Assertion Practice Questions

  1. If signal “a” is high on a given positive clock edge, then within 1 to 4 clock cycles, the signal “b” should be high.
property p1 @(posedge clk)
  a |-> ##[1:4]b;
endproperty
 
a1: assert property(p1)

2. If signal “a” is high on a given positive clock edge, then signal “b” will be high eventually starting from the next clock cycle.

property p2 @(posedge clk)
    a |=> ##1 b;
  endproperty
  a2: assert property(p2)

3.  If the signal “a” is high on given posedge of clock, then signal “b” should be high for 3 clock cycles followed by “c” should be high after ”b” is high for third time.

property p4 @(posedge clk)
          a|-> ##1 b[->3] ##1 c;
 endproperty
 a4: assert property(p4)

4. Write an assertion checker to make sure that an output signal never goes X.

property p1;
  @(posedge clk) 
  !$isinknown(output_signal);
endproperty

a1: assert property (p1) 
  else $error("assertion got failed")

5. When signal_a is asserted, signal_b must be asserted, and must remain up until one of the signals signal_c or signal_d is asserted.

property p1;
  @(posedge clk) disable iff (rst)
  sig_a |-> sig_b throughout (!sig_c && !sig_d);
endproperty

a1: assert property (p1) 
  else $error("assertion got failed");

6. write a assertion to verify dut clock frequency of 10ns.

module tb;
  
  time pre_time;
  
  property p1;
    @(posedge clk) disable iff(rst)
    $rose(clk) |-> (($time - pre_time)== 10);
  endproperty
  
  assert property(p1)
    else $error("clk period is not 10ns");
    
    always @(posedge clk or posedge rst) begin
      if (rst) 
            pre_time <= 0;
        else 
            pre_time <= $time; 
    end

endmodule

7. When req is high , grant should be asserted within 2 to 20 clk cycles until request should be high. In the next clk cycle, req should be low.

sequence s1;
  req |-> ##[2:20] grant throughout req;
endsequence
 
sequence s2;
  s1 |=> !req;
endsequence
 
property p1;
   @(posedge clk) disable iff(rst)
  s1 |-> s2;
endproperty
 
a1: assert property(p1)
  else $error("assertion got failed");

8. Write a SV assertion that monitors for an ack. If the ack is not received within 500clks, it issue an error.

property p1;
  @(posedge clk) disable iff(rst)
  (!ack) |=> ##[0:499]ack;
endproperty
 
a1: assert property(p1)
  else $error("Error:ACK not received within 500 clock cycles!");

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