Introduction

Technology and its corresponding standards are forever changing and progressing. That holds true for the evolution that is taking place in the design of Computer on Modules (COMs) from PCI and ISA-based applications to PCI Express and Serial ATA-based solutions. The COM Express standards initiated by the PCI Industrial Manufacturers' Group (PICMG) were developed to enable the migration that will result in enhanced embedded systems. The challenge today for many developers is finding a way to smoothly transition from the inevitable end of these legacy technologies to a solution that supports and takes advantage of emerging and future technologies. Another intermediate step is necessary in order to provide the scalability and longevity needed by COMs designers and manufacturers who are faced with demand for higher throughputs. Clearly there is a gaping need to find an easy pathway solution so that embedded systems manufacturers have the resources they require to remain competitive.

The answer lies in the next round of standardization for COM Express. A new “micro” form factor addition has been proposed to go along with the "Basic" and "Extended" form factors that the COM Express standard now includes. The “micro” form factor keeps the same footprint of existing PCI modules (such as PC/104) but provides the needed pin out compatibility with the existing “Basic” and Extended” form factors that will ensure future scalability. This second round of standardization gives developers the option to utilize and pay for only what they require for a particular application. For this reason, the current COM Express as well as its pending addition should happily co-exist to support separate, but equally important application requirements.

Minimizing Size while Maximizing Performance and Application Potential

In order to build PCI-only based designs on the smallest possible “micro” form factor, the module standard that has come to be known as COM Express needs to be revised. The revisions that Kontron has proposed extends the existing specification to include a PCI-only version (zero PCI Express lanes) and another version that features up to two PCI Express lanes. The physical design of the “micro” form factor differs only in size and the addition of one extra mounting hole to mount the smaller module from the original COM Express standard that defines the “Basic” and Extended” module versions. Any feature that could not fit within the physical limits of the new smaller size (95 x95 mm) was trimmed out.

Likewise, as with the “Basic” and “Extended” COM Express form factors, the “micro” version also uses the 220-pin high-speed SMT connectors that are designed specifically to support large performance reserves. These connectors are specified for transfer rates of up to 6.25 GHz LVDS and 5 GHz PCI Express (in the second generation), enabling them to support the next generation of interfaces without compromising speed.

This higher performance can be achieved for PCI-only based solutions as well by combining the PCI bus with the latest interfaces, including SATA, LVDS, USB 2.0, Gigabit Ethernet and dual-channel RAM, on a modular solution. These new capabilities mark a smooth entrance point for developers who may need faster data transfer, but not the entire range of features found on current “Basic” and “Extended” COM Express modules. Several well-known companies have already made commitments to produce the smaller 95 x 95 mm form factors enabling a broader range of design choices for wider and faster adoption of the proposed “micro” COM Express revision.

Compatibility Achieved

These new “micro” modules for PCI and PCI Express-based designs are fully compatible and provide a clear line for continued product scalability. They also create an easy upgrade path to “Basic” or “Extended” COM Express modules for future upgrades. Although classic ISA, keyboard, mouse, RS232, and analog graphics interfaces are no longer available on these new, smaller modules, “micro” COM Express modules are ideal for compact high-end systems.

For compatibility and ease of design, the position of the two high-speed connectors on the back side of the “micro” COM Express module remain the same in relation to the carrier board. Therefore, it is possible to treat this new small COM as a drop-in replacement as many of its integrated features utilize the same pins as the current COM Express standard. This provides a distinct advantage for more than just ease of documentation.

All pins for periphery, network and memory interfaces – such as PCI, IDE, 10/100 LAN and USB 2.0 – are mapped identically, so that for a switch from PCI to PCI Express or to combinations of both bus technologies, nothing has to be changed on the baseboard layout. Ultimately, future-proof support can be provided with only one carrier board for embedded formats with full scaling for processors, IDE to SATA, PCI to PCI Express and 10/100 to Gigabit Ethernet. Thus, manufacturers can expand their product lines in the future to include PCI Express and SATA into the design on the single carrier board and use them immediately through a simple exchange of modules as needed. Support for PCI and/or PCI Express is provided by the respective chipset. Modules with SATA and PCI Express in this new “micro” format are already beginning to become available with Kontron providing one of the first products – the microETXexpress-PM that features the Intel® Pentium® M processor and the Intel 855GME chipset.

Low-Cost Development

An embedded system incorporating the “micro” form factor of the COM Express standard is supported with a single carrier board and is completely scalable in terms of processors, IDE to SATA, PCI to PCI Express and 10/100 to Gigabit Ethernet. With fewer conducting paths per bus segment, the layout of the carrier board is facilitated, which ultimately provides a significant cost savings for developers. It also provides an easy and low-cost transition for manufacturers of x86 processor-based systems to migrate to next-generation designs.

Kontron COM Products – Addressing a Variety of Needs

The introduction of Kontron’s microETXexpress offers large performance reserves without requiring PCI Express lanes all within a smaller size. It is an easy solution that provides a compatible, scalable and cost-effective transition for legacy technologies to newer, more robust next-generation technologies.

ETXexpress from Kontron features a larger form factor for more PCI Express lanes, PCI Express graphics and therefore more functionality. ETX is the original standard and is ideal for low or medium power designs and will continue to play an important role in COM development. Kontron’s complete product suite is designed to offer developers what they need today to meet customer requirements while also establishing a pathway to enable future technologies and performance requirements. Each product provides select combinations designed to ensure a natural evolution in COM design.

The following table compares the features and capabilities of the ETX, microETXexpress and the ETXexpress form factor COM products:

	ETX	microETXexpress	ETXexpress
Dimensions	95mm x 114mm	95mm x 95mm	95mm x 125mm (Basic) 155mm x 110mm (Extended)
PCI Express Lanes	N/A	0 to 2 lanes	0 to 2 lanes
Serial ATA	N/A	Yes	Yes
PICMG COM Express Standard	N/A	Pending	Yes

Table 1. Summary of capabilities defined for COM Express functional blocks

Next Round of Standards

It is estimated that it will take at least until the end of 2006 for the official standardization process in the PCI Industrial Computer Manufacturers’ Group to be completed, taking into account procedures and time limits for appeals. The new proposed “micro” update for the COM Express standard is a variant that does not change features but rather only leave out elements that are not currently needed. Therefore, the process is expected to go smoothly. Moreover, PICMG has agreed in principle to support this type of expansion of the COM Express standard.

Further information

www.kontron.com/ETXexpress
www.picmg.org
http://intel.com/technology/ecsff/index.htm