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Time-triggered systems can be viewed as a subset of a more general event-triggered (ET) system architecture (see event-driven programming).. Implementation of an ET system will typically involve use of multiple interrupts, each associated with specific periodic events (such as timer overflows) or aperiodic events (such as the arrival of messages over a communication bus at random points in time).
The scheduler is an operating system module that selects the next jobs to be admitted into the system and the next process to run. Operating systems may feature up to three distinct scheduler types: a long-term scheduler (also known as an admission scheduler or high-level scheduler), a mid-term or medium-term scheduler, and a short-term scheduler.
A scheduled-task pattern is a type of software design pattern used with real-time systems. [1] It is not to be confused with the "scheduler pattern".While the scheduler pattern delays access to a resource (be it a function, variable, or otherwise) only as long as absolutely needed, the scheduled-task pattern delays execution until a determined time.
The real-time scheduler developed in the context of the IRMOS Archived 2018-10-10 at the Wayback Machine European Project is a multi-processor real-time scheduler for the Linux kernel, particularly suitable for temporal isolation and provisioning of QoS guarantees to complex multi-threaded software components and also entire virtual machines.
Discrete event simulators run in virtual time, peeling events off the event queue as quickly as possible and advancing their notion of "now" to the scheduled time of the next event. Running the event simulator in "real time" instead of virtual time created a version of cron that spent most of its time sleeping, waiting for the scheduled time to ...
An event driven architecture may be built on four logical layers, starting with the sensing of an event (i.e., a significant temporal state or fact), proceeding to the creation of its technical representation in the form of an event structure and ending with a non-empty set of reactions to that event. [10]
Barring the scheduler from preempting tasks while they are processing kernel functions simplifies the kernel design at the expense of system responsiveness. The distinction between user mode and kernel mode , which determines privilege level within the system, may also be used to distinguish whether a task is currently preemptable.
A task switch can be explicitly triggered with a CALL or JMP instruction targeted at a TSS descriptor in the global descriptor table. It can occur implicitly when an interrupt or exception is triggered if there's a task gate in the interrupt descriptor table (IDT). When a task switch occurs the CPU can automatically load the new state from the TSS.