Schedulability Analysis(SCHA)

SCHA Overview
SCHA Execution
SCHA Settings
SCHA Result View
SCHA Configuration

SCHA Overview

Scheduleability analysis predicts whether execution can be completed up to the baseline set by each process based on priority, execution cycle, baseline, and longest execution time. You can use schedulability analysis to predict the maximum response time required for scheduling, the slack in the process, and so on.

SCHA Execution

The project must be open. If the project is not open, the Analysis menu is disabled.
SCHA does not require modules.

To create an analysis

Create an analysis accordint to Creating Analysis
In the Analysis Type window, select SCHA. Then, the Settings window will appear.

To setup the analysis

Set-up the analysis accoring to SCHA Settings, and click Apply button

SCHA Settings

Basic Info

Name: the name for this analysis.
Processor Name: the name of the processor.
WCS Time: the maximum context switch time.
Description: the description of this analysis.

Schedule Process List

Process: The unique name of the process. If the process names are the same, the existing information is overwritten.
Priority: Priority between processes. The lower the number, the higher the priority.
WCET: The longest time to follow the process. The longest time it takes from start to finish.
Deadline: The maximum time required from the start of a process to the end.
Perios: The cycle at which the process must be repeated

You can change the value directly in the table. In this case, the invalid value is displayed in red.
If invalid process information exists, the modifications cannot be reflected in the analysis.

Apply WCETA Results

Imports the results of Worst-case Execution Time Analysis.

Click Apply WCETA Result button.
Select results to import.
Click Apply button.

A WCETA result is matched to a process uging the task name and the root function name.
A new process is created when no process is matched for a WCETA result.

Edit Process Dialog

Opens when adding or editing an individual process.

If you make changes to the process, the OK button is activated only if the changes are made.

WCET, deadline, and period must meet the following formula:: WCET <= Deadline < Period
If the constraints are not satisfied, you will not be able to apply them.

SCHA Result View

Summary of analysis results

System slack: The range of free time for the entire process (%)

Analysis detailed results

Process: Process Name
Priority: Cross-process priority (lower numbers have higher priority)
Capacity: Longest execution time (the longest time it takes from the start of a process to the end of execution)
Deadline: The maximum time required for a process to start and end execution
Period: The period during which the process runs periodically
WCRT: Maximum response time
Slack Time: Process Slack

Slacks are the percentage by which we can increase the execution times of some operations while keeping the system schedulable (for positive slacks) or the percentage by which we have to decrease the execution times to make the system schedulable (for negative slacks).
If the Slack Time of each process is positive, it represents the maximum amount by which the longest execution time of that process can increase while still allowing the entire system to be scheduled. If it's negative, it indicates the minimum amount the longest execution time of that process needs to be reduced for the entire system to become schedulable.
The lowst value of a process' Slack Time is "-Capacity", which means the system cannot satisfy schedulability regardless of the process' worst-case execution time.

SCHA Configuration

Default Values

Default WCS(ns) is default Worst-case Context Switching time in nano-second.
Default process nameis used as the process name when adding a new process
Default WCET(ns) is used as the WCET when adding a new process
Default period(ns) is used as the Period when adding a new process
Default deadline(ns) is used as the Deadline when adding a new process
Default priority is used as the priority when adding a new process

Changing default values does not affect process configuration of existing analyses.