Basics of Assertions

What is an Assertion?
An assertion is simply a check against the specification of your design that you want to make sure never violates. If the specs are violated, you want to see a failure.
When the user listens to assertion first green and red arrows come in the mind.
Assertions, also known as a checkers.

Why is an assertion required?

- Provide the protocol check and functional check.
- Supports Multi-Clock Domain Crossing.
- Provide good control to Enable/Disable the assertion.

Application:
- Scenario 1: Signals 'a' and 'b' always should be sync.

- Scenario 2: Either signal 'a' or 'b' should be high.
- Scenario 3: Signal 'a' should not go high.

USER WANTS CODE:

module basic_assertion();
  bit a,b,clk;
  always #5 clk =~ clk;

  always @(posedge clk)
  begin
  assert (a && b)
  begin
    $display("A && B assertion PASS");
  end
  else
  begin
    $display("A && B assertion FAIL");
  end
  assert(a || b)
  begin
    $display("A || B assertion Pass");
  end
  else
  begin
    $display("A || B assertion FAIL");
  end
  assert(!a)
  begin
    $display("!A assertion FAIL");    
  end
  else
  begin
    $display("!A assertion FAIL");
  end
  end
  initial
  begin
    clk = 0;
    a = 0;
    b = 0;
    #5;
    a = 1;
    b = 1;
    #15;
    a = 0;
    b = 0;
    #15;
    a = 1;
  end
  initial
  begin
    #100;
    $finish;    
  end

endmodule

To run simulation click on below link:

Link: https://www.edaplayground.com/x/3MUW