EMX combines COMs, SBCs, and stackable I/O into an efficient form factor
The introduction of the EMX form factor and I/O module connector specifications bring the advantages COM Express and Qseven modules together into the industry’s first standardized COM-based SBC. This size-efficient, cost-effective standard offers clear advantages over existing SBC and COM form factors, while providing plenty of I/O flexibility for today’s applications and future developments.
The recent combination of COMs and SBCs has offered designers the best of both components’ worlds without their separate disadvantages. While COMs on their own offer performance scalability, increased product longevity, and greater efficiency for high volumes, they require custom baseboard development, which is often beyond a company’s time and resources. On the other hand, SBCs offer off-the-shelf systems, a short time to market, and other advantages, but switching SBC products involves major re-engineering effort. The two-board COM-based SBC, however, consists of an off-the-shelf COM for processing and a baseboard for I/O, power supply, and connectors, offering the benefits of both components with the shortcomings of neither. Additionally, in the face of shrinking systems, a two-board unit occupies half the area of an SBC with the same circuitry, with a minimal sacrifice in height.
One component missing from the otherwise efficient and effective COM-based SBC is an industry standard for I/O expansion. This prevents an easy combination of COMs and stackable I/O, offsetting slightly the overall advantage of COM-based SBCs. An open industry standard would provide a wide range of interoperable off-the-shelf products, confidence in longevity due to products from multiple vendors, and a ready market due to technology familiarity. The introduction of EmbeddedXpress (EMX) and its accompanying I/O module connector form factor for COM-based SBCs addresses this issue, and brings together high-performance COM Express and low-power Qseven COMs.
The elements of EMX
The EMX standard’s processor module aligns with two COM Express Types: Basic (95 mm x 125 mm) for the EMX Basic form factor, and Compact (95 mm x 95 mm) for EMX Compact, allowing for easy utilization of these popular COM Express form factors (See Figure 1). CPU modules can be Basic or Compact size, and I/O modules are always Compact size and work with all CPU modules. The emerging Qseven form factor (70 mm x 70 mm) also fits within the EMX Compact outline, providing a first for Qseven expansion. EMX adds further flexibility by allowing an SBC to consist of either a traditional single board or a two-board COM plus baseboard combination. Both configurations utilize the exact same footprint.
When defining the stacking method for I/O expansion, efficiency, and impact on SBC size, and cost were primary goals, which led to the rejection of PCIe/104 and SUMIT. In addition, these connector options also have an outline and mounting hole configuration that is incompatible with COM Express – four more mounting holes would be needed to address this, making for an odd mix of incompatible shapes and using up PCB space that could be better used for other purposes. Instead, the decision was made to develop a new connector. resulting in the EMX expansion connector that is smaller and lower cost than the alternatives. The connector is located inside the board outline, freeing up more “coastline” (perimeter space) for I/O connectors and allowing the EMX I/O boards to accommodate more features than other boards of a similar size.
The EMX connector’s size (at 6 mm x 27 mm, less than half the size of other expansion methods) was determined through consideration of the most popular expansion buses, as well as processor and chipset roadmaps of Intel and other chip manufacturers. By only including support for the most-used and most-necessary features, the connector ensures compatibility and cost efficiency (Table 1). The ample reserved pins provide the capacity to support new features as they become available and extend its lifetime.
A notable absence on the connector is PCIe x4, x8, and x16 interfaces. This is due to their rare usage in small form factor systems and their large pin count, which drives up both size and cost. Though these signals were omitted, a second connector can be added to the standard interface if they are needed, thus creating a scalable expansion bus.
The final connector specification compares favorably with alternatives. Measuring in at only a 0.276" bottom height and 0.24" x 1.06" PCB area, the EMX connector offers comparable PCIe x1, USB 2.0, LPC, and SATA interfaces to competing stacking architectures PCIe/104 Type 2 and SUMIT A+B, but at a fraction of the cost ($4.59 per 1,000). In addition, EMX reserves 12 pins for future upgrades (8 more than both main competitors), as well as GPIO and IOReady support (both of which are unsupported by PCIe/104 Type 2 and SUMITA+B). It is well suited to the expansion interfaces of COM Express and Qseven (See Figure 2 for an illustration of the Qseven carrier board). As well as supporting 4 PCIe x1, 2 USB 2.0, and 2 GPIO interfaces, standard EMX modules also include 1 each of SATA, LPC, and SMBus to further facilitate compatibility.
This is not to say that EMX’s predecessors are poor designs. However, they were developed in the early years of PCIe, when customer needs were less understood. With the passage of time, customer needs have become clearer, enabling the development of a more optimized expansion connector.
EMX keeps its cool
Thermal management is a big concern for embedded systems, and EMX has addressed this challenge with a highly efficient cooling method. All EMX stack configurations have a metallic heat spreader at the bottom that also serves as a uniform mounting surface to a system chassis. The design increases the usable operating temperature range of the electronics and keeps components cooler inside the box than a traditional SBC heat sink approach.
With a heat sink, the system’s inside air temperature reaches 84 °C and the CPU 105 °C – a warm 33 °C above ambient temperature. In contrast, a conduction-cooled EMX system with a heat spreader reaches 79 °C inside – less than 10 °C over ambient temperature – and the CPU stays at a cooler 82 °C. This configuration also allows I/O modules to be installed above the conduction-cooled SBC, whereas installation is undesirable, difficult, or even impossible with an SBC that has a tall profile heat sink.
Paving the way for future small form factor development
COM-based SBCs are attractive for many reasons, including the ability to use a wide range of COMs with varying levels of performance, price, and power levels, and easy upgrades by swapping out one COM for another. EMX brings this to another level by integrating COM Express and Qseven modules that were otherwise inefficient choices, due to the need to design complex carrier boards, into an interoperable, off-the-shelf format. And with a new I/O expansion connector that is optimized for size, cost, interconnectivity, and flexibility for future upgrades, the long lifecycle COM-based SBC can last even longer in this ever-changing industry.
Diamond Systems Corporation email@example.com www.diamdondsystems.com