What do you use your smartphone, tablet, or Ultrabook for if you had enough battery life so that you don’t have to worry about recharging for extra 40 minutes? Maybe you’re a gamer, immersing yourself in 3D worlds and fast-paced action. Perhaps you download and stream movies in high-definition. Or maybe you take your own high-definition videos of the kids, uploading them to YouTube to share with the rest of the family. James Tschanz, Research Scientist at Intel Labs, tells that “If you are using your computing devices for these purposes, chances are that much of the heavy lifting is done by the graphics processor – a small yet powerful computing engine that sits right next to the processor in the silicon chip ‘brain’ of your computer.” As our handheld devices have become powerful computers in their own right, Intel – along with others in industry – has recognized the importance of graphics and has dramatically improved graphics capabilities with each new design, enabling new usages that would have been unthinkable only a few years in the past.
With all of this exciting graphics capability, though, comes a major challenge – power. Keeping up with advanced 3D games or computation required to drive an HD display takes energy, and this energy is provided by the tiny battery hidden in your phone. Besides driving the display on your phone, this battery also provides the power to the processor cores (the ‘brain’), radio features (the ‘ears’), camera (the ‘eyes’), bright screen, and all of the other essential features. Therefore the engineers that design these graphics processors need to be very creative – creative with how much power to use, creative with how the computations are performed, and creative with how to deliver the absolute best performance while sipping minimal energy from the battery.
This year at International Solid State Circuits Conference 2014, Intel Labs is presenting an energy-efficient graphics processing core built on the latest 22nm tri-gate SoC process technology. This graphics core incorporates several new features that allow it to improve energy efficiency by 40% – essentially giving longer battery life for the same performance or improving performance when you really need it. This core also has the ability to very quickly go into standby mode where power savings is 10X compared to active – yet another way of saving energy for when it is absolutely needed without the need to worry about charging frequently.
I asked James, where does this energy efficiency improvement come from?
He says, “First, it is well known that the best way to reduce power is to reduce voltage, so Intel’s graphics cores are designed to take advantage of our 22nm tri-gate transistor technology which allows high-performance operation even as voltage is lowered. However even with these advanced transistors, some specialized circuits (such as memory arrays) inside the graphics core can still limit the minimum voltage (called Vmin) which can be used. Therefore this design demonstrates a new “selective boosting” technique which uses a slightly higher “boosted” voltage for key parts of Vmin-limiting memory arrays in the core. What does this accomplish? By dynamically boosting only small parts of the core, the rest of the core can go to even lower voltage – giving dramatic energy efficiency improvements.
Even with this voltage-reduction technique, however, there is still room for improvement. When the graphics core is operating, it is switching units on and off very quickly to optimize power and performance. All of this switching can cause ‘noise’ on the internal power supply – voltage droops and glitches which if not handled correctly could cause an error or failure inside the core. Have you ever turned on a high-powered appliance in your house – maybe a vacuum cleaner or space heater – and noticed that the lights slightly dim? A similar effect can happen inside the processor chip, and although there are advanced voltage regulators to minimize this issue, a small voltage ‘safety margin’ is added to ensure that everything still works 100% correctly. The only problem with this safety margin is that it increases voltage, which – as we just discussed – is the opposite of what we are trying to do to save energy. In this graphics core we therefore include a technique – called adaptive clocking – to reduce this safety margin by detecting voltage droop events and slowing down the clock frequency of the core to prevent failures. These droops are infrequent and very fast, so slowing down the clock is not perceptible to the user. The user will notice, however, the extra battery life achieved by this technique!
Finally, this core includes special circuits that allow it to go very quickly into a ‘sleep’ state, saving all of the important data but consuming very little power. Just as in selective boosting, this requires a separate voltage supply which is kept ‘on’ even in sleep mode, allowing the voltage to all of the other circuits in the core to be completely turned off. In fact, even the separate ‘retention’ supply can be lowered in sleep mode through an on-die sleep voltage regulator, giving further power savings.”
These techniques are currently found in a testchip within Intel Labs. They demonstrate how they have the potential to greatly improve experience on future mobile devices and may provide a truly wire-free experience.