My colleague Martin introduced the MicroTCA.4 specification in one of his blog posts last year (https://nutaq.com/blog/will-microtca4-be-adopted-scientific-community). In this post, I expand on his introduction by describing how MicroTCA.4 systems differ from typical MicroTCA systems.
The MicroTCA.4 chassis
Figure 1 shows a typical 10-slot MicroTCA chassis back plane. Each slot is 73.5 mm high and is designed to house single-width advanced mezzanine card (AMC) devices. On top of the 10 AMC slots, the chassis can accommodate two MicroTCA carrier hubs (MCH) and two power modules, as well as the chassis cooling units.
Figure 1: 10-slot MicroTCA chassis
MicroTCA.4 systems essentially replicate the same design but use the double-width AMC specification (148.5 mm) instead for its slot height. The AMC connectors are located at the same positions. A hole is left in the chassis backplane to enable the interconnection of the AMC devices with the MicroTCA.4 rear transition modules (RTM).
Figure 2: 10-slot MicroTCA.4 chassis
The chassis hole enables an AMC to connect with its RTM. The chassis depth is doubled, enabling RTM cards to be installed in slots from the back. The front and rear areas are distinct and can be cooled independently.
Figure 3: MicroTCA.4 RTM
MicroTCA.4 AMC device
MicroTCA.4 uses double-width AMC devices for its primary units. Double-width AMCs follow the same specifications as single-width AMCs for connector ports and power supply voltages (see my last blog for details). Their power consumption, however, can be up to 80W. Double-width devices come with the added advantage of being able to carry two FPGA mezzanine card (FMC) ports instead of just one. Also note that a MicroTCA.4 chassis can also support single-width AMCs, which provides full backwards compatibility with previous MicroTCA systems.
Rear transition module
The primary purpose of the MicroTCA.4 specification is the inclusion of RTMs. The RTM’s main functions are to add real-estate for processing or data storage and to extend the AMC front panel in order to provide additional system connectivity. High-speed interface connectors on the RTM back panel can be used to create multiple interconnections within the system or with the external world, thus providing a level of versatility that previous MicroTCA systems could not reach. RTMs enable much more customization of signal routing than the MCHs alone permit.
Another improvement brought forth by the MicroTCA.4 specification is the addition of high-precision telecom clocks and the definition of AMC ports 17–20 as trigger ports.
A typical MicroTCA.4 system
Let’s look at a typical MicroTCA.4 system, in this case, a high-bandwidth recording system.
Our system’s double-width AMC uses its two FMC connectors to host two analog-to-digital converter (ADC) cards to capture the signals. The double FMC connectors, coupled with multi-channels ADC cards, allows for an impressive number of channels (up to 64 in certain configurations), to be acquired on the same FPGA (thus creating a very high channel density). The ADC signals are relayed to the AMC’s FPGA device where the processing is done. The processed data can be transmitted through Gigabit Ethernet, PCI Express, or Serial RapidIO on the AMC connector, and switched to other AMC devices within the system by the chassis MCH. The FPGA’s output is also routed to the AMC’s RTM connector, and therefore to the RTM card itself.
On the RTM, two SATA connectors provide support for two 1.8-inch solid state disks, which store a high-throughput recording of the acquired and processed signals. On top of that, the back panel can host additional SATA connectors for the recording of additional channels.
Figure 4: A typical MicroTCA.4 system
While this example illustrates a recording system, it is easy to see that multi-channel playback systems could just as easily be implemented using digital-to-analog converter (DAC) FMCs. The different MicroTCA.4 RTMs available on the market implement a variety of high-speed communication protocols, enabling a nearly unlimited range of potential applications for the MicroTCA.4 architecture.