3U VPX Takes Creative Design Solutions

3U VPX is much more than just a half size version of 6U VPX. It can actually match the speed and bandwidth of the 6U version and has creative design options.

Although 3U VPX has a much more limited number of potential IO channels than the larger 6U version, it probably has more than enough connectivity for most applications. Using the right routing schemes, 3U VPX is compatible with existing PMC mezzanine modules as well as the newer XMC mezzanine modules. The substantial existing ecosystem for of PMC modules means that many interface standards can be supported immediately, through the use of either XMC/PMC carrier cards or VPX SBC cards with a PMC/XMC socket.

The flexibility of the backplane interconnect topologies is an important feature. The 3U VPX architecture has three backplane connectors in each slot. The J0 contains power at three voltage levels and such system signals as geographic address, power fail, JTAG and a reference clock. The other two connectors provide a total of 64 differential signal pairs and associated reference grounds.

The J1 and J2 connectors can be configured as x1, x2 or x4 channels. The Multi-Gig connector supports XAUI 2.5 Gbps signaling and is scaleable to at least 6.25 Gbps. Because the VPX architecture allows the end user to define how the differential channels in J1 and J2 can to be used, there is great flexibility to emphasize either channel interconnect mapping or rear panel IO.

The most common configuration for 3U VPX cards thus far is for two x4 10 Gigabit channels at the top of the J1 connector. The remaining channels in J1 together with those in the J2 leave 24 XAUI capable bi-directional ports that can be utilized entirely for rear panel IO if desired. Traditionally, a channel comprised of one or two bi-directional links is referred to as a “thin pipe.” A channel comprised of four bi-directional links is referred to as a “fat pipe.” The 24 thin pipe channels remaining can be used by a PMC or XMC mezzanine or simply allow the 3U VPX modules to interface with external equipment, networks, displays or storage systems. For more complex topologies that may be desired the entire J1 connector can be configured as x4 10Gigabit channels for slot to slot transport. This still leaves the 16 XAUI capable bi-directional thin pipes in J2 for user IO.

A new VPX subsidiary document under preparation would make use of two of two thin pipes on each VPX slot is the VITA 46.20 VPX Gigabit Ethernet Control Plane. With the addition of a GigE switch, this architecture would provide a separate star or dual star network for out of band communication. This can be particularly important for an implementation of system management and for software and firmware upgrades and even for initiating new processes on specific boards.

Imagine a 4-slot mesh with both the input to and the output from the mesh connected through a single card. This card is frequently populated with a SBC supporting the user interface. In this hybrid example, a single star distributed thin pipe switch per VITA 46.20 overlays the mesh allowing all the cards to be addressed separately from any card within the system or from available GigE ports to the outside world or a WAN.

For more on 3U VPX Backplanes, contact Bustronic.

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