  The field of edge computing has witnessed remarkable growth owing to the
increasing demand for real-time processing of data in applications. However,
challenges persist due to limitations in performance and power consumption. To
overcome these challenges, heterogeneous architectures have emerged that
combine host processors with specialized accelerators tailored to specific
applications, leading to improved performance and reduced power consumption.
However, most of the existing platforms lack the necessary configurability and
extendability options for integrating custom accelerators. To overcome these
limitations, we introduce in this paper the eXtendible Heterogeneous
Energy-Efficient Platform (X-HEEP). X-HEEP is an open-source platform designed
to natively support the integration of ultra-low-power edge accelerators. It
provides customization options to match specific application requirements by
exploring various core types, bus topologies, addressing modes, memory sizes,
and peripherals. Moreover, the platform prioritizes energy efficiency by
implementing low-power strategies, such as clock-gating and power-gating. We
demonstrate the real-world applicability of X-HEEP by providing an integration
example tailored for healthcare applications that includes a coarse-grained
reconfigurable array (CGRA) and in-memory computing (IMC) accelerators. The
resulting design, called HEEPocrates, has been implemented both in field
programmable gate array (FPGA) on the Xilinx Zynq-7020 chip and in silicon with
TSMC 65nm low-power CMOS technology. We run a set of healthcare applications
and measure their energy consumption to demonstrate the alignment of our chip
with other state-of-the-art microcontrollers commonly adopted in this domain.
Moreover, we present the energy benefits of 4.9x and 4.8x gained by exploiting
the integrated CGRA and IMC accelerators compared to running on the host CPU.
