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6.8 Input Data Dynamically from a File (VHDL)

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6.8 Input Data Dynamically from a File (VHDL)

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6.8 Input Data Dynamically from a File (VHDL)

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VHDL test benches can read data from a file during simulation. This is not supported in Verilog, but there is away to mimic this feature by initializing an array during the test bench build process as described in Section 6.9 Initialize Array from File.

The test bench can read data from a file that is in the SynaptiCAD Test Vector Spreadsheet format.TestBencher Pro uses a project-level variable of type File Input to read from the file. The variable is defined by a class with fields (one field per column in the test vector spreadsheet file). This file variable and class definition are automatically created when an input file, with the proper header information, is added to the Project’s Test Vector List - File Input folder.

1) Create a SynaptiCAD Test Vector Spreadsheet File that will be used to make a Class:

Step 1 of Section 6.7 Output Data to a File, describes the first two rows of the Test Vector Spreadsheet file and how to make the file. For an input file, each additional row is a list of all of the signal states in tab-separated columns. Each time TestBencher reads from the file, it will read the next line in the file.

[Vectors]  Radix=hex

Addr       Data[7:0](bin)

A4         10110011

54         11011010

....

Note: Test vector spreadsheet files can also be imported by WaveFormer and TestBencher, so test vector files can be edited as timing diagrams inside the tool and saved in their modified form. They can also be edited using all major spreadsheet programs like Excel.

2) Add Test Vector File to project to Automatically create file class and variable:

When a file is added to the project’s Test Vector List - File Input folder, TestBencher will automatically parse the file and create a Class definition with a field for each column of the file. TestBencher also instantiates the class as a variable in the project. The file variable can be accessed anywhere in the project.

•Under the Test Vector Lists folder, right click on either File Input or File Output to open the context menu.

file_input_menu
•Choose one of the menu options to attach the file to the project and create the file class and variables. The Add Files to menus will add the file and path to the project. The Copy Files to will make a local copy of the file in the project directory.

Next investigate the file class and variable that was created:

•Right click on the Class Library List folder and choose Classes and Variables to open the Classes and Variables dialog.

Cv_dlg_opening_just_class
•In the Class Definitions tab, notice that a class was created and named filename_STRUCTURE. The fields of the structure are the column headings of the file.

file_class

file_fields

•In the Variables tab, notice that a file variable named filename was created. Its Structure will be File Input. The Data Type will be the class that defines the fields of the file, filename_STRUCTURE.

file_variable

•At the bottom of the Variables tab is the File Name with Structure Definition/Initialization box that shows the name of the associated file.
•If you need to change the file you can come to this tab and press the Reparse File to force TestBencher to remake the class and variables associated with this file.

file_name_with_structure

How To Access a File Variable:

Once a file variable is created at the project level, it can be accessed in any of the project's timing diagrams. Use the @filevariablename.fieldname to read or write to that field. This code can be entered anywhere a variable can be used, such as in a waveform state (Section 2.4 Waveform States and Conditions), samples (Section 3.2 Sample Checking and Actions), parameters (Chapter 4: Transaction Delays, Setups, and Holds), and in markers (Section 5.6 HDL Code Markers).

If an input file variable is accessed within a timing diagram transactor, one line will be read from the file each time the transactor begins a transaction. If the file variable is referenced again in the same transaction, the values will come from the original read of the file. The next time a transactor is called that references the file variable, the next line will be read from the file.

For output files, a line of data is written at the end of any transaction that references the file variable.