Sub-Assemblies I Enclosures
MicroTCA steps up a gear
A new version of the MicroTCA specification, MicroTCA.4, has been developed to provide a platform for control systems at advanced test-and-measurement facilities. Keith Reynolds and Christian Ganninger take a closer look at the specification and what it has to offer
T
here are many research institutes around the world whose activities are concerned with photons, elementary particles and astro-particle physics. These institutes build and operate complex physical systems such as particle accelerators, X-ray lasers and neutrino scales. Up to now, these experiments have frequently been controlled using VME systems. A few years ago, however, a group of staff from several research institutes began to look for a suitable platform for the next generation of their control systems. As a result they committed themselves to the xTCA standard, i.e. AdvancedTCA and MicroTCA.
Although both of these specifications
are well suited as platforms for such applications, they did lack certain important features. Whereas AdvancedTCA only required additional signals to be defined in zone 3, the MicroTCA specification needed to be adapted to a greater extent; the result is the recently adopted sub-specification MTCA.4, ‘Enhancements for Rear I/O and Precision Timing’. The researchers settled on xTCA for one principal reason: the integrated carrier and shelf management, which both AdvancedTCA and MicroTCA specifications offer. This capability makes
it possible to constantly monitor the status of all components in a system and to respond to any error alerts. Furthermore, it also allows the monitoring of operational parameters to be carried out from a remote location, such as a control room. This is vital for particle accelerators, for example, since no access is permitted to any part of the accelerator ring (where the control and monitoring systems are installed) while experiments are in progress.
Another significant benefit of xTCA is
the redundancy that allows elements to be replaced while the system is in operation, i.e. hot-swap capability. However, other features that were
required were not implemented in the MicroTCA.0 base specification. For one thing, additional rear transition modules (RTMs) were necessary to accommodate the large number of I/Os and to physically separate digital and analogue I/Os. Also, the advanced physics community requires high-precision clock and trigger signals, which had not been considered necessary when xTCA was originally developed for the telecoms sector. The PICMG working group ‘xTCA for Physics’ was therefore set up, and this has now defined a suitable MicroTCA sub- specification known as MicroTCA.4. This specification is, however, also of interest
Figure 3: MicroTCA.4 cube system for development purposes.
to other market segments and has therefore been named ‘Enhancements for Rear I/O and Precision Timing’ to reflect this wider appeal.
Figure 1: Front and rear modules are inserted directly. 34 February 2012 Components in Electronics
MicroTCA.4 architecture The module size used in the front section of the MicroTCA.4 system was the double mid-size module (height 150mm, width 4HP, depth 180mm). The mid-size width allows the maximum possible number of 12 AdvancedMC modules - including two MCHs (MicroTCA carrier hubs) and up to four power modules - to be fitted into one 19in. wide system. The area allocated to the rear transition modules was chosen to be the same size as the front section, making the MicroTCA.4 system about twice as deep as a MicroTCA.0 system. In developing the I/O area at the rear of the system, the general idea was to feed in sensitive high-frequency analogue signals to the I/O section, process them there, convert them into digital signals and then pass them forward to the processor units in the front board cage. In order to make effective use of the existing xTCA eco-system, the rear module is essentially a front module rotated through 180°, so that the rear I/O connector and its mating connector are both on top (see Figure. 1). As the front modules plug directly into the rear modules via a connector - not via a backplane – the biggest challenge was to
ensure that these connectors were securely mated and that the MicroTCA connector also contacted securely. This sounds simple but it actually
required extensive tolerance calculations and ultimately the adoption of the special screw fitting defined in the Rugged MicroTCA specification MTCA.1, which holds the AdvancedMC module securely in its centred mounting position. A further significant addition over
MicroTCA.0 was the expansion of the clock and trigger signals available. MicroTCA.0 defines three telecoms clocks. Revision 2.0 of the AdvancedMC specification increases this to four telecoms clocks and one fabric clock for PCI Express (PCIe). For measuring purposes, however, additional, extra high- precision clock and trigger signals are required. These topologies have now been implemented in the previously undefined section of the pinouts of the AdvancedMC board.
Extended management Extensions were also required in the area of management for MicroTCA.4. In MicroTCA.0, IPMB-L and IPMB-0 are already defined. IPMB-L links the MCMC (MicroTCA carrier management controller) of the MCH (MicroTCA carrier hub) with the MMCs (module management controllers) of the AdvancedMC modules in a radial architecture. IPMB-0 links the
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