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Load Balancing


Load Balancing

SEP 2.0 provides the guidelines in which the devices should communicate with one another. It defines various device properties that can be manipulated. These properties (also known as resources”) work together in logical groups to implement SEP 2.0 functionalities (called the function sets”). A metering system, or pricing system, is an example of an application-specific function set. Devices like smart meters implement one or more function sets to provide value-added services such as usage statistics and trends. These pricing statistics and trends can then be used by either the energy provider or the consumer to further manage services or usage, respectively.

Function sets and their resources on a device are accessed through HTTP URLs. These devices dynamically discover relevant services on the network using technologies like mDNS and DNS-SD and register themselves to further access resources to implement SEP 2.0 functionality. To provide for a truly interoperable ecosystem of interconnected smart energy devices, use of TCP/UDP and IP-based networking is necessary. Support for security features within a device is critical because of vulnerabilities from exposure to a broader network, and more importantly, the access a device provides to the energy grid. Since many smart devices serve up continuous, reliable, and real-time data, they must be Always-ON” and Connected” which necessitates that all smart energy devices be power efficient themselves. Lastly, they must also support both wired and wireless networking capabilities.


A majority of existing home appliance devices are not built to support the advanced features of the emerging M2M wave, so incorporating many different capabilities into a single device means significant and expensive hardware upgrades, resulting in an increased bill of materials and cost. Manufacturers must balance the benefits of delivering smart energy-enabled appliances with the additional cost.

Moving forward, appliance manufacturers have more options to find cost effective solutions to design home appliances that are smart energy enabled. The choice of SoC hardware for these home appliance devices should be made by striking the right balance between functionality, form factor, software support, and cost. 32-bit microcontrollers (MCUs) provide a unique blend of processing power, memory, and connectivity to make them a strong candidate. The current generation of microcontrollers, such as Freescale Kinetis, STMicroelectronics STM32, or the TI Stellaris (ARM Cortex-M core), offer tremendous amounts of features and capabilities at a very compelling price point. Selecting the right hardware is only the beginning. The differentiator in this equation is the software choice.

The software technology requirements laid out by the SEP 2.0 specifications include: a rich TCP/IP stack with UDP support; IPv6 services with dynamic service discovery capabilities like mDNS and DNS-SD; and a HTTP implementation with support for primitives like GET, PUT, POST, and DELETE. SEP 2.0 also mandates support for security implementations like SSL/TLS and several modern day Internet technologies like the RESTful architecture, XML, and EXI encoding schemes etc. Such extensive support for software technologies is readily available in Linux, but unfortunately, the use of microcontrollers with RAM sizes in the range of 96K to 128K eliminates Linux as an option. Developing such technologies in-house is expensive and time consuming, which leads to the possible implementation of a real-time operating system (RTOS) for these devices.


RTOSes are not only fast, efficient and robust, they typically include an extensive networking stack, a solid support for security using SSL or TLS, and most certainly meet the heavily constrained footprint and other memory requirements these devices require. The Nucleus RTOS provided by Mentor Graphics is an example of one such solution (Figure 3). Nucleus is a widely deployed and scalable RTOS that meets all smart grid device requirements. It has both hard, real-time performance and integrated power management services. Such an RTOS can fit in a memory-constrained MCU, yet still provide the large set of functionality required by a connected, smart grid device.



With the projected rapid growth in the adoption of smart grid technologies, designing fully compliant devices that keep the bill of materials minimized will become a major challenge for manufacturers. To create a device compliant with the SEP 2.0 specification, a homegrown software design is likely not an option due to the high number of functional requirements and the expensive in-house development efforts. On the other extreme, using a general purpose operating system will result in unacceptable cost increases because of the need for significantly upgraded hardware resources. Device manufacturers need to find the right balance when choosing both the software design and hardware platform. The use of a scalable, power-efficient, real-time operating system with extensive networking support (wired and wireless) — along with one of the 32-bit MCUs now available in the market—is the closest to meeting all of these requirements. Following this design paradigm, designers will significantly reduce their time-to-market and still realize all of their smart grid application goals. About the authors Srinath Balaraman is a software development engineer in the Embedded Software Division of Mentor Graphics, also known as Mentor Embedded. In his eight years at Mentor, his main area of focus has been the design and development of networking and security products for Nucleus RTOS. Srinath holds an MS degree in Computer and Information Sciences from the University of South Alabama.

Anil Khanna has over 15 years of technical and product marketing experience with a background in both design automation tools (EDA) as well as programmable logic hardware design. Anil is currently senior product marketing manager of Mentor Embedded Sourcery Tools. Prior to moving into Mentor Embedded, Anil was responsible for worldwide market development for Mentor’s ASIC/FPGA synthesis solutions including Catapult and Precision Synthesis. Anil holds a Masters in Electrical and Computer engineering from Portland State University in Portland, Oregon.

Serial communications based on RS-422 and RS-485 communicates digital information over twisted pair wire from transmitters to receivers. RS-422/485 systems can communicate at rates up to 10 Mbps (though most systems operate at lower bit rates). Both systems utilize balanced outputs and differential inputs, which provide better noise immunity than single-ended systems. RS-485 is used as the basis for many commercial and industrial data communications systems, like Profibus, Interbus and Modbus.

Serial communications are commonly used to link programmable logic controllers (PLC), supervisory control and data acquisition (SCADA) systems, remote terminal units (RTU) and other equipment in custom networked systems. The RS-422 and RS-485 standards do not define protocols. They are simply physical layer standards (and even then, do not specify connectors or pin-outs). This means that RS-422 and RS-485 can be implemented in many systems and applications. This was all working very well, which is why humans invented USB to replace it.

USB uses completely different protocols, completely different cabling and completely different ports. Better still, it has an effective range of only 15 meters. Granted, that can be extended up to 30 meters using USB hubs like B&B Electronics’ UHR204. But it’s still just a fraction of the 4000 ft. range achieved by RS-485, which — to humans – was a key selling point. Additionally, USB connectors don’t grip the cables very firmly, unless you’re using high retention ports like those, for example, in B&B Electronics’ USOPTL4. As USB carries 5 V DC power, this creates an opportunity for fire when vibration shakes a cable loose. Humans love fires, and they report them on the news whenever they think they’ve had a good one. Serial connectors generally employ thumbscrews to hold them in place. This reduced ability to create newsworthy conflagrations was one reason for trying to move away from the serial standard.

Serial Communications and the Expansion Port

Humans equip their desktop computers with card slots that allow computers to be configured in numerous ways and for numerous purposes. As new generations of computers are designed and built, the nature of this bus is continually reconfigured in order to keep older cards from functioning in newer machines. Humans love to recycle, and they are enchanted by the fact that an ISA card that once sold for $175 can be broken down into its constituent elements and recycled for a total profit of three cents.


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