Analytical Characterization of End-to-End Communication Delays With Logical Execution Time

Abstract

Modern automotive embedded systems are composed of multiple real-time tasks communicating by means of shared variables. The effect of an initial event is typically propagated to an actuation signal through sequences of tasks writing/reading shared variables, creating an effect chain. The responsiveness, performance and stability of the control algorithms of an automotive application typically depend on the propagation delays of selected effect chains. Indeed, task jitter can have a negative impact on the system potentially leading to instability. The Logical Execution Time (LET) model has been recently adopted by the automotive industry as a way of reducing jitter and improving the determinism of the system. In this paper, we provide a formal analysis of the LET model for real-time systems composed of periodic tasks with harmonic and non-harmonic periods, analytically characterizing the control performance of LET effect chains. We also show that by introducing tasks offsets, the real-time performance of non-harmonic tasks may improve, getting closer to the constant end-to-end latency experienced in the harmonic case. Further, we present a heuristic algorithm to obtain a set of offsets that might reduce end-to-end latencies, improving LET communication determinism. Finally, we apply this technique to an industrial case study consisting of an automotive engine control system.

LET Paradigm Scheduling Algorithm Considering Parallel Processing on Clustered Many-core Processor

“…The LET section must be equal to or longer than the latency of the task, and typically, the task period is adopted as the length of the LET section [6], [7]. Therefore, as shown in Fig.…”

“…The adaptation of the LET paradigm to AUTOSAR models has LET and DAG Schedulability by the many-core processor RTAS 2018 [37] SIES 2018 [38] TCAD 2018 [7] ECRTS 2017 [22] ISED 2018 [6] DS-RT 2020 [39] Our paper received much attention in order to improve the determinism of automotive systems [37], [38], [40], [41]. Biondi et al [37] described the application of the LET paradigm to the AUTOSAR model for implementation in actual automotive systems using multi-core platforms.…”

Pushing Mechatronic Applications to the Limits via Smart Motion Control

“…To ensure predictably mastering the parallel computing bandwidth provided by modern computing systems, it is essential to equip existing real-time operating system via scheduling approaches to decrease the interference due to the simultaneous execution of many tasks on individual cores, concurring for the access to the shared HW and SW resources [17,[53][54][55][56]. In contrast to that, industrial applications need the chance to execute the actual control code base with little modification, therefore, we propose the usage of a hypervisor level to isolate different domains trying to provide enhanced guarantees.…”

Developing AL-ARQ Module for Automatic Measurement of One-Way Data Transmission Delay

“…Real-time traffic requires strong bounds on packet delay and Jitter, the effect of those components appears at different stages of packet transmission. An analysis of those different components is essential tounderstand the overall cause of the irregular arriving interval of packets and determining a betterQoS performances [6,7]. The different types of delays encountered in a packet-switched network are shown in (Fig.…”