By Alan Vincent, Sales Director, Foremost Electronics
Designers of embedded systems face several significant challenges: increasing performance and system stability, yet at lower cost.
Existing platforms like industrial PCs, COM-systems or eNUC (embedded next unit of computing) solutions are designed to deliver a certain computing power whilst keeping product costs low. These systems, however, are definitely not the right choice for high-performance applications such as data acquisition or image processing. In addition to high computing power, such applications require high grade availability and easy manageability. To cover these requirements, a commercial-off-the-shelf (COTS) system is needed, such as the open-standard platform MicroTCA.
Benefits of MicroTCA
MicroTCA is a PCI Industrial Computer Manufacturers Group (PICMG) standard, describing a modular standard for building high-performance switched fabric computer systems in small packages. It has its origins in the open-standard AdvancedTCA that was initially developed for telecoms applications. MicroTCA preserves many of the important principles of AdvancedTCA, including the basic interconnect topologies for high-speed data transfer and the management structure.
Using open standards enables developers to concentrate on an application, without worrying about the infrastructure or environment for 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 different-sized advanced mezzanine card (AMC) modules are supported, allowing the system designer to use as many or as few computing and I/O resources as necessary.
By configuring highly-diverse collections of processing and I/O AMCs in a MicroTCA shelf, many different application architectures can easily be realised. Because of its modularity and flexibility, the MicroTCA standard provides the best infrastructure and environment in almost all markets, including industrial control and automation, test and measurement, traffic control and transportation. Possible applications could be digital video and image processing, automation and machine control systems or signal processing.
Another important function of MicroTCA is the Ethernet hub with system management. Both functions are covered in the micro carrier hub (MCH), which typically occupies one full-size AMC slot or two full-size slots in a redundant architecture. The MCH provides the central system management and delivers data switching and hub functionality for 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 a centralised clock distribution to all AMCs in the system.
With all these features and benefits, MicroTCA is one of the best choices for high-performance applications, although some may require only a small number of AMC slots. For these applications, the MTCA systems that are currently available may be oversized and therefore not cost-efficient. To meet this demand, Pentair, along with partner NAT, has developed a two-slot MicroTCA system with an embedded micro carrier hub (eMCH). Both AMC slots can be used for payload boards whilst retaining the switch and enhanced management functionality. This system offers the comprehensive performance of MTCA and keeps the form factor and cost at a manageable level.
This MTCA system is designed to host two mid- or even full-size AMC boards. The card cage is fully EMC-shielded, so the slots could be used for different processors or I/O cards. The chassis is developed in accordance to the PICMG MTCA.0 (R1.0) specification, guaranteeing a full interoperability with all modules that are compliant to the PICMG AMC.0 (R2.0) specification. This makes it easy for every embedded system designer to create the desired application without worrying about matters such as cooling, switching and managing.
Power supply is also part of this defined environment. The power modules (PM) are usually installed in special, designated slots in the chassis. In this system, the PM functionality is put on a mezzanine board behind the backplane, providing 12V and all of the specified power management functions. The included power module supplies 150W, more than enough to serve 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.
Figure 1: Two-slot MicroTCA with eMCH
High performance requires efficient cooling
One big issue in small form factor applications is heat dissipation. Cooling is one of the most important functions to avoid overheating and to ensure the high grade of system availability. In fact, the ambient temperature does have an impact on the lifetime of the system components and AMC modules. Therefore, the MTCA system is equipped with a powerful cooling unit, providing a free blowing air flow of more than 2m³ per minute. The integrated air filter protects the AMCs against dust and dirt and is easily replaced.
Fan speed is normally managed by the MCH, which reads the temperature sensors on the AMCs and chassis. The communication between MCH and cooling unit (CU) usually happens through the intelligent platform management bus (IPMB). This strategy, however, requires a powerful processor on the CU with dual IPMB connections to the MCH. Pentair uses a lower cost implementation in its small two-slot chassis, with a small processor with just 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 – even though, from user perspective, there is no difference in function or performance between the two.
Signal integrity for high data transfer
Besides cooling and power supply, the system backplane is another important part with huge impact on performance. The common purpose of a backplane is the interconnection between all devices, including but not limiting to the AMC modules. A high data transfer rate requires a sophisticated routing as well as test capabilities to ensure signal integrity. As mentioned before, 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 a data transfer rate up to 64Gbs.
Figure 2: Backplane topology two-slot MTCA with eMCH
System monitoring and control
Another highlight of this system is the embedded MCH, although why would such a small system need it?
For NAT and Pentair, it’s very important to maintain their products within the PICMG standards. By embedding the MCH, the goal is to provide an attractive high-performance, low-cost platform whilst keeping the whole system compliant to the open-standard specification. The eMCH supports and manages the AMC modules, the cooling units and load sharing. As soon as an AMC is inserted, the MCH starts the communication through the IMPI bus, reads the e-keying of the AMC, and enables the power once the AMC is identified. Further, the eMCH provides clocking and a 1Gb fabric to both AMC slots and a 1Gb uplink through the system’s front panel, allowing full management and fault isolation of the power supply, cooling unit and AMCs.
Another important function of the eMCH is hot-swap ability, which allows the removal or insertion of AMCs during operation. This feature was originally required for high-availability systems in the energy and telecoms markets, but is now found in more applications, including automation and transportation, where AMCs can be replaced without shutting down the system.
The MTCA system can be integrated into existing management architectures via simple network management protocol (SNMP) or remote management control protocol (RMCP). The intended configuration can be set through NATView, which is a MicroTCA visualisation and management tool. The eMCH is fully compatible to all existing NAT MCHs, which maintains a clear migration path from small to larger systems, as and when the application requires it.
Figure 3: NAT’s embedded micro carrier hub
Serviceability and scaleability
The system’s simple construction makes it very service-friendly; individual components are easy to maintain and replace. The top cover can be removed by simply undoing a few screws, allowing the fan unit and air filter to be easily replaced. Small indentations in the base and top plates allow the included rubber feet to be attached. The feature allows the stacking of multiple systems and therefore scaling the number of slots.
Figure 4: 2-Slot MTCA System with eMCH