Minima, ARM apply 'real-time' voltage scaling to Cortex-M3

November 28, 2017 // By Peter Clarke
Low power logic IP company Minima Processor Oy (Oulu, Finland) has provided more details of its dynamic margining approach to near-threshold voltage design with the publication of a joint white paper with ARM (referenced at foot of this article).

However, as Minima gets closer to market with its mixed software and hardware intellectual property approach to the market it appears to have pulled back from earlier sub-threshold voltage discussion and instead talks about the benefits of near-threshold voltage operation.

Minima offers ultra-wide dynamic voltage and frequency scaling (DVFS) and a framework to change the frequency and/or operating voltage of a processor based on active system function parameters and software calls. Minima is claiming that even at near-threshold voltages of down to 0.4V the energy savings over all applications when both dynamic margining and ultra-wide DVFS are deployed is up to 15x to 20x lower energy compared to a nominal voltage design.

Minima inserts timing and voltage monitors along paths to monitor power and performance during operation. If a critical path monitor is activated by a voltage drop, whether due to process variation, temperature conditions, or variability or aging, then software and dynamic feedback responds by temporarily slowing the path for a clock cycle, or until conditions allow a resumption of previous performance. The OS-controlled middleware acts like an automatic braking system that adjusts to conditions. Instead of driving based on worst-case assumptions, Minima goes as quickly as possible at a given voltage and only slows operation or increases voltage when necessary – and only for as long as necessary.

This also means that Minima IP can work with conventional gate libraries rather than libraries made robust for low-voltage operation. Minima claims that its light-touch, real-time, interactive approach can take any existing processor or DSP into the microwatt power consumption range.

The technology has been applied in silicon with two semiconductor test-chip runs and one chip, a RISC with crypto accelerator, has been taped out. Minima and Arm are partnering to produce a low-power implementation of a Cortex-M3 processor core, which is available without paying an up-front licensing fee through ARM's DesignStart program. But it should also be noted that Minima Processor is also a founding member of the RISC-V Foundation, which promotes open processor hardware.

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