This paper presents a novel method to obtain an optimized static schedule of CSP-like communications between a collection of concurrent hardware processes implemented on "System on a Programmable Chip" (SoPC). The hardware processes are the applications tailored "cells" in the Processor-Coupled Polymorphous Fabric ([Polymorphous fabric-based systems: Model, tools, applications], [A new polymorphous computing fabric]) implemented on the Altera Excalibur Arm SoPC platform. In our global approach, a static communications schedule is adopted to reduce hardware overhead due to inter-cells message transfer synchronization and to speed-up application execution. The scheduling problem is defined and solved using constraints programming approach. This approach makes it possible to obtain optimal communication schedules in a number of real cases. It makes also possible to easily generate pipelined schedules that improve significantly performance of the final implementation. Our method is illustrated with a Fabric-based implementation of the K-means clustering algorithm. An optimal communication scheduled is achieved for this application.