RTC Magazine

The advent of VPX, formerly VITA 46, in the VMEbus world brings with it some significant strides forward that will deliver state-of-the-art performance to the high-end embedded computing applications of today and tomorrow. Specifically, through its adoption of the 6.25 Gbit/s Tyco Multigig RT2 connector, it brings support for serial switched fabrics together with other high-speed serial I/O technologies, such as digital video, serial ATA and FPGA interconnects. At the same time, VPX offers complete electrical and dimensional compatibility with existing 6U and 3U VME products. VPX boards are, therefore, VME boards as we know them in all important respects except one, the connector.

However, as it has always done, this increased processing power and throughput capability comes at a price: the additional heat that must be dissipated. Serial switched fabrics are, in themselves, a technology response to the need to provide ever higher bandwidth interconnects between ever more capable processors. Not only does the current generation of processors dissipate more heat than their predecessors, but the very high speeds at which the fabrics are driven also adds to the total thermal load.

Enter VITA 48/REDI

The arrival of VPX has, then, refocused attention on power dissipation and the requirement for cooling paradigms and technologies that enable systems designers to leverage the inherent capability of today’s embedded commercial components. In parallel to the development of the VPX standard is the work that has been undertaken on VITA 48, now known as Ruggedized Enhanced Design Implementation (REDI).

There are three important things to understand about REDI. First, while it describes a standard for creating rugged systems wherever they may be deployed, this standard is primarily driven by unusually harsh environments such as those found in military and aerospace computing. It is also driven by the fact that no commercial standards have yet addressed this requirement, just as they have not addressed requirements to deal with shock, vibration, humidity and ambient temperature extremes.

Second, REDI is a mechanical standard that is entirely independent of the VPX electrical standard. Third, although REDI is unquestionably highly complementary to VPX and the two are often discussed in the same breath, REDI should be viewed as a discrete standard that is highly applicable outside the VPX world.

REDI is thus a standard for ruggedization, which means that it deals with all aspects of creating high-performance embedded systems for environments that are far from benign. It describes board area and module volume, as well as structural ruggedization. It specifically addresses two-level maintenance, an approach that delivers greater logistical simplicity and the resulting substantial cost saving. Finally, it deals with thermal management.

How REDI Addresses Cooling

How, then, does REDI address the cooling issue? As with all VITA standards, VITA 48 comprises a number of disparate but related elements (Figure 1). It is expected that all will have been approved by the end of 2006. In its comprehensiveness, REDI goes beyond the work previously done by the VITA 34 working group. While VITA 34 was designed to accommodate liquid cooling, VITA 48 addresses it specifically. Because REDI deals with all forms of cooling within a single standard, it embraces common mechanical design approaches. This makes it simpler for manufacturers to create single board designs that can be cooled by convection, by conduction or by liquid, an important step forward.

One of the first things that REDI does is increase the maximum pitch between modules from the IEEE 1101 standard of 0.8 in. to 1.0 in. This increase is designed to do three things. First, it allows for the greater PCB thickness demanded by today’s sophisticated multi-layer boards, which can reach up to 24 layers. Second, the greater pitch makes it possible for more thermally demanding components to be placed on the secondary side of the board. Third, it provides a number of cooling options to board manufacturers and systems designers. Perhaps the most important of these options is the ability to fit side covers that can be used for either conduction or liquid cooling (Figure 2).