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Cortex-M55 Supports Tiny-AI Ethos

March 10, 2020

Author: Mike Demler

Cortex-M55 is Arm’s first CPU to support the v8.1-M vector extension (MVE, also called Helium), a set of optional features that enable Cortex-M cores to perform 128-bit vector/SIMD operations. The previous v7-M ISA allows Cortex-M4 and similar CPUs to execute 32-bit SIMD operations, but it lacks the 8-bit multiply-accumulate (MAC) operation typical of convolutional neural networks (CNNs), so programmers must instead employ 16-bit instructions. Helium allows Cortex-M55 to execute eight INT8 MACs per cycle. Whereas the older Cortex-M cores take eight cycles to complete a 128-bit vector MAC, the M55 requires only two. Arm plans to release production RTL for the new design by the end of 1Q20, with first silicon likely arriving in 1Q21.

To further improve neural-network performance in Cortex-M devices, the intellectual-property (IP) vendor added a deep-learning accelerator (DLA) to its Ethos line. The new DLA, which Arm dubbed Ethos-U55, targets IoT end points and other low-power embedded devices. It supports configurations of 32–256 INT8 MAC units. To minimize area and power, it supports a subset of the larger DLAs’ machine-learning instructions. The company plans to release it for general licensing this summer. NXP has already signed up as the lead customer, and STMicroelectronics plans to use the DLA in future products.

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