Juan Zamorano

An Open Ravenscar Real-Time Kernel for GNAT

This paper describes the architecture of ORK, an open source real-time kernel that implements the Ravenscar profile for the GNAT compilation system on a bare ERC32 computer. The kernel has a reduced size and complexity, and has been carefully designed in order to make it possible to build reliable software for on-board space applications. The kernel is closely integrated with the GNAT runtime library, and supports Ada tasking in an efficient and compact way.

The design and implementation of the open Ravenscar kernel

This paper describes the design and implementation of Open Ravenscar Kernel (ORK), an open-source real-time kernel of reduced size and complexity, for which users can seek certification for mission-critical space applications. The kernel supports Ada 95 tasking on an ERC32 (SPARC v7) architecture in an efficient and compact way. It is closely integrated with the GNAT runtime library and other tools.

Hierarchical scheduling with ada 2005

Hierarchical scheduling is a basic technique to achieve temporal isolation between applications in high-integrity systems when an integrated approach is opted for over traditional federation. While comparatively heavyweight approaches to hierarchical scheduling have been prevailing until now, the new scheduling features of Ada 2005 enable lighter-weight techniques to be used. This will expectedly result in increasing the efficiency and flexibility of hierarchical scheduling, thus enabling new ways to developing critical applications in Ada. The paper explores the new opportunities opened by Ada 2005 and proposes some concrete techniques for implementing hierarchical scheduling in the new version of the language.

Implementing Ada.Real_Time.Clock and Absolute Delays in Real-Time Kernels

A real-time kernel providing multitasking and timing services is a fundamental component of any real-time system. Timing services, which are crucial to the correct execution of this kind of applications, are usually provided by a real-time clock and timer manager, which is part of the kernel and implements the required functionality on top of the one or more hardware timers. Kernel timing services must be implemented carefully in order to avoid race problems and inconsistencies which may be caused by the fact that many common hardware timer chips are not intended at a direct implementation of software timing services. This paper provides advice on the implementation of two of the Ada timing services: Ada.Real_Time.Clock, and absolute delays (delay until). The example implementation of both services in the Open Ravenscar Kernel, which is based on the ideas presented in the paper, is also described.

Execution-time clocks and Ravenscar kernels

The kind of high-integrity real-time systems to which the Ada Ravenscar profile is targeted often require overrun detection for enhanced reliability in the time domain Execution-time clocks and timers have been proposed to fulfill this need, but only programming patterns based on asynchronous transfer of control, and thus incompatible with the profile, have been provided up to now. In this paper an assessment of the compatibility of the proposed execution-time mechanisms with the Ravenscar profile is made, and some programming patters for using them are proposed. The patterns are intended to provide basic overrun detection and handling capabilities to high-integrity real-time systems.

Implementing the new Ada 2005 real-time features on a bare board kernel

A real-time kernel providing timing services is a key component of any real-time system. The current revision of the Ada standard provides a range of real-time mechanisms that can be used to ensure the required temporal behaviour of real-time tasks. However, kernel timing services must be implemented carefully in order to avoid overheads and inaccuracies. This paper describes the implementation of the Ada timing services in an evolved version of the Open Ravenscar Kernel. The interrelation among the different timing mechanisms is also analysed and evaluated.

BUILDING SAFETY-CRITICAL REAL-TIME SYSTEMS WITH REUSABLE CYCLIC EXECUTIVES

Abstract Many real-time systems have strict safety requirements, and concurrent processes cannot be used in their development. Thus, these safety-critical systems are developed using synchronous architectures based on cyclic scheduling. This paper describes a reusable cyclic executive implementation in Ada 95, based on a generic architecture for synchronous real-time systems. This generic architecture is described by means of an object-oriented design notation. New Ada characteristics, as well as exceptions and generics, are used to build the component blocks of this generic architecture. In order to develop real-time systems, guidelines for using these reusable components are also provided. Copyright

A framework for lab work management in mass courses. Application to Low Level Input/Output without hardware

Abstract This paper describes a complete lab work management framework designed and developed in the authors’ department to help teachers to manage the small projects that students are expected to complete as lab assignments during their graduate-level computer engineering studies. The paper focuses on an application example of the framework to a specific lab work related to Low Level Input/Output. Special emphasis is laid on the most complex aspects of such environments. The management framework provides specific tools for dealing with these issues: the management of student work delivery and evaluation results accessibility, automatic or semi-automatic assessment of student work, and detection of lab assignments that are highly suspect of having been copied. Additionally, the lab work framework represents a method through which a closer peer-to-peer or one-to-many communication with students can be attained. The lab work described in the paper is a small project based on a specification document. It is designed to get students to gain an in-depth knowledge of the computer Input/Output subsystem. While the framework has been in use for over 10 years, the specific Input/Output lab work has been managed by the framework tool-chain for the last 6 years, and used by over 2000 students. The lab work management framework is a step towards the feasibility of a closer-to-the-student higher education system, where the main interaction between students and teachers can be based on individual or on small group tutorials. Using the tool-chain, the academic load of teachers in mass course environments can be kept at acceptable levels, making for higher quality education.

Analysis of WCET in an experimental satellite software development

This paper describes a case study in WCET analysis of an on-board spacecraft software system. The attitude control system of UPMSat-2, an experimental micro-satellite which is scheduled to be launched in 2013, is used for an experiment on analysing the worst-case execution time of code automatically generated from a Simulink model. In order to properly test the code, a hardware-in-the-loop configuration with a simulation model of the spacecraft environment has been used as a test bench. The code has been analysed with RapiTime, with some modifications to the original instrumentation routines, in order to take into account the particularities of the test configuration. Results from the experiment are described and commented in the paper.

A Platform for Real-Time Control Education with LEGO MINDSTORMS®

A set of software development tools for building real-time control systems on a simple robotics platform is described in the paper. The tools are being used in a real-time systems course as a basis for student projects. The development platform is a low-cost PC running GNU/Linux, and the target system is LEGO MINDSTORMS NXT, thus keeping the cost of the laboratory low. Real-time control software is developed using a mixed paradigm. Functional code for control algorithms is automatically generated in C from Simulink models. This code is then integrated into a concurrent, real-time software architecture based on a set of components written in Ada. This approach enables the students to take advantage of the high-level, model-oriented features that Simulink offers for designing control algorithms, and the comprehensive support for concurrency and real-time constructs provided by Ada.