Kal-El Tegra SoC to use 5 cores
Recent news from NVIDIA has unveiled some interesting new technical details about the upcoming Kal-El ARM-based Tegra SoC. While we have known for some time that this chip would include a quad-core processor and would likely be the first ARM-based quad-core part on the market, NVIDIA's Matt Wuebbling spilled the beans on a new technology called "Variable SMP" (vSMP) and a fifth core on the die.
An updated diagram shows the fifth "companion" core - Courtesy NVIDIA
This patented technology allows the upcoming Tegra processor to address a couple of key issues that affect smartphones and tablets: standby power consumption and manufacturing process deviations. Even though all five of the cores on Kal-El are going to be based on the ARM Cortex A9 design they will have very different power characteristics due to variations in the TSMC 40nm process technology that builds them. Typical of most foundries and process technologies, TSMC has both a "high performance" and a "low power" derivative of the 40nm technology usually aimed at different projects. The higher performing variation will run at faster clock speeds but will also have more transistor leakages thus increasing overall power consumption. The low power option does just the opposite: lowers the frequency ceiling while using less power at idle and usage states.
CPU power and performance curves - Courtesy NVIDIA
NVIDIA's answer to this dilemma is to have both - a single A9 core built on the low power transistors and quad A9s built on the higher performing transistors. The result is the diagram you saw at the top of this story with a quad-core SoC with a single ARM-based "companion." NVIDIA is calling this strategy Variable Symmetric Multiprocessing and using some integrated hardware tricks it is able to switch between operating on the lower power core OR one to four of the higher power cores. The low power process will support operating frequencies up to only 500 MHz while the high speed process transistors will be able to hit well above 1-1.2 GHz.