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System Design & Boards

Standardising the next generation The options available for high performance systems. By Martin Traut and Keith Reynolds VMEbus International Trade Association). While the classic parallel VMEbus is of decreasing importance, many systems and backplanes based on the VME64x extension are still in use. The next step was VXS, which provided the serial data transfer capability required for today’s high speed systems. This specification included a set of protocol layer standards – including RapidIO, and InfiniBand – to define the specific serial interconnect used in a system implementation. While backward compatibility with VME64 extensions was assured, the more recent serial specification, VPX, uses entirely new high speed connectors, so VPX and VME64x backplanes are no longer compatible.

CompactPCI In the mid 1990s, PICMG developed the CompactPCI specification as a cost effective open platform standard for high end 19in systems. Featuring rugged 3U or 6U Eurocard formats and twice as many slots as the standard desktop PCI specification, CompactPCI offered a packaging scheme better suited to use in industrial systems. However, since CompactPCI provides no serial interfaces via the In telecommunications, ATCA systems have their main use in the core network, backplane, the specification was extended in where large data volumes come together and must be processed 2005 with CompactPCI Express, which uses serial, rather than parallel, data transmission. ince the days when classic open platform have serial extensions based on the traditional For many users, this new specification was ‘too technologies, such as VME and Eurocard format, whilst newer technologies open’, making it difficult for them to create SCompactPCI, were established in the 1980s – such as ATCA and MicroTCA – have employed systems with standardised backplanes. and 1990s, the processing power available to serial techniques from the outset, albeit with a Furthermore, in CompactPCI Express the system designers has continued to increase different form factor that eliminates backward number of rear I/O connections was too small rapidly. In particular, the emergence of multicore compatibility. and it lacked important features, such as processor technology has created a need for ever In future, as bus drivers and cpu chipsets support for S-ATA, USB and Ethernet. higher data throughput, driven by applications become unavailable or reach end of life status, PICMG has developed a new backplane like mobile internet and video on demand. designers who used VME or CompactPCI will be standard – CompactPCI Serial – which The infrastructure of modular computer forced to choose a new technology addresses these perceived shortcomings and systems has had to adapt to these new offers data transfer speeds of up to 32Gbit/s. conditions and one of the most significant VMEbus and its descendants Though only finalised in March 2011, developments has been the move from parallel VMEbus was the first open platform standard, CompactPCI Serial systems, backplanes and architecture to serial bus technology using fast mainly promoted by Motorola with the 68000 boards are now available. data transfer protocols. generation of processors. In 1994 its data transfer The main focus for CompactPCI Serial is on The ‘old’ parallel open platform standards now rate was increased from 32bit to 64bit by VITA (the applications in industrial automation and

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System Design Backplanes & Boards

performance and possibly less stringent One area of application for CompactPCI Serial systems is in traffic and transport engineering. availability requirements. In the ATCA standard, AdvancedMC modules are inserted into AdvancedMC carriers; in MicroTCA, these sub- assemblies are defined as functional modules that are used directly in the system. MicroTCA therefore allows compact, powerful computer systems to be built. MicroTCA is being used in a number of non telecoms applications, where large volumes of data need to be processed, including real time motion control, industrial and medical image processing and test and measurement systems. Recognising MicroTCA’s broader appeal, PICMG set up four MicroTCA sub specifications to address the requirements of applications outside the telecoms sector. The first of these, transportation. The standard can be used not subracks are installed within a 19in cabinet. To MicroTCA.1, defines ruggedised, air cooled only for simple machine control systems, but ensure the ATCA blades provided sufficient space systems for demanding mechanical and thermal also for applications that require large amounts to accommodate all the necessary components conditions. MicroTCA.1 products are already in of data to be processed: for example, video and to allow them to be cooled effectively, the use in the field. The second sub specification, capture and analysis. In transportation form factor was enlarged in comparison to MicroTCA.2, is concerned with air cooled, robust engineering, CompactPCI Serial is suitable for Eurocards: 8U high, 6HP wide and 280mm deep. MicroTCA systems for military applications and is control systems on trains, passenger In addition, the specification defined the 70mm still in development. The third, MicroTCA.3, deals information and entertainment systems both on deep rear transmission module, through which a with conduction cooled, robust MicroTCA trains and at stations, signal box control systems large number of data sources would be linked. systems for military applications; this sub- and trackside measurement systems. Unlike previous generations of sub specification has already been finalised. assemblies, such as the PMC boards used in VME A further area of application outside telecoms ATCA: serial from the start and CompactPCI systems, AdvancedMC modules is described by in MicroTCA.4 as ‘Enhancements In 2001, PICMG published the AdvancedTCA were designed to be hot swappable and for Rear I/O and Precision Timing’. This defines specification to provide the first unified standard controlled from the shelf management system. additions and modifications to make MicroTCA for modular computer systems in the telecoms This, coupled with redundancy of key sub useful for the physics research community. industry. This defined all system aspects, assemblies, ensured a minimum availability of Systems of this type will be used, for example, to including mechanics, backplane and cooling. It 99.999%. This means a system is only allowed to control particle accelerators for high energy also defined management – the controlled be inoperable for 5.3 minutes per year. physics experiments. However, MicroTCA.4 is also startup, shutdown and monitoring of boards. In suitable for other segments, including test and conceptual terms, ATCA is a scalable, high Small form factor, high performance measurement. performance architecture with high function Following ATCA, PICMG developed another density and 99.999% availability. This makes it modular standard called MicroTCA, which Conclusion particularly suitable for server applications in the focuses on cost sensitive, physically smaller The parallel bus in open platform standards has core network, where large volumes of data need applications with reduced capacity and been replaced by the faster serial data to be processed. transmission model. Both technologies are, An important innovation was the change from however, sure to coexist for another five to parallel data buses to fast serial point to point seven years. Which bus technology and which connections, which made it possible to send degree of migration is best for each particular common protocols (such as Ethernet, RapidIO area of application should always be carefully and PCI Express) via the backplane. considered, including the cost aspects, before The basic building blocks of an ATCA system any general technology migration is undertaken. are the ATCA board or ‘blade’ and the AdvancedMC carrier, which may house up to eight Advanced Author profiles: Mezzanine Card (AdvancedMC) modules. Several Martin Traut is product manager at Schroff blades and carriers can be assembled into a GmbH. Keith Reynolds is technical/marketing subrack and, in a typical system, populated A MicroTCA.4 cube system for development purposes manager at Schroff UK.

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