Simulation and Synthesis in VLSI
In the design flow of digital circuits, simulation and synthesis are two crucial steps.
Simulation:
A design must be checked to ensure that it is functionally correct, after it has been specified and entered.
- Simulation is the process of running a design through a software simulator to see how it works and behaves.
- An input stimulus or test vector is applied to the design during simulation, and outputs are compared against what was expected. The designers can then identify and debug any design errors or issues.
Synthesis:
An important step in digital design is synthesis. Synthesis uses high-level hardware description languages such as Verilog or VHDL, to translate the design into a hardware circuit. Typically, FPGA or ASIC are used for this purpose.
- A behavioral-level design is transformed into a gate-level or register-transfer level (RTL) representation during synthesis.
- The synthesis tool analyses the design description and generates a netlist, which represents the logical and structural connections between different circuit elements (gates, flip-flops etc.) required to implement the design.
- The synthesis process is typically carried out incrementally, starting with smaller behavioral-level modules and gradually refining them to gate-level or RTL-level modules. As a result of this iterative process, each module is converted step-by-step until the entire design is available as gate and RTL data.
Functional Verification
Testing : Any hardware circuit design process requires testing. Tests are performed in two dimensions: functionally and timing-wise. With Verilog, both can be accomplished. To test/verify functionality, a “test bench” is often established.
After the design has been instantiated, the test bench generates comprehensive test signals, which are applied to the instantiated design. Throughout the testing process, the outputs from the design are looped back to the test bench for analysis. It is necessary to configure input signals, waveforms, and sequences in advance before conducting testing. This ensures a systematic and thorough evaluation of the design’s performance through a well-defined set of input scenarios.
The use of behavioral-level test benches ensures comprehensive testing of the design’s functionality by accommodating different types of test scenarios.
“When testing a module, it is often necessary to access variables embedded within other modules, which are instantiated within the master module. Hierarchical addressing is an effective means of navigating the design structure.”