Distributed Timed Multitasking - A Model of Computation for Hard Real-Time Distributed Systems

Abstract

The paper presents a new type of system architecture for distributed embedded systems, whereby a system is composed from embedded actors that communicate transparently by exchanging labeled messages (signals), independent of their allocation onto network nodes. Signals are exchanged at precisely specified time instants in accordance with the concept of Timed Multitasking, whereby actors can be viewed as real-time tasks with eventtriggered input and output drivers activated by timing or external events. The combination of actors, signal-based communication and timed multitasking has resulted in a new operational model-Distributed Timed Multitasking (DTM). The latter has been used to derive a task execution model and requirements specifications for a real-time kernel, which have been used to develop the timed-multitasking version of the HARTEXkQWiQX. In this context, the paper presents a discussion of specific implementation issues related to the execution of periodic and sporadic tasks under DTM.

Component-Based Design of Safe Real-Time Kernels for Embedded Systems

“…This has resulted in a number of advanced solutions: The detailed presentation of the above features goes beyond the scope of this paper. More information can be found in [8] - [10]. The following discussion gives an overview of HARTEX component functionality and specific techniques, such as Boolean vector processing, which is an outstanding feature of HARTEX components.…”

“…That is why it is not quite suitable for time-critical and safety-critical applications. This has stimulated the development of advanced models, such as the Timed Multitasking model of computation [6] and its enhanced version -Distributed Timed Multitasking [10], which has been developed in the context of the COMDES framework [7].…”

A Timed Multitasking Architecture for Distributed Embedded Systems

“…The latter is determined by the event type, e.g. release task and register its input drivers with the Task I/O Manager -with a task release event, or register output drivers if the task has finished before its deadline -with a deadline event [12].…”

“…This has motivated the development of an enhanced operational model denoted as Distributed Timed Multitasking (DTM), which extends timed multitasking to distributed systems in the context of actor-based architecture and transparent signal-based communication, as defined in COMDES-II [12]. This paper presents an improved version of the above model, featuring complete separation of computation and communication, as advocated by embedded system design experts [15], [19].…”

“…These communicate with each other and the outside world via an interface shell consisting of input and output signal drivers. Accordingly, the node-resident kernel has to manage separately the execution of actor tasks and signal drivers, in response to incoming events [12].…”