Monitor variable changes, send a LIN signal, and manually set an incorrect checksum

Thanks to Alex for providing the example

CAPL Analysis

The provided CAPL example is as follows:

on envVar EnvChecksumError  
{
  if (1 == getValue(EnvChecksumError))  // Checksum err
  {
     write("Checksum err");
    linSetManualChecksum(frmAC_1, linGetChecksum(frmAC_1) - 1);
    //linSetManualChecksum(frmReq, linGetChecksum(frmReq) - 1);
    
    //output(frmReq);
    output(frmAC_1);
  }
}

CAPL Code Walkthrough

The core logic of this CAPL script is:

1. Environment variable listen: on envVar EnvChecksumError listens for changes to the EnvChecksumError environment variable
2. Condition check: When the variable value is 1, trigger error injection logic
3. Error injection:
   • linGetChecksum(frmAC_1) obtains the correct checksum value
   • linSetManualChecksum(frmAC_1, checksum - 1) manually sets an incorrect checksum (minus 1)
   • output(frmAC_1) sends a LIN message with an incorrect checksum

NOTE

• Technical note: The LIN bus checksum mechanism is critical for ensuring data integrity. By deliberately setting an incorrect checksum, you can test the error handling capability of the receiving node.
• Test equipment: We choose LinCable as the testing device because it can flexibly inject various LIN errors.

Variable Configuration in EcuBus-Pro

Step 1: Create an environment variable

To implement variable watching, first create the corresponding environment variable in EcuBus-Pro. Environment variables are an important bridge between scripts and the user interface.

Path: Others → Variable → Add Variable

Key variable settings

• Name: EnvChecksumError (must match the variable name in the CAPL script)
• Type: Integer
• Initial value: 0 (normal state)
• Range: 0–1 (0 = normal, 1 = trigger error)

Step 2: Verify the variable

After creation, you can view and manage the variable in the variable list:

In the variable list, you can:

• View the current value of the variable
• Modify the variable configuration
• Delete unnecessary variables
• Export/Import variable configurations

UI Control Panel Configuration

Step 3: Create the control panel

To dynamically control the variable value during testing, create a user interface panel. Through the graphical interface, testers can switch the variable state in real time without modifying code.

Path: Home → Panel → Add Panel

Panel design recommendations

• Use a switch or toggle control to represent the 0/1 state
• Set descriptive button text such as "Send checksum error frame"
• Lay out the controls clearly to ensure intuitive operation

Step 4: Bind the variable

After creating the panel control, bind it to the environment variable to establish a two-way data association between the control and the variable.

Binding settings

• Target variable: Select the previously created EnvChecksumError variable
• Control type: Boolean Switch
• Mapping: OFF = 0 (normal), ON = 1 (trigger error)

Step 5: Preview the UI

After configuration, you can preview the final user interface:

UI highlights

• Display the current variable state in real time
• Support one-click toggle operations
• Provide intuitive visual feedback

EcuBus-Pro TypeScript Implementation

Step 6: Write the TypeScript script

Now we convert the CAPL logic into an EcuBus-Pro TypeScript script. Compared with CAPL, TypeScript provides better type safety and a better development experience.

Util.OnVar("EnvChecksumError", ({ value }) => {
    if (value == 1) {
        console.log("Checksum err");
        const msg: LinMsg =
        {
            frameId: 0x3c,
            direction: LinDirection.SEND,
            data: Buffer.from([0x60, 0x01, 0xb5, 0xff, 0xff, 0xff, 0xff, 0xff]),
            checksumType: LinChecksumType.CLASSIC,
            lincable:{
                checkSum:3,// wrong checksum
            }
        }
        output(msg);
    }
});

Detailed Script Walkthrough

1. Variable watch mechanism

Util.OnVar("EnvChecksumError", ({ value }) => {
    // Callback, triggered when the variable value changes
});

• Util.OnVar() is the variable watch API provided by EcuBus-Pro
• Destructuring assignment is supported to directly obtain the value parameter
• The callback is automatically triggered when the variable value changes

2. LIN message construction

const msg: LinMsg = {
    frameId: 0x3c,              // LIN frame ID (hex)
    direction: LinDirection.SEND, // Send direction
    data: Buffer.from([...]),    // Data byte array
    checksumType: LinChecksumType.CLASSIC, // Checksum type
    lincable: {
        checkSum: 3             // Manually set incorrect checksum
    }
}

3. Key parameter descriptions

Parameter	Description	Example
frameId	LIN frame identifier	0x3c (60)
direction	Message direction	LinDirection.SEND
data	Data payload	8-byte data array
checksumType	Checksum type	CLASSIC or ENHANCED
checkSum	Manual checksum	3 (intentionally incorrect)

4. Error injection principle

Under normal circumstances, the checksum of a LIN message should be calculated automatically based on the data content. In testing scenarios, we manually specify an incorrect value (e.g., 3) via lincable.checkSum to simulate a transmission error and test the receiving node’s error-handling capability.

Test Run and Verification

Step 7: Run the test

After completing all configurations, run the test. Use the toggle button on the UI to control the variable value and observe the sending of LIN messages.