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VXS and VPX REDI Pave Road to Next-Generation VME

Choosing among next-gen VME choices like VXS and VPX REDI–and their subsets–calls for careful consideration of the thermal, I/O and power dissipation issues of each.


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There’s no question that the VME market is still strong, with a robust ecosystem, and remains the leading form-factor in shipment revenue. For the system developer who is looking to evolve from VME into higher performance form-factors, the VITA community has crafted several standards to choose from. With so many form-factor choices out there—both VITA and non-VITA—these days, systems designers must carefully consider the thermal, I/O and power dissipation issues of each alternative.

Among the most established of the next-gen VME alternatives is ANSI/VITA 31.1. The ANSI/VITA 31.1 standard, which implements Gbit Ethernet on VME64x Backplanes—was completed several years ago, but only recently achieved critical mass in the VME ecosystem with compliant boards available from several vendors.

Patterned after PICMG 2.16, ANSI/VITA 31.1 provides an Ethernet switch fabric for VME64x cards using the standard VME64x P0/J0 connector. In fact, ANSI/VITA 31.1 uses the PICMG 2.16 Fabric Slot connectors and pinout, allowing PICMG 2.16 Fabric Boards to be used for the Ethernet switching in ANSI/VITA 31.1 systems. ANSI/VITA 31.1 is a low-cost alternative that has been flying under the radar. It is a good alternative for applications that don’t require the performance provided by VXS or VPX, and provides complete backward compatibility with VME.

VXS Market Maturing

VXS products have been in the market for several years, and the market is maturing. The VXS ecosystem is strong, with 54 board-level products from 28 vendors. This includes both air-cooled and conduction-cooled products. VXS allows VME to address new applications that require additional bandwidth and higher performance than VME can support. Table 1 lists a summary of the VXS ANSI/VITA standards and draft standards. VXS is an evolution of VME, and as such it provides good backward compatibility with VME systems. VME64x modules without P0 connectors can plug into VXS slots. And VXS payload modules can plug into VME64x slots without J0.

VPX Gathering Momentum

VPX has a number of significant advantages for embedded mil/aero applications. It supports both 3U and 6U form-factors, and offers a large amount of high-speed rear I/O. Four 4x fabric links to each slot give VPX double the fabric bandwidth of VXS. And most importantly for military applications, VPX with its companion REDI standards, is designed from the ground up to support two-level maintenance.

VPX products have been in the market for less than a year, and the market is still developing. The VPX ecosystem is growing very quickly, with more than 26 COTS products announced by seven vendors. This includes air-cooled, conduction-cooled and liquid flow-through (demonstrator) products. Table 2 lists a summary of the VPX and REDI VITA standards, all of which are still in draft phase.

Thermal Challenges

High-performance switched fabric-based embedded computing industry standards are rapidly increasing in popularity. Maturing industry standards include PICMG’s AdvancedTCA (ATCA) and VITA’s VXS (VITA 41), as well as emerging industry standards such as PICMG’s AMC and MicroTCA, and VITA’s XMC (VITA 42), VPX (VITA 46) and REDI (VITA 48). These new industry standards support high power densities as compared to mature industry standards such as CompactPCI, PMC and VME. Figure 1 depicts the thermal density in mW/cm3 for various embedded board technologies and power levels.

For plain VME, 60W was a very hot board. But for a VXS or VPX board, that’s considered very low power. Figure 2 shows the range of actual power dissipation for various embedded board technologies. Rising power dissipation levels for new technologies such as VXS and VPX create significant packaging challenges. High-performance VXS and VPX chassis in the 100 W/slot to 200 W/slot range are practical today, but require detailed thermal analysis in the design phase to ensure a robust thermal design for the specific application and payload.

An example test chassis product supporting VITA 46/VPX and VITA 48/REDI is Hybricon’s line of open frame desktop test chassis (the OF-XC Series) (Figure 3). The OF-XC Series chassis has open side access for engineering and test personnel to use for debugging VPX REDI boards. Designed to the latest VITA 46.0, VITA 46.1, VITA 46.3, VITA 46.10, VITA 48.0 and VITA 48.1 draft standards, the standard hybrid mixed VME64x-VPX Backplane provides 11 slots based on VITA 48.1 VPX REDI with 1.0-inch pitch, including support for 80 mm Rear Transition Modules in both VME64x and VPX slots. Part of Hybricon’s extreme cooling chassis family, the chassis has a 2 kW Power Supply and high-performance fans with 20 cfm per slot to power and cool the most demanding new VPX boards.

The OF-XC chassis are initially available with Hybricon’s standard hybrid mixed VME64x-VPX switch fabric backplane. Hybricon’s backplanes have been computer simulated in Hybricon’s signal integrity laboratory to ensure low signal cross talk and trouble-free system operation. The enclosures are available with 2k watts of power.

Marrying Form-Factor to Application Needs

System developers now have several choices for embedded system applications. As they have done many times before, the VITA standards community has developed new standards to extend the performance of VME as well as provide an evolutionary path for VME-based systems. Table 3 lists a detailed comparison of VME versus VXS and VPX. ANSI/VITA 31.1 is a good, low-cost choice for 6U applications that require an Ethernet switch fabric. It is fully backward compatible with VME. For applications that fit this profile, it is worth a look.

VXS provides significant performance advantages over ANSI/VITA 31.1, and it has become a popular choice for signal processing applications because of the well developed board ecosystem as well as the performance level. VXS changes the VME64x P0/J0 connector, limiting the backward compatibility with VME64x boards and backplanes that use P0/J0. That said, VXS does otherwise provide very good backward compatibility with VME. It’s expected to continue to enjoy design wins for that reason alone.

Meanwhile, VPX REDI is new, but the ecosystem is developing at an explosive rate. VPX REDI has significant performance advantages over VXS based on performance, I/O capability, two-level maintenance and robust 3U form-factor support. VPX REDI has a bright future and will be widely adopted as the ecosystem develops. Several programs have already selected VPX. One thing to keep in mind with VPX is that the connectors are incompatible with VME, so backward compatibility can only be achieved with hybrid systems having a mixture of VPX slots and VME/VXS slots. When choosing a form-factor, the important point is matching it to the application.

Ayer, MA.
(978) 772-5422