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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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下面的表格按从高优先级到低优先级的顺序列出了特性操作符，并显示了非一元操作符的关联性。&nbsp;</p>
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<strong>表17-2：特性操作符的优先级和关联性</strong>&nbsp;</p><div class="Element63">
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SystemVerilog特性操作符&nbsp;</div></td><td class="Element65" valign="top" width="30%">
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关联性&nbsp;</div></td></tr><tr>
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<span style="color: #0000FF">not</span>&nbsp;</div></td><td class="Element67" valign="top" width="30%">
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----&nbsp;</div></td></tr><tr>
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<span style="color: #0000FF">and</span>&nbsp;</div></td><td class="Element67" valign="top" width="30%">
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左&nbsp;</div></td></tr><tr>
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<span style="color: #0000FF">or</span>&nbsp;</div></td><td class="Element67" valign="top" width="30%">
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左&nbsp;</div></td></tr><tr>
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<span style="color: #0000FF">if</span>...<span style="color: #0000FF">else</span>&nbsp;</div></td><td class="Element67" valign="top" width="30%">
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右&nbsp;</div></td></tr><tr>
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<span style="color: #800080">|-&gt; |=&gt;</span>&nbsp;</div></td><td class="Element67" valign="top" width="30%">
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右&nbsp;</div></td></tr></table></div></div>
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一条<strong><span style="color: #0000FF">disable iff</span></strong>子句可以被附加到一个<span class="Element146">property_expr</span>以便产生一个<span class="Element146">property_spec</span>。 </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00675"><pre class="Element12"><span style="color: #0000FF">disable iff</span> <span style="color: #800080">(</span>expression_or_dist<span style="color: #800080">)</span> property_expr</pre></div></div>
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<strong><span style="color: #0000FF">disable iff</span></strong>表达式被称为复位表达式。<strong><span style="color: #0000FF">disable iff</span></strong>子句允许指定异步复位。对于<span class="Element146">property_spec</span>的一次计算，具有一个底层<span class="Element146">property_exp</span>r的计算。如果在计算完成之前复位表达式变为“真”，那么<span class="Element146">propterty_spec</span>的整个计算都为“真”。否则，<span class="Element146">property_spec</span>的计算与<span class="Element146">property_expr</span>的计算结果相同。对于<span class="Element146">property_spec</span>的不同的计算尝试，复位表达式都被独立地检测。显式地或者通过实例中的特性实现<strong><span style="color: #0000FF">disable iff</span></strong>子句的嵌套是不被允许的。</p></div>
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<a href="00868.html" target="topic">第十七章 断言</a></p></div>
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主题&nbsp;</div></td><td class="Element204" valign="top" width="50%">
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描述&nbsp;</div></td></tr><tr>
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<a href="00146.html" target="topic">17.11.1 蕴含</a>&nbsp;</div></td><td class="Element206" valign="top" width="50%">
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蕴含结构指出一个特性检查是在一个有序前项匹配的基础上有条件地执行的。 &nbsp;</div></td></tr><tr>
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<a href="00147.html" target="topic">17.11.2 特性的例子</a>&nbsp;</div></td><td class="Element206" valign="top" width="50%">
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下面的例子演示了特性的格式。 &nbsp;</div></td></tr><tr>
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<a href="00148.html" target="topic">17.11.3 递归特性</a>&nbsp;</div></td><td class="Element206" valign="top" width="50%">
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SystemVerilog允许使用递归的特性。如果一个命名特性的声明调用了其本身的一个实例，那么这个命名特性是递归的。递归提供了一种灵活的框架来对特性进行编码以便作为正在进行的假设、检查器或覆盖率监视器使用。<br><br>例如： &nbsp;</div></td></tr><tr>
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<a href="00149.html" target="topic">17.11.4 有限长度与无限长度行为</a>&nbsp;</div></td><td class="Element206" valign="top" width="50%">
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The formal semantics in Annex H defines whether a given property holds on a given behavior. How the outcome of this evaluation relates to the design depends on the behavior that was analyzed. In dynamic verification, only behaviors that are finite in length are considered. In such a case, SystemVerilog defines four levels of satisfaction of a property:<br><br>Holds strongly:
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<li class="Element601">no bad states have been seen</li>
<li class="Element601">all future obligations have been met</li>
<li class="Element601">the property will hold on any extension of the path</li>
</ul>Holds (but does not hold strongly):
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<li class="Element601">no bad states have been seen</li>
<li class="Element601">all future obligations have been met... <a href="00149.html" target="topic">more</a>&nbsp;</div></td></tr><tr>
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<a href="00150.html" target="topic">17.11.5 Non-degeneracy</a>&nbsp;</div></td><td class="Element206" valign="top" width="50%">
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It is possible to define sequences that can never be matched. For example: &nbsp;</div></td></tr></table></div></div>
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<a href="00868.html" target="topic">第十七章 断言</a>, <a href="00949.html" target="topic">主题</a></div>
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