For more than two decades, single board computers (SBCs) built on open standards have been largely based on specifications from two preeminent industry organizations, VITA and PICMG. For the 6U Eurocard format, each organization has developed a platform that has provided the basis for standardized SBCs; where VITA introduced the VMEbus standard and derivatives, PICMG introduced CompactPCI bus and its derivatives. Both bus structures use a parallel bus architecture, which has its performance limitations, hence the recent movement to use fabric-based technologies.

Figure 1. Multi-Gig-2 Wafer Based Connector

Updating hardware to include advancing technologies in embedded computing is nothing new, with the latest iteration being the incorporation of Intel and Freescale processor chipsets with internal serial bus interfaces into the SBC architecture. For PICMG, its original CompactPCI standard was followed by ATCA and MicroTCA, (albeit it in different form factors), where both new standards support serial fabric interconnects.

VITA started supporting serial fabrics with the release of VITA 41, or VXS, in 2006 followed by the ANSI ratification of VITA 46, or VPX, in 2007. The latest upgrade to the world of Eurocard form factor SBCs is the recently VITA/ANSI-approved OpenVPX, or VITA 65, based on VITA 46.0 and VITA 46.1.

A Legacy Continues

Originating from the VPX standard, OpenVPX provides a framework to build high performance, high power SBCs that incorporate the latest fabric-based technologies, including PCIe, one and ten Gigabit Ethernet as well as Serial Rapid I/O (SRIO). Applying this standard requires new thinking in the area of board-to-board interconnects, since the serial interfaces used require point-to-point interconnect between boards or, in other words, the use of central switching.

Designers using OpenVPX need to address the SBC interface design and board level interconnect, while taking into account the higher levels of throughput OpenVPX provides over the former bus architectures.

The OpenVPX standard supports the use of differential pairs of point-to-point interconnects, which replace the legacy parallel bus connection used on DIN connectors employed in the original VMEbus standard. OpenVPX provides SBC designers with the following features:

  • 3U or 6U form factor, 0.8" or 1.0" spacing;
  • Convection or conduction cooled formats;
  • Increased power;
  • High bandwidth differential interconnects up to 6.25 Gbps;
  • Profiles that describe module pin out and physical protocol;
  • Multi-topology support: mesh, star, dual-star signal planes;
  • Single or multi-plane architecture: control, data and expansion planes;
  • Several physical fabric protocols: PCI Express, Ethernet, SRIO, Aurora, etc.;
  • System management.