  Recurrent neural networks (RNNs) are state-of-the-art in voice
awareness/understanding and speech recognition. On-device computation of RNNs
on low-power mobile and wearable devices would be key to applications such as
zero-latency voice-based human-machine interfaces. Here we present Chipmunk, a
small (<1 mm${}^2$) hardware accelerator for Long-Short Term Memory RNNs in UMC
65 nm technology capable to operate at a measured peak efficiency up to 3.08
Gop/s/mW at 1.24 mW peak power. To implement big RNN models without incurring
in huge memory transfer overhead, multiple Chipmunk engines can cooperate to
form a single systolic array. In this way, the Chipmunk architecture in a 75
tiles configuration can achieve real-time phoneme extraction on a demanding RNN
topology proposed by Graves et al., consuming less than 13 mW of average power.
