Worst-Case Execution Time Analysis(WCETA)

1. WCETA Overview
2. WCETA Execution
3. WCETA Settings
4. WCETA Result View
5. WCETA Configuration

WCETA Overview

Worst-Case Execution Time(WCET)

The duration of a particular program is the time it takes from the start of the program to the end of execution. The duration of the program depends on which path is performed on different possible paths. Program performance time will also affect the hardware performance on which the program performs. Worst-Case Execute Time (WCET) means the longest of these hours required to perform on a particular hardware without being interrupted by other programs (processors, tasks, etc.).

The WCET of a program is 10ms, which means that the program has no more than 10ms of time.

Worst-Case Execution Time Analysis(WCETA)

The goal is to predict (measure or calculate) the longest and most accurate time to be followed. The longest-time analysis techniques include dynamic and static techniques.

Dynamic analysis

Dynamic techniques are a method of measuring by performing a program directly. Perform the program's performable path and measure its time to select the largest of the measured times as the longest action time. This technique is time-consuming and expensive because the program actually needs to run multiple times. In addition, it is difficult to apply if the number of executable paths increases. The paths a particular program can perform have a number of different cases, and in the worst case, the number of paths that can be performed occurs in a limit.

Therefore, typically, you will extract the typical run paths and add additional correction values to the longest path of them to choose the longest execution time

However, the safety of the results is not guaranteed in that there may be routes that have not been executed that take longer than the longest measured time.

Static Analysis

Static techniques are a method of analyzing program structures to predict the longest time to follow. HKSAT calculates the longest performance time based on the IPET technique among static techniques.

Static analysis requires the analysis of the characteristics of the target hardware along with the program control structure. This is because the duration depends on the nature of the hardware that is performed even with the same program.

Static techniques use abstraction techniques to ensure safety during the calculation process, so the longest processing time calculated by them will have a value greater than the actual longest performance time. Therefore, the actual performance time is guaranteed to be no greater than the longest calculated carry-out time.

For static techniques, the more information you extract from the program structure, the less difference between the calculated value and the actual value. HKSAT automatically extracts program flow information to perform calculations, and if necessary, users can add information to improve the accuracy of the results.

WCETA Execution

To create an analysis

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

To setup the analysis

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

To execute the analysis

• See Executing Analysis

To see the result

• See Viewing Analysis Result

Generating Analysis Report

• See Generating Analysis Report

WCETA Settings

Analysis Basics

• Analysis Name: Enter a name for the analysis.
• Target Module: Select the module to be analyzed.
• Add Module button: You can add a new module to use.
• Compile Options: Specify the compile options to apply when generating the binary for analysis.
• Compile Options Edit Button: Displays the compile options editing screen.

Root Function

• Left List: Shows the functions available for selection in the module.
• Right list: Shows the function selected as the root function in the module.

• Function: The name of the function
• Caller IN: The number of functions that call that function.
• Callee OUT: The number of functions that the function calls.

Function Execution Time Assumption

• Function: The name of the function that exists in the target module.Function: The name of the function that exists in the target module.
• Is External?: You cannot specify whether an external option is arbitrary, and it is designated as an external only if there is no source code. The external function must provide the assumed value of the cycle. (Even if it is a system function, it does not have source code and can be specified as an external function.)
• Is Assumed?: Time assumptions or not. If you want a time family, check the Time Family check box, or enter a positive number for the assumed number of cycles.
• Assumed Cycle: Assumed number of cycles. The number of assumed hours of carrying out for the function converted to cycles. -1 is displayed if the time assumption is not made.

• Default: The default value used for the external action performing assumption. You can change it in preferences.
• Apply library function time Home: Gets the longest performance time for a system API that has been prepared by performing in advance.

Assume the maximum number of iteration of loops

• Circular statement ID: ID for the loop present in the module. The tool granted.
• Function: Displays the function name and the defined file.
• Assumed: Whether the loop is assumed. If automatic extraction is successful, it is not checked, otherwise it is checked.
• Assumption: Displays the maximum number of times the loop can be repeated, the extracted value if automatic extraction is successful, and the default value if it fails.

• Default: The default value used for the external action performing assumption. You can change it in preferences.
• Source code: Whether to show the source code corresponding to the circular statement selected in the list.

Target Settings

To setup the target

• The processor settings screen depends on the compiler set up in the project.
• For processors that support pipeline analysis, display options to enable it. If you choose to use a pipeline architecture, the WCET is calculated based on the cycles saved by pipeline application, otherwise the WCET is calculated assuming that all pipelines are not applied.

Criteria

It displays the duplicate code evaluation criteria of the Hyundai/Kia ES specification.

WCETA Result View

Summary Result

Displays a summary of the number of root items analyzed and the number of assessments.

Detailed results

• Function: root functions
• Unit cycle: The number of CPU cycles required to perform a function once.
• Assumed: Whether the function is assumed to be in the time of action.
• Execution Count: If the longest execution time is required, the number of times the function is executed
• Total Cycles: The sum of cpu cycles spent for the function to occur.
• WCET: Displays the longest time of a function as a time
• Verdict: Pass, Conditional Pass, or Fail

Check WCETA Bottleneck Nodes

After performing the analysis, you can check the analysis results in the graph view, and you can easily check the nodes that take a lot of time through color.

• Click the Show Current Analysis Result button (refer to the Graph View Toolbar) in the Function Call Graph and Control Flow Graph to display the analysis results on the graph.
• You can check the results by clicking on the analysis results in the project view.
• In addition, you can check the result by clicking the value of the longest running time (WCET) in the result view.

• At the top of the node, the cycle and the number of executions are displayed and displayed in the form of [cycle x times].

• When it is displayed as [(cycle1 + cycle2) x times], cycle1 is the cycle value of the node, and cycle2 is the unit cycle value of the function called from the node.

WCETA Configuration

Default Values

• Default assumed function cycle: Time Assumption Defaults for External Functions
• Default assumed loop bound: Loop bound default
• Warn recursive function during the analysis: Whether the recursive number is alerted during analysis

Code View Highlight Colors

• Functions with WCET is the color for WCET analyzed functions in code blocks in the code view.