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<HTML><HEAD> <META NAME="GENERATOR" CONTENT="Adobe PageMill 2.0 Mac"> <LINK REL="STYLESHEET" HREF="ch03.css"> <TITLE> 3.11 Name spaces</TITLE></HEAD><BODY BGCOLOR="#ffffff"><P><A NAME="pgfId=612"></A><HR ALIGN=LEFT></P><P><A HREF="ch03.htm">Chapter start</A> <A HREF="ch03.a.htm">Previous page</A></P><H1>3.11 Name spaces</H1><P><P CLASS="Body"><A NAME="pgfId=613"></A>In Verilog HDL, there are sixname spaces; two are global and four are local. The global name spaces are<I>Definitions</I> and <I>Text macros</I> . The <I>definitions name space</I>unifies all the <B>module</B> (section 12.1), <B>macromodule</B> (section 12.1),and <B>primitive</B> (section 8.1) definitions. That is, a module anda macromodule or a primitive cannot have the same name.</P><P><P CLASS="Body"><A NAME="pgfId=445"></A>The <I>text macro name space</I>is global. Since text macro names are introduced and used with a leading<B>`</B> character, they remain unambiguous with any other name space (section 16.3).The text macro names are defined in the linear order of appearance in theset of input files that make up the description of the design unit. Subsequentdefinitions of the same name override the previous definitions for the balanceof the input files.</P><P><P CLASS="Body"><A NAME="pgfId=615"></A>There are four local name spaces:<I>Block</I> , <I>Module</I> , <I>Port</I> , and <I>Specify</I> <I>Block</I>.</P><P><P CLASS="Body"><A NAME="pgfId=616"></A>The <I>block name space</I> isintroduced by the named block (section 9.8), function (section 10.3)and task (section 10.2) constructs. It unifies the definitions of thenamed blocks, functions, tasks and the register type of declaration (section 3.2.2).The register type of declaration includes <B>reg</B>, <B>integer</B>, <B>time</B>,<B>real</B>, <B>realtime</B>, <B>event</B> and <B>parameter</B> declarations.</P><P><P CLASS="Body"><A NAME="pgfId=619"></A>The <I>module name space</I>is introduced by the <B>module</B>, <B>macromodule</B>, and <B>primitive</B>constructs. It unifies the definition of functions, tasks, named blocks,instance names, net type of declaration and register type of declaration.The net type of declaration includes <B>wire</B>, <B>wor</B>, <B>wand</B>,<B>tri</B>, <B>trior</B>, <B>triand</B>, <B>tri0</B>, <B>tri1</B>, <B>trireg</B>,<B>supply0</B>, and <B>supply1</B> (section 3.7).</P><P><P CLASS="Body"><A NAME="pgfId=620"></A>The <I>port name space</I> isintroduced by the <B>module</B>, <B>macromodule</B>, <B>primitive</B>, <B>function</B>and <B>task</B> constructs. It provides a means of structurally definingconnections between two objects that are in two different name spaces. Theconnection can be unidirectional (either <B>input</B> or <B>output</B>)or bidirectional (<B> inout</B>). The port name space overlaps the moduleand the block name spaces. Essentially, the port name space specifies thetype of connection between names in different name spaces. The port typeof declarations include <B>input</B>, <B>output</B> and <B>inout</B> (section 12.3).A port name introduced in the port name space may be reintroduced in themodule name space by declaring a register or a wire with the same name asthe port name.</P><P><P CLASS="Body"><A NAME="pgfId=623"></A>The <I>specify</I> <I>block</I><I>name space</I> is introduced by the <B>specify</B> construct (section 13.2).A <B>specparam</B> name can be defined and used only in the specify blockname space. Any other type of name can not be defined in this name space.</P><P><HR ALIGN=LEFT></P><P><A HREF="ch03.htm">Chapter start</A> <A HREF="ch03.a.htm">Previous page</A></BODY></HTML>?? 快捷鍵說明
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