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ASIC.FYI

Q131FreeDesign Verification

Expire memory expectations without full scans

Difficulty
Hard
Topic
Reference Models
Language
SV
Interview prompt

Question

Replace the full pending-memory scan with a deadline-ordered structure while preserving fast per-address matching.

Address lookup map and deadline-ordered queue sharing transaction objects
Matching marks the shared object, while expiration examines only ordered queue heads and skips matched entries lazily.
Starting point

Question code

expected_txn by_addr[longint][$];
expected_txn deadlines[$];

function void golden_write(longint addr, int data);
function void dut_write(longint addr, int data);
function void tick();
Reviewed example

Trace one case

Input
expect A due cycle 5 and B due cycle 7; match B at cycle 3; process deadlines at cycle 5 then 7
Expected output
A expires once at cycle 5; matched B is lazily skipped at cycle 7

The deadline queue visits only its expired head objects and the matched marker prevents B from being reported after successful lookup removal.

What to cover

Requirements

  1. Store the same transaction object in both lookup structures.
  2. Mark a matched object so deadline processing can skip it lazily.
  3. Process only expired objects at the deadline queue head.
  4. Assume expectations enter in nondecreasing cycle order.
Continue practicing
Q074 · Reference ModelsCheck delayed and reordered memory writesQ009 · Reference ModelsMatch out-of-order packets by IDQ178 · Reference ModelsRelease reordered responses in request order