Operating Systems for Reconfigurable Embedded Platforms: Online Scheduling of

Real-Time Tasks

-Ramkumar Shankar

Reference

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C.Steiger, H.Walder and M.Platzner, “Operating Systems for Reconfigurable Embedded Platforms:Online Scheduling of Real-Time Tasks” ,IEEE Transactions on computers vol 53, No.11, pp. 1393-1407 Nov. 2004

Web link: http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1336761

Outline

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Models and Limitations Practical OS

Target Architecture OS Modules

Scheduling Real-Time Tasks Techniques for 1D and 2D model

Results, Conclusion and Future Scope

Preliminaries

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Hardware task Digital circuit that has been preplaced and prerouted.

Functional characteristics transparent to the OS.

Structural characteristics visible to the OS. Area and timing requirements

1D and 2D area model

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Limitations of the area model

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Internal Fragmentation External Fragmentation Assumes Homogeneity of the RC Device.

OS takes up some of the special resources Tasks not relocatable

Target Architecture

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Partitioning of the RC device

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Operating system modules

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Operating System Modules on CPU

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Task Scheduler Resource Manager Task Preparation Unit Raw Task Repository COMM Driver C/R Driver

Operating System Modules on RC Device

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Task Controller Memory Management Unit(MMU) Device Drivers OS Bridge

Scheduling Real-Time Tasks

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Factors affecting the scheduling: arrival time, execution time, deadline Width, height

Constraints for the scheduler Scheduled tasks must not overlap in space and

time The tasks must meet the deadline

1D Horizon Technique

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Execution list (E) Maintains tasks (Ti), Finish time(fi) and

placement(xi) Reservation List (R)

Stores all tasks scheduled but not executing Horizon List(H)

Stores the position and time step at which the units become available.

1D Horizon Technique example

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1D Stuffing Technique

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Maintains Execution and Reservation lists Maintains a free space list.

Placement Algorithms and related issues

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Free space management Merging free spaces in Horizon Technique. Mimic future tasks for Stuffing Technique.

Strip Packing Scheduling tasks for 2D mesh – very costly

Evaluation

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Results

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Conclusion and Further Work

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Design issues for RC Hardware operating system.

Scheduling techniques for 1D and 2D area models

Scheduling tasks for non-real time systems Tasks with unknown execution times Tasks without deadlines Periodic tasks

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Questions

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