MicroTCA enclosures for highly demanding applications

Author : Alan Cook, Managing Director at Foremost Electronics

03 July 2018

2-slot MicroTCA with embedded MCH (eMCH)
2-slot MicroTCA with embedded MCH (eMCH)

For embedded systems designers to balance the technical and commercial requirements (discussed in this piece), a commercial-off-the-shelf (COTS) system is needed. This article discusses how the open standard platform, MicroTCA is able to meet the industry’s technical requirements and keep cost within budget, providing a compelling solution for highly demanding applications.

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To address such demanding applications, firstly consider the twin challenges that designers of embedded systems must balance: while technical requirements, such as performance and system stability, are constantly increasing, they must also contend with commercial limitations. Existing platforms like industrial PCs, COM or eNUC are designed to deliver a certain computing power, while keeping product cost low.

These systems, however, are often not the optimum solution for demanding applications, such as data acquisition or image processing. In addition to high computing power, such applications require high levels of availability and easy manageability.

Accordingly, COTS systems offer many benefits to their users: MicroTCA is one of several PICMG standards and describes a modular standard for building high performance switched fabric computer systems in a small form factor. It has its origin in the open standard AdvancedTCA, which was initially developed for high reliability telecom applications.

MicroTCA preserves many of the important features of AdvancedTCA, including basic interconnect topologies for high speed data transfer, and the system management structure to ensure high availability.

Benefits of MicroTCA

Using open standards allows designers to concentrate development on the application-specific part of their product. They don’t need to worry about the infrastructure or environment of the system, since this is already defined by the open standard specification.The core specification, MTCA.0, defines the basic system, including backplane, card cage, cooling, power and management.

A variety of differently-sized AMC (Advanced Mezzanine Card) modules are supported, allowing the system designer to use as much or as little computing and I/O as necessary. By configuring highly diverse collections of processing and I/O AMCs in a MicroTCA shelf, many different application architectures can be easily realised.

Because of its modularity and flexibility, the MicroTCA standard provides an ideal infrastructure and environment for sectors from industrial control and automation to test & measurement, traffic control and transportation; possible applications include digital video and image processing, automation and machine control systems, and electronic signal processing.

Another important function of MicroTCA is switching and system management. Both functions are taken care of by the Micro Carrier Hub (MCH), which typically occupies one full-size AMC slot, or even two full-size slots in a redundant architecture. The MCH provides central system management and delivers data switching and hub functionality for the various system fabrics – including Gigabit Ethernet (GbE), PCI-Express (PCIe Gen 3) and Serial Rapid I/O (SRIO Gen 2). Furthermore, the MCH is also able to provide centralised clock distribution to all AMCs in the system.

2-slot MTCA: high performance in small form factor

Based on these features and benefits, MicroTCA is a good choice for high performance applications. Some such applications, however, only require a low number of AMC slots. For these applications, currently-available MicroTCA systems may be oversized, and therefore not cost efficient.

In order to meet this demand, Schroff, along with partner N.A.T., has developed a 2-slot MicroTCA system with an embedded MCH (eMCH). Both AMC slots can be used for payload boards, whilst retaining the switching and enhanced system management functionality. This system offers the comprehensive performance of MicroTCA, but keeps the form factor and cost at a manageable level.

This MicroTCA system is designed to host 2 mid- or even full-size AMC boards. The card cage is fully EMC-shielded, so the slots can be used for any kind of processor or I/O card. The fact that this chassis has been developed in accordance with the PICMG MTCA.0 (R1.0) specification guarantees full interoperability with all modules that are compliant with the PICMG AMC.0 (R2.0) specification. This makes it easy for embedded system designers to create the desired application without worrying about system infrastructure, including cooling, switching and system management.

Power supply is also part of this defined environment. Power modules (PM) are usually installed in special designated slots in the chassis, occupying valuable space. In this system, however, the PM functionality is on a mezzanine board behind the backplane, providing 12V and all of the specified power management functions.

The integrated power module supplies 150W, which is more than sufficient to serve both the payload boards and the embedded MCH and cooling units. Having the power module mounted on a mezzanine card decreases the required space, and consequently, the cost.

High performance requires efficient cooling

One major issue in small form factor applications is heat dissipation. Cooling is one of the most important functions to avoid overheating and ensure the high level of system availability. In fact, ambient temperature has an impact on the lifetime of the components in the system, as well as on the AMC modules. Therefore, the MicroTCA system is equipped with a powerful cooling unit, providing free blowing air flow of more than 2m³ per minute. The integrated air-filter protects AMCs against dust and dirt and can be replaced easily for service.

The speed of the fans is normally managed by the MCH. The MCH reads the temperature sensors on the AMCs and in the chassis, and then determines the optimal fan speed. The communication between the MCH and cooling unit (CU) is usually achieved through the IPMB bus. This strategy, however, requires a powerful IPMC management processor on the CU, with dual IPMB connections to the MCH. In order to meet the commercial challenges, Schroff uses a lower cost implementation in their small 2-slot chassis.

This CU uses a small processor with a private I2C connection to the MCH. In this case, the MCH includes special firmware that treats the low cost CU as if it were a normal CU. From the user’s perspective, there is no difference in function or performance between the regular CU and the low cost CU.

Signal integrity to ensure high data transfer

Besides cooling and power supply, the backplane of the system is another important component that has a huge impact on performance. The common purpose of a backplane is the interconnection between all devices, including – but not limited to – the AMC modules. A high data transfer rate requires sophisticated routing, as well as test capabilities, to ensure the required level of signal integrity. As previously mentioned, MicroTCA offers different interface protocols for high speed data transfer. SATA, Fat Pipe and the Extended Fat Pipe for PCI Express are connected between the two slots, offering data transfer rates of up to 64Gbs.

Maintain system monitoring and control

Another highlight of this system is the embedded Micro Carrier Hub. Why does such a small system need an MCH? For both N.A.T. and Schroff, it’s important to maintain their products within the standards of PICMG. Therefore, their major goal here is to deliver a compelling platform with regard to commercial and technical aspects – but still keep the whole system compliant to the open standard specification.

The eMCH supports and manages the AMC modules, the cooling units and the load sharing of the system. As soon as an AMC is inserted, the MCH commences communication through the IMPI bus, reads the e-keying of the AMC, and ultimately enables the power, once the AMC is identified. Further, the eMCH provides the clocking and a 1Gb base fabric to both AMC slots and a 1Gb uplink through the system’s front panel. This allows full system management and fault isolation of the power supply, the cooling unit – and of course – the AMCs.

Another important function of the eMCH is its ability to manage hot swapping. This allows the user to remove or insert AMCs, even during operation. The feature was originally required for high availability systems in the energy or telecom market. But even for systems in automation or transportation applications, it may be important to replace an AMC without the need to shut down the system.

Via SNMP or RMCP, the MicroTCA system can be integrated in existing management architectures. The intended configuration can be set through NATView, which is a visualisation and management tool for MicroTCA. The embedded MCH is fully compatible with all existing NAT-MCHs, which means a clear migration path from small systems to larger systems can be maintained (in case the application grows, and therefore requires a larger infrastructure).

Achieving high levels of serviceability and scalability

The simple construction of the system makes it very service-friendly: individual components are easy to replace or maintain. The top cover can be removed by undoing a few screws, allowing the fan unit and air filter to be easily replaced. Small indentations in the base and top plates allow rubber feet (included) to be attached.

This feature facilitates the stacking of multiple systems, and therefore, also enables users to scale the number of slots. Thanks to the 2-slot MicroTCA system with embedded MCH, Schroff offers an effective turnkey solution. The user does not need to worry about the equipment environment, including housing, cooling and power supplier: by inserting the appropriate AMC modules, the application can be easily developed.

With its system management features, MicroTCA delivers high performance and reliability. Any failures are predictable and can be isolated and eliminated before it occurs. The open standard approach reduces the engineering cost and accelerates the time-to-market. Furthermore, it offers a high amount of flexibility to keep the application always up-to-date.

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