Assertion

1. An Assertion specifies the behaviour of the system.
2. It validates the behaviour of design 
3. In addition, assertion can be used to provide functional coverage and generate input stimulus for validation


The advantage of assertion:
1. Improving observability 
2. reduce the debug time 
3. bugs can be found earlier and more isolated 
4. can interact with C function



types of assertion:
1.Immediate 
2. concurrent 


Immediate                                                                concurrent                            

based on simulation event                                       based on a clock cycle 
used without property keyword                                used with property keyword
placed in procedure block definition                        placed in procedural blocks, modules, interfaces or program                                                                                     definition

i) Immediate assertions are useful for combinational expression, similar to if else statement but with assertion control.
ii) Assertions are non-synthesizable
iii) Assertions can be written in design and TB both but in design, while synthesising need to remove so use `define


Difference between assert and cover :

assert: if you want scenario to be hold true then you write an assertion.
cover : Whether scenario ever happened in your simulation or not.


|-> implication operator

sequence s;
    @(posedge clk) a ##1 b;
  endsequence
 
  property p;
    a |-> s;
  endproperty
 
  assert property (p);
  cover property (p);