WDL Overview


A more substantial description is provided by the book chapter.

Detailed information may be found in the project document:s

Waveform Description Language, Library Entities, FM3TR Decomposition

An extract of the final report follows.

Overview

The block diagram representation of the WDL concept is shown in Figure 3.1. WDL consists of two distinct aspects:

The initial parameterisation of a STANAG or specification would be done using a schematic editor tool or text entry. The WDL language has two interchangeable formats. One is free format like C or ADA and is suitable for reading and manual editing. The other is an eXtensible Mark-up Language (XML) dialect that will be used for persistent storage and to support access by third party tools such as Xeena or Spy for direct XML maintenance, or Diva for schematic entry.

WDL supports the capture of a system specification using decomposition to express the required behaviour as a hierarchy of sub-specifications. Decomposition proceeds until the specification of a pre-existing sub-system can be re-used, or until it is appropriate to define the behaviour using mathematical expressions. The WDL further supports the progressive refinement of a specification into a program that may then be compiled and executed. This refinement may involve relatively minor addition of detail to support a reference model, or potentially wholesale changes to adapt the specification to exploit pre-existing component libraries. The refinement process may be assisted by special purpose refinement tools that assist in the resolution of detailed system design issues such as filter implementations. The integrity of a design may be validated by further tools that check system properties such as processing loads or implementation losses.

The refinement activities are shown in more detail in Figure 3.2. The specification may be written in more than one level, with a relatively abstract specification perhaps only defining concepts such as the need for OSI layers and data coding, leaving an actual specification to define protocols and algorithms. The waveform sponsor may perform a minor refinement to produce a reference model in which example implementations of non-mandatory algorithms may be provided. The more major refinements are performed by the vendor, who will be concerned to tune the design to minimise computational requirements and match the implementation to particular hardware platforms for which optimised component implementations may already be available. Exploitation of these resources requires the WDL to be refined to describe the required hardware partitioning and to define the interfaces of available components.

Direct compilation of WDL would involve an unacceptable degree of software tool development to support a wide variety of target platforms. The compilation process is therefore broken down into stages as shown in Figure 3.3 so that COTS compilers and the Ptolemy system can be exploited. Ptolemy is a freeware product developed by the University of California at Berkeley, it supports scheduling of DSP simulations using a wide variety of computational models, and can be adapted to support code generation. The WDL Scheduler and WDL Code Generator are therefore based upon Ptolemy. The WDL translator presents a resolution of the WDL refinement process and WDL abstractions in a form suitable for use by Ptolemy. Existing or hand-optimised component libraries are exploited by incorporating their code with the appropriate phase of COTS compilation or linking, and by providing a WDL definition of the interface as part of the refinement process. The UK PDR phase 1 activities involve investigating the first level parameterisation (the Abstract and Actual Specification in Figure 3.2), reviewing COTS tools to implement the WDL and investigating issues associated with the WDL Compiler.

Example Parameterisation

The concept that is adopted to parameterise a waveform is to progressively break down the waveform specification into smaller more focused sub-specifications, using state and message flow diagrams, until leaf entities are identified that can mathematically define the specification. In order to define the decomposition process, the semantics and syntax of a language need to be developed. The first pass at defining the language is detailed in [9]. Examples of the language used to parameterise FM3TR and SATURN, are given in [6] and [7]. As a summary, the following sections briefly shows example parameterisation diagrams for FM3TR, illustrating the basic WDL concepts and use.

An extensive example of the use of WDL is provided by the example parameterisation of the FM3TR waveform. A brief summary of the full FM3TR Decomposition is available.


Last updated 06 September 2002