Luca Fossati

A Dual-Criticality Memory Controller (DCmc): Proposal and Evaluation of a Space Case Study

Multicore Dual-Criticality systems comprise two types of applications, each with a different criticality level. In the space domain these types are referred as payload and control applications, which have high-performance and real time requirements respectively. In order to control the interaction (contention) among payload and control applications in the access to the main memory, reaching the goals of high bandwidth for the former and guaranteed timing bounds for the latter, we propose a Dual-Criticality memory controller (DCmc). DCmc virtually divides memory banks into real-time and high-performance banks, deploying a different request scheduler policy to each bank type, which facilitates achieving both goals. Our evaluation with a multicore cycle-accurate simulator and a real space case study shows that DCmc enables deriving tight WCET estimates, regardless of the co-running payload applications, hence effectively isolating the effect of contention in the access to memory. DCmc also enables payload applications exploiting memory locality, which is needed for high performance.

Deconstructing bus access control policies for Real-Time multicores

Multicores may satisfy the growing performance requirements of critical Real-Time systems which has made industry to consider them for future real-time systems. In a multicore, the bus contention-control policy plays a key role in systems performance and the tightness of the Worst-Case Execution Time (WCET) estimates. In this paper we develop analytical models of the contention that requests from different tasks running in different cores suffer for the two most-used contention control policies: Time-Division Multiple Access (TDMA) and Interference-Aware Bus Arbiter (IABA), which allows us to compare them. We further show the benefits of having such models for real-time system designers and chip providers. Our results show that WCET estimates obtained with TDMA are slightly (2%) tighter than those obtained with IABA, at the cost of knowing the exact cycle at which every access of every task accesses the bus. However, average performance is 10% worse with TDMA than with IABA. Overall, IABA is the most appealing contention-control policy since it allows achieving tight WCET estimates and high average performance with little burden for the user.

The future of embedded systems at ESA: Towards adaptability and reconfigurability

Embedded devices used in the space industry have to face stringent requirements imposed by their deployment environment, namely high reliability, limited resources, and challenges in heat dissipation. In addition, to make matters worse, the demand for advanced processing capability is growing steadily to meet future exploration and deep space mission requirements. At the European Space Agency, ongoing studies are focusing the use of reconfigurable and adaptable systems to help finding solutions to the aforementioned issues as well as to how reconfigurable systems can aid in mission cost reductions. After giving a general overview of the efforts spent in this direction, this paper presents two concrete examples of on going research activities funded by the European Space Agency.

A reliable fault classifier for dependable systems on SRAM-based FPGAs

This paper presents an algorithm for the discrimination of faults in FPGAs based on their recovery possibility; some faults can be recovered by reconfiguring the faulty part of the device, others have a destructive effect. After classification has been carried out, the suitable fault recovery strategy is applied, with the final aim of enabling the exploitation of FPGAs, in particular SRAM-based ones, for critical applications, such as the ones in the space environment. In this scenario, we investigate the reliable implementation of the fault classification algorithm, that can be so integrated in an overall reliable system.

Probabilistic timing analysis on time-randomized platforms for the space domain

Timing Verification is a fundamental step in real-time embedded systems, with measurement-based timing analysis (MBTA) being the most common approach used to that end. We present a Space case study on a real platform that has been modified to support a probabilistic variant of MBTA called MBPTA. Our platform provides the properties required by MBPTA with the predicted WCET estimates with MBPTA being competitive to those with current MBTA practice while providing more solid evidence on their correctness for certification.

AHRB: A high-performance time-composable AMBA AHB bus

Hard real-time systems are moving toward complex systems comprising chips with different IP components connected with standard buses. AMBA is one of the most used bus interfaces and has already been included in processors in the real-time domain. However, AMBA was not designed to provide time composable Worst Case Execution Time (WCET) estimates, which are desirable to reduce timing validation and verification costs. This paper analyzes and extends the AMBA Advanced High-performance Bus (AHB) specification to enable time-composable WCET estimates by design. Concretely, (1) we analyze in detail the AMBA AHB in the context of hard real-time systems proving that it fails to provide time composability; (2) we define a restricted subset of AMBA AHB features, named restricted AHB (resAHB), that allows deriving time-composable, yet not tight, WCET estimates; and (3) we define an extension of resAHB, named Advanced High-performance Real-time Bus (AHRB), that includes the timing constraints in the specification. This allows deriving time-composable and tight WCET estimates. Our results show that AHRB can provide 3.5x tighter estimates than resAHB on average for EEMBC benchmarks.