  The fast proliferation of extreme-edge applications using Deep Learning (DL)
based algorithms required dedicated hardware to satisfy extreme-edge
applications' latency, throughput, and precision requirements. While inference
is achievable in practical cases, online finetuning and adaptation of general
DL models are still highly challenging. One of the key stumbling stones is the
need for parallel floating-point operations, which are considered unaffordable
on sub-100 mW extreme-edge SoCs. We tackle this problem with RedMulE
(Reduced-precision matrix Multiplication Engine), a parametric low-power
hardware accelerator for FP16 matrix multiplications - the main kernel of DL
training and inference - conceived for tight integration within a cluster of
tiny RISC-V cores based on the PULP (Parallel Ultra-Low-Power) architecture. In
22 nm technology, a 32-FMA RedMulE instance occupies just 0.07 mm^2 (14% of an
8-core RISC-V cluster) and achieves up to 666 MHz maximum operating frequency,
for a throughput of 31.6 MAC/cycle (98.8% utilization). We reach a
cluster-level power consumption of 43.5 mW and a full-cluster energy efficiency
of 688 16-bit GFLOPS/W. Overall, RedMulE features up to 4.65x higher energy
efficiency and 22x speedup over SW execution on 8 RISC-V cores.
