VME 25th Anniversary

VPX and VPX-REDI Standards Coming on Strong

The latest set of standards expected from the VITA Standards Organization (VSO) will address the support of robust serial interconnects over the backplane along with ruggedized specs that provide for a selection of cooling methods.


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The VPX and VPX-REDI standards are currently a major focus area for the VITA Standards Organization (VSO). VPX, formally referred to as VITA 46, offers 6U and 3U board formats with a modern high-performance connector set that is capable of supporting today’s plethora of high-speed fabric interfaces such as Serial RapidIO, PCI Express, 10 Gigabit Ethernet and others. While VPX maintains the very familiar mechanical and dimensional aspects of 6U VME and 3U CompactPCI such as the standard 0.8” pitch, VPX-REDI, formally known as VITA 48, offers extended mechanical configurations designed to support higher functional density. Being targeted primarily for harsh-environment embedded applications, VPX and VPX-REDI go hand in hand to enable defense system integrators to fully exploit today’s advanced component technology.

Figure 1 illustrates the suite of documents that together make up the VPX standard. As with other backplane standards, such as AdvancedTCA (ATCA), VPX uses the concept of a base specification to define the common elements and then a range of subsidiary specifications, commonly called “dot specifications,” after the convention in which they are numbered. The base specification for VPX is VITA 46.0, “46” being derived from the number of the VSO working group developing the VPX standard. Figure 2 shows a representative VPX module in a conduction-cooled format.

VITA 46.0 defines the basic mechanical and electrical underpinnings of VPX:

-6U and 3U board sizes and mechanical details based heavily on IEEE 1101.1 and IEEE 1101.10 for air-cooled cards and IEEE 1101.2 for conduction-cooled cards—all on a 0.8” pitch

-the use of the MultiGig 7-row RT2 connector, rated for signaling rates of up to 6.5 Gbaud

-the use of a mechanically robust alignment and keying system—the alignment aspect brings the payload card into alignment with the backplane slot before the connectors mate, while the keying aspect prevents cards from being inserted into an incorrect slot accidentally

- definition of voltages and current

capacities of the power rails

- utility signals such as geographical addressing, SYSRESET*, Reference Clock and JTAG

- signals allocated for a system management bus implementation

The VITA 46.0 specification provides a highly capable baseline for module implementations. Some notable aspects of the VPX connector system as implemented on a 6U module include:

- A total of 707 non-power electrical contacts

- A total of 464 signal contacts (non-power, non-ground), providing for:

- 64 signals implemented as 32 high-speed differential pairs for core fabric

- 104 signals used for a full VME64 implementation

- 268 for general-purpose user I/O including 128 high-speed differential pairs

- 28 for system utilities (reset, geographical addressing, etc.) and spares

- Each high-speed differential pair is rated up to 6.5 Gbaud

The large number of high-speed differential pairs supported by VPX modules allows for a rich complement of backplane I/O including: multiple ports of high-speed fabrics such as PCI Express, Serial RapidIO, 10GbE XAUI and InfiniBand; mass storage interfaces such as Serial ATA and high-speed digital video; and special-purpose interconnects such as RocketIO from Xilinx FPGAs.

The VPX specification hierarchy presented in Figure 1 illustrates a range of optional elements for a VPX module, one or more of which need to be implemented to provide a functional module. For 6U VPX modules an implementation of a full A32:D32 VME64 bus is defined within the VITA 46.1 specification. Such an implementation enables a VPX module to provide the performance benefits of a modern fabric-connected module while still maintaining the ability to interface to standard VME modules, assuming that an appropriate hybrid backplane is provided. This eases the transition to VPX by allowing previous investments in VME modules to be leveraged for new systems.

Integral to the working concept of VPX is what is referred to as the core fabric interface. A 6U VPX module is specified to have 4 core fabric ports, each port having 4 lanes (a Tx and Rx pair) in each direction. The allocation of 4 lanes per port fits naturally with Serial RapidIO, 10GbE XAUI and 4-lane implementations of PCI Express and InfiniBand. By provisioning for four (4) ports of fabric, a VPX module provides enough fabric connectivity to implement a large range of systems without the need for a dedicated switch slot—an important consideration for space, weight and power (SWAP)-sensitive systems often associated with military/aerospace applications.

To work together in a system all of the VPX modules must use the same core fabric, and while from one perspective it may have been ideal if one, and only one, standard fabric could have been chosen for VPX, due to the range of application scenarios envisioned for VPX no such “one size fits all” approach was deemed possible. So, like ATCA, a range of fabric options is provided for VPX.

Currently, dot specifications detailing the implementation of Serial RapidIO (VITA 46.3) and PCI Express (VITA 46.4) are available for VPX. A placeholder, VITA 46.7, for an eventual 10GbE implementation is defined. When other fabrics become of interest to the working group additional dot specifications can be created. The core fabric dot specifications contain two main types of information. The most fundamental information they contain are pin-out tables for the specific fabrics. This establishes a basic level of interoperability among backplanes and modules—ensuring that the Ins and Outs of the signals have been connected properly. However, for true multi-vendor interoperability in a set of cards connected together by a serial fabric such as Serial RapidIO, it is necessary to ensure that the serial links are meeting the required signal integrity budgets. This guarantees that when signals arrive at the receiver inputs they are of sufficient amplitude and low enough noise to be reliably received. Thus the fabric dot specifications define signal integrity budgets for VPX plug-in modules and backplanes so that system integrators can mix and match products from multiple vendors with confidence that they will work together reliably.

Support for PMC and XMC modules is an important element of VPX—in fact a key selection criterion for the 7-row RT2 connector is that its dimensions are compatible with the use of a standard-length PMC/XMC module. To facilitate multi-vendor interoperability the VPX series of standards includes VITA 46.9, a specification that standardizes the mapping between the Pn4 and Pn6 I/O connectors of PMC/XMC modules and the VPX backplane connectors. VITA 46.9 includes a definition of how pins should be paired to support the routing of differential signals from Pn4 and Pn6 to the backplane. This will allow makers of PMC/XMC modules that incorporate high-frequency signals such as Fibre Channel or digital video to be able to design their module with confidence that—from a signal integrity perspective—it will work on any VITA 46.9-compliant basecard.

The scope of VPX also includes the definition of a System Management (SM) bus and backplane signals are reserved for that purpose. The VPX SM bus will be fully defined in an eventual addition to the VPX suite of standards. The VPX SM bus specification, referred to as 46.xx in Figure 1, will be tailored to the requirements of embedded systems and will carefully consider the tradeoffs between functionality and the amount of board real estate required for the SM interface circuitry. Some of the capabilities expected in an eventual SM implementation are the collection of BIT results and the real-time monitoring of operating conditions such as temperature and power supply voltages.

While the rich fabric connectivity supported by VPX is expected to enable a high percentage of applications to be implemented by directly connecting modules together in mesh-based architectures, there will be VPX applications that require a centralized switch. The definition of a VPX switch slot will be encapsulated in the VITA 46.20 specification and encompass definitions for both single-fabric and hybrid (fabric plus GbE) switches.

Given that VPX is targeted to harsh-environment military/aerospace applications, it was very important to substantiate that the module would hold up to the intended application environments. To this end, the VITA Standards Organization (VSO) VITA 46 Working Group successfully conducted an extensive third-party qualification program including the following environmental parameters:

- Vibration (power spectral density of 0.1 g2/Hz from 50 Hz to 2000 Hz, 1.5 hours/axis)

- Shock (50g, 11 msec)

- Temperature (-40°C to 100°C)

- Humidity

- Durability (500 mate/unmate cycles)

- Dust and sand

- Electrostatic discharge (ESD) protection (EN 61000-4-2)

The test results are publicly available and may be downloaded on the VITA Web site.

As mentioned above, the VPX mechanical formats closely follow those of IEEE 1101.x and preserve the 0.8” pitch that is the standard for VME and CompactPCI. VPX-REDI (Ruggedized Enhanced Design Implementation) is a complementary mechanical standard to VPX, and defines alternate mechanical formats that go beyond the traditional IEEE 1101.1 and .2 formats to provide new enhanced capabilities. These new capabilities include an increase in usable PWB area and improved thermal

management (air-cooled, conduction-cooled, liquid flow-through cooling), which enables increased functional density. VPX-REDI also supports use as a line replaceable module (LRM). The VPX-REDI formats are described in a suite of specifications consisting of VITA 48.0 (common elements), VITA 48.1 (air-cooling), VITA 48.2 (conduction-cooling) and VITA 48.3 (liquid flow-through cooling).

Concurrent with the finalization of the VPX and VPX-REDI standards within the VITA Standards Organization, product development and announcements from the vendor community are continuing. In addition to a growing list of VPX module vendor product announcements there have also been chassis from Elma Bustronic, Parker-Hannifin and Hybricon.

More information on VPX and VPX-REDI can be found at