Energy efficient designs for a “greener” planet

In a world of ever-increasing always-connected devices, one of the major problems we are facing in terms of power consumption is the standby power. Also called vampire power or phantom power, standby power refers to the electricity consumed by appliances when they are switched off or are in standby mode (or idle mode). The typical power loss per appliance when multiplied by the billions of appliances in houses and in commercial locations, represent a significant fraction of the world’s total electricity use. According to researchers, standby power accounts for as much as 10 percent of a household power-consumption. In fact, one computer left on all day would cause an emission of 1,500 pounds of carbon dioxide (CO2) in a year. It would take 100 to 500 trees to absorb that amount of extra CO2 released into the atmosphere!

Thus, we have a grave problem at our hands. This has led to an increased global stress and awareness on “green” operation. With the emergence of regulations from the United States (ENERGY STAR) and the European Union (EuP or Energy-using Products), etc., more and more devices today are being designed to increasingly support low power modes. While on one hand, fast responsive network services are driving the processing requirements of embedded applications, counter balancing this are governmental and social pressures for energy efficiency. More and more applications and appliances are getting powered by silicon devices. There is an increase in processing requirement, increased frequencies, greater integration – all leading to requirements to be energy efficient not only during standby but during normal operation as well.

For a typical use case, say a network printer in an office environment, where the printer cannot be shut down, it is a waste to keep the chip fully throttled up during low or no traffic, for instance during night time. It would be desirable to have techniques to monitor the traffic profile and adjust the frequencies of the CPUs on-the-fly to reduce runtime power. Further, the device should be able to shut itself down to the MAX by switching off power to unneeded peripherals, while staying aware on critical interfaces like Ethernet, USB, interrupts, etc., to wakeup on programmed events. This will help reduce the leakage power.

Freescale Semiconductor’s latest QorIQ P1022 device is a step in this direction. The highly integrated communications processor combines performance of dual Power Architecture processor cores with high-performance system peripherals required for media, printer, communications, and industrial applications. It also integrates SATA, USB, multi-lane PCI Express, Gigabit Ethernet, LCD interface and 64bit DDR memory. But above all of these are its Advanced Power Management features. The device is designed to reduce both runtime as well as standby energy consumption.

The objective for the QorIQ P1022 was to meet the One Watt Initiative, an energy saving proposal by the International Energy Agency to reduce standby power use in all appliances to just 1W. 1W for the entire appliance meant much lesser power budget for P1022. This needed careful yet aggressive partitioning of the design to turn OFF as much as possible in standby. In addition, runtime power management techniques were applied as well to give a complete solution.

There were several challenges during the development, out of which the following were the most defining ones:
- Meeting peak performance - increases the peak power, while meeting the low standby power.
- Switching off a major portion of the chip and sequencing it back to wake up.
- Ensuring that the system built around the device is visible on network, and can wake up when required while the device is in standby mode (major portion is OFF).

To meet all of these objectives, an intelligent energy management technology was needed. An overview of this is illustrated in the following figure.


FIGURE 1

Let us take the same example use case – a multifunction network printer in an office environment. Typically the workloads on the printer vary, there are times when the printer is heavily used and times when the usage is low. At times the printer is not used at all, but it is required that the printer is visible on the network so that one can still fire a print job. Conventionally, the processors used in printers run a fixed frequency and do not have any power management; this implies either they are ON – consuming power running at the fixed frequency which is usually the maximum; or they are switched OFF. The QorIQ device adjusts to the workloads and manages the power consumption of the device by transitioning into an appropriate power save mode.

During runtime, it can deploy a mode called JOG, to systematically tune up or down the processors’ frequencies, based on traffic and processing requirements. This lowers the dynamic power and saves a lot of energy over extended period of operation. Further, it has the DEEPSLEEP feature wherein a large portion of the chip is turned OFF during standby. The device can detect wakeup events to bring itself back in operation only when required. Besides, the device is intelligent enough to show active status on the network. Consuming close to 5W (typical) during full mode operation, the device is able to go down to a meager 0.2W in standby!

Devices of the future would continue to get more and more intelligent; multicore, multipurpose, adaptive, hyper-connected, that is, communicating with each other and humans, to make mankind more efficient in all its endeavors. But, all this may come at the cost of our planet, if measures to increase energy efficiency are not taken and implemented. There is huge amount of power trickling down underutilized and unused devices. Energy efficient solutions are the only way to go.
Author Information
Mohit Satsangi is Senior Design Engineer for Freescale Semiconductor India.
Kalyana Chakravarthy is Staff Design Engineer for Freescale Semiconductor India.