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Architectures


The architecture contains the actual specification of how a design behaves. The entity specifies the interface and may have many different models of behavior, so there may be more then one architecture for a given entity. The architecture declaration is as follows: 
arch-item-declarations : subprogram-declaration |
  subprogram-prototype | type-declaration | subtype-declaration | 
  constant-declaration | signal-declaration | file-declaration | 
  alias-declaration | component-declaration | attribute-declaration | 
  attribute-specification | configuration-specification |
  disconnect-specification | use-clause 
arch-statements : block-statement | process-statement | procedure-call |
  assertion-statement | signal-assignment | component-instantiation |
  generate-statement 
architecture-declaration : 
    ARCHITECTURE simple-name OF simple-name IS
      {arch-item-declarations} 
    BEGIN
      {arch-statements}
    END [simple-name] ";"

If the name appears after the END keyword then it must be the same as the name of the architecture. The name following the OF is the name of the entity that defines an interface for the design. An architecture can contain many different object declarations and statements that are described throughout this and the next chapter.

Each combination of an architecture and its entity constitutes a design. Every entity must have at least one corresponding architecture.