tchaxx / rplc

Invoke RPC methods from TwinCAT PLC using ADS

rplc

Invoke RPC methods from TwinCAT PLC using ADS.

How?

Prerequisites

A RPC server (here another PLC on same machine LocalAmsNetId, but different ADS Port 852) provides following method signature:

NOTE
The method has to have the attribute TcRpcEnable in order to be invocable via RPC,
see Beckhoff InfoSys - Attribute 'TcRpcEnable'

{attribute 'TcRpcEnable'}
METHOD Greet : T_MaxString
VAR_INPUT
	sName : T_MaxString;
END_VAR
VAR_OUTPUT
	nLen : INT;
END_VAR
VAR_IN_OUT CONSTANT
	stLibVersion : ST_LibVersion;
END_VAR

Instantiate client

fbRpc : tchaxx.FB_RPC(sAmsNetId:= tchaxx.GCL.cLocalAmsNetId, 
                      nAmsPort:= 852, 
                      sInstancePath:= 'MAIN.fbRpcServer', 
                      sSymbol:= 'Greet');

// Arguments and RetVal
sArg  : T_MaxString := _AppInfo.AppName;
nLen  : INT;
stLibVersion : ST_LibVersion;
sRetVal : T_MaxString;
stRetVal : ST_AdsStatus;

Invoke RPC method

To invoke the RPC method, simply use fluent-api to describe it, e.g.

stRetVal := fbRpc.VarInput(sArg)
                 .VarOutput(nLen)
                 .VarInOut(stLibVersion)
                 .ReturnValue(sRetVal)
                 .Invoke();

NOTE
Unlike the TwinCAT ADS .NET library, this implementation does not check the datatypes of the arguments before invoking.
It only matches the total size of all arguments (inputs, var-in-out and return value).

Examples

See example projects RpcServer and RpcClient or unit-tests in TESTs/FB_RPC_Tests for more examples.

Publisher / Subscriber example

This examples in RpcServer/RpcClient project, showcases the use of FB_RPC_Dynamic.

• FB_Publisher in RpcServer

  A client can subscribe to events, by invoking Subscribe method, with following arguments:

  VAR_INPUT CONSTANT
      sAmsNetId		: T_AmsNetID;
      nPort			: T_AmsPort;
      sInstancePath	: STRING;
      sSymbol			: STRING;
  END_VAR
  

  These arguments are used to configure a FB_RPC_Dynamic instance in the array aSubscribers of type ST_Subscriber.

  Subscribe := S_PENDING;
  
  (* start of critical section *)
  IF fbCrititcalSection.Enter() THEN
      
    FOR i := 0 TO cSubsUpperBound DO	
      IF aSubscribers[i].nHandle > 0 THEN
        CONTINUE;
      END_IF
      nHandleCnt := nHandleCnt + 1;
      aSubscribers[i].nHandle := nHandleCnt;		
      aSubscribers[i].fbRPC.Configure().WithAmsNetId(sAmsNetId).WithAmsPort(nPort).WithSymbolPath(sInstancePath, sSymbol).Build();
      nHandle := nHandleCnt;
      Subscribe := S_OK;
      EXIT;
    END_FOR
    
      (* end of critical section *)
    fbCrititcalSection.Leave();
  END_IF
  

  The publisher invokes each registered subscriber:

  METHOD PRIVATE InvokeSubscribersCallback
  VAR_INPUT
    nTrigger : UDINT;
  END_VAR
  
  VAR
    i 	: UDINT;
    refSub : REFERENCE TO ST_Subscriber;
  END_VAR
  

  FOR i:= 0 TO cSubsUpperBound DO
    refSub REF= aSubscribers[i];
    
    IF refSub.nHandle = 0 THEN
    	CONTINUE;
    END_IF
    
    refSub.stAdsStatus := refSub.fbRPC.VarInput(nTrigger).NoReturnValue().Invoke();
  
  END_FOR
  

• FB_Subscriber in RpcClient
  In order to subscribe to events, a client must register with the publisher, which in this case is the FB_Publisher of the RpcServer:

  VAR
    fbRpcPublisherSubscribe 	: tchaxx.FB_RPC(sAmsNetId:= tchaxx.GCL.cLocalAmsNetId, nAmsPort:= 852, sInstancePath:= 'MAIN.fbPublisher', sSymbol:= 'Subscribe');
  END_VAR
  

  With the variable sSymbolCallback "pointing" to the callback-method PublisherEventCallback:

  VAR
    sSymbolCallback			: STRING := 'PublisherEventCallback';
  END_VAR
  

  This method is invoked by the publisher, in case of an event.

  IF NOT bSubscribed AND bSubscribe THEN
    stAdsStatus := fbRpcPublisherSubscribe.VarInput(anyArg:= sAmsNetId)
            .VarInput(anyArg:= _AppInfo.AdsPort)
            .VarInput(anyArg:= sInstancePath)
            .VarInput(anyArg:= sSymbolCallback)
            .VarOutput(anyArg:= nHandle)
            .ReturnValue(anyRetVal:= hr)
            .Invoke();
            
    bSubscribed := NOT stAdsStatus.bBusy AND NOT stAdsStatus.bError;
    IF bSubscribed THEN
      bSubscribe := FALSE;
    END_IF
  END_IF;
  

Call external RPC methods

• See TcHaxx/Snappy.

Acknowledgments

• TcUnit
  An unit testing framework for Beckhoff's TwinCAT 3

rplc's Issues

Add an example for PubSub communication

Can you also provide an example on how to setup event based communication like PubSub?

Getting started

Currently working on a project which requires communication between tc3 and a nuxt/vue/typescript application.

Before getting started I have a couple of questions.

Is it just for PLC/PLC communication or can it also be used for different applications?

Does it work with grpc or with trpc?

Could it for example be used in combination with https://trpc-nuxt.vercel.app/get-started/usage/simple?

Does it require a special license like opc-ua?

Publish on Twinpack

Hi! We implemented a package manager for TwinCAT, similarly to nuget.

https://github.com/zeugwerk/twinpack

It is integrated in TcXAEShell and Visual Studio and also offers a simple command line interface for downloading and uploading packages on CI environments. Ultimately we want to make DevOps more accessible in the PLC world and having an open source package manager is our first step towards this goal.

Would you upload rplc to Twinpack to facility the installation of it for TwinCAT users?