  A key challenge for ultra-low-power (ULP) devices is handling peripheral
linking, where the main central processing unit (CPU) periodically mediates the
interaction among multiple peripherals following wake-up events. Current
solutions address this problem by either integrating event interconnects that
route single-wire event lines among peripherals or by general-purpose I/O
processors, with a strong trade-off between the latency, efficiency of the
former, and the flexibility of the latter. In this paper, we present an
open-source, peripheral-agnostic, lightweight, and flexible Peripheral Event
Linking System (PELS) that combines dedicated event routing with a tiny I/O
processor. With the proposed approach, the power consumption of a linking event
is reduced by 2.5 times compared to a baseline relying on the main core for the
event-linking process, at a low area of just 7 kGE in its minimal
configuration, when integrated into a ULP RISC-V IoT processor.
