VHDL architecture structure – what appears first to introduce the variable signals, component declarations, and other items used between BEGIN and END?

Introduction / Context:
A VHDL architecture defines how an entity behaves. Inside an architecture, there is a clear organization: a declarative region followed by the concurrent statements between BEGIN and END. Recognizing what properly belongs in the declarative part is essential for clean, synthesizable code and comprehensible testbenches.

Given Data / Assumptions:

• An architecture is associated with an entity.
• Items used in concurrent statements (signals, component declarations, constants, type declarations, subprograms) must be introduced first.
• Standard coding style places these items in the architecture’s declarative region.

Concept / Approach:
The architecture begins with a declarations section (the declarative part). There, you declare signals, constants, types/subtypes, component declarations (unless direct entity instantiation is used), and subprograms (or reference them via packages). After the keyword begin, concurrent statements (signal assignments, component/entity instantiations, generate statements) follow and may reference anything declared earlier.

Step-by-Step Solution:

Verification / Alternative check:
Any basic VHDL reference or IEEE standard shows the grammar: architecture_declarative_part precedes architecture_statement_part. Real-world code (for example, FIFO controllers) places signal and component declarations before begin, validating the rule.

Why Other Options Are Wrong:
“type keyword only” and “vectors list” are subsets of declarations; the architecture needs a general declarative region, not a single kind of item. “functions only” is too narrow. “library use clauses only” typically appear earlier at file scope, not inside the architecture declarative section exclusively.

Common Pitfalls:
Declaring items after begin (illegal), or scattering declarations in packages unnecessarily when they are local to the architecture. Keep local declarations local for clarity.

Final Answer:
declarations