Building an IOC Application

This section provides instructions how to build and configure an EPICS IOC to communicate with an OPC UA server.

It also explains how to use the example application that is part of the Device Support module.

Use the Example Application

The Device support module contains an example application that builds an IOC binary and creates two IOC instances, for connecting to a Siemens S7-1500 series PLC and for connecting to the Unified Automation C++ demo server.

Structure of the Example Application

Under .../exampleTop, you will find

templateDbSup - contains useful template databases
opcuaIocApp - builds the OPC UA IOC binary
DeviceDbApp - creates the databases for the two IOCs
iocBoot - contains the startup directories for the two IOCs

The IOC for the demo server provides a number of records that connect to variables in the demo server. It shows scalars of different types, arrays of scalars, “dynamic” variables (updated by the demo server), “static” variables (can be read and written by the IOC) and the “WorkOrder” as an example for structured data.

The IOC for the S7-1500 contains some example records for an imaginary “DB1” on the PLC. As the names are completely determined by the application code on the PLC, the example application cannot show more details.

Both IOCs contain “server” records. These are connecting to server variables in namespace 0, which are part of the OPC UA specification and mandatory: every OPC UA server must provide them.

Start Up Command File `st.cmd`

Sessions and subscriptions are set up in your IOC’s startup script (e.g., st.cmd).

Input Records

record(longin, "$(P)$(R)liuint16") {
    field(DTYP, "OPCUA")
    field(INP,  "@$(SUBS) ns=2;s=Demo.Dynamic.Scalar.UInt16")
    field(SCAN, "I/O Intr")
    field(TSE,  "-2")
    field(TPRO, "$(DEBUG=0)")
}

Which is an longin input record, monitoring an OPC UA variable of type UInt16 from the “Dynamic” set that gets updated by the server code.

$(P)$(R)liuint16: The record name. $(P) and $(R) are prefixes defined in your st.cmd.
DTYP, "OPCUA": Specifies that this record uses the OPC UA Device Support.
INP, "@$(SUBS) ns=2;s=Demo.Dynamic.Scalar.UInt16": This is the crucial link field.
- @$(SUBS): The name of the OPC UA subscription to use, set through a macro.
- ns=2: The namespace index of the OPC UA item.
- s=Demo.Dynamic.Scalar.UInt16: The string identifier of the OPC UA item.
SCAN, "I/O Intr": Configures the record to process upon reception of new data from the OPC UA server, which is efficient for subscriptions.
TSE, "-2": Use OPC UA timestamps as EPICS record timestamp.
TPRO, "$(DEBUG=0): Set debug level through a macro.

Output Records (Bidirectional)

record(aao, "$(P)$(R)aaobool") {
    field(DTYP, "OPCUA")
    field(OUT,  "@$(SUBS) ns=2;s=Demo.Static.Arrays.Boolean")
    field(FTVL, "UCHAR")
    field(NELM, "10")
    field(TSE,  "-2")
    field(TPRO, "$(DEBUG=0)")
}

Which is an array output record of type UCHAR, linked to an OPC UA variable that is an Array of Boolean from the “Static” set that gets you can read and write.

$(P)$(R)aaobool: The record name. $(P) and $(R) are prefixes defined in your st.cmd.
DTYP, "OPCUA": Specifies that this record uses the OPC UA Device Support.
OUT, "@$(SUBS) ns=2;s=Demo.Static.Arrays.Boolean": This is the crucial link field.
- @$(SUBS): The name of the OPC UA subscription to use, set through a macro.
- ns=2: The namespace index of the OPC UA item.
- s=Demo.Static.Arrays.Boolean: The string identifier of the OPC UA item.
FTVL, "UCHAR": Type of the EPICS array.
NELM, "10": Capacity of the EPICS array.
TSE, "-2": Use OPC UA timestamps as EPICS record timestamp.
TPRO, "$(DEBUG=0): Set debug level through a macro.

Records Linking to Structured Data

record(opcuaItem, "$(P)$(R)itemRBK") {
    field(DTYP, "OPCUA")
    field(INP,  "@$(SUBS) ns=2;s=$(WO_NODEID)")
    field(TSE,  "-2")
}

record(stringin, "$(P)$(R)assetidRBK") {
    field(DTYP, "OPCUA")
    field(INP,  "@$(P)$(R)itemRBK element=AssetID")
    field(TSE,  "-2")
}

record(stringin, "$(P)$(R)starttimeRBK") {
    field(DTYP, "OPCUA")
    field(INP,  "@$(P)$(R)itemRBK element=StartTime")
    field(SCAN, "I/O Intr")
    field(TSE,  "-2")
}

An opcuaItem record representing the Item (structure). It is configured “normally”, addressing the OPC UA Item (like the earlier examples), with the string identifier supplied through a macro.

Two stringin records are pointing to structure elements. In their INP links, @$(P)$(R)itemRBK is pointing to the opcuaItem record that represents the structured item, and the element=AssetID and element=StartTime parts link them to specific elements.

Create an IOC for OPC UA from Scratch

Create a new EPICS application:

cd <your_epics_area>
/path/to/epics/base/bin/<arch>/makeBaseApp.pl -t ioc MyExampleIOC
/path/to/epics/base/bin/<arch>/makeBaseApp.pl -i -t ioc MyExampleIOC

Add the OPC UA Device Support: Add an entry setting OPCUA = <path_to_the_opcua_module> to your RELEASE.local file.

Add opcua to your Makefile: Edit MyExampleIOCApp/src/Makefile and add opcua to the list of libraries to link against and to the list of DBD files to use.

# Include dbd files from all support applications:
MyExampleIOC_DBD += opcua.dbd
# ...
# Add all the support libraries needed by this IOC
MyExampleIOC_LIBS += opcua

Build the application:
```
make
```
Finish your Application: Add databases. Load the databases and create the necessary OPC UA Sessions/Subscriptions
in your st.cmd script.