Nvidia drives down power with five-core processor
Next member of Tegra family will have four main cores and a fifth one to handle basic tasks at low power
Published: 21 September, 2011
READ MORE: nVidia | Processor | Tablet
In the endless battle to drive down power consumption in mobile devices, Nvidia is adopting the novel approach of packing an extra core into its processor. Its next generation CPU, Kal-El or Tegra3, is officially a quad-core design, but it actually has a fifth core, which takes over automatically to run a gadget in low power mode.
The technique Nvidia has adopted is called vSMP (variable symmetric multiprocessing). This involves intelligence which automatically switches between a single low power 'companion core' and the full quad-core processing capability, depending on the needs of the task. When the latter comes into play, the companion shuts down, and the device can activate between one and four of the main cores according to the workload. The switch takes less than two milliseconds.
All the cores run on the ARM Cortex A9 platform, but the companion element is clocked at 500MHz rather than 1GHz or more, and is made in a low power process technology. All the cores share the same L2 cache.
Nvidia claims, in a white paper describing its technique, that it can deliver power savings of between 14% and 61% compared to a conventional quad-core design like those planned by Qualcomm for Snapdragon. The Tegra maker claims its offering will consume 2-3 times less power than Snapdragon or equivalent chips from Texas Instruments - 579 milliwatts when running at 480MHz, compared to 1501mW and 1453mW respectively for the TI OMAP 4 and Snapdragon QC8660, when operating at 1GHz. Even at 1GHz, the Tegra3 will perform more efficiently, at 1261mW, says Nvidia.
This is likely to be a first step towards making quad-core processors sufficiently power efficient to get into smartphones and other very small devices, whereas they are initially expected to be confined to tablets. The large-screen ARM device base remains largely restricted to that form factor, with x86 still dominant in mobile PCs, yet its growth trajectory looks less steep than strong tablet players like Nvidia had hoped (especially as the leader, Apple, uses its own processor design). This makes it important to push the cutting edge silicon into a wider range of devices, with overheating being the main barrier to that.
"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," Linley Gwennap, principal analyst at the Linley Group, said, as quoted by EETimes.
The other important change to reduce power consumption will be manufacturing the processors in the 28nm process or below, but that will not happen for the main Kal-El cores until later next year. The first generation, which could turn up in tablets at the end of this year, will be manufactured at 40nm. It will have a 12-core graphics processor, trebling the graphics performance of Tegra2, while the second wave of the new family is also likely to boast an integrated baseband, courtesy of Nvidia's acquisition of Icera, making it even more competitive with Snapdragon, and helping to reduce total handset power further.
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