Custom-Coded Block- C/C++

VisualSim provides facilities to use C\C++ code and software applications directly in VisualSim using the Custom_C Block. VisualSim automatically generates code to wrap the programs. This section focuses on how to create VisualSim models that access C\C++ application or program. For compiling and creating executable models, all example models are given and also available under demo/Interfaces/UserNativeC directory. To complete this section, a C compiler is required.

Following are the general procedures:

An Example Model

The example model shown in Figure 1 is located under VS\demo\Interfaces\UserNativeC\YearInfo directory. This model uses a Custom_C Block, which takes date as input and outputs two values namely,

1. “True” if input date is a leap year, else “false”.
2. Day for the date.

Figure 1: YearInfo model

Steps involved in creating this model are explained in the following segments.

Using and Configuring the Custom_C Block

This chapter explains how to use and configure the Custom_C to interface with an application. The Custom_C Block is located in the Full Library > System_Language > C and CPP. The block can be placed on the canvas in the same way as any other blocks. After the Custom_C Block has been placed on the canvas, the block needs to be configured.

Configuring the Interface

The Custom_C block is configured for functions which are executed every time data is available on all the inputs. Multiple CustomC blocks can be instantiated in the model. Each block calls the same or unique functions. First specify the function by right-clicking Custom_C block and selecting Customize > Configure.

Drag the Custom_C block from Full Library > System_Language > C and CPP > Custom_C. The parameters are as follows:

Figure 2: Configuring the Custom_C block

• The parameter libraryDirectory is the directory name for the block that will be created under the base directory. The base for the library directory of the block is always set to VS_C_Library directory. It is sufficient to provide the directory structure within this level.
• The parameter native files specify the location of the “. C/.CPP” files which contain the definitions for the C functions to interface with VisualSim. The absolute path for the file should be specified when they are located outside the library Directory. Use only forward slash ‘/’ when specifying absolute path since the tool permits only forward slash to maintain platform independence.

Port Definition:

Now use the standard block port settings to add ports to the block. To do so, right-click on the block and select Configure > Ports.

Configuring the Arguments

Having configured the global parameters, the arguments for the interface to this C code must now be configured. To do this,

• Select Context Menu of the Custom_C block and select “Configure Arguments”.
• The first time the button is pressed the following window appears.

Figure 3: Configure Arguments for the Interface Block

• Click the "Add" button and the Add Arguments Window opens as shown in figure below:

Figure 4: Add Arguments

Enter the name of argument, native type (type in C) and the function name. Enable the required Kind and click OK to add the arguments. Each port can be configured to execute a different function inside the .cpp file.

Figure 5: View of Argument window after entering the values

Types supported:

• The basic native types supported are: char, long (unsigned), bool, double.
• The corresponding Java types are: char, int, boolean, double.
• The one dimension arrays supported are: char[], long[] (unsigned), short[], double[]

Note that when code generation has been executed once, there is no need to repeat it. The following table shows the native C\C++ types and their corresponding Java Types.

Table 1: Native C\C++ types and their corresponding VisualSim Types

Generating C Wrapper Functions

Creating an executable

After the Custom_C Block is configured and all the fields of its arguments and ports are specified, the next step is to generate the interface code, which allows executing the Custom_C block. Use Interface > Generate Wrapper as shown below:

 

Figure 6: Menu Bar view to select Generator

If there are no return argument configured for the Custom_C block, then a default value is automatically created and its type is set as void. Following Warning Message is displayed while setting the default value:

Figure 7: Result of the Generation

• After the button is pressed, the block is renamed as “<libraryname>I<function name>”.

Figure 8: Look and Feel of the New Block Created

• Successful compilation of the source files creates a Jni<libraryname>I<return argument name>.dll file under the blocks directory. The file extension “. dll” or ".so" indicates that the file is a dynamic link library.

Note: Open the “vsout.txt” file under the libraryDirectory to verify the errors that could have caused any unsuccessful compilation process. These could help to correct any mistakes in the interface C code.

• The blocks directory under VS_C_Library directory is required to hold “. Dll and .so” files. The Block directory must be in the PATH.
• After the “Generate Wrapper” is selected, the port types are of type “unknown” by default. Change this to your specific type or select "general".

Figure 9: Configuring Ports

If the type is not supported, an Error Message window appears as below. The following error message is displayed if the type is specified as “bool” instead of “boolean”.

Figure 10: Error Message for incorrect data type at the interface

• The following table shows the C\C++ Argument types and their equivalent VisualSim types.

Table 2: C\C++ Arguments and Equivalent VisualSim Types

Note: { Name=char[5]; Id=int} is representation for the C\C++ structure like the one below:

struct Example{

char Name[ ];

int Id; };

Running the Executable Model

The “MoniterValue” result block can be dragged on to the canvas on the right from the Result library under Text. Similarly the “Const” input block can be obtained from the Function > Math and Trig. Control-click to create the relations from the toolbar.

Connect all the blocks as shown in the Figure 3, add an Untimed Digital Simulator (located under “Model\Simulator Engine) and change the number of iterations from 0 to 1 by double-clicking the Untimed Digital Simulator.

Click the “Run” button in the IDE or Press Ctrl+R to execute the model.