Hi,
From what I’ve understood so far, uvm_components have each phase so that all objects are able to go to the next phase when all the same phase of every uvm_component objects are finished.
If so, all uvm_component should finish its own run_phase to go to the next phase. All uvm_components eventually complete all run_phase. Then why do we need to have phase.raise_objection & phase.drop_objection?
Can you help me where I misunderstand…?
Thank you,
Seunghyun Lee
In reply to dv_lee86:
The build phases and cleanup phases are implemented as functions, so they are all expected to complete in 0 time.
The run phases will consume time, so the UVM scheduler will fork these tasks in parallel. After forking the tasks, the UVM scheduler uses the objection mechanism to determine what tasks are still actively generating stimulus. When the stimulus tasks are finished and drop their objections, it will then kill all the remaining tasks that were forked. This mechanism allows drivers/monitors to execute in forever loops since they have no knowledge of when to finish.
In reply to cgales:
Thank you for reply.
I am still confused and I have two questions.
If so, it’s conflicted with my thought that all the uvm components always do the same phase at the same time and should complete the previous phase to go to the next phase. It’s conflicted with my thought because only uvm_component with raise/drop_objection seem to be able to finish. And only those which have finished can go to the next phase such as check_phase, and report_phase.
Please correct me.
//////////////////////////////////////////////////
class comp1
...
task run_phase
phase.raise_objection
...
phase.drop_objection
endtask: run_phase
task check_phase
...
endtask: check_phase
//////////////////////////////////////////////////
class comp2
task run_phase
// no phase.raise_objection / drop_objection
endtask: run_phase
task check_phase
...
endtask: check_phase
//////////////////////////////////////////////////
Thank you,
Seunghyun Lee
In reply to dv_lee86:
The UVM scheduler will start the same phase of each component at the same time.
For a time consuming phase, the scheduler will wait for all objections to be dropped. When all objections are dropped, any additional tasks which are still running will be killed. In the case where no component raises an objection, the phase will immediately be terminated and the next phase will start. This can result in tests immediately finishing in 0 time.
In your example, the run_phase in comp1 and comp2 are forked. Since comp1 raises an objection, the scheduler will wait for the objection to be dropped. When this happens, since there are no outstanding objections, the run_phase of comp2 will be killed. The scheduler will then proceed to the next phase.
A component can’t start a phase on its own. The execution of phases is controlled by the scheduler.
All these process start when we invoke run_test() or unm_root…
In reply to dv_lee86:
Here is a simplified example showing how the UVM executes each phase (without objections)
class Component;
string m_name;
Component m_parent;
static Component list[$];
function new(string name, Component parent);
m_name = name;
m_parent = parent;
list.push_back(this);
endfunction
function string get_fullname;
if (m_parent == null)
return m_name;
else
return {m_parent.get_fullname(), "." , m_name};
endfunction
virtual function void build_phase;
endfunction
virtual task run_phase;
endtask
virtual function void report_phase();
endfunction
endclass
class A extends Component;
function new(string name, Component parent);
super.new(name,parent);
$display("A Constructing: ", get_fullname);
endfunction
task run_phase;
#10 $display("Running from ",get_fullname(),,$time);
endtask
function void report_phase;
$display("Reporting from ",get_fullname(),,$time);
endfunction
endclass
class B extends Component;
function new(string name, Component parent);
super.new(name,parent);
$display("B Constructing: ", get_fullname);
endfunction
A a;
function void build_phase;
a = new("a",this);
endfunction
task run_phase;
#20 $display("Running from ",get_fullname(),,$time);
endtask
endclass
class Root extends Component;
function new(string name, Component parent);
super.new(name,parent);
$display("env Constructing: ", get_fullname);
endfunction
A a;
B b;
function void build_phase;
a = new("a",this);
b = new("b",this);
endfunction
task run_test;
// build_phase
for(int item=0;item<list.size();item++)
list[item].build_phase();
// run_phase
foreach(list[item])
fork
int k = item;
list[k].run_phase();
join_none
wait fork;
// report phase
foreach(list[item])
list[item].report_phase();
endtask
endclass
module top;
Root root;
initial begin
root =new("root",null);
root.run_test();
end
endmodule
In reply to cgales:
Thank you all for kindly helping me understand. I did not know that scheduler do wait in time-consuming phase.
Thank you,
Seunghyun Lee