Simulation complete via $finish(1) at time 85 NS + 0 The simulator provides the following output after execution of the above testbench. #20 $finish // Finish simulation at time 85ns #5 clk = 0 // Assign clk to 0 at time 5ns

Also called stimulus, we simply assign different values to the variables $monitor('Time = %0t clk = %0d sig = %0d', $time, clk, sig) This system task will print out the signal values everytime they change Initial block : Process starts at time 0ns Process starts at time 0ns and loops after every 5ns The initial block contains a set of statements that assign different values to both the signals at different times. This is done by the always statement by alternating the clock's value after every 5ns. clk represents a clock which is generated within the testbench. There are two variables or signals that can be assigned certain values at specific times. However, in this example we have not used any design instances. The testbench called tb is a container to hold a design module. The Verilog code is divided into multiple processes and threads and may be evaluated at different times in the course of a simulation, which will be touched upon later. Verilog is defined in terms of a discrete event execution model and different simulators are free to use different algorithms to provide the user with a consistent set of results. There are several EDA companies that develop simulators capable of figuring out the outputs for various inputs to the design. Simulation allows us to view the timing diagram of related signals to understand how the design description in Verilog actually behaves. It is also similar to how a fabricated chip will be used in the real world and how it reacts to different inputs.įor example, the design above represents a positive edge detector with inputs clock and signal which are evaluated at periodic intervals to find the output pe as shown. Essentially, simulation is a well-followed technique to verify the robustness of the design. Simulation is a technique of applying different input stimulus to the design at different times to check if the RTL code behaves the intended way. Verilog is a hardware description language and there is no requirement for designers to simulate their RTL designs to be able to convert them into logic gates.

Systemverilog simulator free