VPX

VPX, formerly known as VITA 46, is an ANSI standard (ANSI/VITA 46.0-2007) that provides VMEbus-based systems with support for switched fabrics over a new high speed connector. Defined by the VITA (VME International Trade Association) working group (comprising major industry organizations such as Boeing, Curtiss-Wright, GE Fanuc Embedded Systems, Mercury Computer Systems and Northrop Grumman), it has been designed specifically with defense applications in mind, with an enhanced module standard that enables applications and platforms with superior performance. VPX retains VME’s existing 6U and 3U form factors, supporting existing PCI Mezzanine Card and XMC mezzanines (PMC with high-speed serial fabric interconnect), and maintaining the maximum possible compatibility with VMEbus.

New generations of embedded computing systems based on the VPX standard reflect the growing significance of high speed serial switched fabric interconnects such as PCI Express, RapidIO, Infiniband and 10 Gigabit Ethernet. These technologies are starting to replace traditional parallel communications bus architectures for local communications, because they offer significantly greater capability with higher bandwidth, throughput and performance. Switched fabrics provide an optimum technology to support the implementation of multiprocessing systems that require the fastest possible communications between multiple processors (e.g., digital signal processing applications). VPX gives the large existing base of VMEbus users access to these switched fabrics.

Specification

In common with other similar standards, VPX comprises a ‘base line’ specification, which defines the basic mechanical and electrical elements of VPX, together with a series of ‘dot level’ specifications, one or more of which must be implemented to create a functional module. The specifications are as follows:

Connector

The single biggest difference between today’s VMEbus boards and VPX boards is that VPX boards use a new connector, developed by Tyco and known as the MultiGig RT2. This means that VPX boards cannot be used in a standard VMEbus chassis, although the use of hybrid chassis is foreseen by the VPX standard. A 6U VPX board features six 16-column 7-row RT2 connectors and one 8-column 7-row RT2 connector, while a 3U board features two16-column 7-row RT2 connectors and one 8-column 7-row RT2 connector.

Also new for VPX boards are alignment/keying blocks which are designed to be sufficiently robust to prevent pin stubbing. The blocks also provide card keying and a safety ground. A 6U board has three such keying blocks, while a 3U board has two.

The MultiGig RT2 connector is specifically designed to enable high performance. It accomplishes this through a 7-row 16-wafer (wafers can be power, differential or single-ended) that delivers highly controlled impedance, minimal insertion loss and less than 3% crosstalk at transfer rates up to 6.25 Gbit/s. The new connector enables a 6U VPX board to feature a total of 707 non-power electrical contacts and a total of 464 signal contacts. The latter are usable as:

* 64 signals implemented as 32 high speed differential pairs for core fabric
* 104 VME64 signals
* 268 for user I/O including 128 high speed differential pairs (giving a total of 160 high speed differential pairs)
* 28 for system utilities or spares

The connector is designed to allow a typical stiffening bar and a standard length PMC.

Power and ruggedization

A VMEbus slot is limited to a maximum of 90 watts at 5 volts. VPX raises this to 115 watts at the same voltage, or up to 384 watts at 12 volts or 768 watts at 48 volts. The specification of 6U VPX calls for computer cooling via a conduction-cooled envelope compliant with the IEEE standard IEEE-1101.2, which is compatible with existing enclosures. Provision is also made for air-cooling via an IEEE 1101.1/10 form factor version.

For more stringent cooling requirements, the REDI (Ruggedized Enhanced Design Implementation – previously known as VITA 48) standard describes how to implement layout techniques to better support cooling methodologies on specific form factors. This provides a specification not only for ESD metal covers on two sides of VPX boards, but also for forced air, conduction- and liquid-cooling implementations. REDI also addresses spray cooling. To allow for greater power and heat dissipation, REDI includes provision for increased board-to-board spacing and increased board thickness.

Products

A number of manufacturers have announced products based on the VPX standard, in both 3U and 6U form factors. These include single board computers (based on both Intel and PowerPC architectures), graphics processors, mass storage, switches and complete, integrated subsystems.

See also

* VMEbus
* CompactPCI

External links

Tutorials
* [http://www.gefanucembedded.com/news-events/whitepapers/3631/AFC-WIK VPX White Paper (GE Fanuc)] Overviews VPX as an update to the VMEbus Specification

Overviews
* [http://www.vita.com/vpx.html VPX Brief] Brief overview from VITA