UVM Phasing Interview Questions

1. build_phase (Function, Top-down)
2. connect_phase (Function, Bottom-up)
3. end_of_elaboration_phase (Function, Bottom-up)
4. start_of_simulation_phase (Function, Bottom-up)
5. run_phase (Task, Parallel, Time-consuming)
6. extract_phase (Function, Bottom-up)
7. check_phase (Function, Bottom-up)
8. report_phase (Function, Bottom-up)
9. final_phase (Function, Top-down)

Top-Down: `build_phase` and `final_phase`. Build must be top-down so parents are created before they try to create children.

Bottom-Up: `connect_phase` and most others. Connect is bottom-up so you connect children ports before connecting the parent to the outside.

UVM 1.2 introduced 12 runtime sub-phases (pre_reset, reset, ... main, ... shutdown). These run sequentially. The `run_phase` runs in parallel to these 12 phases.

Advice: Avoid mixing them. If you use `run_phase`, stick to it. If you use `main_phase`, stick to the sub-phases.

You must raise an objection. UVM naturally ends when no component has a raised objection.

phase.raise_objection(this);
// Do work
phase.drop_objection(this);

Phase jumping allows you to abort the current phase and move to another (backward or forward). Useful for Warm Resets.

phase.jump(uvm_phase::get_phase_by_name("reset_phase"));

Impact: All components are killed in the current phase and restarted in the target phase.

Yes. You need to extend `uvm_phase`, create a singleton instance, and insert it into the schedule using `uvm_domain::add_phase()`. For example, inserting a `training_phase` for link training before the `main_phase`.

You will need to manually call `super.connect_phase()` or rely on the `uvm_phase` base methods to ensure it's integrated correctly.

1. Check Objections: Use `+UVM_OBJECTION_TRACE` to see who raised but never dropped an objection.

2. Check Timeout: Use `+UVM_TIMEOUT=1000000ns,YES` to force a stop and print stack traces.

3. Check Deadlock: Drivers waiting for items that never come (sequencer empty but objection raised).