UVM FAQ2

Why phasing is used? What are the different phases in uvm?

UVM Phases is used to control the behavior of simulation in a systematic way & execute in a sequential ordered to avoid race condition. This could also be done in system verilog but manually.

 

Which phases of UVM are Top-Down?
build_phase() & final_phase() are Top-Down, rest all phases are Bottom-Up.

Which phases of UVM are task?

run_phase(),
pre_reset_phase(), reset_phase(), post_reset_phase(),
pre_configure_phase(), configure_phase(), post_configure_phase(),
pre_main_phase(), main_phase(), post_main_phase(),
pre_shutdown_phase(), shutdown_phase(), post_shutdown_phase()

How do uvm phases initiate?

Calling run_test() constructs the UVM environment root component and then initiates the UVM phasing.

Why is the build_phase() in UVM executed in a Top - Down fashion and the other phases in Bottom - Up fashion?

The build phase has to be that way because the parent component's build_phase constructs the child components. You couldn't call the child's build_phase before the parent's build_phase because they the child objects haven't been constructed yet. You need a constructed object to call its method.

The build_phase() is also executed top-down so that the parent can provide override setting that the children will use when they execute their build_phase()

The ordering within the other phases should not matter, except you might want know that the top level's report_phase comes last.

What is the order of execution of run_phase() ?

The run_phase() of each component is executed concurrently with no defined order you can depend on.

During the run_phase() is there something like super.run_phase(phase) called?

You only need to call super.method() if you are extending a class an need the functionality of the base method. There is nothing inside the run_phase() of a uvm_component, so there is no need to call super.run_phase() when extending from it.

You may want to call it when extending your classes from your base classes.

What is the difference between run_phase and main_phase in uvm_component?

Actually, you can start a sequence in any phase. It is more important to understand the domain/scheduling relationships between the task based (i.e. runtime) phases.

UVM undergoes a number of pre-simulation phases (build, connect, end_of_elaboration, start_of_simulation) that are all implemented with functions. Once those are completed, the task based phases begin.

The standard includes two schedules.

• One is simply the run_phase, which starts executing at time zero and continues until all components have dropped their objections within the run_phase.
• The other schedule contains twelve phases that execute parallel to the run phase. They are: pre_reset, reset, post_reset, pre_config, config, post_config, pre_main, main, post_main, pre_shutdown, shutdown, and post_shutdown. They execute in sequence.

Every component has the opportunity to define or not define tasks to execute these phases. A phase starts only when all components in the previous phase have dropped their objections. A phase continues to execute until all components have dropped their objections in the current phase.

Why connect_phase() is bottom-up?