  In this paper, we introduce a low-cost and low-power tiny supervised
on-device learning (ODL) core that can address the distributional shift of
input data for human activity recognition. Although ODL for resource-limited
edge devices has been studied recently, how exactly to provide the training
labels to these devices at runtime remains an open-issue. To address this
problem, we propose to combine an automatic data pruning with supervised ODL to
reduce the number queries needed to acquire predicted labels from a nearby
teacher device and thus save power consumption during model retraining. The
data pruning threshold is automatically tuned, eliminating a manual threshold
tuning. As a tinyML solution at a few mW for the human activity recognition, we
design a supervised ODL core that supports our automatic data pruning using a
45nm CMOS process technology. We show that the required memory size for the
core is smaller than the same-shaped multilayer perceptron (MLP) and the power
consumption is only 3.39mW. Experiments using a human activity recognition
dataset show that the proposed automatic data pruning reduces the communication
volume by 55.7% and power consumption accordingly with only 0.9% accuracy loss.
