OPC Device Support

last Modified: by winkler
8.11.2006 08:00


Overview and Features
New in this version:
Directory structure
Install and Compile
iocShell Commands for OPC interface
opcIor: IO report
Setup the OPC client
opcSetServer: Creates an OPC server instance
opcSetGroup: Creates a new OPC item group at current server
opcSetGroupRefresh: Forced refresh time for OPC groups
opcSetNames: Item name mapping
Set up a st.cmd for the ioc shell
Record related issues
Record scanning
Device types and data conversion
Timestamps
Known Problems
Application dies after some hours
Running many process variables in one iocShell
Out records: The value written by EPICS is ignored by the PLC

Author : Kuner, Winkler

Overview and Features

The OPC device driver provides direct access for EPICS records to items located on an OPC server. It has the following features:

• Data conversion for all integer and float data types - array support is not yet implemented.

Out-records become bidirectional In/Out-records. The EPICS Out-record will be updated if the OPC item is written by another device (e.g. PLC).

• Support for the following record types:

• The data conversion capabilities of the binary records (bi, bo, mbbi, mbbo, mbbiDirect, mbboDirect) are supported with two dtypes "opc" and "opcRaw" as described in the Record Reference Manual for the "Soft Channel" and "Raw Soft Channel" types.

• Timestamp is generated by OPC server or EPICS (source is determined by the record's TSE field).

• OPC quality is mapped to record's STAT/SEVR fields.

Setup the OPC client with special features:

• Available console commands for debugging purposes:

New in this version:

Directory structure

The windows installable will install these files (full installation):

  C:\Program Files\OpcIocShell\
                            unins000.dat
                            unins000.exe
                            bin\
                                asHost.dll
                                asIoc.dll
                                ca.dll
                                ca_test.dll
                                caget.exe
                                cainfo.exe
                                camonitor.exe
                                caput.exe
                                caRepeater.exe
                                cas.dll
                                Com.dll
                                dbIoc.dll
                                dbStaticHost.dll
                                dbStaticIoc.dll
                                dbtoolsIoc.dll
                                gdd.dll
                                iocsh.dll
                                miscIoc.dll
                                opcIocShell.exe
                                opcSupport.dll
                                recIoc.dll
                                registryIoc.dll
                                rsrvIoc.dll
                                SOCltad.DLL
                                SOCmnad.DLL
                                SODaCad.DLL
                                softDevIoc.dll
                                testDevIoc.dll
                            dbd\
                                opcIoc.dbd
                            demo\
                                DemoRecord1.db
                                DemoRecord2.db
                                st.cmd
                                startDemo.bat
                            src\
                                res\
                                    icon3.ico
                                    OpcIocShell.ico
                                    uninstall.ico
                                ait.h
                                devOpc.c
                                devOpc.h
                                drvOpc.cpp
                                drvOpc.h
                                installationNotes.html
                                iocShellMain.cpp
                                Opc.cpp
                                Opc.h
                                opcApp.rc
                                opcApp.sln
                                opcApp.vcproj
                                opcSupport.dbd
                                opcSupport.sln
                                opcSupport.suo
                                opcSupport.vcproj
                                opcToEpics.h
                                recProp.h
                                resource.h
                                softing.h
                                

Install and Compile

The opcIocShell_3_3.exe will install the precompiled iocShell and its .dll's in a proper way.

For recompilation of the opcIocShell the OPC Toolkit from Softing is neccessary. We use OPC Toolkit version 3.01. To run the example, "MMI OPC" OPC-server simulator should be installed. It comes with the "OPC Explorer" from MMI OPC .

iocShell Commands for OPC interface

opcIor: IO report

Create a report of all records that use OPC device support. Output format:

  epicsName, Record Type, Dtype, opcName, opcFullName

Syntax :

  opcIor

Setup the OPC client

There is a special way to add groups and items to an OPC server. The st.cmd file is more than the commands of the iocShell. It is also parsed by the opc interface routine! The idea is to have one file to setup the iocShell and also the opcClient. See the example:

Example : of an st.cmd that shows the OPC client setup:

    iocShell_registerRecordDeviceDriver(pdbbase)
    opcSetNames("../names.txt")
    opcSetServer("localhost","MMIOPC.Simulator")
    opcSetGroup("myGroup3seconds","3000")
    dbLoadRecords("./DemoRecord1.db")
    opcSetGroup("myGroup6seconds","6000")
    dbLoadRecords("./DemoRecord2.db")
    iocShell_registerRecordDeviceDriver(pdbbase)
    iocInit()

opcSetServer: Creates an OPC server instance

Used only in st.cmd, not from the command line. It configures iocShell for connecting to OPC server.

It's possible to connect iocShell to miscellaneous OPC servers.

Syntax :

opcSetServer("hostName", "serverName")

Parameters :

opcSetGroup: Creates a new OPC item group at current server

Used only in st.cmd, not from the command line. It creates a new OPC item group at current OPC server. It's possible to create miscellaneous groups with several update rates at same server. According to the OPC "Data Access" specification it is mandatory to define at least one group.

Syntax :

opcSetGroup("groupName","n_scanRate")

Parameters :

opcSetGroupRefresh: Set refresh-cycle

Set refresh-cycle in ms for last defined Group. This forces a read from OPC server for all OPC items in appropriate group.

Syntax :

opcSetGroup("n_refreshRate")

Parameters :

opcSetNames: Item name mapping

Used only in st.cmd, not from the command line. It sets the file for name mapping.

The problem is that the record's INP or OUT fields have a limited length for the name of the OPC item. On the other hand, OPC servers can have huge name lengths for those items. So a map file may be defined to map the long OPC server names to short names suited for the record's link field.

The map file format is:

# allowed are comments and lines like this with leading spaces: epicsName = opcName # don't forget a blank line at end of file

Syntax :

opcSetNames("fileName")

Parameters :

Set up a st.cmd for the ioc shell

This example shows how to set up an IOC

   # Make sure that the dbd contains the lines for "opc" and "opcRaw"
   dbLoadDatabase("./iocShell.dbd",0,0)
   iocShell_registerRecordDeviceDriver(pdbbase)
   # registerRecordDeviceDriver(pdbbase)  <= old command, won't work with epics base 3.14.6 and higher!!!
   #
   # Name mapping is not required here
   # opcSetNames("../names.txt")
   #
   # This example uses the "MMI OPC" OPC-server simulator at local host
   opcSetServer("localhost","MMIOPC.Simulator")
   # very slow group, scanning every 3 seconds
   opcSetGroup("myGroup3seconds","3000")
   dbLoadRecords("./DemoRecord1.db")
   #
   # very slow group, scanning every 6 seconds
   opcSetGroup("myGroup6seconds","6000")
   dbLoadRecords("./DemoRecord2.db")
   #
   iocInit()

Record related issues

Record scanning

• In-records

The device support accepts all but "Passive". Due to the update facilities of the OPC group it is not reasonable to define a scan rate faster than the update rate of the group. To get the same scan rate for the record set SCAN="I/O Intr". To allow a slower than the update rate (for whatever reason) the fixed scan rates are supported: SCAN=".1 second" to SCAN="10 second".

• Out-records

As mentioned before out-records are now bidirectional in/out-records. They will be updated to the new value if it is changed on the OPC server by any other way (e.g. the PLC or another OPC client).

For out-records the SCAN field is ignored by the device support and should be set to "Passive". Nevertheless, if the OPC server gets a new value for the OPC item the record will be processed to update the value, send monitors, check for limits, set severities and process forward links.

Writing to the hardware from two sides (EPICS and the hardware covered by the OPC server) at the same time can cause problems.

For values that are frequently written by the PLC a write by the EPICS record will be overwritten in the opc-server by the PLC before it is sent to the PLC from the opc-server. In this case a caput will not be recognized by the PLC!

This is a behaviour due to the opc-server and PLC, no bug in the EPICS device support.

Also an EPICS write that follows immediately after a PLC write (very short time), may be discarded by the device support.

Device types and data conversion

There are two types available: DTYP="opc" for all records and the DTYP="opcRaw" for the binary records: bi, mbbo, mbbi, mbboDirect and mbbiDirect. The behaviour of the record is listed below and is according to the desccription of the raw data types in the Record Reference Manual.

For the analog records ai and ao the LINR field determines the data conversion.

Record DTYP Conversion
ai opc no conversion: LINR="NO CONVERSION" (record default)
ao opc no conversion: LINR="NO CONVERSION" (record default)
bi opc no conversion, VAL may be any value
bi opcRaw conversion: RVAL=0 -> VAL=0, RVAL>0 -> VAL=1
bo opc conversion: VAL=0 -> RVAL=0, VAL>0 -> RVAL=1 send RVAL to the hardware
mbbi opc for VAL=0..15 record is set to the according state. NOBT, SHFT ignored
mbbi opcRaw if RVAL=xxVL record is set to state xxST. NOBT, SHFT processed
mbbo opc ?
mbbo opcRaw ? further experimets will give new and exciting information,
mbbiDirect opc ? what this records does! See next version.
mbbiDirect opcRaw ? mbboDirect opc ?
longin opc no conversion
longout opc no conversion
stringin opc no conversion stringout opc no conversion
waveform opc no conversion

The multibit records (mbbo, mbbi, mbboDirect and mbbiDirect) have the fields NOBT and SHFT to select a special part of the 16 bit data input. This is also supported by the device support.

Timestamps

It is possible to choose the timestamp source. Default is the EPICS timestamp, but if the field TSE="-2" the timestamp of the OPC item will be used.

Known Problems

Application dies after some hours

If you run opcIocShell.exe at a hyperthreaded system, application dies after some hours with any system warning.
Solution: append /ONECPU in your boot.ini at [operating systems]

Running many process variables in one iocShell

If there are more than ca. 1800 PVs running on an iocShell following occures:

It seams to be a problem of the Windows task priorities.

Solution: Try more groups. - We reached best result with iocShell instances at several virtual machines.

Out records: The value written by EPICS is ignored by the PLC

see section "Record scanning " - Out Records