Nvida ups ante with five-core mobile chip

September 21, 2011 // By Rick Merritt
Nvidia will pack five cores into its next-generation mobile CPUs using a novel technique it describes as Variable Symmetric Multiprocessing (vSMP) to claim a power efficiency edge over rivals Qualcomm and Texas Instruments.

The company revealed in a blog posting its quad-core Kal-El processor first shown in February actually has a fifth core. The extra core takes over automatically when workloads permit running the system in a low power mode.

Nvidia described the vSMP approach in a white paper describing the chip, also known as Tegra 3. The device uses what Nvidia calls a CPU Goveror and CPU management logic to analyze system workloads and automatically switch between the one low power core, called a Companion core, or the quad-core complex as needed for maximum efficiency.

Both cores are based on the ARM Cortex A9. The Companion core running up to 500 MHz is made in a low power process technology; the quad core complex running up to a GHz is made in a general purpose or high performance process.

Although it provided no details, Nvidia presumably implements the device as two die in a system-in-package, an approach previously used in multicore desktop chips by both AMD and Intel.

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 2 milliseconds. "The Companion and main cores share the same L2 cache, and the cache is programmed to return data in the same number of nanoseconds for both Companion and main cores," the white paper said.

Nvidia claims the approach provides power savings in all use modes ranging from 14 to 61 percent compared to a standard quad core. In a rare direct comparison with competing chips, Nvidia said the five-core chip consumes two to three times less power than chips from Qualcomm and Texas Instruments.

The Nvidia chip consumes 579 milliwatts when performing at about 5,000 Coremarks and running at 480 MHz. By contrast the TI Omap 4 and Qualcomm