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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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<title>8.8 命名块与语句标签</title>
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<a href="00846.html" target="topic">第八章 过程语句和控制流</a></div>
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<a href="#" onmousedown="showPopup(this, 'popup00156');"><img src="seealsolink.png" border="0" alt="" title=""></a> SystemVerilog 3.1a语言参考手册</div>
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8.8 命名块与语句标签</div>
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<div class="Element13"><div class="Element12" id="code00287"><pre class="Element12">seq_block ::=           <span style="color: #008000">// 引用自附录A.6.3</span>
    <strong><span style="color: #FF0000">begin</span></strong> [<strong><span style="color: #FF0000">:</span></strong>block_identifier] {block_item_declaration} {statement_or_null}
    <strong><span style="color: #FF0000">end</span></strong> [<strong><span style="color: #FF0000">:</span></strong>block_identifier]

par_block ::=
    <strong><span style="color: #FF0000">fork</span></strong> [<strong><span style="color: #FF0000">:</span></strong>block_identifier] {block_item_declaration} {statement_or_null}
    join_keyword [<strong><span style="color: #FF0000">:</span></strong>block_identifier]

join_keyword ::= <strong><span style="color: #FF0000">join</span></strong> | <strong><span style="color: #FF0000">join_any</span></strong> | <strong><span style="color: #FF0000">join_none</span></strong></pre></div></div>
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<strong>语法8-8 — 块和标签语法（摘录自附录A）</strong></p><p class="Element10">
&nbsp;</p>
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Verilog允许命名一个<span style="color: #0000FF">begin</span>...<span style="color: #0000FF">end</span>、<span style="color: #0000FF">fork...join</span>、<span style="color: #0000FF">fork...join_any</span>或<span style="color: #0000FF">fork...join_none</span>语句。一个命名的块可以用来标识整个语句块。一个命名的块产生了一个新的层次范围。块的名字在<span style="color: #0000FF">begin</span>或<span style="color: #0000FF">fork</span>关键字之后，并在前面加上一个冒号来说明。例如： </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00288"><pre class="Element12"><span style="color: #0000FF">begin</span> <span style="color: #800080">:</span> blockA <span style="color: #008000">// Verilog-2001命名的块</span>
    ...
<span style="color: #0000FF">end</span></pre></div></div>
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SystemVerilog允许在块的<span style="color: #0000FF">end</span>、<span style="color: #0000FF">join</span>、<span style="color: #0000FF">join_any</span>或<span style="color: #0000FF">join_none</span>关键字之后说明一个匹配的块名字，并在名字的前面加上一个冒号。当块是一个嵌套的块的时候，这种方式可以帮助理解哪一个<span style="color: #0000FF">end</span>、<span style="color: #0000FF">join</span>、<span style="color: #0000FF">join_any</span>或<span style="color: #0000FF">join_none</span>与哪一个<span style="color: #0000FF">begin</span>或<span style="color: #0000FF">fork</span>相关联。块尾部的名字不是必须的，但如果它与块起始处的名字不一致的话，会引起一个错误。 </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00289"><pre class="Element12"><span style="color: #0000FF">begin</span><span style="color: #800080">:</span> blockB <span style="color: #008000">// begin或fork后的块名字</span>
    ...
<span style="color: #0000FF">end</span><span style="color: #800080">:</span> blockB</pre></div></div>
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与C语言一样，SystemVerilog允许在任何语句之前指定一个标签。一个语句标签被用来识别单条语句。标签名字在语句之前说明并跟着一个冒号。 </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00290"><pre class="Element12">labelA<span style="color: #800080">:</span> statement</pre></div></div>
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一个<span style="color: #0000FF">begin</span>...<span style="color: #0000FF">end</span>、<span style="color: #0000FF">fork...join</span>、<span style="color: #0000FF">fork...join_any</span>或<span style="color: #0000FF">fork...join_none</span>块被当作一条语句，并且可以在块的前面具有一个语句标签。 </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00291"><pre class="Element12">labelB<span style="color: #800080">:</span> <span style="color: #0000FF">fork</span>  <span style="color: #008000">// begin或fork之前的标签</span>
    ...
<span style="color: #0000FF">join</span> <span style="color: #800080">:</span> labelB</pre></div></div>
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在<span style="color: #0000FF">begin</span>或<span style="color: #0000FF">fork</span>之前具有标签而在这两个关键字的后面具有块名字是非法的。标签不能出现在<span style="color: #0000FF">end</span>、<span style="color: #0000FF">join</span>、<span style="color: #0000FF">join_any</span>或<span style="color: #0000FF">join_none</span>之前，因为这些关键字不会组成一条语句。&nbsp;</p>
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&nbsp;</p>
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带有标签的语句可以使用<span style="color: #0000FF">disable</span>语句关闭。关闭一条语句与关闭一个命名块具有相同的行为。&nbsp;</p>
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&nbsp;</p>
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参看<a href="00602.html" target="topic">9.6节</a>中有关<span style="color: #0000FF">fork...join</span>、<span style="color: #0000FF">fork...join_any</span>或<span style="color: #0000FF">fork...join_none</span>的其它讨论。</p></div>
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