Based on its announcement last week of what has been referred to as “a secret fifth core,” Nvidia has ensured that its forthcoming Tegra processor known as “Project Kal-El” will be one of the most intriguing CPUs of the year.

Nvidia disclosed “Kal-El” back at the Mobile World Congress show in February, expecting the quad-core processor to be out in tablets by August and in smartphones by the end of the year. That schedule obviously has slipped some, but the company still expects Kal-El-based tablets in the next month or so.

In the original announcement, Nvidia said the chip had four CPU cores and 12 graphics engines, compared with two CPU cores and eight graphics engines in the existing Tegra 2. At the time, Nvidia didn’t specify the CPU core, though now the company has said it is an ARM Cortex-A9, which was generally expected.

The new chip can provide up to five times the performance of Tegra 2, said Nvidia. It then showed impressive game demos. The company now says that’s up to twice the performance of the CPU and three times the performance of the graphics, and has produced a white paper showing some big numbers. (As always, I take such performance numbers with a grain of salt until I see the final chips.)

What’s different now— and what makes this chip so interesting—is the use of what the company calls Variable Symmetric Multiprocessing (vSMP) technology. This involves an additional “companion core” that can run on very low power, executing tasks at a low frequency, under 500 MHz. Nvidia said the core will be used for active standby mode, music playback, and even video playback. When the device needs more power, like when actively running an application, it will switch to the main set of four CPUs, running at higher frequencies.

All of the CPUs are identical ARM Cortex A9 CPUs, and the device can individually turn the cores on and off (via aggressive power gating) based on the work load. In low power, only the “companion core” is running; in high power, it could be running one to four of the other CPUs at various frequencies, designed to optimize performance. Nvidia said this process is “OS transparent,” meaning that the OS and applications are not aware of it, so they do not need to be modified.

This works because the power consumption of any device consists of both leakage power (the amount of power lost just keeping the chip awake) and dynamic power (which rises proportional to the chip’s operating frequency and as a square of the operating voltage). 

All this seems to be made possible by the new 40nm LPG (low-power triple gate oxide) process offered by Taiwan Semiconductor Manufacturing Corp. (TSMC). As the world’s leading chip foundry, it’s where Nvidia actually manufactures the bulk of its products.

Generally, most semiconductor logic has been made on either a “low power” (LP) process, or a “high performance” process, which TSMC calls “General Purpose Superb” or “G.” In the general or high performance cases, transistors run on more voltage and have fast frequencies, but typically show more leakage. In the low power case, the chip runs on much lower voltage, but can’t attain the frequencies needed by today’s applications without consuming a lot more energy. TSMC’s LPG process allows designers to mix “LP” and “G” transistors onto the same die.

(Correction added 9/30/11: Actually, in normal operation, the G process runs on a lower voltage (though it has more leakage) than the LP process;  the LP process would need a lot more voltage to hit high frequencies.)

There have been other products made on the LPG process but, as far as I know, Kal-El will be the first general purpose microprocessor designed to mix both low-power and high-power cores for the main CPU.

Kal-El targets mainly tablets at first, but will consider smartphones. Recently, I had a chance to talk with Nvidia CEO Jen-Hsen Huang and he thought both Nvidia and Qualcomm were going to be the two leaders in high-end mobile devices. Both have both CPU and radio capability, and certainly they, along with TI, appear to be making the processors most of the highest-end phones use. (Qualcomm has its own quad-core processor due out on a 28nm process next year, while TI is using the next generation Cortex-15 in its next product. There are a number of other makers of ARM-based processors aimed at low-end and mid-range phones, including smartphones.)

Actually, Broadcom, Marvell, Mediatek, Samsung, and ST-Ericsson all also make both ARM-based processors and radios, though many of them address more low-end and mid-range phones, including smartphones. Even more intriguing, Huang said he expects to see a number of more traditional “clamshell” notebooks running Windows 8 on ARM when it comes out next year.