Link for ModelSim

To VCD File

Generate a value change dump (VCD) file

Library

Link for ModelSim

Description

The To VCD File block generates a VCD file that contains information about changes to signals connected to the block's input ports and names the file with the specified filename. VCD files can be very useful during design verification. Some examples of how you might apply VCD files include

• For comparing results of multiple simulation runs, using the same or different simulator environments

• As input to post-simulation analysis tools

• For porting areas of an existing design to a new design

In addition, VCD files include data that can be graphically displayed or analyzed with postprocessing tools. For example, the ModelSim vcd2wlf tool converts a VCD file to a WLF file that you can view in a ModelSim wave window. Other examples of postprocessing include the extraction of data pertaining to a particular section of a design hierarchy or data generated during a specific time interval.

Using the Block Parameters dialog, you can specify the following:

• The filename to be used for the generated file

• The number of block input ports that are to receive signal data

VCD files can grow very large for larger designs or smaller designs with longer simulation runs. However, the size of a VCD file generated by the To VCD File block is limited only by the maximum number of signals (and symbols) supported, which is 94³ (830,584). Each bit maps to one symbol.

For a description of the VCD file format see VCD File Format.

Dialog Box

VCD file name

The filename to be used for the generated VCD file. If you specify a filename only, Simulink places the file in your current MATLAB directory. Specify a complete pathname to place the generated file in a different location. If you specify the same name for multiple To VCD File blocks, Simulink automatically adds a numeric postfix to uniquely identify each instance.

Note   If you want the generated file to have a .vcd file type extension, you must specify it explicitly.

Number of input ports

The number of block input ports on which signal data is to be collected. The block can handle up to 94³ (830,584) signals, each of which maps to a unique symbol in the VCD file.

In some cases, a single input port maps to multiple signals (and symbols). This occurs when the input port receives one of the following:

• Vector of real numbers

• Fixed-point real number

Simulink Blocks — Alphabetical List

VHDL Cosimulation