Nvidia’s new Kal-El chipset won’t be the first quad-core chip for phones and tablets: it’ll be the first quint-core.
In a white paper today, Nvidia revealed that Kal-El will include a surprise fifth core, a “companion core” built using a different process which will keep Kal-El devices running at very low power when in standby mode.
Nvidia calls its approach “variable symmetric multiprocessing” and says it lets Kal-El devices use the minimum amount of power necessary for all tasks, conserving battery life.
The trick is based on the four main cores and the “companion” core being based on different silicon processes, Nvidia says. CPUs based on low-power process technologies run very efficiently at slow speeds, but require a lot of power to run at high speeds, the company said. CPUs based on fast process technologies run efficiently at high speeds, but “leak” power at low speeds.
The companion core is based on a low-power process and handles all tasks suitable for a single core running at under 500 MHz, Nvidia says. That includes cell standby, checking email, and music and video playback. (In Nvidia’s design, music and video are mostly processed by separate hardware decoders that aren’t part of the CPU.)
When more power is needed, the companion core shuts off and the main cores kick in: first one, then two, then four. Nvidia offers Web browsing as an example of a single-core application, Flash and video chat as dual-core applications, and high-end gaming and “media processing” for quad-core use.
How Four Cores Actually Save Power
Kal-El will also use less power than Nvidia’s current Tegra 2 line does for the same applications, Nvidia said. That should be obvious with standby mode, where the “companion core” operates at very low power. But having four cores allows applications to run all of the cores at lower speeds than on systems with fewer cores, saving power even in more demanding applications.
As an example, Nvidia shows the work needed to achieve a Coremark benchmark score around 5,000. Kal-El’s four cores run at 480 MHz each to get the work done, drawing 579 mW of power. TI’s OMAP4 runs two cores each at 1Ghz, drawing 1501 mW to accomplish the same task. Power used is proportional to the square of voltage, and lower frequencies use less voltage, so you can run more cores with less juice if they’re running at lower frequencies.
Run the four cores faster, of course, and you get more processing power. With each Kal-El core running at 1 GHz, the system scores 11667 on Coremark while using 1261 mW of power, double the performance of the dual-core chips Nvidia tested.
Kal-El will be the first “quad-core” mobile chipset on the market, but Nvidia’s rivals aren’t far behind. Qualcomm announced the 2.5Ghz, quad-core APQ8064 back in February, but said that it wouldn’t appear in products until 2012. TI’s upcoming OMAP5 is only dual-core, but it uses a new ARM Cortex-A15 architecture and piles on a ton of other dedicated processors for imaging, media, security, and general assistance.
We expect to see the first Kal-El-based, five-core Android tablets in October.