System-level Logical Execution Time

Abstract

Logical Execution Time (LET) is a timed programming abstraction, which features predictable and composable timing. It has recently gained considerable attention in the automotive industry, where it was successfully applied to master the distribution of software applications on multi-core electronic control units. However, the LET abstraction in its conventional form is only valid within the scope of a single component. With the recent introduction of System-level Logical Execution Time (SL LET), the concept could be transferred to a system-wide scope. This article improves over a first paper on SL LET, by providing matured definitions and an extensive discussion of the concept. It also features a comprehensive evaluation exploring the impacts of SL LET with regard to design, verification, performance, and implementability. The evaluation goes far beyond the contexts in which LET was originally applied. Indeed, SL LET allows us to address many open challenges in the design and verification of complex embedded hardware/software systems addressing predictability, synchronization, composability, and extensibility. Furthermore, we investigate performance trade-offs, and we quantify implementation costs by providing an analysis of the additionally required buffers.

A Platform Programming Paradigm for Heterogeneous Systems Integration

“…The choice of the RT programming paradigm mainly determines whether it is easy or difficult to translate the functional model into a correct implementation. It is desirable that an RT programming paradigm for CPSs features [8]: 1) time predictability;…”

“…Unfortunately, the most common RT programming paradigm-namely the BET paradigm [2], which models the variability of execution times observed on conventional platforms, has limited time predictability and does not feature data flow determinism, composability, and platform independence [8]. For this reason, the resulting implementation has to be extensively tested to assure that the implemented CPS fulfills the safety requirements.…”

“…The automotive industry has therefore introduced LET as an RT programming paradigm satisfying all of the above-named properties; it is now included in the AUTOSAR standard [9]. However, LET is applicable only in the scope of single-core and multicore processors, an extension for distributed systems was recently proposed under the name of SL LET [8] but only systems with register-like communication semantics between FBs have been discussed.…”

“…Synchronous-reactive programming relies on the ZET paradigm, while the BET paradigm is widely used in the field of classic scheduling theory [10]. The LET paradigm [10], [11], which connects these two worlds, is becoming increasingly popular in the domain of automotive RT software [8]. A relatively new approach is the reactor-based programming paradigm proposed in [12].…”

“…Moreover, this approach mixes application design and network design which are separate fields both from a technical and an organizational perspective. SL LET [8] extends the LET programming paradigm to distributed systems by introducing the notion of time zones and explicit LET interconnect tasks.…”