Jing Kwok from Curtiss-Wright Controls outlines the significance of the new VPX (VITA 46) embedded board standard
The VPX (VITA 46) embedded board standard is the most significant evolutionary enhancement to the popular and long-lived VMEbus yet developed. The goal of VPX is to provide customers with access to open standard systems capable of meeting emerging application demands which exceed the capabilities of traditional VME boards and systems. It was defined co-operatively by leading board vendors through a working group at VITA (the VMEbus International Trade Association).
While VME, now celebrating its 25th anniversary, will continue to satisfy a wide variety of embedded applications for many years to come, several emerging technology and application trends can only be met with a new approach that goes beyond VME with more bandwidth, a greater number of I/O pins, extended power provisioning and electrostatic discharge (ESD) protection.
Some of the application trends that VPX addresses include the growing use of serial fabrics to replace traditional parallel busses for local communications. Examples of these fabrics include, PCI Express, Advanced Switching Interconnect, Serial RapidIO, Infiniband, and 10Gbit Ethernet XAUI.
Meanwhile, standard I/O interfaces are quickly moving to high-speed signals. In the video realm these high-speed interfaces include DVI, LVDS, and SMPTE 292M (HDTV). In storage applications it is becoming increasingly common for customers to select Fibre Channel, Serial ATA, and Serial attached SCSI. And in sensor applications, Serial FPDP, and Xilinx RocketIO are driving demand for greater bandwidth on the system backplane.
Meanwhile, density improvements at the chip level are driving demand for more I/O pins at the board level. In many cases, existing products are already limited by the 205-pin capacity of VME64X.
Military and aerospace system integrators are especially sensitive to these emerging technology trends as applications such as radar processing and the growth of network-centric battlefield communications increasingly exceed the capabilities of the 320Mbyte/s VMEbus (VME64x using 2eSST).
 |
Tyco's 7-row connector uses a wafer style connection
and provides the increased I/O and bandwidth
|
VPX was designed to provide military and aerospace system integrators with a more capable module standard that allows for better exploitation of the new technologies, while enabling more cost-effective end systems.
In defence applications, VPX boards are ideal for ultra high performance applications like avionics mission computers and airborne radar data processors. While these applications are today dominated by proprietary, non-standards based systems, switched serial fabric architectures hold the promise of orders-of-magnitude improvements in performance over common bus approaches like traditional VME64 and CompactPCI.
The VPX standard provides significantly greater bandwidth, support for serial switched fabrics and a greatly increased total I/O complement while retaining the standard 6U and 3U form-factors common to the traditional VME eco-system. Familiar VME characteristics retained by VPX include height, depth, pitch, front panel arrangements, and conduction-cooled interfaces.
To protect a customer’s investment in legacy VME hardware and software, VPX supports VME and PCI interfaces. VPX and VME64X boards can be integrated into the same chassis using a hybrid backplane, defined within the VPX standard. Because the VPX specification supports the VMEbus electrical specifications, a hybrid backplane can be used to house VPX modules alongside the traditional VME64 modules in a single 6U chassis. For military system integrators, this hybrid backplane is already a familiar part of typical technology insertion plans.
Like VME, VPX supports standard-length PMC modules, but also provides support for the new higher speed XMC modules. To provide support for high-speed serial fabrics on the backplane, VPX adopted a different connector than that used in VME.
The VPX connector - Tyco’s MultiGig RT2, 7-row connector - uses a wafer style connection and provides the increased I/O pins and bandwidth required to handle high-speed signals and serial switch fabrics. The connector also provides built-in ESD grounding protection to enable in-the-field ‘2-Level Maintenance’ of modules, which can greatly reduce the time and cost of subsystem repair and replacement.
 |
A 6U VPX board with ESD covers
|
The VPX standard defines both 6U and 3U module variants.
The 6U version of VPX provides for an IEEE-1101.2 conduction cooled compliant envelope, compatible with existing enclosures. It also includes an air cooled IEEE 1101.1/10 form factor version. VPX provides the bandwidth and pin counts needed by customers whose applications require distributed switching and large amounts of streaming I/O, but also need to maintain access to low speed discrete I/O. VPX addresses the I/O connectivity limitations of current 6U VME64x cards, whose P0 and P2 connectors have a total of only 205 I/O pins.
In a typical 6U configuration the VPX connector systems deliver: 128 differential pairs for user I/O that can alternatively be used as single-ended signals, giving 256 such signal lines if no high speed signalling is required; and 12 single-ended signals for a grand total of 268 user I/O signals while simultaneously allowing for a full A32:D32 VME interface and 32 differential pairs allocated to the core fabric. Compared to VME, VPX’s 160 high-speed differential pairs, each rated for up to 6.25Gbaud, delivers a tremendous amount of high-speed capable I/O.
To address the increasing power demand that greater chip densities and hotter processors put on embedded boards, VPX raises power provisioning from the maximum 90W at 5V limit of VME, to 115W at 5V power (up to 384W at 12V and 768W at 48V).
For advanced levels of ruggedisation and cooling, VPX can be extended with the VPX-REDI (VITA-48) standard that provides ESD metal covers for VPX modules and defines forced air, conduction and liquid cooling options.
The VPX standard, collaboratively developed by COTS industry leaders and prime military integrators, delivers a high-speed serial interconnect with a form-factor and feature set specifically designed to meet demanding military/aerospace applications for the next 25 years.
Jing Kwok is principal engineer in the technology group at Curtiss-Wright Controls Embedded Computing
www.cwcembedded.com