UVM Internals - UVM_TIMEOUT

This posts explains how +UVM_TIMEOUT works.

Starting with how it is used

<sim command> +UVM_TIMEOUT=200000,NO

UVM_TIMEOUT is read in uvm_root.svh which parses the value and override strings and calls set_timeout.

  timeout_count = clp.get_arg_values("+UVM_TIMEOUT=", timeout_settings);
  if (timeout_count ==  0)
    return;
  else begin
    timeout = timeout_settings[0];
    if (timeout_count > 1) begin
      string timeout_list;
      string sep;
      for (int i = 0; i < timeout_settings.size(); i++) begin
        if (i != 0)
          sep = "; ";
        timeout_list = {timeout_list, sep, timeout_settings[i]};
      end
      uvm_report_warning("MULTTIMOUT",
        $sformatf("Multiple (%0d) +UVM_TIMEOUT arguments provided on the command line.  '%s' will be used.  Provided list: %s.",
        timeout_count, timeout, timeout_list), UVM_NONE);
    end
    uvm_report_info("TIMOUTSET",
      $sformatf("'+UVM_TIMEOUT=%s' provided on the command line is being applied.", timeout), UVM_NONE);
      void'($sscanf(timeout,"%d,%s",timeout_int,override_spec));
    case(override_spec)
      "YES"   : set_timeout(timeout_int, 1);
      "NO"    : set_timeout(timeout_int, 0);
      default : set_timeout(timeout_int, 1);
    endcase
  end

set_timeout sets the phase_timeout in uvm_root

function void uvm_root::set_timeout(time timeout, bit overridable=1);
  static bit m_uvm_timeout_overridable = 1;
  if (m_uvm_timeout_overridable == 0) begin
    uvm_report_info("NOTIMOUTOVR",
      $sformatf("The global timeout setting of %0d is not overridable to %0d due to a previous setting.",
         phase_timeout, timeout), UVM_NONE);
    return;
  end
  m_uvm_timeout_overridable = overridable;
  phase_timeout = timeout;
endfunction

then eventually when task uvm_phase::execute_phase() is called, it waits until for that timeout

                 if (m_phase_trace)
                    `UVM_PH_TRACE("PH/TRC/TO_WAIT", $sformatf("STARTING PHASE TIMEOUT WATCHDOG (timeout == %t)", top.phase_timeout), this, UVM_HIGH)
                  `uvm_delay(top.phase_timeout)

`define uvm_delay(TIME) #(TIME);

Side note, UVM_DEFAULT_TIMEOUT is set to 2900s by default which sounds like arbitrary number. Who chose it?

`define UVM_DEFAULT_TIMEOUT 9200s