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GreenWaves GAP9 Goes Faster

January 14, 2020

Author: Linley Gwennap

After debuting its first AI-accelerated microcontroller last year, GreenWaves is back with a much faster version. GAP9 is similar to the original GAP8, but a process shrink from 55nm CMOS all the way to 22nm FD-SOI enables 3x more performance and 5x better power efficiency. The French company also made several design improvements, including more on-chip memory, data compression, and floating-point support. The new deep-learning accelerator (DLA) delivers nearly 50 billion operations per second (GOPS) at 50mW and can operate at even lower power. GAP9 development boards will be available by midyear, with production scheduled for late 2020.

The new GAP9 DLA reaches 400MHz. Compared with GAP8, it also adds a ninth core; although the new core is intended to supervise the other eight, offloading this task from the application CPU, it can perform computation as well. The nine 32-bit DLAs, based on the open-source RI5CY design, can each process four INT8 MACs per cycle for a total of 29 GOPS. The HWCE delivers an additional 20 GOPS while using just a few milliwatts. Whereas the convolution engine is optimized for neural networks, the RISC-V cores can also handle signal processing and other math-intensive tasks.

GAP9 includes 1.6MB of internal RAM, three times more than GAP8. The new design also adds floating-point support to the RI5CY design. In addition to standard FP32 and FP16 formats, the design handles Bfloat16 and a proprietary FP8 format that matches the range (exponent size) of FP16 but reduces the accuracy—a good tradeoff for some neural networks. The cores process FP MAC operations at the same rate as integer MACs, but the HWCE remains integer only, limiting peak performance to 14Gflop/s for FP16. Customers can choose the data type to trade off storage and performance.

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