HDL development granularity and hierarchy Each block, starting at the simplest level of the design hierarchy, should be implemented in HDL so it can be simulated, verified, and reused cleanly.

Introduction / Context:
Modular HDL design improves scalability and verification efficiency. By defining and coding self-contained blocks, teams can simulate and validate functionality early, enabling parallel development and consistent integration as the project grows.

Given Data / Assumptions:

• The design is hierarchical, composed of blocks and subsystems.
• Each block has a clear interface and purpose.
• Reusable IP is desirable for future projects.

Concept / Approach:
“Block” is the fundamental unit of HDL organization. A block maps to a module/entity with ports, generics/parameters, and a well-defined behavior. Coding from the simplest blocks upward allows unit testing, code review, and resource/timing estimation at each layer.

Step-by-Step Solution:

Verification / Alternative check:
Use regression tests per block so that later changes do not break earlier functionality; track coverage and assertions.

Why Other Options Are Wrong:
“subsystem” is a higher aggregation of blocks. “circuit” is too generic and informal for HDL hierarchy. “function” in HDL is a coding construct, not necessarily a compiled verification unit with ports.

Common Pitfalls:
Overly large blocks that hinder reuse; ambiguous interfaces; lack of independent testbenches for leaf blocks.

Final Answer:
block