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RISC-V Enables IoT Edge Processor

February 27, 2018

Author: Bob Wheeler

Processor startup GreenWaves is taking IoT edge computing to the extreme, pushing complex image and signal processing into the sensor node. This approach enables rich sensor data to squeeze into low-bandwidth wireless links such as NB-IoT and LoRA. The challenge is to perform this processing within the power and energy limits of battery-operated sensors.

To address that challenge, GreenWaves developed a unique eight-core compute engine and combined it with a microcontroller to form the GAP8 SoC. Both the MCU and compute engine implement the 32-bit RISC-V instruction set plus proprietary DSP extensions. Much of the design, including the CPU, comes from the Parallel Ultra Low Power (Pulp) project at ETH Zurich and the University of Bologna (Italy). GreenWaves expects to deliver samples in April and begin production by the end of the year.

The company paid close attention to power management, implementing dynamic voltage and frequency scaling (DVFS) as well as separate clock and voltage domains for the chip’s MCU and compute sides. This arrangement allows one side to process data while the other shuts down, saving power. The MCU has a typical set of serial I/O interfaces but lacks analog interfaces as well as flash memory. In addition to handling external events, it acts as a cluster controller, launching tasks for the compute engine to execute.

All eight CPUs in the compute engine execute the same code (kernel) from a shared instruction cache. The compute block also includes a hardware convolution engine (HWCE), which can accelerate convolutional neural networks (CNNs). The instruction-set extensions provide the flexibility to handle many other machine-learning and signal-processing algorithms, such as those used for object recognition, vibration analysis, sound analysis, and keyword recognition. GreenWaves targets applications in smart cities, industrial control, security, and consumer devices.

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