Impact of a Restricted Tasking Profile: The Case of the GOCE Platform Application Software

Abstract

We are designing the on-board software for the GOCE satellite platform so that static analysis can verify its real-time requirements. Our aim is to analyse the binary code to derive bounds on the worst-case execution time for each task, followed by a schedulability analysis using preemptive fixed-priority scheduling. The code-analysis step constrains the sequential coding and the schedulability-analysis step constrains the concurrency design (tasking). We use the Ravenscar tasking profile further limited to a single-suspension point per task and a single call of each protected entry. We discuss how this profile matches the real-time requirements and its impact on the designers, the software architecture and the resource usage. The main issue is that the single-suspension-point rule prevents procedural abstraction of operations that involve input-output. Some design patterns emerge from this example.