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📁 这是一本关于verilog编程语言的教程,对学习verilog语言有帮助
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<a href="00864.html" target="topic">第十八章 层次</a>, <a href="00954.html" target="topic">主题</a></div>
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<a href="#" onmousedown="showPopup(this, 'popup00373');"><img src="seealsolink.png" border="0" alt="" title=""></a> SystemVerilog 3.1a语言参考手册</div>
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18.2 包</div>
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SystemVerilog包提供了额外的机制在多个SystemVerilog模块、接口和程序间共享参数、数据、类型、任务、函数、序列以及特性的声明。包是显式命名的作用域，它出现在源文本的最外层（与顶层模块和原语处于同一层次）。类型、变量、任务、函数以及特性都可以在一个包中声明。这些声明可以在模块、宏模块、接口、程序和其它包中通过导入或完整解析的名字来引用。 </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00792"><pre class="Element12">package_declaration ::=              <span style="color: #008000">// 引用自附录A.1.3</span>
    {attribute_instance} <strong><span style="color: #FF0000">package</span></strong> package_identifier<strong><span style="color: #FF0000">;</span></strong>
        [timeunits_declaration] {{attribute_instance} package_item}
    <strong><span style="color: #FF0000">endpackage</span></strong> [<strong><span style="color: #FF0000">:</span></strong> package_identifier]

package_item ::=                    <span style="color: #008000">// 引用自附录A.1.10</span>
    package_or_generate_item_declaration
  | specparam_declaration
  | anonymous_program
  | timeunits_declaration

package_or_generate_item_declaration ::=
    net_declaration
  | data_declaration
  | task_declaration
  | function_declaration
  | dpi_import_export
  | extern_constraint_declaration
  | class_declaration
  | class_constructor_declaration
  | parameter_declaration<strong><span style="color: #FF0000">;</span></strong>
  | local_parameter_declaration
  | covergroup_declaration
  | overload_declaration
  | concurrent_assertion_item_declaration
  | <strong><span style="color: #FF0000">;</span></strong>

anonymous_program ::= <strong><span style="color: #FF0000">program;</span></strong> {anonymous_program_item} <strong><span style="color: #FF0000">endprogram</span></strong>

anonymous_program_item ::=
    task_declaration
  | function_declaration
  | class_declaration
  | covergroup_declaration
  | class_constructor_declaration
  | <strong><span style="color: #FF0000">;</span></strong></pre></div></div>
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<strong>语法18-1 — 包声明语法（摘录自附录A）</strong></p><p class="Element10">
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包声明产生了一个作用域，它包含了用于在一个或多个编译单元、模块、宏模块、接口或程序间共享的声明。位于包内的项目通常是类型定义、任务、以及函数。位于包内的项目不能具有层次化的引用。包还可能包含参数、变量和线网。对于那些不方便通过层次向下传递的全局项目，这种方式可能有用。与在一个编译单元或模块内声明的变量相同，位于包内的变量声明赋值应该出现在任何<span style="color: #0000FF">initial</span>、<span style="color: #0000FF">always</span>、<span style="color: #0000FF">always_comb</span>、<span style="color: #0000FF">always_latch</span>或<span style="color: #0000FF">always_ff</span>块被启动之前。&nbsp;</p>
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&nbsp;</p>
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下面是包的一个例子： </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00793"><pre class="Element12"><span style="color: #0000FF">package</span> ComplexPkg<span style="color: #800080">;</span>
    <span style="color: #0000FF">typedef struct</span> <span style="color: #800080">{</span>
        <span style="color: #0000FF">float</span> i<span style="color: #800080">, </span>r<span style="color: #800080">;</span>
    <span style="color: #800080">}</span> Complex<span style="color: #800080">;</span>

    <span style="color: #0000FF">function</span> Complex add<span style="color: #800080">(</span>Complex a<span style="color: #800080">, </span>b<span style="color: #800080">);</span>
        add<span style="color: #800080">.</span>r<span style="color: #800080"> =</span> a<span style="color: #800080">.</span>r <span style="color: #800080">+</span> b<span style="color: #800080">.</span>r<span style="color: #800080">;</span>
        add<span style="color: #800080">.</span>i <span style="color: #800080">=</span> a<span style="color: #800080">.</span>i <span style="color: #800080">+</span> b<span style="color: #800080">.</span>i<span style="color: #800080">;</span>
    <span style="color: #0000FF">endfunction</span>

    <span style="color: #0000FF">function</span> Complex mul<span style="color: #800080">(</span>Complex a<span style="color: #800080">, </span>b<span style="color: #800080">);</span>
        mul<span style="color: #800080">.</span>r <span style="color: #800080">= (</span>a<span style="color: #800080">.</span>r <span style="color: #800080">*</span> b<span style="color: #800080">.</span>r<span style="color: #800080">) - (</span>a<span style="color: #800080">.</span>i <span style="color: #800080">*</span> b<span style="color: #800080">.</span>i<span style="color: #800080">);</span>
        mul<span style="color: #800080">.</span>i <span style="color: #800080">= (</span>a<span style="color: #800080">.</span>r <span style="color: #800080">*</span> b<span style="color: #800080">.</span>i<span style="color: #800080">) + (</span>a<span style="color: #800080">.</span>i <span style="color: #800080">*</span> b<span style="color: #800080">.</span>r<span style="color: #800080">);</span>
    <span style="color: #0000FF">endfunction</span>
<span style="color: #0000FF">endpackage</span> <span style="color: #800080">:</span> ComplexPkg</pre></div></div>
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描述&nbsp;</div></td></tr><tr>
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<a href="00204.html" target="topic">18.2.1 引用包中的数据</a>&nbsp;</div></td><td class="Element206" valign="top" width="50%">
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为了在包被导入的作用域内能够识别包中定义的项目，包必须存在。<br><br>使用一个包中所作声明的一种方法是使用域解析操作符“<span style="color: #800080">::</span>”进行引用。 &nbsp;</div></td></tr><tr>
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<a href="00205.html" target="topic">18.2.2 搜索顺序规则</a>&nbsp;</div></td><td class="Element206" valign="top" width="50%">
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对于从一个包中导入的声明，表格18-1为其描述了搜索顺序规则。为了方便以后的讨论，考虑下面的包声明： &nbsp;</div></td></tr></table></div></div>
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