Verilog Translator

h1. Getting Started

This is a step-by-step instruction for getting started with developing a "VeriTrans":http://forge.ispras.ru/projects/veritrans backend and using it within the Verilog translator environment. The term _backend_ refers to a component that traverses an _abstract syntax tree_ (_AST_) of the Verilog description and processes it in some way (e.g., constructs the internal representation and/or converts the description into some other language). The document is illustrated by the example of @VerilogPrinter@ (see the package @ru.ispras.verilog.parser.sample@).

h2. Developing a Backend

Technically, a backend is a Java object that implements the @VerilogBackend@ interface (the method @start@). Here is an example:

<pre><code class="java">

package ru.ispras.verilog.parser.sample;

import ru.ispras.verilog.parser.VerilogBackend;

import ru.ispras.verilog.parser.model.*;

...

/**

 * This class illustrates development of a Verilog backend.

 */

public final class VerilogPrinter extends VerilogBackend

{

    /**

     * Processes the abstract syntax tree (AST).

     *

     * @param root the AST''s root.

     */

    public void start(final VerilogNode root)

    {

        ...

    }

}

</code></pre>

To ease development of a backend, one can use @VerilogTreeWalker@, a "VeriTrans":http://forge.ispras.ru/projects/veritrans class that implements AST traversal. The @VerilogTreeWalker@''s constructor takes two parameters: (1) a reference to the tree''s root and (2) a visitor to be applied to the tree nodes:

<pre><code class="java">

...

import ru.ispras.verilog.parser.walker.*;

public void start(final VerilogNode root)

{

    // Create the AST traverser.

    VerilogTreeWalker walker = new VerilogTreeWalker(root, new VerilogNodePrinter());

    walker.start();

}

</code></pre>

The most substantial part of backend development concerns creation of the AST nodes’ visitor, a subclass of the abstract class @VerilogNodeVisitor@. The visitor should implement two methods for each of the node types:

<pre><code class="java">

// Pre-visitor: it is invoked before the child nodes are visited.

public void on<NodeType>Begin (final <NodeType> node);

// Post-visitor: it is invoked after the child nodes are visited.

public void on<NodeType>End   (final <NodeType> node);

</code></pre>

Supported node types include (see the package @ru.ispras.verilog.parser.model@):

| *Activity* |<. process (@always@ or @initial@) |

| *AssignBegin* |<. continuous assignment (@assign@) |

| *AssignStatement* |<. assignment statement (@=@, @<=@, @assign@, @deassign@, @force@ or @release@) |

| *Assignment* |<. assignment |

| *Attribute* |<. attribute |

| *BlockGenerate* |<. generate block |

| *BlockStatement* |<. block statement (@begin@ or @fork@) |

| *CaseGenerate* |<. generate case selection |

| *CaseGenerateItem* |<. generate case item |

| *CaseStatement* |<. case statement (@case@, @casex@ or @casez@) |

| *CaseStatementItem* |<. case statement item |

| *Code* |<. source code |

| *Declaration* |<. declaration (@input@, @output@, @inout@, @event@, @parameter@, @specparam@, @localparam@, @defparam@, @genvar@ or variable) |

| *DelayedStatement* |<. delayed statement |

| *DisableStatement* |<. disable statement |

| *Generate* |<. generate construct |

| *IfGenerate* |<. conditional generate construct |

| *IfGenerateBranch* |<. if generate branch (@then@ or @else@) |

| *IfStatement* |<. conditional statement |

| *IfStatementBranch* |<. if statement branch (@then@ or @else@) |

| *Instantiation* |<. instantiation construct |

| *LoopGenerate* |<. generate loop |

| *LoopStatement* |<. loop statement (@forever@, @repeat@, @while@ or @for@) |

| *Module* |<. module declaration |

| *NullStatement* |<. null statement |

| *PathDeclaration* |<. path declaration |

| *Port* |<. port declaration |

| *PortConnection* |<. port connection |

| *Procedure* |<. procedure declaration (@function@ or @task@) |

| *PulseStyle* |<. pulse style specification |

| *ShowCancelled* |<. show-cancelled construct |

| *Specify* |<. specify construct |

| *Table* |<. UDP (user-defined primitive) table |

| *TableEntry* |<. UDP table entry |

| *TaskStatement* |<. task statement |

| *TriggerStatement* |<. trigger statement |

| *WaitStatement* |<. wait statement |

A visitor example is given below.

<pre><code class="java">

package ru.ispras.verilog.parser.sample;

import ru.ispras.verilog.parser.model.*;

import ru.ispras.verilog.parser.walker.*;

...

/**

 * This class illustrates development of a Verilog node visitor.

 */

public final class VerilogNodePrinter extends VerilogNodeVisitor

{

    @Override

    public void onActivityBegin(final Activity node)

    {

        indent();

        switch(node.getType())

        {

        case INITIAL:

            text("initial");

            break;

        case ALWAYS:

            text("always");

            break;

        }

        endl();

        begin();

    }

    @Override

    public void onActivityEnd(final Activity node)

    {

        end();

    }

    ...

}

</code></pre>

h2. Registering a Backend