System Verilog Interview Question: What is the Difference Between always_comb and always @*?

When working with System Verilog, it is essential to understand the distinctions between always_comb and always @*. These two constructs are commonly utilized in combinational logic design.

always_comb

The always_comb construct is a sequential block that executes whenever one of its sensitive signals changes. It is primarily used for combinational logic, ensuring that the assigned statements are evaluated at simulation time whenever inputs change, and outputs are updated accordingly.

always @*

The always @* construct, also known as the wildcard sensitivity list, triggers its block whenever any signal in the design changes. It is used for both combinational and sequential logic, capturing changes on any signal within the block.

Key Difference:

The main difference between always_comb and always @* lies in their sensitivity lists. While always_comb triggers on the signal(s) explicitly declared in its sensitivity list, always @* triggers on any signal change within the block.

Understanding these differences is crucial for writing efficient, error-free System Verilog code. By utilizing the appropriate construct based on the design requirements, designers can ensure proper functionality and simulation accuracy.