Config Object Factory: Typed Policy with Override Flexibility

Why factory for cfg classes

Factory-created cfg objects let tests swap policy models while keeping env creation stable.

[TEST][UVM][ENV] cfg factory model

base cfg type:
  env_cfg

scenario-specific cfg:
  perf_env_cfg extends env_cfg
  low_power_env_cfg extends env_cfg

test chooses cfg subtype via factory or direct create

class env_cfg extends uvm_object;
  `uvm_object_utils(env_cfg)
  rand int unsigned num_agents;
  rand bit enable_cov;
  string mode;
endclass

class perf_env_cfg extends env_cfg;
  `uvm_object_utils(perf_env_cfg)
  rand int unsigned max_outstanding;
endclass

Key takeaways

• Cfg classes are first-class API, not throwaway containers.

• Factory allows controlled specialization by scenario family.

• Typed cfg fields improve debug and refactoring safety.

Common pitfalls

• Using untyped associative arrays instead of cfg objects.

• Deep cfg inheritance without clear ownership.

• Factory overrides that are not logged in test startup.

Cfg factory workflow

Tie cfg creation to test intent and preserve visibility through startup logs.

Creation and cast pattern

function env_cfg make_cfg();
  env_cfg c;
  c = env_cfg::type_id::create("cfg");
  if (!$cast(c, c))
    `uvm_fatal("CFG_CAST", "cfg create cast failed")
  return c;
endfunction

virtual function void configure_scenario_cfg(ref env_cfg c);
  perf_env_cfg pc;
  if ($cast(pc, c)) begin
    pc.max_outstanding = 64;
    pc.mode = "PERF";
  end
endfunction

Review checklist

• Every cfg subclass documents additional required fields.

• Scenario code checks cast success before subtype assignments.

• Factory print appears in logs for reproducibility.

• Cfg object includes print/convert2string support.

[UVM] cfg subtype debugging

symptom: field assignment silently ignored
cause: base handle not cast to expected subtype
fix: explicit $cast with fatal on failure

Common pitfalls

• Relying on subtype-specific fields without cast guards.

• Mixing direct new() and factory create() unpredictably.

• No regression coverage for each cfg subtype path.