Print, Copy, Compare, and Pack: Using Generated Object Methods

Auto-generated method workflows

Field macros generate do_print, do_copy, do_compare, do_pack so scoreboards, predictors, and debug logs can introspect transactions without hand-written boilerplate.

[UVM] generated method call graph

  sprint()     -> do_print()     -> per-field print per FLAGS
  copy(rhs)    -> do_copy()      -> deep copy per uvm_field_object
  compare(rhs) -> do_compare()   -> field-by-field per FLAGS
  pack/pack_bytes -> do_pack()   -> binary packing per FLAGS

bus_txn a = bus_txn::type_id::create("a");
assert(a.randomize());
`uvm_info("TXN", a.sprint(), UVM_MEDIUM)

bus_txn b = bus_txn::type_id::create("b");
b.copy(a);
if (!a.compare(b)) `uvm_error("CMP", "copy/compare mismatch after clone")

Key takeaways

• sprint() is the fastest debug path for transaction contents.

• copy() + compare() is the standard scoreboard reference-model check.

• Custom do_compare overrides auto-compare when semantics are non-trivial.

Common pitfalls

• Comparing before randomize settles — stale fields cause false mismatches.

• Shallow copy on nested objects when uvm_field_object was omitted.

• Calling compare() across unrelated types without casting guard.

Compare customization and pack patterns

When auto-compare is too strict, override do_compare. Use pack for streaming or recording, with NOPACK on heavy fields.

Custom compare

class timed_txn extends bus_txn;
  int cycle;

  `uvm_object_utils_begin(timed_txn)
    `uvm_field_int(cycle, UVM_ALL_ON | UVM_NOCOMPARE)
    `uvm_object_utils_end

  function bit do_compare(uvm_object rhs, uvm_comparer comparer);
    timed_txn r = timed_txn'(rhs);
    return (addr == r.addr && data == r.data);  // ignore cycle
  endfunction
endclass

[UVM] compare decision tree

fields match with same semantics?
  yes -> rely on auto-compare via field macros
  no  -> UVM_NOCOMPARE on excluded fields
        OR override do_compare for composite rules

Pack and record usage

// Pack for streaming or waveform record
bit [7:0] bytes[];
a.pack_bytes(bytes);

// Selective pack: exclude large payload
`uvm_field_array_int(payload, UVM_ALL_ON | UVM_NOPACK | UVM_NOCOMPARE)

• Use UVM_NOCOMPARE on timestamps and simulator-time fields.

• Use UVM_NOPACK on large arrays used only for stimulus, not checking.

• Prefer sprint at UVM_MEDIUM for interactive debug, UVM_HIGH for field dumps.

Common pitfalls

• Overriding do_compare without calling super when base fields still matter.

• Packing objects with UVM_ALL_ON on multi-kilobyte arrays — regression slowdown.

• Using compare() in hot loops without trimming FLAGS first.