Difficulty: Medium · Puzzle 3 of 6 · Topic: Handle and Copy Puzzles
A monitor reuses one transaction object every cycle and sends it over analysis port. Why does scoreboard history show all entries with the final sample value?
class mon extends uvm_component;
`uvm_component_utils(mon)
uvm_analysis_port #(tr) ap;
tr t;
function new(string name, uvm_component parent);
super.new(name, parent);
ap = new("ap", this);
endfunction
task run_phase(uvm_phase phase);
t = tr::type_id::create("t");
forever begin
@(posedge vif.clk);
t.addr = vif.addr;
ap.write(t);
end
endtask
endclass
function void sb::write(tr t);
exp_q.push_back(t);
endfunctionAsk whether `write()` transfers a new object or the same handle.
1) `ap.write(t)` passes a handle, not a deep-copied object.
2) Scoreboard stores that same handle each cycle, so queue entries alias one object.
3) Next cycle updates `t.addr`, and all previously stored handles appear to change.
4) Clone in monitor before write, or clone in subscriber on receipt.Answer: All entries alias the same reused object handle; the scoreboard never captured immutable snapshots.
Assuming TLM analysis behaves like pass-by-value instead of pass-by-handle.
Where should cloning happen for best performance and ownership clarity: monitor, analysis FIFO, or scoreboard?