Nvidia powers down Kal-El with fifth core

Nvidia's upcoming Kal-El quad-core chip, aimed at tablets, has a hitherto unannounced fifth core that turns off the other four cores when handling simple tasks and so saves on power
Written by Jack Clark, Contributor

Nvidia has lifted the curtain on a previously unannounced fifth core within its Kal-El quad-core processor, which it says can dramatically lower power consumption when mobile devices are syncing background data.

Kal-El diagram

Nvidia has given details of previously unspecified fifth core on its quad-core Kal-El processor, which helps save power. Image credit: Nvidia

The extra core, which Nvidia revealed on Tuesday, is designed to lower the overall power consumption of the Kal-El system-on-a-chip when a device is carrying out simple tasks. It does this by turning off the main four cores and operating solely from the low-power 'companion' core.

"During less power-hungry tasks like web reading, music playback and video playback, Kal-El completely powers down its four performance-tuned cores and instead uses its fifth companion core," Matt Wuebbling, the director of marketing for Nvidia's Tegra division, wrote in a blog post on Tuesday.

"For higher performance tasks, Kal-El disables its companion core and turns on its four performance cores, one at a time, as the work load increases," he added.

During less power-hungry tasks, Kal-El completely powers down its four performance-tuned cores and instead uses its fifth companion core.
– Matt Wuebbling, Nvidia

The Kal-El Tegra-based processor was announced by Nvidia in February. It is targeted at mobile devices capable of graphically and computationally intensive tasks, such as detailed video games and video encoding.

The company calls its quintet structure of cores a 'Variable Symmetric Multiprocessing' (SMP) technology. The fifth core is based on the same ARM Cortex A9 CPU design as the other four cores, but uses a "low-power silicon process that executes tasks at low frequency for active standby mode, music playback, and even video playback", Nvidia wrote in a paper outlining the technology (PDF).

The companion core is built on a process that results in a low amount of leakage, which is how much power seeps from the chip when it is idle. However, it has a slower switching time at normal voltage levels compared with its four contemporaries. For this reason, the core will operate at 500MHz or less, depending on task intensity, Nvidia said. When a task demands a greater operating frequency, it hands processing over to any of the other four cores, which will come online as task intensity increases. 

Nvidia suggested a single standard core will be good for playing 2D games and web browsing, two cores will be ideal for multitasking and browsing Flash-based web pages, while four cores will be used for "console-class gaming".

In May, the chipmaker demonstrated a Kal-El processor running a graphically impressive game called Glowball on a tablet.

OS transparent

No special tweaks will need to be made to applications and operating systems to get the benefits of the companion core, Nvidia said. For example, Google's Honeycomb Android operating system supports devices with multiple processors.

"The Variable SMP architecture is also completely OS transparent," Wuebbling wrote. "Which means that operating systems and applications don't need to be redesigned to take advantage of the fifth core."

Power-wise, Nvidia said the Kal-El is expected to demonstrate major energy savings compared with its predecessor, the Tegra 2. HD video playback should consume 61 percent less power, while MP3 playback should consume 14 percent less than with the Tegra 2, it has said. 

Nvidia is a graphical specialist, and Kal-El incorporates a GPU. However, power consumption is the central focus these days for chipmakers' mobile-device efforts. Intel has pinned its mobile-device hopes on its upcoming tablet and phone-targeted Medfield chip, and it has worked to reduce the power draw and lift the mobile capabilities of Ivy Bridge

When Kal-El was first shown, Nvidia said it was getting samples over to equipment makers that had plans to bring out devices in the autumn. Asked on his blog whether this was still the case, Wuebbling replied: "I can confirm it's coming soon, very soon."

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