PtidyOS: A Lightweight Microkernel for Ptides Real-Time Systems

Ptides, a programming model for distributed real-time embedded systems, was proposed previously. In this work, we focus on a work flow that applies Ptides in a single-CPU environment using model-based design techniques. Our work flow starts with a programming environment where a real-time application is expressed as a Ptides model. The model captures both the functionality of the system and the desired timing of interactions with the environment. The Ptides simulator supports simulation of both of these aspects. Once the designer is satisfied with the design, a code generator can be used to glue together the application code with a real-time operating system called PtidyOS. To ensure the responsiveness of the real-time program, PtidyOS's scheduler combines Ptides semantics with the earliest-deadline-first policy. To minimize scheduling overhead associated with context switching, PtidyOS uses a single stack for event scheduling and execution, while still enabling event preemptions. We demonstrate the Ptides work flow through a motion control application. The automatically generated code running on PtidyOS is compared with a manual C implementation running on bare silicon. We discuss the trade offs in functionality and performance between these two implementations.