CircuitOnline/public/js/verilog_documentation.md

Circuit2Verilog Module

Primary Contributors:

1. James H - J Yeh, Ph.D.
2. Satvik Ramaprasad

Introduction

This is an experimental module which generates verilog netlist (structural verilog) given the circuit. Currently, the module generates fully functional verilog code for basic circuits. For complex circuit, additional (manual) work may need to be done in order to make it work. We are continuously improving this module to work with more and more complex circuits.

Algorithm

The basic algorithm is fairly straight forward. We have the circuit graph in memory. We just need to convert this graph into verilog netlist. It is done by performing a DFS on the circuit graph. The DFS involves the following steps

1. Creating verilog wires as and when required
2. Connecting verilog wires in element instantiations

Some background information

The different sub circuits form a DAG (Directed Acyclic Graph) or dependency graph. Each sub circuit itself (called scope internally) is actually a (cyclic) graph on its own. Therefore the verilog generation is done in a 2 step DFS approach. The first DFS is performed on the dependency graph. The second DFS is done on individual sub circuit (scope).

Code/Algorithm workflow

1. exportVerilog() - entry point
2. exportVerilogScope() - DFS(1) on Sub Circuits Dependency Graph
   1. Set Verilog Labels for all elements
   2. generateHeader() - Generates Module Header
   3. generateOutputList() - Output Output List
   4. generateInputList() - Generates Input List
   5. processGraph() - DFS(2) on individual subcircuit/scope
      1. DFS starts from inputs
      2. Calls processVerilog() on all circuit elements (graph nodes) - resolves label names and adds neighbors to DFS stack.
      3. Calls generateVerilog() on all circuit elements to get final verilog.
   6. Generate Wire initializations

Functions

Verilog Module Functions:

1. verilog.exportVerilog() - Entry point
2. verilog.exportVerilogScope() - Recursive DFS function on subcircuit graph
3. verilog.processGraph() - Iterative DFS function on subcircuit scope
4. verilog.resetLabels() - Resets labels in scope
5. verilog.setLabels() - Sets labels in scope
6. verilog.generateHeader() - Generates Verilog Module Header
7. verilog.generateInputList() - Generates Verilog Module Input List
8. verilog.generateOutputList() - Generates Verilog Module Output List
9. verilog.sanitizeLabel() - Sanitizes label for node/wire
10. verilog.generateNodeName() - Helper function to resolve node/wire name

CircuitElement Functions:

These functions can be overriden by derived classes.

1. CircuitElement.prototype.processVerilog() - Graph algorithm to resolve verilog wire labels
2. CircuitElement.prototype.verilogName() - Generate verilog name
3. CircuitElement.prototype.generateVerilog() - Generate final verilog code
4. CircuitElement.prototype.verilogType - Verilog type name
5. CircuitElement.moduleVerilog - Custom module verilog for elements