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The original Verilog simulator, Gateway Design's Verilog-XL was the first (and only, for a time) Verilog simulator to be qualified for ASIC (validation) sign-off. After its acquisition by Cadence Design Systems, Verilog-XL changed very little over the years, retaining an interpreted language engine, and freezing language-support at Verilog-1995.
Verilog-2001 is a significant upgrade from Verilog-95. First, it adds explicit support for (2's complement) signed nets and variables. Previously, code authors had to perform signed operations using awkward bit-level manipulations (for example, the carry-out bit of a simple 8-bit addition required an explicit description of the Boolean algebra ...
A simple example is a test-suite—the input/output pairs specify the functionality of the program. A variety of techniques are employed, most notably using satisfiability modulo theories (SMT) solvers, and genetic programming, [7] using evolutionary computing to generate and evaluate possible candidates for fixes. The former method is ...
The names "logic" and "reg" are interchangeable. A signal with more than one driver (such as a tri-state buffer for general-purpose input/output) needs to be declared a net type such as "wire" so SystemVerilog can resolve the final value. Multidimensional packed arrays unify and extend Verilog's notion of "registers" and "memories":
The logic values observed at the device's primary outputs, while applying a test pattern to some device under test (DUT), are called the output of that test pattern. The output of a test pattern, when testing a fault-free device that works exactly as designed, is called the expected output of that test pattern. A fault is said to be detected by ...
Logic simulation may be used as part of the verification process in designing hardware. [3]Simulations have the advantage of providing a familiar look and feel to the user in that it is constructed from the same language and symbols used in design.
If each route has a different delay, then it quickly becomes clear that there is the potential for changing output values that differ from the required / expected output. E.g. A logic circuit is meant to change output state from 1 to 0, but instead changes from 1 to 0 then 1 and finally rests at the correct value 0. This is a dynamic hazard.
Historically, one way to check the equivalence was to re-simulate, using the final netlist, the test cases that were developed for verifying the correctness of the RTL. This process is called gate level logic simulation. However, the problem with this is that the quality of the check is only as good as the quality of the test cases.