Technology deployed
MCU
USB Ethernet ZigBee
Flash
Wi-Fi
Bluetooth
Appliance
Smart Meter
Figure 1
Bluetooth Connection
Home Network
Energy Co.
In a typical Smart home, devices such as a washing machine, an in-home display and a power meter can all work together in tandem—to make the grid smarter.
curity and cryptographic algorithms. SEP specifies the use of IPSec, SSL or TLS depending on the function set and the layer at which security is desired. SEP is designed to work over any link layer technology. So, depending on the application, Ethernet, Wi-Fi, ZigBee, PPP, Bluetooth, etc. are all possible technologies (Figure 2). Besides wired and wireless connections for network communications, several service oriented tasks like firmware download/upgrades, security certificate updates, running diagnostics etc. require a direct connection. For this purpose, SEP also specifies the use of direct connection methods like USB and serial. This expansive set of requirements adds to the challenges device manufacturers will have to address. Foremost, device manufacturers must select a hardware design that supports achieving this level
of functionality—with little to no cost increase to the end-user. Consumers will not be exposed to most of the underlying functionality, so paying more for their appliance so it can plug into the Smart Grid is hard to justify. After selecting the suitable hardware, a software architecture is also required that meets these requirements and supports execution in a low-cost hardware design. The following sections explore both the hardware and software sides of these challenges.
Choosing Low Cost Hardware
A device must comply with the SEP specifications and provide the required functionality to be classified as a Smart Grid device. Furthermore, all of this functionality needs to be supported in a low-cost hardware solution. Considering the device functionality, power require-
ments and the available silicon, 32-bit MCUs are the best suited hardware for such a device. Most 32-bit MCUs offer enough memory and processing power to deliver the performance necessary to meet the requirements outlined in the SEP specification. They can support all the peripherals necessary in a Smart Grid device like Graphical User Interfaces (GUIs), Ethernet, UARTs, USB, Bluetooth, ZigBee and Wi-Fi. Such MCUs also provide realtime clocks for time tracking, SPI and I2C buses for device communications, and support operating at different power levels. Furthermore, these system-on-chips (SoCs) contain up to 1 Mbyte of on-chip flash memory and a maximum of 192 Kbytes of on-chip SRAM. The following are some examples of the MCUs currently available in the market that are a good fit RTC MAGAZINE JUNE 2012
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