Partitioned software architectures were conceived to fulfill security and avionics requirements where predictability is extremely important. Both, the availability of new processors and an increased necessity of security, have opened new possibilities to use efficiently this approach. Avionic industry has consolidated the Integrated Modular Avionics (IMA) as a solution to manage the software growth in functionality and in efficiency. Now, the aerospace sector is adapting these concepts on its developments. One of the solutions used to achieve partitioned systems is based on virtualisation techniques. In this paper we present XtratuM, a bare-metal hypervisor which implements para-virtualization and dedicated device techniques. XtratuM provides a virtual machine that is 'near' the native one. It permits to execute a set of partitions, containing each one an operating systems and its applications. Security is based on the temporal and spatial isolation properties provided by the hypervisor. This paper describes the main design criteria used to achieve temporal and spatial partition isolation and an approach to extend the trusted environment from the hardware level to the hypervisor level in order to verify the temporal and spatial isolation properties

Dynamic storage allocation (DSA) algorithms play an important role in the modern software engineering paradigms and techniques (such as object oriented programming). Using DSA increases the flexibility and functionalities of applications. There exists a large number of references to this particular issue in the literature. However, the use of DSA has been considered a source of indeterminism in the real-time domain, due to the unconstrained response time of DSA algorithms and the fragmentation problem. Nowadays, real-time applications require more flexibility: the ability to adjust system configuration in response to workload changes and application reconfiguration. This aspect adds value to the definition and implementation of dynamic storage allocation algorithms. Considering these reasons, DSA algorithms with a bounded and acceptable timing behaviour must be developed to be used by real-time operating systems (RTOSs). In this paper a DSA algorithm called two-level segregated fit memory allocator (TLSF), developed specifically to be used by RTOS, is introduced. The TLSF algorithm provides explicit allocation and deallocation of memory blocks with a temporal cost Θ(1).

Real-time systems are often designed using a set of periodic tasks. Task periods are usually set by the system requirements, but deadlines and computation times can be modified in order to improve system performance. Sensitivity analysis in real-time systems has focused on changes in task computation times using fixed priority analysis. Only a few studies deal with the modification of deadlines in dynamic-priority scheduling. The aim of this work is to provide a sensitivity analysis for task deadlines in the context of dynamic-priority, preemptive, uniprocessor scheduling. In this paper, we present a deadline minimization method that computes the shortest deadline of a periodic task. As undertaken in other studies concerning computation times, we also define and calculate the critical scaling factor for task deadlines. Our proposal is evaluated and compared with other works. The deadline minimization proposed strongly reduces jitter and the response time of control tasks, which can lead to a significant improvement in system performance.