Hi, Let’s understand this in a practical way.
In UVM, phase objections are a control mechanism used to tell the simulator: “I am still doing useful work — don’t end this phase yet.”
They are mainly used in task-based phases like run_phase.
Each UVM phase (especially run_phase) ends when all objections are dropped.
UVM maintains an internal objection counter:
- raise_objection() → increment counter
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drop_objection() → decrement counter
-
Phase ends only when counter = 0
In UVM, multiple components run in parallel in UVM like driver, monitor, sequences, scoreboard, test etc. UVM needs a way to know, Is anyone still active?
Without objections, run_phase would finish immediately — even before your stimulus runs.
Now, let’s understands this in a real life analogy.
Think of a classroom exam:
-
Teacher = UVM phase
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Students = UVM components
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Each student raises hand → “I’m still writing”
-
When done → student lowers hand
Teacher ends exam only when all hands are down.
Raise = hand up
Drop = hand down
If one student forgets → exam never ends.
Hope this clears your doubt. For examples and more details you can read this article:
“If this still feels confusing, ask the VLSI AI assistant on VLSIWORLDS ”
Or we can further discuss in comments.