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VITA 41 VxS and VITA 46 VPX (last updated October ’05) There is much debate in the VME community about the two new principal VME standards, VITA 41 and VITA 46. Because each has legitimate merits and drawbacks, and because there is not a significant amount of incremental development work for a board-level supplier such as Micro Memory to produce one in addition to the other, Micro Memory’s product road map includes offerings on both formats for each of its primary Othello carriers. VITA 41 VxS VITA 41 provides high speed serial backplane connectivity essential to supporting new interconnects such as Serial RapidIO, PCI-Express, and Infiniband. Requiring a new P0 connector, VITA 41 can support two independent ports:
A major advantage of VITA 41 is that it provides this high speed serial connectivity while maintaining true backwards compatibility with current boards designed to the VME and VME64 specifications, utilizing the same P1 and P2 connectors. However, the P0 connector is replaced so VME64x boards that currently utilize P0 are not compatible over P0 with VITA 41 boards. The result is that while VITA 41 boards do require a new backplane, legacy VME boards can be inserted into these systems and communicate with the VITA 41 boards over the parallel VME bus. This change in the P0 connector is relatively gradual, and thus VITA 41 is an evolutionary and organic upgrade path. One of the more positive aspects of VITA 41 is that the specification is stable and most of the associated “dot” specs have at this time been finalized, resulting in the near term release of VITA 41 boards, backplanes and chassis subsystems.
Figure 1
Figure 2 Figures 1 and 2 above from the VITA 41 VXS specification illustrates how a dual star configuration can be created with switch cards and payload cards. Combined with VITA 1.7, the spec that provides 2 Amps per pin, VITA 41 payload slots can provide over 100 watts per board. Drawbacks to VITA 41 include its relatively limited serial connectivity when compared to VITA 46 or other equivalent new Eurocard form factors designed to support multi-gigabit LVDS, such as ATCA®. VITA 41 payload cards can only support two serial ports, while VITA 46 boards will start with support for four serial ports and include capabilities for additional connectivity and future expansion. VITA 41 also requires the use of payload cards and dedicated switch cards. This typically results in a dual star configuration, as opposed to a full mesh fabric. VITA 46 VPX The advantages of VITA 46 are, for the most part, the drawbacks previously cited for VITA 41, including its dense connectors that support massive high speed serial connectivity. In addition to I/O bandwidth, the specification provides for power in the range of 700W per slot. While 700W in a single slot would generate far more heat than can be dissipated by today’s typical forced air and conduction cooling methods, liquid and spray cooling methods have been proven to dissipate this type of heat in other systems and are expected to be successfully applied to the VME VITA 46 format per the VITA 48 ERDI specification. While VITA 41 requires the use of switch cards for most implementations (more than three boards), VITA 46 provides for full mesh connectivity without the use of a switch card. This provides higher performance but does require that each board in the system include its own on-board crossbar switch. Notable is that VITA 46 also has provisions for a 3U form factor. VITA 46’s backwards compatibility has spawned significant debate within the VME community. While VITA 46 does include an interface fully capable of supporting the parallel VMEbus, VITA 46 cards have completely different backplane connectors than VME32, VME64, VME64x, or even VITA 41. This creates a major departure from previous improvements to VME as legacy boards will be difficult to readily include in new systems. Specifically, it will not be possible to utilize VITA 46 boards in current VME chassis. One solution to this issue will be in new hybrid chassis that include both legacy VME64 slots and new VITA 46 slots. In these systems, VITA 46 boards and legacy VME boards will be able to communicate with full interoperability over the VME bus, answering some of the criticisms with regards to life cycle management and product obsolescence. The basic VITA 46.0 specification has been agreed upon but more work is required to finalize the “dot” specs for specific interconnects (Serial RapidIO, PCI-Express, Infiniband, etc.). Below is an excerpt from the VITA 46.3 (Serial RapidIO) payload card specification, which is nearing finalization. While VITA 46.3 does not define backplane topologies, the following is an example implementation that provides full mesh connectivity for five payload cards wherein each card has a direct connection to the other.
Figure 3 Full technical details on both VITA 41 VXS and VITA 46 VPX can be obtained through the VITA trade organization, www.vita.com
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