TECHNOLOGY IN CONTEXT
Standard Modules Offer Power and I/O Choices
VITA 74: Small, Conduction-Cooled, Rugged and Modular
The VITA 74 standard brings the modularity of the VME and VPX formats to smaller systems that previously would have had to be custom built, saving time and cost.
BY WAYNE MCGEE, CREATIVE ELECTRONIC SYSTEMS
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The VITA 74 committee was chartered by the VITA Standards Organization in May 2010 and soon attracted a diverse group of suppliers and potential customers for the new standard. The sponsors include Bustronics, CES, Molex, Samtec and Themis. The standard will consist of four specifications: the base specification and three clarifying specifications.
VITA 74.0 is the base specification and the primary definition of the vision. The specification describes a plug-in module designed for backplane systems with one or more modules communicating over the backplane. I/O is routed via the backplane to connectors on the enclosure.
VITA 74.1 describes a stand-alone enclosed computer module with cabled I/O. This is a special case implementation of the 74.0 specification. This specification has not yet been released.
VITA 74.2 is the 74.0 rear transition module specification. This specification allows the user I/O to be brought out of the enclosure to standard connectors. This specification is intended to promote a development environment prior to the purpose-built backplane likely required for deployment. This has not yet been started.
VITA 74.3 is a CPU module definition and is an optional standard I/O proposal to promote consistency and interchangeability of CPU modules. While desirable from a user standpoint, the widely varied needs for different I/O will require multiple profiles for varying classes and architectures of processor modules. This has not yet been started.
We will now examine the base specification. The standard defines two different form factors for the modules. Both modules are 89 mm x 75 mm but differ in thickness (card pitch). They both support backplane pins for location and ESD protection. The 12.5 mm variant uses a single base card and a 4-row, 200-pin connector. This is intended to support peripheral functions such as I/O, GPS and storage and is shown in Figure 1. The 19 mm variant allows for a base as well as a NanoETXexpress-sized mezzanine card. It uses an 8-row, 400-pin connector and is intended to support single board computer, graphics, video and FPGA functions and is shown in Figure 2.
An example of a single-wide VITA 74 module.
An example of a double-wide VITA 74 module.
As the standard was being defined, deliberate efforts were taken to incorporate previously proven technology. The signaling methodology was similar to the VITA 46 (VPX) and VITA 65 (OpenVPX) standards. The connectors used were adopted from the VITA 57 (FMC) standard. FRU inventory records for discovery over IPMI were reused from VITA 42 (XMC). The 19 mm module is wide enough to permit use with the PICMG COM.0 revision 2.1 NanoEXTexpress specification, although this is not part of the VITA 74.0 specification.
In designing small form factor modules and systems, careful consideration must be given to power dissipation and heat removal. VITA 74 modules are conduction-cooled, with 19 mm modules limited to 20W and 12.5 mm modules limited to 10W. Later revisions to the specification may allow these limits to be raised. The mechanical design utilizes a typical skyline interface heat spreader with thermal gap pad material to remove heat from the chips. The heat spreader then connects to the module case, which provides additional heat spreading capabilities on three sides. An exploded view of a typical 19 mm module is shown in Figure 3. This same technique is applicable to both the VITA 74.0 and 74.1 modules. The external cooling provided to the system should be designed to keep the temperature of the module case at the heat exchanger thermal interface at or below 85°C.
An expanded view of the double-wide module with heat spreader and case.
The backplane connector is a high-speed, rugged Samtec Searay series, the same as was used for VITA 57. This connector is not proprietary and is available from other connector manufacturers. The electrical bus partitioning is similar to VPX. There are three partitions. S0 is the utility plane containing power, control, clocks and management signaling. S1 is the bus fabric, which can be PCI Express Gen 1 or 2 with up to 16 lanes. S2 contains the user I/O and has 18 differential pairs or 36 single-ended lines in a full ground grid. The connector also provides separate locator pin/receptacles and ESD protection similar to VPX. An I/O transition module can be connected to the backplane to provide connectors for the various power and I/O signals needed for the system. An example of this is shown in Figure 4.
An example of a VITA 74 5-slot backplane with I/O transition module.
When the various modules, the backplane and the I/O transition module are combined into a packaged system, the result could be much like the system shown in Figure 5, a cubic configuration. The computing power provided by such a system, limited mostly by the power consumption, would be comparable to that of a tablet computer.
An example of how the VITA 74 modules and backplane can be packaged for deployment.
Applications and Deployment Benefits
VITA 74 enables deployable systems with a smaller footprint and cost point than VME, cPCI or VPX. The increasing availability of standard modules in the growing ecosystem opens up many possibilities. Standard SBCs, video processor, storage and I/O modules are already available. Full systems with the functionality of a small PC, with additional video processing capability and adapted I/O, are already available as a rugged box, ready to be installed in any embedded or industrial environment.
Thanks to the modular architecture, the processing functions, external interfaces and storage capacity can be combined into the optimal solution for each unit. Thanks to the small size and high-performance interconnects, multiple units can be installed in a distributed system, allowing system designers the freedom to decentralize their designs and provide dedicated subsystems with simplified and carefully segregated functionality. For safety-certified systems, this will make DO-178B certification easier to achieve. High-speed interconnects eliminate the need to have all functions in a single chassis, eliminating one of the single points of failure. Placing the control function closer to sensors reduces fidelity issues with measuring low-level analog signals. Simplified dedicated controllers also make it easier to deploy redundant subsystems in critical areas.
The VITA 74 system is smaller, lighter and less costly than a 3U VPX computer. This makes it ideal as a single or distributed subsystem controller for many different types of rugged vehicles. Figure 6 shows a typical distributed architecture for unmanned vehicles, whether flying, rolling or floating. There is a growing market worldwide for mini-UAVs that require smaller payloads. In addition to military usage, there will be increased deployment for security and border patrol as well as commercial uses such as aerial mapping.
A typical distributed vehicle control architecture shown with optional intelligent display subsystem.
Transportation is another area of possible deployment. Buses and passenger cars for subways and trams in many places display what the next stop is and which connections will be available. Add a location-aware advertisement server, and the passenger is made aware of the merchants at the next stop while the carrier now derives a revenue stream from advertisements.
The need for small rugged computers with a wide temperature range also exists in many industrial control applications. The growing domestic oil and gas market will see an increased need for down-hole monitoring and data collection with the precision drilling controls needed to process shale oil deposits.
For mining, many of the large vehicles contain multiple control systems and require an ultimate vehicle health monitor. In many cases, the airborne particulate matter makes non-sealed air-cooled computers unusable. VITA 74 systems are well suited for such an environment.
Another application VITA 74 is well suited to address is 180° and 360° video capture. A quad input video capture card with four 90° cameras provides a complete situational awareness view. Many conventional police dash-cams are limited to a 90° forward view and lose sight of the officer if the person being stopped runs out of the field of view. A 360° system eliminates the evidential questions about conduct outside of the current field of view.
While VITA 74 is a perfect fit for the ever increasing demand for smaller, more complex autonomous vehicles, the VITA 74 module itself is a perfect platform to take advantage of the processor revolution coming out of the commercial tablet and smartphone market. Demand for tablets and smartphones is predicted to rise to over 1 billion units per year by 2014 and this, in turn, is providing billions of dollars for mobile processor R&D. This investment is clearly evident in complex System on Chip (SoC) processors like Samsung’s Exynos, Qualcomm’s Snapdragon, Apple’s A6, Texas Instruments’ Davinci and Intel’s Atom. And these never before heard of volumes, coupled with ever increasing commercial pressures, are driving these mobile processor platforms down to unheard of price levels. The predominantly ARM-based modern mobile SoC processor is a great feature match for VITA 74: small size; low cost; low power; multi-GHz clock speeds; multiple cores, including dedicated DSP engines; high-speed DRAM interfaces; high degree of SoC peripheral integration; networking; peripheral interfaces; HD video capture, compression, decompression and display are highly prevalent in these processors. They even regularly endure environments that are comparable to many an embedded computing system.
In summary, the VITA 74 specification brings to life a proven set of technologies to provide a superior size, weight and power (SWaP) performance package. Combined with an extended temperature range, extended shock and vibration capability and conduction cooling, the new specification brings enhanced computing power to a wide range of applications.
Creative Electronic Systems
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