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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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17.9 在一个序列匹配时调用子程序</div>
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任务、任务方法、<span style="color: #0000FF">void</span>函数、<span style="color: #0000FF">void</span>函数方法以及系统任务可以在一个序列成功匹配的结束处调用。子程序调用，例如局部变量赋值，出现在紧跟着序列的以逗号分割的列表中。子程序调用被称为附加到序列。序列以及之后的列表以括号包围。 </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00664"><pre class="Element12">sequence_expr ::=         <span style="color: #008000">// 引用自附录A.2.10</span>
    ...
  | <strong><span style="color: #FF0000">(</span></strong>expression_or_dist{<strong><span style="color: #FF0000">,</span></strong> sequence_match_item }<strong><span style="color: #FF0000">)</span></strong> [boolean_abbrev]
  | <strong><span style="color: #FF0000">(</span></strong>sequence_expr{<strong><span style="color: #FF0000">,</span></strong> sequence_match_item}<strong><span style="color: #FF0000">)</span></strong> [sequence_abbrev]
    ...

sequence_match_item ::=
    operator_assignment
  | inc_or_dec_expression
  | subroutine_call</pre></div></div>
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<strong>语法17-13 — 序列中子程序调用的语法（摘录自附录A）</strong></p><p class="Element10">
&nbsp;</p>
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例如： </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00665"><pre class="Element12"><span style="color: #0000FF">sequence</span> s1<span style="color: #800080">;</span>
    <span style="color: #0000FF">logic</span> v<span style="color: #800080">,</span> w<span style="color: #800080">;</span>
    <span style="color: #800080">(</span>a<span style="color: #800080">, </span>v<span style="color: #800080"> = </span>e<span style="color: #800080">) ##</span><span style="color: #FF0000">1</span>
    <span style="color: #800080">(</span>b<span style="color: #800080">[-&gt;</span><span style="color: #FF0000">1</span><span style="color: #800080">],</span> w = f<span style="color: #800080">,</span> <span style="color: #0000FF">$display</span><span style="color: #800080">(</span><span style="color: #575D94">&quot;b after a with v = %h, w = %h\n&quot;</span><span style="color: #800080">,</span> v<span style="color: #800080">,</span> w<span style="color: #800080">));</span>
<span style="color: #0000FF">endsequence</span></pre></div></div>
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&nbsp;</p>
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上面的例子定义了一个序列<span class="Element146">s1</span>，它在一次<span class="Element146">a</span>出现后第一次出现<span class="Element146">b</span>的时候匹配。在匹配的时候，执行系统任务<span style="color: #0000FF">$display</span>来写入一条消息，它声明这次匹配并显示赋给局部变量v和w的值。&nbsp;</p>
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&nbsp;</p>
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所有被附加到一个序列的子程序调用均在序列的每一次成功匹配处执行。对于每一次成功的匹配，附加调用以它们在列表中出现的顺序调用。与一个动作块一样，子程序调用在<span class="Element146">Reactive</span>区域调度。&nbsp;</p>
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&nbsp;</p>
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一个附加到了一个序列的子程序调用的每一个参数必须或者作为一个输入通过值传递，或者通过引用传递（<strong><span style="color: #0000FF">ref</span></strong>或<strong><span style="color: #0000FF">const ref</span></strong>；参见<a href="00007.html" target="topic">10.4.2节</a>）。通过值传递的实参表达式使用底层变量的采样值并且与用来计算序列匹配的变量值一致。&nbsp;</p>
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&nbsp;</p>
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局部变量可以被传递到附加到了一个序列的子程序调用。任何流出序列或者在紧跟序列的列表中但在子程序调用之前进行赋值的局部变量都可以用在调用的实参表达式中。如果一个局部变量出现在了一个实参表达式中，那么参数必须通过值传递。</p></div>
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