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This talk introduces a formal framework for describing the relationship between a criticality-aware scheduler and a set of application tasks that are assigned different criticality levels. The exposition employs a series of examples starting with scheduling simple jobs and then moving on to mixed-criticality tasks. The proposed formalism extends the rely-guarantee approach, which facilitates formal reasoning about the functional behaviour of concurrent systems, to address real-time properties.

AEiC 2021 - 25th Ada-Europe International Conference on Reliable Software Technologies

Formally specifying the behaviour of a mixed criticality scheduler

2021 Annual Conference of the North American Chapter of the Association for Computational Linguistics.

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### Welcome Message from our Co-Chairs

Through this message, we want to give you our warmest welcome to the 25th Ada-Europe International Conference on Reliable Software Technologies (AEiC 2021). The special circumstances we all go through have made the conference a virtual event. Nonetheless, this will allow us to take advantage of the benefits of this format by using the Underline.io platform that allows remote participation of speakers and attendees and a virtual exhibition.
The platform will also provide a virtual space through Gather.Town to facilitate social interaction among participants, which, in addition to presenting state of the art research results, is one of the most important goals of a conference. This platform will hold various social events together with breaks and a poster session. 

The conference schedule includes a four-day program and exhibition from Monday to Thursday, with parallel tutorials on Monday, and keynotes, technical sessions and a Work-in-Progress session on the remaining three days. The technical sessions include the presentations of 13 journal-track papers, 5 industrial presentations and 6 invited talks on leading topics on reliable software technologies. The program will be completed with three outstanding keynotes that will delight the participants.

The main conference activities will be from 13:00 to 18:00 Central European Summer Time (CEST) to allow participants from America to Central Asia to attend to the conference sessions. Virtual social events are scheduled at the beginning and the end of each day. We encourage you to participate in these activities as well as visiting the exhibition. We look forward to meeting you virtually in June 2021!

**J. Javier Gutiérrez and Mario Aldea Rivas**
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This paper describes the Ember library for highintegrity embedded robotics and GNC applications developed in SPARK 2014 with formal verification. The
library is based on generic packages and includes functionality as linear algebra, complex numbers, quaternions, and kinematics. Preliminary test results for linear
algebra performance are very promising.
Keywords: Numerics, robotics, embedded, SPARK

Ember: An embedded robotics library in SPARK

Global static scheduling (one scheduling table generated off-line per processor) for Mixed Criticality (MC) systems demonstrate excellent results in terms of acceptance ratio and number of preemptions. But, no practical implementation and empirical evaluation have been presented yet for multi-processors systems. In this paper, we present two contributions on the implementation of global static schedulers for MC systems to enforce low latency mode changes. This work interest is illustrated scheduling scheduling tables produced by GMH_MC_DAG, a meta-heuristic to compute schdeduling tables for multi-periodic Directed Acyclic Graphs of Mixed Criticality tasks with multiple criticality level.

Contributions to the implementation of global schedulers for mixed-criticality systems

The use of hardware caches became essential in modern embedded systems to address the speed gap between processor and memory. In such systems, cache-related preemption delay (CRPD) may represent a significant proportion of task execution time. Addressing this delay in scheduling simulation of these systems stays an open and under-examined problem. Assumptions are often made to simplify the computation model used in simulation and capture the worst-case effect. Nevertheless, they can introduce situations in which scheduling simulation is considered not only pessimistic but also non-sustainable. In this article, we discuss the problem and propose a less pessimistic CRPD computation model that allows sustainable scheduling simulation regarding the capacity parameter. With the proposed model, a system that is schedulable with simulated worst-case execution times remains so when these parameters are reduced. These results improve the applicability of scheduling simulation in the early verification stage for systems with caches. Experiments conducted with our CRPD computation model show a 5% to 12% improvement of schedulability task set coverage and a 30% to 50% reduction of preemption cost with regard to existing CRPD computation models. An integration in a scheduling simulator and a performance evaluation are also realized for the proposed model.

Feasibility interval and sustainable scheduling simulation with CRPD on uniprocessor platform

Since 1973, Earliest Deadline First (EDF) uniprocessor scheduling has been known to be superior to its Rate Monotonic (Fixed-Priority, FPS) counterpart. Such superiority manifested in optimality, the capacity of EDF to feasibly sustain full utilization, which FPS can only achieve in certain favorable circumstances. In 2005, further research results argued that EDF's superiority would also extend to finer-grained performance indicators, such as preemption count, release and response-time jitter, resilience to transient overload. Recent work allowed EDF uniprocessor scheduling to be used in place of default FPS in Ada Ravenscar systems with unchanged application code: this development provides an interesting and practical avenue for empirical EDF-to-RM performance comparisons in an especially lean and efficient embedded setting. We leveraged that opportunity to develop a toolbox that enables quantitative comparison of EDF-to-RM uniprocessor scheduling with lightweight run-time tracing and offline analytic. In this work we present that toolbox and illustrate results we obtained with it, which shed new light on the presumed superiority of EDF to RM.

Removing bias from the judgment day: A Ravenscar-based toolbox for quantitative comparison of EDF-to-RM uniprocessor scheduling

The Robot Operating System (ROS/ROS2) is a de facto standard in many fields of robotics research, with increasing 
presence in the industry. RCLAda is a binding to the ROS2 framework that enables programming for ROS2 in pure 
Ada with seamless integration into the ROS2 workflow. 
During this tutorial, participants will learn how to install ROS2 and RCLAda, the necessary basic information about 
the ROS2 build system and RCLAda integration, and will program basic examples and simulated mobile robots of the 
kind used in the DARPA Subterranean Challenge

Programming mobile robots with ROS2 and the RCLAda Ada Client Library

This tutorial presents the fundamental notions that make the development of safety‐critical software different from 
the development of more casual software. It presents the context, the applicable standards, and the techniques used 
for achieving high reliability. It explains why Ada and Spark are especially suited for writing safety‐critical software. 
Although required for demanding applications, the general principles that are detailed can be applied to, and help 
improve, all kinds of software development.

Introduction to the development of safety‐critical software

The increasing computational capacity of cyber‐physical systems (CPS) due to more powerful processors and, 
especially, multi‐core systems has caused their implementation in control systems to have a greater impact than 
initially expected. One of the consequences is the inclusion of a large number of CPS in the development of cars, 
airplanes, trains, etc. The need to reduce consumption, weight, wiring, etc., in these systems has led to the integration 
of the multiple functions performed in a system in a few computing platforms. In this line of development, 
hypervisors play a relevant role in the design, development and certification of the system. Hypervisors allow to 
integrate in the same computing platform the different functionalities that are performed in dedicated CPS. The aim of 
this presentation is to show that the use of hypervisors for CPS development presents fundamental advantages in the 
design, development and certification with respect to more traditional CPS systems.

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