Behavioral Representations at the ALGORITHMIC Level

The model described in the previous section provides a philosophical backdrop upon which more detailed representations and S5mthesis steps may be described. The rest of this chapter begins to present these details. First, the Algorithmic level behavioral representations used as input to the Workbench tools are presented. Second, the Register-Transfer representations generated by the Workbench are presented. With this more-detailed background, the synthesis steps necessary to 

Values are transferred from one carrier to another through statements describing transfer operations and data operations, much the same as in any other procedural language. In the example, the statement  

Statements are separated in one of two ways. First, the NEXT construct specifies that all the statements before it must execute before any of the statements after it may start. Second, the semicolon construct specifies that execution of the ISPS statements may proceed in an arbitrary order as long as the lexical data precedences are maintained. Note that this does not conform to the original ISPS language and simulator definition which specified semicolon to mean order independence regardless of the lexical data precedences. All examples in this book follow the revised definition. 

ISPS also supports procedures and procedure calls the ISPS Reference Manual refers to a procedure as an entity with a behavioral expression for a body, and to a procedure call as the activation of an entity. As in most procedural languages, procedures can be passed a set of parameters (values), and a single value can be explicitly returned by the procedure. Furthermore, values may be transferred to the procedure through global carriers and modified, causing side effects. 

ISPS provides several looping constructs. The REPEAT operation, shown in the example, specifies that the contents of the following block of statements (delimited by BEGIN and END operations) are to be executed repeatedly. Another operation, the RESTART operation, can be used at the end of a labeled block of statements, also causing a block of statements to be execute repeatedly. Once started, a labeled block of statements can be left via LEAVE, TERMINATE, RESTART, or RESUME operations only the LEAVE statement is shown in this example. 

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