In the summer of 2006, the PCI Industrial Computer Manufacturers Group (PICMG) approved the MicroTCA telecommunications architecture, a small-form-factor platform addressing tight size and cost constraints. MicroTCA takes advantage of mezzanine cards developed for the AdvancedTCA platform by eliminating the need for carrier cards. What results is a scalable low-cost platform for building next-generation packet networks.
MicroTCA is the latest generation of open-architecture platforms developed by PICMG for telecom equipment design. The first telecom platform, AdvancedTCA, merged together a hot-swappable, multiprotocol, switched-fabric backplane with large form-factor cards and high-power capability. Such a combination made it possible to create high-density, high-performance telecom systems.
Then in 2005 we saw the arrival of AdvancedMC mezzanine modules, which enhanced the modularity of AdvancedTCA systems. Developers were able to create blades combining individually hot-swappable interface modules, mixing and matching functions as needed.
MicroTCA takes this modularity a step further. It leverages AdvancedMC modules to meet the needs of compact, low-cost systems by connecting AdvancedMC cards directly to a backplane without the need for a carrier card. By eliminating the Advanced Telecommunications Computing Architecture (ATCA) carrier, MicroTCA can offer a wide variety of form factors for designers to choose from, including custom “pico” assemblies for applications that need only a few modules for the entire system.
Understanding AdvancedMC Modules Direct connection of AdvancedMC modules to a backplane implies that an understanding of MicroTCA must start with an examination of the AdvancedMC module itself. These modules employ a field-replaceable, serial packet interface that can have up to 20 I/O channels running as fast as 12.5 Gbits/s per channel. Because these channels are protocol-agnostic, they can support a variety of packet-oriented communications protocols, including Ethernet, PCIExpress, and Serial RapidIO (sRIO).
Physically, the modules offer several footprints as well as power capacity that tops out at 80 W (Fig. 1). AdvancedMC modules are hot-swappable, so they can be individually field-replaced without taking the system offline. In addition, they support Integrated Peripheral Management Interface (IPMI) system management, which enhances availability and serviceability by allowing shelf management to identify faults and take corrective action at the module level.
IPMI utilizes an I2C-based physical interface that enables the monitoring of system health characteristics, such as voltages, temperatures, and fan speeds. It also supports automatic event notification, remote shutdown and restart, and dynamic power allocation to individual AdvancedMC modules.
In MicroTCA, AdvancedMC modules (which ride on carrier cards in ATCA systems) plug directly into the backplane without requiring any modification. To replace the control functions of the ATCA carrier, MicroTCA uses a MicroTCA Carrier Hub (MCH). This module provides the switched fabric, shelf management, and optional clock distribution for a chassis. It acts as a fabric-star hub that offers one or more high-speed serial lanes to each module, along with a central switch for the lanes. One MCH module can support as many as 12 AdvancedMC modules in a system.
The backplane of a MicroTCA system can be designed to support star, dual-star, and mesh topologies. For high-availability system designs, the backplane can provide redundant IPMI interfaces, allowing two MCH modules to be employed in a single chassis. In addition, the backplanes support the connectivity for redundant power sources, the intelligence being provided by the power modules themselves.
The backplane and modules aren’t the only elements of a MicroTCA system, which consists of at least one AdvancedMC, at least one MCH, and all of the interconnect, power, cooling, and mechanical resources needed to support them (Fig. 2). These resources include the sub-rack, power modules, backplane, and cooling units. Together, the cards and their support resources form a shelf that can operate as a standalone system or be combined with other shelves to create a larger system.
MicroTCA Management The management of a MicroTCA system has two levels: the shelf manager and the carrier manager. The shelf manager monitors overall system health, serving as an aggregation point for hardware information from one or more carrier managers. It also watches over other system units, identifying anomalous conditions and taking corrective action where possible. It manages the cooling units, ensuring the proper airflow through the shelf, by passing commands to the units through the carrier manager.
Furthermore, the shelf manager serves as the interface to any higher-level system-management functions required by the design. Thus, it provides overall system health information for such purposes as indicating status or triggering alarms. It may be implemented on its own AdvancedMC module in the system as a software application or as a function of the MCH.
The carrier manager, which is MicroTCA’s management workhorse, resides on the MCH in the MicroTCA Carrier Management Controller (MCMC). The carrier manager controls the AdvancedMC cards, the power modules, and the cooling units. It gathers status to convey to the shelf controller. It also handles the activation of individual modules. The carrier manager also interacts with module management controllers (MMC) within the AdvancedMC cards and the enhanced module management controllers (EMMC) on the power modules to manage system power distribution as well as hot-swap functions.
One important function of the carrier manager is to prevent incompatible devices from harming each other or disrupting communication in a MicroTCA system. Known as Electronic Keying (E-Keying), this function uses information from the AdvancedMC module, which indicates the capabilities of each port the module implements, and information within the carrier manager on the backplane’s connectivity.
By coordinating the information from these sources, the carrier manager decides which ports on each AdvancedMC switch fabric to enable or disable. It then communicates this information to the modules, ensuring that only compatible interfaces are enabled and controlling when the module is powered on.
Another carrier-manager function is to ensure the proper powering up and down of modules. Power modules within the MicroTCA system provide two feeds: 3.3-V management power and 12-V payload power, both under the control of the carrier manager. AdvancedMC modules use the management power feed to power the circuits needed for interacting with the carrier manager.
Subsequently, they use the payload power feed to power the rest of the module, including its fabric interfaces, after completing the E-Keying sequence. The carrier manager sends commands to the power modules, and they enable or disable the payload power feeds to each individual AdvancedMC module.
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