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Startup Develops Near-Threshold CPUs

February 6, 2018

Author: Bob Wheeler

For always-on devices, dynamic power is the enemy of battery life. Finnish startup Minima Processor aims its near-threshold-voltage designs at these applications, claiming an order-of-magnitude reduction in CPU and DSP power compared with conventional designs. It’s modifying CPU cores to incorporate its technology, starting with an Arm Cortex-M3 that should be available in 1H18.

The company is addressing a fundamental design problem: circuit-speed changes increase with process and temperature variations as the operating voltage is decreased from nominal. When applying conventional dynamic voltage and frequency scaling (DVFS) to near-threshold designs, the designer must employ excessive timing margin to avoid tanking chip yields. The trick is to compensate for operating temperature and actual silicon speed, enabling presilicon timing margins similar to what nominal-voltage design employs.

Whereas some companies have used special test circuits to monitor silicon performance, Minima’s approach adds detection logic in the normal data path. When it detects a timing violation, the design delays the clock to prevent errors in the main data path. A hardware controller monitors the timing-violation rate and increases the circuit’s operating voltage when violations become too frequent.

Because its design requires circuit-level changes to a CPU or DSP core, Minima will deliver its intellectual property (IP) as hard macros. Arm’s Cortex-M3 is a logical starting point because its RTL is already available without up-front license fees, and it implements the popular ARMv7-M 32-bit instruction set. Minima’s technology is a good fit for functions with a 100% duty cycle, but devices that spend much of their time in sleep mode—such as many IoT designs—will see less benefit. 

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