Day 8: Pre-Class Self-Check Quiz

Hierarchy, Parameters & Generate

Q1: What is the difference between parameter and localparam?

Answer

parameter can be overridden at instantiation time using the #(.PARAM(value)) syntax — use for configurable values like widths, thresholds, and counts. localparam is internal to the module and cannot be overridden — use for derived constants (e.g., localparam MAX = (1 << WIDTH) - 1).

Q2: Is generate for a runtime loop? Explain what it actually does.

Answer

No! generate for runs at elaboration time (compile time). It physically creates N independent copies of the hardware. Each iteration produces a separate instance with its own flip-flops and logic. It is NOT a sequential loop — it is hardware replication.

Q3: What does $clog2(1000) return and why is it useful?

Answer

It returns 10 — because ceil(log₂(1000)) = 10. You need 10 bits to represent values 0 through 999. It's useful because it automatically derives the correct bit width from a parameter, eliminating manual calculation and the bugs that come with it. When the parameter changes, the width adjusts automatically.

Q4: Why should you name generate blocks (e.g., begin : gen_debounce)?

Answer

Named generate blocks create hierarchical paths visible in simulation waveforms and synthesis reports. Debugging gen_debounce[2].db.r_count is much easier than navigating anonymous generated instances. It also makes $display and $dumpvars output meaningful.