![]() ![]() Testbenches use the = and != operators for comparisons of equality and inequality, respectively, because these operators work correctly with operands that could be x or z. In SystemVerilog, comparison using = or != is effective between signals that do not take on the values of x and z. The $error system task in the else statement prints an error message describing the assertion failure. The SystemVerilog assert statement checks whether a specified condition is true. Otherwise, the process would begin again, repeatedly applying the pattern of test vectors.Īssert (y = 1) else $error('000 failed.') Īssert (y = 0) else $error('001 failed.') Īssert (y = 0) else $error('010 failed.') Īssert (y = 0) else $error('011 failed.') Īssert (y = 1) else $error('100 failed.') Īssert (y = 1) else $error('101 failed.') Īssert (y = 0) else $error('110 failed.') Īssert (y = 0) else $error('111 failed.') It then applies 001 and waits 10 more ns, and so forth until all eight possible inputs have been applied.Īt the end, the process waits indefinitely. The process statement first applies the input pattern 000 and waits for 10 ns. Hardware has no way of magically executing a sequence of special steps when it is first turned on. ![]() initial statements should be used only in testbenches for simulation, not in modules intended to be synthesized into actual hardware. It then applies 001 and waits 10 more units, and so forth until all eight possible inputs have been applied. In this case, it first applies the input pattern 000 and waits for 10 time units. fpga4student.The initial statement executes the statements in its body at the start of simulation. ![]()
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