Migration of legacy WSR-8D algorithms and product generators to the open system RPG

A substantial part of the current Weather Surveillance Radar-1988 Doppler (WSR-88D) Radar Product Generation (RPG) software consists of the product generation and meteorological algorithms, which were implemented through about 50 tasks. These tasks, written in FORTRAN with CONCURRENT extensions and running under the CONCURRENT 05/32 operating system (OS), can not be directly compiled and run under a UNIX OS. Intertask communication is implemented through using shared memory segments, requiring all tasks to be running on the same computer hardware. Tasks must fit into a predefined data flow network and are controlled by a central control module. This makes the system sensitive to task failure and difficult to be. Dynamically reconfigured (redistributing the tasks among hosts, adding new tasks and so on). These tasks contain sophisticated algorithms and lengthy code. The authors decided to take a direct porting approach to migrate these tasks to the Open System RPG (ORPG). The porting approach is unique in that only a single version of the source code is maintained. The ported version uses the original RPG code without any change for all subroutines except the main subroutine, which is replaced by a new version. A preprocessor is developed to convert the CONCURRENT FORTRAN code to a standard FORTRAN code, that can be compiled on a UNIX machine. This converted version is used only temporarily at compile time. A set of supporting functions, emulating the current RPG API, is developed to provide data flow and processing control support. All inter-process data exchanges are implemented through message passing in the supporting functions. "Wrapped" by the new supporting functions, the tasks turn into independent, data driven and dynamically relocatable components that can be used in a distributed environment.