Slovak University Of Technology In Bratislava Institute Of .

Slovak University of Technology in BratislavaInstitute of Information Engineering, Automation, and MathematicsPROCEEDINGS17thInternational Conference on Process Control 2009Hotel Baník, Štrbské Pleso, Slovakia, June 9 – 12, 2009ISBN 9Editors: M. Fikar and M. KvasnicaSysel, M.: TCP/IP Output from the Simulink, Editors: Fikar, M., Kvasnica, M., In Proceedings of the 17thInternational Conference on Process Control ’09, Štrbské Pleso, Slovakia, 634–637, 2009.Full paper online: 061.html

17th International Conference on Process Control 2009June 9–12, 2009, Štrbské Pleso, SlovakiaLe-Fr-5, 061.pdfTCP/IP OUTPUT FROM THE SIMULINKM. Sysel** Tomas Bata University in Zlín, Faculty of Applied InformaticsNad Stráněmi 4511, 760 05 Zlín, Czech Republicphone : 420 57 603 5180 and e-mail : Sysel@fai.utb.czAbstract: This paper describes an option for TCP/IP output from the programMATLAB/Simulink. The new developed Simulink block and instructions for buildingthis one are described here. This client block enables Simulink models to communicatewith remote applications and devices over TCP/IP communications. A very similarfunctionality (more complex) is provided by the TCP/IP block in the Instrument Control Toolbox offered by MathWorks.Keywords: Simulink, communications, TCP/IP, client.block to add it to a Simulink model. After writingS-function and place its name in an S-Functionblock (available in the User-Defined Functions blocklibrary), it can customize the user interface usingmasking. (Anon. 2008 a).1 INTRODUCTIONSimulink can communicate with remote applicationsusing developed Simulink block. This block enablessending live data from Simulink model to an application using TCP/IP. The base element of the blockis S-function block, which use C MEX file. (Anon.2008 c)2.1 S-function Simulation StagesTo create S-functions, it is needed to understand howS-functions work. It requires understanding how theSimulink engine simulates a model.Execution of a Simulink model proceeds in stages.First comes the initialization phase. In this phase,the Simulink engine incorporates library blocks intothe model, propagates signal widths, data types, andsample times, evaluates block parameters, determines block execution order, and allocates memory.The engine then enters a simulation loop, whereeach pass through the loop is referred to as a simulation step. During each simulation step, the engineexecutes each block in the model in the order determined during initialization. For each block, the engine invokes functions that compute the block states,derivatives, and outputs for the current sample time.The entire simulation loop then continues until thesimulation is complete.2 S-FUNCTIONS-functions (system-functions) provide a powerfulmechanism for extending the capabilities of the Simulink environment. An S-function is a computerlanguage description of a Simulink block written inMATLAB, C, C , Ada, or Fortran. C, C , Ada,and Fortran S-functions are compiled as MEX-filesusing the mex utility. As with other MEX-files, Sfunctions are dynamically linked subroutines that theMATLAB interpreter can automatically load andexecute. S-functions use a special calling syntaxcalled the S-function API that enables to interactwith the Simulink engine. This interaction is verysimilar to the interaction that takes place betweenthe engine and built-in Simulink blocks. S-functionsfollow a general form and can accommodate continuous, discrete and hybrid systems. By following aset of simple rules, it can be implemented an algorithm in an S-function and used the S-FunctionA MEX S-function consists of a set of callback methods that the Simulink engine invokes to performvarious block-related tasks during a simulation.MEX S-functions can be implemented in C, C ,Ada, or Fortran. The engine directly invokes MEXS-function routines instead of using function handles634

17th International Conference on Process Control 2009June 9–12, 2009, Štrbské Pleso, SlovakiaLe-Fr-5, 061.pdfas with M-file S-functions. Because the engine invokes the functions directly, MEX S-functions mustfollow standard naming conventions specified by theS-function API.3 WINDOWS SOCKETSTraditional network programming implemented inWindows environment uses Windows Sockets API(Winsock API - WSA). WSA is similar to LinuxSockets programming with a few exception such asheader files, that provided to suit Windows environment and enhances the functionalities. WindowsSockets 2 (Winsock) enables programmers to createadvanced Internet, intranet, and other networkcapable applications to transmit application dataacross the wire, independent of the network protocolbeing used. With Winsock, programmers are provided access to advanced Microsoft Windows networking capabilities. Winsock programming previously centered around TCP/IP. (Anon. 2009).MEX-file S-functions are more appropriate for integrating legacy code into a Simulink model. For morecomplicated systems, MEX-file S-functions maysimulate faster than M-file S-functions because theLevel-2 M-file S-function calls the MATLAB interpreter for every callback method. (Anon. 2008 a).MEX S-functions provide the following sample timeoptions, which allow for a high degree of flexibilityin specifying when an S-function executes: Continuous sample time Continuous, but fixed in minor time step sampletime Variable discrete sample time Inherited sample time Discrete sample time - If the behavior of your Sfunction is a function of discrete time intervals,it can be defined a sample time to control whenthe Simulink engine calls the S-function. It canbe also defined an offset that delays each sampletime hit. The value of the offset cannot exceedthe corresponding sample time. If it is defined adiscrete sample time, the engine calls the Sfunction mdlOutput and mdlUpdate routines ateach sample time hit.There are two distinct types of socket network applications: Server and Client. Servers and Clients havedifferent behaviors; therefore, the process of creatingthem is different. What follows is the general modelfor creating a streaming TCP/IP Server and Client.Server Initialize Winsock. Create a socket. Bind the socket. Listen on the socket for a client. Accept a connection from a client. Receive and send data.Although hand-written S-functions support the widest range of features, they can be difficult to write.The S-Function Builder block simplifies the task ofwriting C MEX S-functions but supports fewer features. The Legacy Code Tool provides the easiestapproach to creating C MEX S-functions from existing C code but supports the fewest features. Disconnect.The important S-function callback methods areshown in figure 1. The implementations of callbackmethods is described below.Client Initialize Winsock. Create a socket. Connect to the server. Send and receive data. Disconnect.The developed Simulink block is a client.4. BLOCK DESCRIPTIONThis chapter contains simplified description of thesource code of the developed Simulink block. Thebase element of the block is S-function block, whichuse C MEX file. Finally, it is necessary compilesource code. Compiling the MEX-Files is similar tocompiling with gcc or any other command line compiler. Following command link the object code together with the library wsock32.lib. Win32 architecture is supposed. (Anon. 2008 a, b). mex -O netout.cpp wsock32.lib -DWIN32Fig. 1. The important S-function callback methods.635

17th International Conference on Process Control 2009June 9–12, 2009, Štrbské Pleso, SlovakiaLe-Fr-5, 061.pdf4.1 Defines and Includesif (!ssSetNumInputPorts(S, 1)) return;The S-function code starts with the following LY SIZED);It defines one dynamically sized input port, that’swhy TCP output is in the special format which iseasy modifiable.#define S FUNCTION NAME netout#define S FUNCTION LEVEL 2ssSetOptions(S,SS OPTION WORKS WITH CODE REUSE SS OPTION EXCEPTION FREE CODE SS OPTION USE TLC WITH ACCELERATOR);#include "simstruc.h"#include "winsock.h"The first define statement specifies the name of theS-function (netout). The second define statementspecifies that the S-function is in the Level2 format.Specifying these options together with exception-freecode speeds up execution of S-function.After defining these two items, the code includessimstruc.h, which is a header file that gives access tothe SimStruct data structure and the MATLAB Application Program Interface (API) functions. Thesimstruc.h file defines a data structure, called theSimStruct, which the Simulink engine uses to maintain information about the S-function. The simstruc.h file also defines macros that enable MEX-fileto set values in and get values (such as the input andoutput signal to the block) from the SimStruct. Thewinsock.h should be added to access sockets underMicrosoft Windows. Next parts describe callbackmethod implementations.4.3 mdlInitializeSizesThe Simulink engine calls mdlInitializeSampleTimes to set the sample times of the S-function. Anetout block executes in specified period (the thirdinput cnParam(S, 2)));4.4 mdlStartSimulink invokes this optional method at the beginning of a simulation. It should initialize the windowssocket. Input parameters Address and Port are used,TCP communication is used here.4.2 mdlInitializeSizesThe Simulink engine calls mdlInitializeSizes to inquire about the number of input and output ports,sizes of the ports, and any other information (such asthe number of states) needed by the S-function.WSAStartup(wVersionRequested, &data);mxGetString(ssGetSFcnParam(S, 0),buf,buflen);host gethostbyname(buf);The netout implementation of mdlInitializeSizesspecifies the following size information:port (int) mxGetScalar(ssGetSFcnParam(S, 1));ssSetNumSFcnParams(S, 3);mySocket socket(AF INET, SOCK STREAM,IPPROTO TCP);It defines three input parameters: serverSock.sin family AF INET;Address – (String input parameter) Name address of the server (IP address) - An InternetProtocol (IP) address is a numerical identification (logical address) that is assigned to devicesparticipating in a computer network utilizingthe Internet Protocol for communication between its nodes.serverSock.sin port htons(port);memcpy(&(serverSock.sin addr),host- h length);host- h addr,connect(mySocket, (sockaddr *)&serverSock, sizeof(serverSock);Port – (Integer input parameter) - In computernetworking, a port is an application-specific orprocess-specific software construct serving as acommunications endpoint used by TransportLayer protocols of the Internet Protocol Suitesuch as Transmission Control Protocol (TCP) orUser Datagram Protocol (UDP). A specific portis identified by its number associated with the IPand the protocol used for communication.4.5 mdlOutputsThe engine calls mdlOutputs at each time step tocalculate the block outputs. The netout implementation of mdlOutputs takes the input signal and writesthe data to the created output socket.send(mySocket, data, strlen(data), 0);4.5 mdlTerminateSample time period – Sampling period of thesignal output.The engine calls mdlTerminate to provide theS-function with an opportunity to perform tasks at636