Time-driven programming
Encyclopedia
Time-driven programming is a computer programming
paradigm, where the control flow of the computer program is driven by a clock and is often used in Real-time computing
. A program is divided into a set of tasks (i.e., processes or threads), which has a periodic activation pattern. The activation pattern for all tasks is stored in a dispatch table, were the Least-Common-Multiple (LCM) of all period-times determines the length of the dispatch table
. The scheduler of the program dispatches all tasks according to the dispatch table, on which end a new instance of the dispatch table is initiated.
The programming paradigm is mostly used for safety critical programs, since the behaviour of the program is highly deterministic. No external events are allowed to affect the control-flow of the program, the same pattern (i.e., described by the dispatch table) will be repeated time after time. However, idle time of the processor is also highly deterministic, allowing for the scheduling of other non-critical tasks through slack stealing techniques during these idle periods.
The drawback with the method is that the program becomes static (in the sense that small changes may recompile into large effects on execution structure), and unsuitable for applications requiring a large amount of flexibility. For example, the execution time of a task may change if its program code is altered. As a consequence, a new dispatch table
must be regenerated for the entire task set. Such a change may require expensive retesting as is often required in safety critical systems.
Computer programming
Computer programming is the process of designing, writing, testing, debugging, and maintaining the source code of computer programs. This source code is written in one or more programming languages. The purpose of programming is to create a program that performs specific operations or exhibits a...
paradigm, where the control flow of the computer program is driven by a clock and is often used in Real-time computing
Real-time computing
In computer science, real-time computing , or reactive computing, is the study of hardware and software systems that are subject to a "real-time constraint"— e.g. operational deadlines from event to system response. Real-time programs must guarantee response within strict time constraints...
. A program is divided into a set of tasks (i.e., processes or threads), which has a periodic activation pattern. The activation pattern for all tasks is stored in a dispatch table, were the Least-Common-Multiple (LCM) of all period-times determines the length of the dispatch table
Dispatch table
In computer science, a dispatch table is a table of pointers to functions or methods. Use of such a table is a common technique when implementing late binding in object-oriented programming.-Perl implementation:...
. The scheduler of the program dispatches all tasks according to the dispatch table, on which end a new instance of the dispatch table is initiated.
The programming paradigm is mostly used for safety critical programs, since the behaviour of the program is highly deterministic. No external events are allowed to affect the control-flow of the program, the same pattern (i.e., described by the dispatch table) will be repeated time after time. However, idle time of the processor is also highly deterministic, allowing for the scheduling of other non-critical tasks through slack stealing techniques during these idle periods.
The drawback with the method is that the program becomes static (in the sense that small changes may recompile into large effects on execution structure), and unsuitable for applications requiring a large amount of flexibility. For example, the execution time of a task may change if its program code is altered. As a consequence, a new dispatch table
Dispatch table
In computer science, a dispatch table is a table of pointers to functions or methods. Use of such a table is a common technique when implementing late binding in object-oriented programming.-Perl implementation:...
must be regenerated for the entire task set. Such a change may require expensive retesting as is often required in safety critical systems.