September 23, 2019 Sam Siewert

CEC 450Real-Time Systems

Lecture – RM Analysis Examples with Cheddar

Using Cheddar [Basics]Download for Windows [here] or Use “T” DriveUse “Edit” to Start

1. Start with Update Processors

2. Add it3. Update Address Spaces,

Add it4. Update Tasks, Add S1…Sn

5. Note Cheddar Runs over LCM

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Newer Versions of the ToolCheddar 2.1 for Windows [on T drive]– Examples-2.1 for CEC450– Download of Cheddar-2.1 for win32

Cheddar 3.0 for Windows [on T drive]– Examples-3.0 for CEC450 [Tested and ported from 2.1]– Cheddar 3.0 User’s Guide - Here

Cheddar 3.1 for Windows [Download or T drive]– Examples-3.1 for CEC450 [Tested and ported from 3.0]– Cheddar 3.1 User’s Guide - Here

Cheddar 3.1 for Linux [Download]– Run on Jetson or NUC [I have not tested yet]

Local copy - http://mercury.pr.erau.edu/~siewerts/cec450/design/Cheddar-tools/

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Use Windows 3.1

Version

Cheddar 3.1 is Latest (2019)Cheddar 3.1 has a new “look and feel”– Run it from -

T:\CEC450\Cheddar-Tools\Cheddar-3.1-win32-bin

– Examples are here -T:\CEC450\Cheddar-Tools\Cheddar-Examples-3.1

Load an XML Example

Hit the Gray Start Button (it is NOT grayed out)

QUICK START document

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#1 - Run

#2 - Browse to Example

#3 - Hit Play and OK

#4 - Review analysis and

change parameters and

re-run as needed

Simulation 2.1Hit Simulation button to StartCalculates LCM, Runs, Produces Timing Diagram and Summary

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Simulation Button

Timing Diagram

Summary – Note theconclusion “seems”

Simulation 3.1

Simulation button looks like grayed out arrowLoad an XML configuration and hit it anyway!E.g. Example-9, with LCM=24 - Check match

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Example 9 Service Freq f f0 multiple Period T WCET Utility LCM/TS1 0.166667 4 T1 6 C1 1 U1 16.67% LCM = 24 4S2 0.125 3 T2 8 C2 2 U2 25.00% 3S3 0.083333 2 T3 12 C3 4 U3 33.33% LUB = 75.68% 2S4 0.041667 1 T4 24 C4 6 U4 25.00% Utot = 100.00% 1

RM Schedule 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24S1

S2

S3

S4

Simulation button in 3.1

v3.1 - Building up a new XML file for Ex 9File New, Use “Edit” to Start

1. Hardware, Core, Add it

2. Hardware, Processor, Select Core from above, Add it

3. Software, Address Space, Add it

4. Software, Tasks, Add S1…Sn

5. Run it!6. Compare7. Note Cheddar

Runs over LCM

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Select Hardware, Software or Deployment#1

#2

#3

#4

#5

Feasibility TestHit Feasibility button to TestFor RM Policy, Cheddar Uses the RM LUBFor All Policies, Cheddar Provides Worst-Case Analysis

Change with “Edit” and Update Processors to EDF

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RM Policy Example

Run Again with EDF to ComparePriorities are Dynamic, So Just Change Processor Scheduler Policy, Re-Run Simulation and Feasibility

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Note EDF

Note LLF

Example-0 Timing DiagramRM, EDF, LLF Succeed, 73.33% CPU Utilization

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Example 0 T1 2 C1 1 U1 0.5 LCM = 30T2 10 C2 1 U2 0.1T3 15 C3 2 U3 0.133 Utot = 0.733

RM Schedule 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15S1S2S3EDF ScheduleS1S2S3TTDS1 2 X 2 X 2 X 2 X 2 X 2 X 2 X 2S2 10 9 X X X X X X X X X X X X XS3 15 14 13 12 11 10 X X X X X X X X X

Example-0 Cheddar RTSSDownload Cheddar RT Analyzer, Example-0 XML

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Cheddar Simulates over LCM (Hyperperiod)

26.66% Free Time

Example-1 Timing DiagramRM FAILS, EDF, LLF Succeed, 98.57% CPU Utilization

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Example 1 T1 2 C1 1 U1 0.5 LCM = 70T2 5 C2 1 U2 0.2T3 7 C3 2 U3 0.285714 Utot = 0.985714

RM ScheduleS1 ????????S2 ????????S3 LATEEDF ScheduleS1S2S3TTDS1 2 X 2 X 2 X 2 X 2 XS2 5 4 X X X 5 4 3 X XS3 7 6 5 4 3 2 X 7 6 5LLF ScheduleS1S2S3LaxityS1 1 X 1 X 1 X 1 X 1 XS2 4 3 X X X 4 3 2 X XS3 5 4 3 2 2 1 X 5 4 3

Example-1 Cheddar RTSSRM Not Feasible by LUB or by Inspection over LCM

EDF?

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Example-1 Cheddar RTSSEDF Simulation over LCM of 70

LLF Simulation over LCM of 70

Worst Case Feasibility Test– Fixed Priority (RM Policy) FAILS LUB and WC Feasibility Test

(Scheduling Point or Completion Test)– Dynamic Priority Succeeds by Two Methods

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Example 9 – RM PolicyHarmonic Services with 100% CPU Utilization

Preemptions – 3 in Total: – @6 S1 preempts S3– @12 S1 preempts S4– @16 S2 preempts S3

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Example 9 harmoni multiple LCM/Tf3 0.167 4 T1 6 C1 1 U1 0.167 LCM = 24 4f2 0.125 3 T2 8 C2 2 U2 0.25 3f1 0.083 2 T3 12 C3 4 U3 0.333 2f0 0.042 1 T4 24 C4 6 U4 0.25 Utot = 1 1

RM Schedule 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24S1S2S3S4

Example 9 – Cheddar RM WC Analysis and Simulation

Run WC analysisRun Simulation to Graph over Longest T or LCM

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Example 9 – RM SimulationAutomates Hand SimulationSimpler Modification for Multiple CPUs, Policies, etc.

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Example 9 – EDF SimulationNo Difference from RM in SimulationTies Could Be Broken Randomly [Most Often Favor Highest Frequency – Same as RM]Worst-Case Analysis However Shows “task set is schedulable”

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EDF ScheduleS1S2S3S4TTDS1 6 X X X X X 6 X X X X X 6 X X X X X 6 X X X X XS2 8 7 6 X X X X X 8 7 X X X X X X 8 7 X X X X X XS3 12 11 10 9 8 7 6 5 X X X X 12 11 10 9 8 7 6 5 X X X XS4 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

TTD metric for dispatch results in “ties”, noted in red

LLF Schedule 2S1S2S3S4LaxityS1 5 X X X X X 5 X X X X X 5 X X X X X 5 4 3 X X XS2 6 5 5 X X X X X 6 6 X X X X X X 6 5 5 4 3 2 X XS3 8 7 6 5 5 5 5 4 X X X X 8 7 7 6 6 5 4 4 3 2 1 XS4 18 17 16 15 14 13 12 11 10 9 8 8 8 7 6 6 5 5 4 3 3 2 1 0

Example 9 – LLF SimulationLLF Hand Sim Tedious (Laxity = TTD – Time_to_go)Much Different than RM or EDFAssume Ties Favor Highest Frequency Service? - YES

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Review Remaining Exampleshttp://mercury.pr.erau.edu/~siewerts/cec450/documents/Timing_Diagrams_Updated_2018/

As Noted in Liu and Layland, Static Priority Policy May Not be Feasible in Cases where Dynamic Priority Policy is Feasible

Are Feasibility and Safety Synonymous?

Is it Wise to have Zero Margin?

Have We Accounted for Context Switch Overhead and ISR Latency? Sam Siewert 20

Cheddar ReferencesHelp, Scheduling ReferencesReferences Used to Build Cheddar – HereGeneral References - Here

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