Ordered FIFO Compare · uvm

On this page

UVM Coding PracticeSenior

Interview prompt

Sketch a scoreboard with expected and actual FIFOs for an in-order APB peripheral response stream.

Diagram

WHITEBOARD CHAIN

1. DECLARE    interfaces / types / ports you need
2. SKELETON   class extends + utils macro + key methods
3. MECHANISM  fill one critical method while narrating
4. PITFALL    name one bug juniors make on this pattern
5. TEST       how you would smoke-test the component

Reference sketch (≤40 lines)

design.sv

class apb_sb extends uvm_scoreboard;
  `uvm_component_utils(apb_sb)
  uvm_analysis_imp_exp #(apb_txn, apb_sb) exp_imp;
  uvm_analysis_imp_act #(apb_txn, apb_sb) act_imp;
  apb_txn exp_q[$], act_q[$];

  function void write_exp(apb_txn t); exp_q.push_back(t); endfunction
  function void write_act(apb_txn t);
    act_q.push_back(t);
    if (exp_q.size() && act_q.size())
      compare_pair(exp_q[0], act_q[0]);
  endfunction
  function void compare_pair(apb_txn e, apb_txn a);
    if (!e.compare(a)) `uvm_error("SB", "mismatch")
    else begin exp_q.delete(0); act_q.delete(0); end
  endfunction
endclass

Buggy snippet — critique verbally

design.sv

function void write_act(apb_txn t);
  compare_pair(exp_q[0], t); // always compare — exp_q may be empty
endfunction

Smoke test (5 minutes)

One directed read/write sequence.
Inject single wrong data — expect one UVM_ERROR.
Check queues drain to zero after match.

Code lab drill

After reading, try Code lab exercise uvm-l8-int-scoreboard-fifo — topic reference: /topics/uvm/coding-practice/scoreboard/ordered-fifo-compare

Common pitfalls

Compare when exp_q empty — index error or bogus match.
No txn.compare() — field-wise typos missed.
Not deleting matched entries — duplicate compares.

Up nextThe UVM Debug Toolkit

Practice this lesson Previous lesson Report an error

WHITEBOARD CHAIN 1. DECLARE interfaces / types / ports you need 2. SKELETON class extends + utils macro + key methods 3. MECHANISM fill one critical method while narrating 4. PITFALL name one bug juniors make on this pattern 5. TEST how you would smoke-test the component

class apb_sb extends uvm_scoreboard; `uvm_component_utils(apb_sb) uvm_analysis_imp_exp #(apb_txn, apb_sb) exp_imp; uvm_analysis_imp_act #(apb_txn, apb_sb) act_imp; apb_txn exp_q[$], act_q[$]; function void write_exp(apb_txn t); exp_q.push_back(t); endfunction function void write_act(apb_txn t); act_q.push_back(t); if (exp_q.size() && act_q.size()) compare_pair(exp_q[0], act_q[0]); endfunction function void compare_pair(apb_txn e, apb_txn a); if (!e.compare(a)) `uvm_error("SB", "mismatch") else begin exp_q.delete(0); act_q.delete(0); end endfunction endclass