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<a href="#" onmousedown="showPopup(this, 'popup00351');"><img src="seealsolink.png" border="0" alt="" title=""></a> SystemVerilog 3.1a语言参考手册</div>
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17.11.2 特性的例子</div>
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下面的例子演示了特性的格式。 </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00686"><pre class="Element12"><span style="color: #0000FF">property</span> rule1<span style="color: #800080">;</span>
<span style="color: #800080">@(</span><span style="color: #0000FF">posedge</span> clk<span style="color: #800080">)</span>
a <span style="color: #800080">|-></span> b <span style="color: #800080">##</span><span style="color: #FF0000">1</span> c <span style="color: #800080">##</span><span style="color: #FF0000">1</span> d<span style="color: #800080">;</span>
<span style="color: #0000FF">endproperty</span>
<span style="color: #0000FF">property</span> rule2<span style="color: #800080">;</span>
<span style="color: #800080">@(</span>clkev<span style="color: #800080">)</span>
<span style="color: #0000FF"> disable iff</span> <span style="color: #800080">(</span>foo<span style="color: #800080">)</span>
a <span style="color: #800080">|-></span> <span style="color: #0000FF">not</span><span style="color: #800080">(</span>b <span style="color: #800080">##</span><span style="color: #FF0000">1</span> c <span style="color: #800080">##</span><span style="color: #FF0000">1</span> d<span style="color: #800080">);</span>
<span style="color: #0000FF">endproperty</span></pre></div></div>
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特性<i><span class="Element146">rule2</span></i>对蕴含中后项的<span class="Element146"><span style="color: #800080">(</span>b <span style="color: #800080">##</span><span style="color: #FF0000">1</span> c <span style="color: #800080">##</span><span style="color: #FF0000">1</span> d<span style="color: #800080">)</span></span>序列取反。<i><span class="Element146">clkev</span></i>为特性指定了时钟。 </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00687"><pre class="Element12"><span style="color: #0000FF">property</span> rule3<span style="color: #800080">;</span>
<span style="color: #800080">@(</span><span style="color: #0000FF">posedge</span> clk<span style="color: #800080">)</span>
a<span style="color: #800080">[*</span><span style="color: #FF0000">2</span><span style="color: #800080">] |-> ((##[</span><span style="color: #FF0000">1</span><span style="color: #800080">:</span><span style="color: #FF0000">3</span><span style="color: #800080">]</span> c<span style="color: #800080">)</span> <span style="color: #0000FF">or</span> <span style="color: #800080">(</span>d <span style="color: #800080">|=></span> e<span style="color: #800080">));</span>
<span style="color: #0000FF">endproperty</span></pre></div></div>
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Property rule3 says that if a holds and a also held last cycle, then either c must hold at some point 1 to three cycles after the current cycle, or, if d holds in the current cycle, then e must hold one cycle later. </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00688"><pre class="Element12"><span style="color: #0000FF">property</span> rule4<span style="color: #800080">;</span>
<span style="color: #800080">@(</span><span style="color: #0000FF">posedge</span> clk<span style="color: #800080">)</span>
a<span style="color: #800080">[*</span><span style="color: #FF0000">2</span><span style="color: #800080">] |-> ((##[</span><span style="color: #FF0000">1</span><span style="color: #800080">:</span><span style="color: #FF0000">3</span><span style="color: #800080">]</span> c<span style="color: #800080">)</span> <span style="color: #0000FF">and</span> <span style="color: #800080">(</span>d <span style="color: #800080">|=></span> e<span style="color: #800080">));</span>
<span style="color: #0000FF">endproperty</span></pre></div></div>
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Property rule4 says that if a holds and a also held last cycle, then c must hold at some point 1 to three cycles after the current cycle, and if d holds in the current cycle, then e must hold one cycle later. </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00689"><pre class="Element12"><span style="color: #0000FF">property</span> rule5<span style="color: #800080">;</span>
<span style="color: #800080">@(</span><span style="color: #0000FF">posedge</span> clk<span style="color: #800080">)</span>
a <span style="color: #800080">##</span><span style="color: #FF0000">1</span> <span style="color: #800080">(</span>b <span style="color: #800080">||</span> c<span style="color: #800080">)[-></span><span style="color: #FF0000">1</span><span style="color: #800080">] |-></span>
<span style="color: #0000FF">if</span> <span style="color: #800080">(</span>b<span style="color: #800080">)</span>
<span style="color: #800080">(##</span><span style="color: #FF0000">1</span><span style="color: #800080"> </span>d<span style="color: #800080"> |-> </span>e<span style="color: #800080">)</span>
<span style="color: #0000FF">else</span> <span style="color: #008000">// c</span>
f;
<span style="color: #0000FF">endproperty</span></pre></div></div>
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Property rule5 has a followed by the first match of either b or c as its antecedent. The consequent uses if...else to split cases on which of b or c is matched first. </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00690"><pre class="Element12"><span style="color: #0000FF">property</span> rule6<span style="color: #800080">(</span>x<span style="color: #800080">,</span>y<span style="color: #800080">);</span>
<span style="color: #800080">##</span><span style="color: #FF0000">1</span> x <span style="color: #800080">|-></span> y<span style="color: #800080">;</span>
<span style="color: #0000FF">endproperty</span>
<span style="color: #0000FF">property</span> rule5a<span style="color: #800080">;</span>
<span style="color: #800080">@(</span><span style="color: #0000FF">posedge</span> clk<span style="color: #800080">)</span>
a <span style="color: #800080">##</span><span style="color: #FF0000">1</span> <span style="color: #800080">(</span>b <span style="color: #800080">||</span> c<span style="color: #800080">)[-></span><span style="color: #FF0000">1</span><span style="color: #800080">] |-></span>
<span style="color: #0000FF">if</span> <span style="color: #800080">(</span>b<span style="color: #800080">)</span>
rule6<span style="color: #800080">(</span>d<span style="color: #800080">,</span>e<span style="color: #800080">)</span>
<span style="color: #0000FF">else</span> <span style="color: #008000">// c</span>
f;
<span style="color: #0000FF">endproperty</span></pre></div></div>
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特性<i><span class="Element146">rule5a</span></i>等价于<i><span class="Element146">rule5</span></i>，但它使用<i><span class="Element146">rule6</span></i>的一个实例作为一个特性表达式。 </p>
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一个特性可以可选地为时钟指定一个事件控制。时钟派生和解析的规则将在<a href="00163.html" target="topic">17.14节</a>中描述。 </p>
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一个命名特性可以通过引用它的名字来实例化。与SystemVerilog命名约定一致，我们可以使用一个层次化的名字。像序列声明一样，对于在一个特性中使用并且不是特性的形式参数的变量，它们从特性被声明的作用域中进行层次化的解析。 </p>
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使用多个时钟的特性将在<a href="00151.html" target="topic">17.12节</a>中描述。</p></div>
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