Factory & Configuration

Factory decides which class; config_db decides how it is configured

Reusability comes from not hard-coding decisions in the environment. The factory picks the class at create time; config_db supplies handles and parameters before build_phase.

Factory & config topic map

Legend: [FACTORY] [CONFIG] [HDL] [UVM]

┌─────────────────────────────────────────────────────────────────────────┐
│  FACTORY & CONFIG — 5 topic hubs (each with 5–6 sub-lessons)            │
├─────────────────────────────────────────────────────────────────────────┤
│  1. FACTORY [FACTORY]   registry │ type_id::create │ registration       │
│  2. OVERRIDES [FACTORY] type vs instance │ precedence │ timing           │
│  3. CONFIG_DB [CONFIG]  set/get │ paths │ wildcards │ resolution         │
│  4. VIF DIST [HDL]      static bridge │ single/multi instance patterns   │
│  5. RESOURCES [UVM]     resource_db │ field macros │ print/copy/compare   │
└─────────────────────────────────────────────────────────────────────────┘

Two mechanisms diagram

[HDL] top ──config_db.set(vif)──► [CONFIG]
      └── run_test() ──factory.create()──► [FACTORY]
                ▼
[UVM] test: set_type_override + config_db.set(cfg)
      env build: type_id::create() + config_db.get(vif)

FACTORY: WHICH class?   CONFIG: WITH WHAT settings?

Topics and sub-topics

1. UVM Factory — 6 sub-lessons on registration, type_id, and create().

2. Type vs Instance Overrides — 6 sub-lessons on scope, precedence, and Liskov safety.

3. uvm_config_db — 6 sub-lessons on set/get, paths, wildcards, and resolution.

4. Virtual Interface Distribution — 6 sub-lessons on HDL→UVM vif patterns.

5. Resources & Field Macros — 6 sub-lessons on resource_db and field automation.

Key takeaways

• Factory = which class is built; config_db = how that instance is configured.

• Overrides before create(); config set before consumer build_phase get().

• Virtual interfaces cross from static HDL into dynamic UVM via config_db.

How to use this section

Keep factory and config separate in your mental model. Most confusion comes from mixing override timing with config_db path mistakes.

• Never use new() for UVM components — always type_id::create() through the factory.

• Set config and overrides in test build_phase before env children build.

• Use instance paths and wildcards deliberately — sloppy paths cause silent misconfiguration.