Frank Singhoff

Cheddar: a flexible real time scheduling framework

This paper describes an Ada framework called Cheddar which provides tools to check if a real time application meets its temporal constraints. The framework is based on the real time scheduling theory and is mostly written for educational purposes. With Cheddar, an application is defined by a set of processors, tasks, buffers, shared resources and messages. Cheddar provides feasibility tests in the cases of monoprocessor, multiprocessor and distributed systems. It also provides a flexible simulation engine which allows the designer to describe and run simulations of specific systems. The framework is open and has been designed to be easily connected to CASE tools such as editors, design tools, simulators, ...

Scheduling and memory requirements analysis with AADL

This article describes an Ada set of packages which allows designers to perform resource requirements analysis of AADL specifications. This set of Ada packages is part of Cheddar, an Ada framework that we are developing at the University of Brest [22].The framework provides tools to check if AADL threads will meet their deadline at execution time. Some new AADL properties are proposed to model and analyze dependent AADL thread sets. It also provides some tools to perform memory requirements analysis on AADL specifications.

AADL modeling and analysis of hierarchical schedulers

A system based on a hierarchical scheduler is a system in which the processor is shared between several collaborative schedulers. Such schedulers exist since 1960 and they are becoming more and more investigated and proposed in real-life applications. For example, the ARINC 653 international standard which defines an Ada interface for avionic real time operating systems provides such a kind of collaborative schedulers. This article focuses on the modeling and the performance analysis of hierarchical schedulers. We investigate the modeling of hierarchical schedulers with AADL. Hierarchical scheduler timing and synchronization relationships are expressed with a domain specific language based on timed automata: the Cheddar language. With the meta CASE tool Platypus, we generate Ada packages implementing the Cheddar language. These Ada packages are part of Cheddar, a real time scheduling simulator. With these Ada packages, Cheddar is able to perform analysis by scheduling simulation of AADL systems composed of hierarchical schedulers. An AADL model of the ARINC 653 hierarchical scheduling is described as an illustration.

Validate, simulate, and implement ARINC653 systems using the AADL

Safety-critical systems are widely used in different domains and lead to an increasing complexity. Such systems rely on specific services such space and time isolation as in the ARINC653 avionics standard. Their criticality requires a carefully driven design based on an appropriate development process and dedicated tools to detect and avoid problems as early as possible. Model Driven Engineering (MDE) approaches are now considered as valuable approach for building safety-critical systems. The Architecture Analysis and Design Language (AADL) proposes a component-based language suitable to operate MDE that fits with safety-critical systems needs. This paper presents an approach for the modeling, verification and implementation of ARINC653 systems using AADL. It details a modeling approach exploiting the new features of AADL version 2 for the design of ARINC653 architectures. It also proposes modeling patterns to represent other safety mechanisms such as the use of Ravenscar for critical applications. This approach is fully backed by tools with Ocarina (AADL toolsuite), POK (AADL/ARINC653 runtime) and Cheddar (scheduling verification). Thus, it assists system engineers to simulate and validate non functional requirements such as scheduling or resources dimensioning.

Can We Increase the Usability of Real Time Scheduling Theory? The Cheddar Project

The Cheddar project deals with real time scheduling theory. Many industrial projects do not perform performance analysis with real time scheduling theory even if the demand for the use of this theory is large. The Cheddar project investigates why real time scheduling theory is not used and how its usability can be increased. The Cheddar project was launched at the University of Brest in 2002. This article presents a summary of its contributions and ongoing works.

Refactoring of an Ada 95 library with a Meta CASE tool

This paper presents the refactoring work of Cheddar, a set of Ada packages which aims at providing performance analysis tools for concurrent real time applications. CASE tools can be used for such a purpose. However, we chose to use a meta CASE tool called Platypus. It seems that few studies exist concerning Ada and meta-modelization. Then, in this paper, we investigate how to use a meta CASE tool in order to automatically produce some parts of an Ada 95 object oriented software.

Towards user-level extensibility of an Ada library: an experiment with cheddar

In this article, we experiment a way to extend an Ada library called Cheddar. Cheddar provides a domain specific language. Programs written with this domain specific language can be interpreted in order to perform real time scheduling analysis of real time systems. By the past, different projects showed that the Cheddar programming language is useful for the modeling of real time schedulers. But these experiments also showed that the interpreter is lacking of efficiency in case of large scheduling simulations. In this article, by designing a Cheddar meta-model, we investigate on how to compile such Cheddar programs in order to extend the Cheddar library. For such a purpose, we use Platypus, a meta CASE Tool based on EXPRESS. For a given Cheddar program and with a meta-model of Cheddar handled by Platypus, we can generate a set of Ada packages. Such Ada packages can be compiled and integrated as builtin schedulers into Cheddar. Then, the efficiency of scheduling simulations can be increased.

Synchronization of Models of Rich Languages with Triple Graph Grammars: an Experience Report *

We report our experience of using Triple Graph Grammars (TGG) to synchronize models of the rich and complex Architecture Analysis and Design Language (AADL), an aerospace standard of the Society of Automotive Engineers. A synchronization layer has been developed between the OSATE (Open Source AADL Tool Environment) textual editor and the Adele graphical editor in order to improve their integration. Adele has been designed to support editing AADL models in a way that does not necessarily follow the structure of the language, but is adapted to the way designers think. For this reason, it operates on a different meta-model than OSATE. As a result, changes on the graphical model must be propagated automatically to the textual model to ensure consistency of the models. Since Adele does not cover the complete AADL language, this must be done without re-instantiation of the objects to avoid losing the information not represented in the graphical part. The TGG language implemented in the MoTE tool has been used to synchronize the tools. Our results provide a validation of the TGG approach for synchronizing models of large meta-models, but also show that model synchronization remains a challenging task, since several improvements of the TGG language and its tool were required to succeed.

Architecture models refinement for fine grain timing analysis of embedded systems

As real-time systems have become more and more complex, architects rely on abstract models of computation in order to design and analyse these systems. In order to ease the production of source code that respects such models of computation, developper can take advantage of code generators and/or middleware. However, when analyzing an abstract model of computation, timing overheads due to generated code or middleware components are not taken into account. Answering this issue is even more problematic in the domain of embedded systems because of the variability of execution platforms. To tackle this problem, we present in this paper a model refinement and timing analysis framework: abstract models of computation are first transformed in more precise models, which include the timing characteristics of the execution platform. These refined models are then used for a more precise timing analysis. The experiment results we present in this paper show that our method can deal with realistic software architecture of real-time systems.

An Ada design pattern recognition tool for AADL performance analysis

This article deals with performance verification of architecture models of real-time embedded systems. Although real-time scheduling theory provides numerous analytical methods called feasibility tests for scheduling analysis, their use is a complicated task. In order to assist an architecture model designer in early verification, we provide an approach, based on real-time specific design patterns, enabling an automatic schedulability analysis. This analysis is based on existing feasibility tests, whose selection is deduced from the compliance of the system to a design pattern and other systems properties. Those conformity verifications are integrated into a schedulability tool called Cheddar. We show how to model the relationships between design patterns and feasibility tests and design patterns themselves. Based on these models, we apply a model-based engineering process to generate, in Ada, a feasibility test selection tool. The tool is able to detect from an architecture model which are the feasibility tests that the designer can apply. We explain a method for a designer willing to use this approach. We also describe the design patterns defined and the selection algorithm.