Using an External Data Source

The External Data Source property of a DataBlock is a useful way of storing test data in an external file rather than in an MxVDev TestCase. It is also an easy way to import data for a single signal. Using an external data source has several advantages:

•It is a more efficient way of storing data. An external CSV file is smaller than an equivalent XML TestCase (.mxc) file .

•Multiple TestCases can use a single data file.

•It is useful way to reduce memory usage when working large data sets such as image data.

External data may come from many sources.  For example, you might:

•Have test data created from a simulation run in Simulink

•Capture test data from test stand instrumentation, such as a digital scope, or CANoe

•Create your own test data using an Excel spreadsheet

•Create a data file from internal MxVDev signal data

•Have data exported from a TestCase

The External Data Source property allows you to use an external data file to specify the commanded values or expected results for a particular Signal.

Notes:

•When you have a DataBlock with an external data source, if you re-select the Data Location option as Internal, the data that was read from the file remains in the TestCase as a sequence of Transitions.  This is one way to import data from a file.

•When loading external data, only the transitions in the selected DataBlock's range are loaded.

•The times in the external data file should be relative to the DataBlock's start time.

hmtoggle_plus1Selecting the External Data Source

To use external data for a DataBlock:

1.Move the cursor over the Signal Plot area to display the name of the DataBlock in a pop-up bubble.

2.Right-click to display the DataBlock menu:

DataBlock_menu

3.Select Properties to display the DataBlock Properties dialog shown below.

4.Click External in the Data Location panel to display the External Data Source Properties panel.

CAN_external_data_source

Use the DataBlock Properties form to provide the following:

•Data Location: Check External to attach an external data file to this Signal. If you attach external data to a signal, and then check Internal, the Signal will retain the values that were read from the file. In this way, you can import data from a data file directly into a TestCase, and you will no longer require the external data file.

•Data Source File: Click 3dots_button to select the file containing the test data.

•After No More Data in Source File: Choose how to behave if the data file is not long enough to specify the value of the signal at every step in the TestCase.  You can specify:

oHold Last Value: The signal maintains its value at the last step for which there was data.  Note that for Message Signals, selecting this option results in no more messages being generated after the external data has been used.

oRepeat Data Set: When the end of the file is reached, return to the beginning and repeat the content of the data file for subsequent steps.

The View Data File button brings up the associated data file for inspection.

Note: If your file contains quotes, Excel is not recommended for editing as it may add or remove quotes unexpectedly.

If the amount of data in the data file exceeds the current number of samples in the TestCase's active range, the system displays:

Conver1

Choosing Yes expands the active range by moving the stop point. Choosing No leaves the stop point where it is, which means that not all data in the file will be used when the associated test case is executed.

Note that an output signal can also be loaded with data from an external data source.

File Format

Two file formats are supported for importing signal values:

There is the file format produced by the Save to External Data File command. It may also be created in other ways. The format requirements are:

•There is one line in the file per transition (one line per message for message type signals).

•Entries on a line are separated by commas (CSV) or, if selected in the Delimiter field, semicolons.

•The first entry on the line is the Time in seconds (in decimal notation) for that data point.

oFor Numeric Signals there is just one more value on the line. This is the value of the Signal at that time.

oFor Message Signals the message is entered in space-separated hexadecimal byte values.  This sequence of bytes is enclosed in quotes. For example:  
 
3.3,"48 45 4C 4C 4F 20 57 4F 52 4C 44"

•Time values in the External Data File should be increasing, but do not have to be equally spaced. If the data file is for a Numeric Signals, the Value is kept steady until the time of the next transition.  For message signals, message data is only sent (or expected) at the time where a message string is provided.

•Comments start with a semicolon (;)

The content of an External Data File providing four value transitions is shown below.  The first column is the Time and indicates that the Signal changes at times 1, 2, 4.5, and 8.  The second column is the Value.

1,0

2,3.3

4.5,4.4

8,5.5

The content of an External Data File showing two four-byte message transitions at times 1.5s and 3.0s is shown below:

1.5,"01 00 00 00"

3.0,"02 00 00 00"

A sample External Data file, ExternalVehSpeed.dat, is included in the ScenariosAndTestCases folder of the TurnDoor Sample Project.

Matrix format files are produced by Exporting Test Data from a TestCase. Each column, except the time column, represents a signal. When you select a Matrix-format external-data file, MxVDev searches the column headings for a signal name that matches the signal associated with the selected DataBlock. If a match is found, that column is loaded into the DataBlock. If no matching name is found, the following warning is displayed. If you click Yes, the first data (non-time) column is loaded into the DataBlock.

External_Data_warning

In the Matrix format, comments start with a semicolon (;), and messages must be enclosed in double quotes with single-space-separated bytes. If your file contains quotes, Excel is not recommended for editing as it may add or remove quotes unexpectedly.

CSVcomma

 
hmtoggle_plus1Creating an External Data File from an MxVDev Signal

You can create an external data file from internal MxVDev Signal data.  Right-click on the Signal Plot Area, select the Signal Menu, then choose the option Save to External Data File.  This creates a text file in the External Data Source (two-column) format.  This is useful if you want to edit a signal manually as a sequence of numbers. You can also use it to reduce memory usage. The file-naming convention <TestCaseName><SignalName>.dat may be helpful.

 

Related Topics:

DataBlock Overview

Importing Test Data

Exporting Test Data