Ask that customer to provide an export of that processor in “L5X” format (xml). Install my Ethernet/IP Class 1 Communications module and create a virtual PLC device (Host Device) with it. Import the L5X into the “Configuration” section of that virtual PLC device. There are only a handful of datatypes that won’t import, like MESSAGE tags. Even AOI types and tags import as long as they aren’t protected.
At this point, the tags and datatypes from the real PLC will be accessible as if you were using the Logix v21 driver, with (mostly) compatible OPC item syntax. Excluding the “internals” and some differences in string handling. Carry on with development. If you wish to emulate some of the PLC functionality for UI testing, you can write jython code in the virtual PLC–that code has access to the virtual PLC’s tags as jython variables. Call such testing code from a gateway timer event to emulate a “Periodic Task”.
When you are ready to deploy, delete or rename the virtual PLC device, and create the appropriate Logix v21 driver with that old name. Your tags and other OPC calls will now work with the real PLC.
If the few slight driver differences are a problem, do the above, but in a second Ignition Gateway. Make sure the virtual PLC is set to listen on that gateway’s local IP address. In the first gateway, use the Logix v21 driver and point it at the second gateway. The virtual PLC emulation includes external access using the standard Logix tag access protocol.
As long as someone else provides the processor file in L5X format, you will not need any Rockwell Software during development.