In SystemVerilog, there are four types of delays that can be used to model the timing behavior of a hardware system: inertial, transport, pure, and delay control. Each type of delay is used under different circumstances and has its own characteristics.
1. Inertial delay: An inertial delay is used to model the behavior of a signal that is changing from one value to another over a period of time. Inertial delays are specified using the “inertial” keyword and are denoted using the “#<" operator. Inertial delays are useful for modeling signals that have a certain minimum duration, such as clock signals, or for modeling signals that are affected by noise or glitches.
#<10ns signal = 1'b0;
2. Transport delay: A transport delay is used to model the behavior of a signal that changes immediately from one value to another. Transport delays are specified using the "transport" keyword and are denoted using the "#" operator. Transport delays are useful for modeling combinational logic or for modeling signals that change immediately in response to an event.
#signal = 1'b0;
3. Pure delay: A pure delay is used to model the behavior of a signal that is delayed by a fixed amount of time, regardless of the signal's value or transitions. Pure delays are specified using the "pure" keyword and are denoted using the "#=" operator. Pure delays are useful for modeling fixed delays in a system, such as delays caused by wires or gates.
#=10ns signal = 1'b0;
4. Delay control: A delay control is used to control the timing of a statement or a block of code. Delay controls are specified using the "wait" or "repeat" keywords and are denoted using the "#" operator. Delay controls are useful for controlling the timing of events in a simulation, such as clock cycles or input stimuli.
wait (#10ns);
Overall, the different types of delays in SystemVerilog are used to model the timing behavior of a hardware system and to control the timing of events in a simulation. The type of delay used depends on the specific behavior that needs to be modeled or controlled, and each type of delay has its own advantages and use cases.