Managing System Power
The split power scheme allows the carrier manager to implement hot-swapping and prevents an AdvancedMC module from accessing the fabric lanes if the module is malfunctioning. When a module is to be powered up, whether at initial system startup or as the result of system insertion, the carrier manager first enables the module’s management power feed. Thus, the module can communicate with the carrier manager and initialize its I/O interfaces to a state compatible with the backplane’s fabric lanes. Once the module is fully configured, the carrier manager can then enable payload power.
Similarly, bringing a redundant module online can simply be a matter of enabling its payload power. The steps in reverse will gracefully power-down a module that’s tagged for removal. If there’s a malfunction, the carrier manager simply disables the module’s payload power, preventing it from interacting with the backplane fabric.
The carrier manager also manages any power-supply redundancy that’s present within the design. Redundant power supplies in a MicroTCA system connect through power switches (pass devices) to a “wired-OR” connection (). Normally, both power sources are enabled. In the event of a power-supply failure, however, the carrier manager can disconnect the failed supply from the system by disabling the corresponding pass device. The wired-OR connection ensures that current continues to flow during a failure and that the failed supply won’t load down the power system.
For the MicroTCA carrier manager to control system power appropriately, however, it’s essential for the AMC module to be designed to fully implement the IPMI control structure. Some early adopters of the ATCA architecture simplified the development of their custom AMC modules by neglecting the IPMI elements not needed on their carrier boards. What resulted were AMC modules that didn’t function correctly in a MicroTCA environment. To ensure proper operation in MicroTCA, developers of custom AMC modules should fully implement the elements of the AMC specification.
Flexible System Footprint
One significant advantage offered by MicroTCA is that it allows ATCA’s functionality to be scaled to very small configurations. The AdvancedMC module’s physical definitions have proven generous enough to allow the implementation of complex telecom functions in a single module, while small enough to allow cost-efficient design partitioning. By using those modules directly, without a carrier card, MicroTCA gives designers considerable flexibility in design reuse.
An ATCA server blade, for instance, might use a processor AMC connected via serial ATA (SATA) or serial attached SCSI (SAS) to a hard-disk AMC or via sRIO to an E1/T1 interface AMC. The carrier board provides the module interconnections, and the whole assembly forms a server blade that would connect with other blades over Gigabit Ethernet (GbE) to form a large network server system for a central-office installation.
Using MicroTCA, the same design can be scaled down to the equivalent of a single blade to meet the needs of a local-area network without implementing a full ATCA system. The processor AMC, E1/T1 AMC, and disk-drive AMC plug directly into the MicroTCA backplane. The MCH automatically establishes the GbE Interface between all of the modules and the rest of the network.
The MCH can also provide sRIO connectivity between the E1/T1 AMC and the processor AMC, so that the mini-server has connectivity to the telecom network. Finally, point-to-point links on the backplane provide the SATA/SAS connection between the processor AMC and the disk-drive AMC. But in some cases, a dedicated AMC controller may manage disk arrays.
This design could take advantage of MicroTCA’s “pico” shelf size, which allows for a minimum configuration of one or two AdvancedMC modules in a fully functional shelf. The pico size is well-suited to systems with modest performance needs and a minimum of available space. Other small-footprint configurations, including custom designs, are also possible within the MicroTCA specification.
Additionally, MicroTCA can target traditional rack-mount enclosure installations, offering several standard options (). Rack-mounted shelves can accept compact, mid, or full single or double modules in mixed configurations. A special configuration, the cube, provides additional flexibility. Cubes can be designed to fit together to occupy a rack width, while remaining independent functions provide a finer degree of modularity than a full rack-wide shelf.
These different system footprints let designers trade off size and system capability to create the optimum mix for their applications. The range of performance levels achievable using MicroTCA, as defined by backplane bandwidth, covers a host of applications. These include wireless basestations, digital loop carriers, optical add/drop multiplexers (ADMs), and fiber-to-the-curb optical network units ().
When designing their systems, though, developers will need to pay careful attention to airflow and heat. The board density achieved by MicroTCA, along with the power ratings supported by AMC boards, means that MicroTCA systems can easily develop hotspots. Design efforts should include a full thermal profile for the system, including evaluating board placement as it affects airflow.
In addition, designers creating custom AMC modules should follow the power limits suggested in the AMC specification and not try to run their boards “hot” to squeeze out additional performance. Variations from the specifications make it harder to obtain MicroTCA’s full benefits.
Reuse Equals Savings
MicroTCA increases the market opportunities for vendors’ AdvancedMC modules, which can reduce costs for system developers. Because the carrier- and shelf-management functions of a MicroTCA system replicate the management of the ATCA architecture, MicroTCA development efforts can apply AdvancedMC modules and their support software without modification.
By extending the applicability of AdvancedMC modules to smaller, lower-cost systems, MicroTCA enables vendors to enjoy greater production volumes and realize economies of scale that ultimately bring down prices. Similarly, developers of custom AMC modules for their own ATCA systems can enjoy the cost-reduction benefits of reusing their module designs to create a product family with a range of performance levels.
Many aspects of the MicroTCA and AdvancedMC standards serve to enhance this reuse. For example, the standards allow three different fitting types for AdvancedMC connectors: compression, surface mount, and press fit. A common footprint was proposed for each of these connector types, with the goal of providing multiple sources for backplane connectors. This will allow competition in that market space and permit the replacement of one connector manufacturer for another.
AdvancedMC modules offer physical compatibility despite individual differences in the module’s manufacturing process. As a result, by providing a common interface requirement, telecom equipment manufacturer (TEM) vendors can provide similar functions. This allows for multiple sourcing, which in turn lowers developer risk when applying the modules. As a byproduct, it encourages the adoption of AdvancedMC. This common interface ability is particularly important in markets where developers don’t want to depend on a single vendor.
The reuse of ATCA elements, along with the size and performance scalability of MicroTCA, now extends the range of ATCA to cover nearly all telecom applications. The original ATCA specification covers the larger end of system needs, while MicroTCA provides a more compact architecture that offers considerable design flexibility for smaller installations. At the same time, by leveraging the modular software and hardware developed for ATCA, MicroTCA keeps development costs down while maintaining the performance and reliability required by telecom applications.