Pat Rogers

Toward Extensions to the Ravenscar Profile

We describe an on-going effort to identify a set of enhancements to the Ravenscar profile, intended primarily for applications in the real-time systems domain, but perhaps also applicable to the other domains supported by Ravenscar as currently defined. In addition to the technical issues we also include matters of cost, leading to the question of whether a new profile is appropriate.

Gem #81: GNAT semaphores

Ada Gem #81 --- A previous Gem (#70, â The Scope Lock Idiomâ ) discussed the occasional necessity of using low-level synchronization mechanisms instead of the higher-level protected object construct. The code in that Gem referenced the facilities of the Semaphores package located in the GNAT hierarchy. In this Gem, we examine the abstractions provided by that package, focusing especially on the design choices.

Gem #70: the scope locks idiom

This Gem marks a brief break from SPARK, which will return in two weeks with the first in a series of six Gems on that topic. Encapsulating shared variables inside protected operations is not always possible. This Gem shows how to add mutual exclusion to existing sequential code using a combination of controlled and protected types, such that the resulting code is robust and minimally changed.

Review of the book: real-time systems and programming languages (4th edition) by Alan Burns and Andy Wellings

There are a number of excellent books on the topic of real-time systems. Few, if any, address the breadth of relevant topics covered by this book, much less to the depth and quality exhibited here. I have each of the three previous editions of this book and this latest is, once again, worth every penny. One of the reasons I hold such a high opinion of the book is that it is written by people who not only know what they are talking about, but can do so with clarity and precision. As leading contributors to real-time systems research and the real-time programming facilities of Ada and Java, Alan Burns and Andy Wellings are internationally recognized experts on real-time systems and programming languages. The texts depth reflects that fact, but it is also clear, concise, and a pleasure to read. Another reason I recommend the book is that it has a good balance between theory and practice. Make no mistake, the necessary theory is covered extensively, but it is then illustrated with concrete examples using programming languages that are in widespread use today: Ada, C, and Java. As neither C nor Java were explicitly designed for concurrent real-time systems, the necessary language extensions are used. For C, the POSIX real-time profile is used. For Java, the Real-Time Specification for Java (RTSJ) is used. When necessary, examples are provided in other languages. In fact these three programming languages form the underlying context for much of the book. They are not themselves the subjects of the book, however, and those readers seeking an introduction to these languages should look elsewhere. Instead, the programming languages are used to explore the distinct nature of real-time systems and the requirements for developing applications in that domain. The code examples thus provide a means of illustrating the topic at hand, but also provide a means for comparing the strengths and weaknesses of the real-time facilities of the languages. The authors are principal contributors to the Ada 2005 Real-Time Systems Annex and the RTSJ for Java, a fact reflected in the detailed critical analysis provided. New material includes additional schedulability analysis theory and material on multi-processor and multi-core architectures. With respect to programming languages, the new material includes extensive coverage of the real-time systems programming additions to Ada 2005, the latest version of the RTSJ, and the new real-time POSIX profile enhancements for C. As for removals, …

Gem #14: interrupt handling idioms (part 2)

Ada Gem #14 -- There are two design idioms commonly used when handling interrupts with Ada. One has more of the characteristics associated with good software engineering, the other somewhat better performance. We explore these two idioms in this gem.

Gem #13: interrupt handling idioms (part 1)

Ada Gem #13 -- There are two design idioms commonly used when handling interrupts with Ada. One has more of the characteristics associated with good software engineering, the other somewhat better performance. We explore these two idioms in this gem.