Phases in UVM

UVM introduces the concept of phases to ensure that all objects are properly configured and connected before starting the runtime simulation. Phases contribute to a better synchronised simulation and enable to the verification engineer to get better modularity of the testbench.

UVM phases consists of:

  1. build
  2. connect
  3. end_of_elaboration
  4. start_of_simulation
  5. run
    1. reset
    2. configure
    3. main
    4. shutdown
  6. extract
  7. check
  8. report
  9. final

The run phase has been simplified to get a better picture of how phases worked. Nevertheless, all subphases in the run phase have a pre_ and post_ phase to add flexibility. Therefore, the run phase is actually composed by the following phases:

  1. run
    1. pre_reset
    2. reset
    3. post_reset
    4. pre_configure
    5. configure
    6. post_configure
    7. pre_main
    8. main
    9. post_main
    10. pre_shutdown
    11. shutdown
    12. post_shutdown

Although all phases play an important role, the most relevant phases are:

  • build_phase: objects are created
  • connect_phase: interconnection between objects are hooked
  • run_phase: the test starts. The run_phase is the only phase which is a task instead of a function, and therefore is the only one that can consume time in the simulation.

UVM phases are executed from a hierarchical point of view from top to down fashion. This means that the first object that executes a phase is the top object, usually

testbench  test  environment agent {monitor, driver, sequencer, etc}

Nevertheless, in the connect phase, this happens the other way round in a down to top fashion.

{monitor, driver, sequencer} agent environment test testbench

How to add UVM in your Verilog test bench

To use UVM in your Verilog test bench, you need to compile the UVM package top. To do so, you need to include it on your file by using:

The uvm_pkg is contained in the that must be passed to the compiler. Therefore, it is necessary to indicate the UVM path to the compiler. In Cadence Incisive Enterprise Simulator (IES) is so easy as to specify -uvm switch.

In Modelsim, from Modelsim console, run:

After compilation, click on Simulate > Start simulation and select the tb in the work library. Then, run the simulation for the desired time.