08 Circuit Verification

We test for functionality and timing through verification and testing.

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Functional Checks

• check logical correctness of the design
• physical circuit timing ignored

Testbench:

• a simulation of the circuit
• a module created specifically to test a design
• Tested design is called the “device under test (DUT)”

Self-Checking Testbench Example

still not scalable

module testbench2(); // No inputs, outputs
  reg  a, b, c;      // Manually assigned
  wire y;            // Manually checked
 
  // instantiate device under test
  sillyfunction dut(.a(a), .b(b), .c(c), .y(y));
 
  // apply hardcoded inputs one at a time
  initial begin
    a = 0; b = 0; c = 0; #10; // apply input, wait 10ns
    if (y !== 1) $display("000 failed."); // check result
    
    c = 1; #10;               
    if (y !== 0) $display("001 failed.");
 
  end
endmodule

Testvectors

• separate clock just for testing
• apply input on rising edge, check outputs on falling edge

Code Example starting at Slide 111

Golden Models

• represent ideal behaviour on the highest abstraction
• compare your behaviour with the Golden Model
• automated testing, scalable, can also compare timing, separation of roles

→ Code Example for automated testing: