Third generation of computer on modules has many faces

Paul Boughton

Users of x86 based computer on modules (COMs) will profit from the perfect easy entrance in the next generation COMs for future proof designs. Martin Bodenschatz and Zeljko Loncaric reports.

The first open standard computer on modules (COM) was the DIMM-PC with ISA bus. The well established ETX standard with PCI and ISA is the second generation of open COM standards. The third and latest generation of COMs is the official PICMG standard ETXexpress (COM Express Spec.COM.0) with PCI Express.

Beside PCI Express, ETXexpress also offers the PCI bus and several new interfaces like serial ATA, Gigabit Ethernet, USB 2.0, dual channel RAM and PCI Express graphics.
With the introduction of the COM.0 compliant microETXexpress COM form factor developers have now the option to use only those interfaces from the COM.0 standard that they require. Depending on the processor and chipset support, microETXexpress on the ‘Compact’ module size, will either offer only PCI based COMs or COMs with PCI and fewer PCI Express lanes, compared to ETXexpress in the ‘Basic’ module size. This will make it easy for high performance applications to swiftly create ETX to ETXexpress compliant designs.

Table 1. illustrates the added benefits of microETXexpress in comparison with ETX and the limitations in relation to ETXexpress:

The emergence of the new PICMG COM standard ETXexpress (COM Express spec.COM.0), originally intended primarily for PCI Express and now also available for PCI-based designs, is highly interesting to developers of current COM-based systems.

The new 220-pin high-speed SMT connectors for ETXexpress/COM Express have enormous performance reserves. They are specified for transfer rates of up to 6.25GHz LVDS and 5GHz PCI Express (2ndgeneration) and so can handle the next generation of interfaces without compromising their speed.

With microETXexpress, Kontron wants to create this capability for PCI-based solutions too, so that the established PCI bus can be combined with the latest interfaces, including SATA, LVDS, USB2.0, Gigabit Ethernet and dual-channel RAM, on a COM.

Developers using microETXexpress can profit from compatibility with ETXexpress/COM Express to transition gradually to ETXexpress.

In addition, they can be sure that they are using a COM standard that will be around for a long time, as it is designed to be compatible with processors and chipsets that are due to come onto the market several years down the line. A commitment to these new 95x95mm (37x37in) variants of the ETXexpress/COM Express form factor has already been made by Advantech, ADlink and Evalue.

The mechanical design of microETXexpress differs from that of ETXexpress/COM Express in only one major respect: size! ETXexpress (BasicCOM Express) measures in at 118.75cm2, or 18.41sqin, (100percent) and microETXexpress (Compact COM Express) at 90.25cm2, or 14.00sqin, (76percent). The existing larger form factor Standard Extended ETXexpress (Extended COM Express) is 170.5cm2, or 26.43sqin, (143.58percent).

Of course, any feature that could not fit within the physical limits of the new, smaller COMs has been eliminated. What remains the same is the position of the two high-speed ETX connectors in relation to the baseboard. It was therefore possible to ‘copy and paste’ many specification details, which is an advantage for more than just ease of documentation.

With the launch of the new form factors for PCI and PCI Express-based designs with new high-performance connectors, Kontron is drawing a clear line to ETX designs and their derivatives: classic ISA, keyboard, mouse, RS232, analog graphics and other interfaces are no longer available on these ETXexpress variants. Developers should also bear in mind that ETX is for low to mid performance designs, microETXexpress (Compact module size) is for mid to high performance designs and finally ETXexpress (Basic module size) is for high performance designs. microETXexpress-PM, the first module on this form factor, is based on the Intel Celeron M and Intel Pentium M processor with the Intel 82855GMchip.

With ETXexpress, Kontron has created a new standard to cater for the new high-end technologies that are essentially changing board and expansion card designs. Making the standard available for PCI-based solutions doesn't mean that Kontron will lose its dominant market position for PCI designs because the installed base is much too big for new solutions offering added value for ETX users not to be implemented. The focus for new ETX developments will be in new processor technologies that combine high performance with extremely low power dissipation.

The pin assignments on the new, compact 95 x 95mm (37- x 37-in) microETXexpress are the same as for ETXexpress. The microETXexpress variants are achieved by eliminating various PCI Express interfaces. All pins for periphery, network and memory interfaces – such as PCI, IDE, 10/100 LAN and 6 x USB2.0 – are assigned identically, so that for a switch from PCI to PCI Express or to combinations during layout on the baseboard, nothing has to be changed. The user can plan PCI Express and SATA into the design on a single baseboard and, when they are needed later, use them immediately through a simple exchange of modules.

Support for PCI and/or PCI Express is provided by the respective chipset. microETXexpress modules with SATA and PCI Express in this new compact format are already planned for 2006.

Ultimately, future-proof support can be provided with only one backplane for both embedded formats – microETXexpress and ETXexpress (COM Express) – with full scaling for processors, IDE to SATA, PCI to PCI Express and 10/100 to Gigabit Ethernet. The fact that baseboard PCB layout is easier with PCI Express due to fewer tracks per bus segment represents a real advantage for developers.

Kontron’s extensive service package will enable developers to familiarise themselves with the new technologies quickly. A simple starter kit will enable developers to write and test application software at the beginning of the development phase, before the application baseboard is available.

ETXexpress was introduced by Kontron and Intel at the end of 2003 to enable the PCI Express bus (PCIe) and other brand-new computer technologies, including SATA, USB2.0, Gigabit Ethernet and dual-channel memory, to be utilized for customer-specific embedded designs on Computer-On-Modules (COMs). Work on the COM Express specifications was officially begun by PICMG at the beginning of 2004. Since July 2005 ETXexpress has become the official standard, under the name of COM Express, thanks to close cooperation between Kontron and the PICMG.

Kontron's first ETXexpress COM is based on the Intel PentiumM processor760 and the Intel 915GM chipset; it is the first mobile platform with PCI Express functionality and extended support over the entire product lifetime. As the flagship of the new ETXexpress Computer-On-Module (COM) product range, the high-speed ETXexpress-PM enables developers of embedded applications to integrate the latest interface technologies into their applications. ETXexpress-PM offers performance of up to 2.13GHz and a maximum of 2GB of DDR2-SODIMM RAM.

With Intel Extreme Graphics 2 and PCI Express graphic support, ETXexpress-PM can take on sophisticated real-time video applications. The 10/100 Base-T Ethernet interface, which will be upgradeable to Gigabit Ethernet in future ETXexpress COMs, provides rapid communication capabilities.

Martin Bodenschatz and Zeljko Loncaric are with Kontron Embedded Modules in Deggendorf, Germany.