Cheddar – Real Time Simulator

Scheduling with task dependencies

Task Dependencies

Meaning…… resources shared by several tasks (ex :

semaphores)

precedencies relationship between several tasks (like constraints between the end of a task and the start of another one).

Types Of Tools

Shared resources analysis tools

Task precedencies analysis tools

Buffer analysis tools

Task precedencies analysis toolsWith Cheddar, dependencies are links

between at least two tasks

Three different types of dependencies Precedencies Message and Buffer dependencies

Types Of Dependencies

Precendencies express order constraints between end or begin of task execution.

Message dependencies expressed relationship between a sender and a receiver task of a given message.

Buffer dependencies expressed relationship between producer and consumer of data in a given buffer.

Precedencies Graph

Tasks -> circles.

Messages -> rectangles.

Buffers -> envelopes.

Typical Precedencies Graph

An Example

Different Parameters

Periodic Tasks - T1(4,1), T2(5,2), T3(5,1) Aperiodic Task – T4(10,2) EDF Scheduler Preemptive Precedence: T3 T2

Precedence Graph

Simulation Result

Some Limitations…

Capacity Is Integer Only.

Aperiodic Job Cannot Be Done On Rate Monotonic Scheduler.

For Task Precedencies, Tasks Must Have Equal Periods…

Project Files

Information stored during a simulation can be saved into Project Files

A project file is a XML file Correct structure of the Project Files can

be checked by the tool dump_sysdump_sys just read, parses and displays

to the screen the content of a XML Cheddar project file.