. Bob Burckle, WinSystems’ (www.winsystems.com) vice president, explains that COMIT targets a standard small processor module that will fit within the footprint of the industry-standard, embedded-systems form-factor boards. This high-speed connector system supports the most common serial I/O and legacy interfaces available from modern, low-power chipsets as designed by Intel with its Intel® Atom™ processor. WinSystems has developed a technology demonstrator board as a COMIT proof-of-concept (see the Figure).

This technology demonstrator board, which measures 62 x 75 mm, was designed to address the need for a COM that could be used as the processing engine for standard board formats like EBX, EPIC, and Intel® Embedded Compact Extended Form Factor (Intel® ECX).

The SIG’s third standard, MiniBlade, is a replaceable, rugged, latchable interface. The postage-stamp-size MiniBlade modules plug into either vertical or horizontal connectors and latch for systems with a lot of shock and vibration requirements. Yet a repair technician also can pull apart the latches and quickly remove the modules. The MiniBlade interfaces include PCI Express and USB 2.0 (although enough signals are provided for USB 3.0). Standard mass-storage interfaces like SATA, MMC, SD, and more are included so that devices that are meant to plug into a MiniBlade socket can pick up one or more of these.

According to SFF-SIG president, Paul Rosenfeld, “We’re separating the concept of interface from the concept of form factor because they’re really not related. You can put the SUMIT interface on any size board that you choose as long as it’s not too small. With PC/104, you have to deal with all of these specifications: EBX, EPIC, PC/104, PC/104-Plus, PCI- 104, and now there’s PC/104 Express. All these standards have buses and form factors tied together. We can do this much more simply because we separate interconnect standards from form-factor standards. Our Industry Standard Module (ISM) and Pico-ITXe form-factor specifications will soon be released. The SUMIT Interconnect standard can go on these and other form factors. And these form factors can use other interfaces as well. So instead of the number of standards being A (A = number of form factors) x B (B = number of interfaces), you end up with A + B. Down the road, you end up with a whole lot less work to do every time something changes.”

The point, of course, is that form factors tend to live a very long time. But interfaces change very quickly. For designers and integrators, this separation should make life easier. An advantage is that the mechanical structure that was built around the form factor won’t have to change when the bus changes. Similarly, the infrastructure around the interface won’t have to change for a new form factor. Yet the industry will have to adapt to providing more specific information.

When a product is specified, the form factor, interface, and bus will now need to be listed on the datasheet. Currently, for example, what is designated a PCI-104 card is actually a PC/104 form factor with a PCI-104 connector. Rosenfeld provides a real-world example with ACCES I/O’s new Pico line of I/O modules: “ACCES I/O has a Pico-I/O board that only uses the USB interface. So to be very clear, the datasheet needs to say: ‘I have a Pico-I/O board with SUMIT A (or B or AB) interface that only uses the USB signals.’”

The companies that need to manufacture smaller products are expected to benefit the most from the SFF-SIG standards. In many application areas, the standards’ small size will allow designers to put intelligence in new places. Regarding MiniBlade, for example, Rosenfeld states, “CPUs can support one or more of the interfaces on a MiniBlade socket. The result can be support for a SATA, SD, or MMC device or even a PCI Express device, which means supporting I/O in addition to mass storage. This would enable support for I/O such as wireless module, Bluetooth, GPS, or any I/O that would fit on a very tiny module.”

The SIG also is working to deliver more power. The second release of the SUMIT specification brings the number of USB ports to four. Previously, SUMIT supported one or two x1 PCI Express lanes and one x4 lane. The new release, which was published this past March, allows the x4 lane to be split into four x1 lanes. Hence, if many x1 lanes are needed, a designer can actually build a SUMIT system with six.

Given the SFF-SIG’s ability to cohesively bring together 20 competitive companies in a working-group style, it’s not surprising that its efforts extend past form-factor, bus, and interconnect standards. The SFF-SIG also is planning to work on additional aspects that make up a small system, such as thermal solutions, display standards, or enclosure standards. Since the SFF-SIG began operation in April 2008, over a dozen products have been released. As Rosenfeld puts it, “People are moving on this technology.” Given the strengths of these solutions, the adoption of these standards should only increase going forward.

Ellen Konieczny is a freelance writer who has extensive experience creating manuals and other technical documents for companies. She can be reached at ellen.konieczny@gmail.com.