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5-core mobile CPUs slash power use

Posted: 23 Sep 2011 ?? ?Print Version ?Bookmark and Share

Keywords:quad-core? mobile CPU?

Nvidia Corp. has announced that it will integrate five cores into its forthcoming mobile CPUs using Variable Symmetric Multiprocessing (vSMP). This process is expected to deliver power efficiency advantage against rivals in the industry.

The company has revealed that its quad-core Kal-El processor has a fifth core that takes over automatically when workloads permit running the system in low power mode. The device uses what Nvidia calls a CPU Governor and management logic to analyze system workloads and automatically switches between the low power core, called a Companion core, or the quad-core complex as needed.

Both cores are based on the ARM Cortex A9. The Companion core running up to 500MHz is made from low power process technology, while that of the quad-core complex running up to 1GHz comes from a general purpose or high performance process. Despite the difference in process technology, the low power and high performance cores share the same die. When using the quad-core complex, the Companion core is shut down and the device activates one to four of its main cores depending on the performance needs of the workload.

The chip can switch between the Companion and main cores in less than 2ms. Nvidia claims the approach provides power savings of 14 to 16 percent in all use modes compared to a standard quad-core. The company added that the five-core chip consumes two to three times less power than chips from Qualcomm and Texas Instruments.

The Nvidia chip uses 579mW when performing at about 5,000 Coremarks and runs at 480MHz. In contrast, the TI Omap 4 and Qualcomm Snapdragon QC8660 consume 1501mW and 1453mW, respectively, at about the same performance level attained when running at about 1GHz. In addition, when running at 1GHz, Nvidia said its chip performed 11,667 on the Coremark benchmark and still consumed less power than competing chips at 1261mW.

Analysts believed the quad-core processors will initially be used only in tablets because of the heat they generate. "Some of the initial quad-core designs will exceed the thermal limits of what you can do in a smartphone, so you will need to throttle them back and then you won't get the performance you expect," noted Linley Gwennap, principal of the Linley Group. "Thus, quad-cores will be more successful in tablets initially because of their better heat dissipation feature" until 28nm versions for smartphones are available.

However, Nvidia has promised that its Tegra 3 will fit into the same power profile as the existing dual-core Tegra 2. Even if it does make the power budget for smartphones, the chip is unlikely to appear in handsets this year given the relatively long cellphone qualification cycles with regulators and carriers.

Kal-El processor

Nvidia's crude rendering of its five-core Kal-El.

- Rick Merritt
??EE Times

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