Academic Paper Review: “Specifying a Real-Time Kernel”

1. Academic Paper Review:“Specifying aReal-Time Kernel” - A case study of an embedded real-time kernel using Z formal specification language - by J. Michael Spivey Published in Software, IEEE Journal - September 1990web search:http://www.ieeexplore.ieee.org Reviewer: Paul Richardson for MSc Course in Formal SpecificationsProfesseor: Ebba Þóra Hvannberg, University of Iceland

2. Abstract synopsis: Formal methods application: Revised specification of safety-critical embedded real-time system Primary Aim: Improve existing documentation of diagnostic X-ray machine Using: Existing documentation and source code Spin-off: Identified design flaw in kernel original specifications Demonstrates: Important role of formal methods in avoiding design flaws

3. The flaw • flaw in the kernel’s design • formal techniques can help avoid design errors. • especially useful in embedded systems • difficult to test effectively. • the design error did not in fact endanger patients • the actual control software avoided circumstances that could lead to deadlock. • hardware timeout protected against hardware or software failure • But it affected machine robustness and reliability • later enhancements to controlling software might reveal the problem

4. Kernel

6. Other Background Processing Operations Select – when processor is idle Pre-condition: Stop – when background is running Pre-condition: SetReady – sets or clears a process’s ready flag Pre-condition:

7. Interrupt handling Operations IEnter – when processor is idle Pre-condition: Interrupt – when background is running Pre-condition: IWait – sets or clears a process’s ready flag Pre-condition: IEXit – sets or clears a process’s ready flag Pre-condition:

9. Conclusions • Formal Specifications can provide benefits by raising the level of abstraction so that problems like the one identified are not obscured by detail.