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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

dest_t b <span style="color: #800080">=</span> dest_t<span style="color: #800080">'(</span>a<span style="color: #800080">);</span></pre></div></div>
<p class="Element10">
位流强制类型转换可以用来在不同的集合类型间转换，例如两个结构体类型，或者一个结构体与一个数组或队列类型之间。对于在串行通信流上传输包数据的建模，这种转换非常有用： </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00098"><pre class="Element12"><span style="color: #0000FF">typedef struct</span> <span style="color: #800080">{</span>
    <span style="color: #0000FF">shortint</span> address<span style="color: #800080">;</span>
    <span style="color: #0000FF">reg</span> <span style="color: #800080">[</span><span style="color: #FF0000">3</span><span style="color: #800080">:</span><span style="color: #FF0000">0</span><span style="color: #800080">]</span> code<span style="color: #800080">;</span>
    <span style="color: #0000FF">byte</span> command <span style="color: #800080">[</span><span style="color: #FF0000">2</span><span style="color: #800080">];</span>
<span style="color: #800080">}</span> Control<span style="color: #800080">;</span>

<span style="color: #0000FF">typedef</span> <span style="color: #0000FF">bit</span> Bits <span style="color: #800080">[</span><span style="color: #FF0000">36</span><span style="color: #800080">:</span><span style="color: #FF0000">1</span><span style="color: #800080">];</span>

Control p<span style="color: #800080">;</span>

Bits stream<span style="color: #800080">[</span><span style="color: #FF0000">$</span><span style="color: #800080">];</span>

p = ... <span style="color: #008000">// 初始化Control包</span>

stream = <span style="color: #800080">{</span>stream<span style="color: #800080">,</span> Bits<span style="color: #800080">'(</span>p<span style="color: #800080">)}</span> <span style="color: #008000">// 将包附加到非压缩位队列</span>

Control q;

q <span style="color: #800080">=</span> Control<span style="color: #800080">'(</span>stream<span style="color: #800080">[</span><span style="color: #FF0000">0</span><span style="color: #800080">]);</span>   <span style="color: #008000">// 将位流转换回一个Contorl包</span>

stream <span style="color: #800080">=</span> stream<span style="color: #800080">[</span><span style="color: #FF0000">1</span><span style="color: #800080">:</span><span style="color: #FF0000">$</span><span style="color: #800080">];</span>      <span style="color: #008000">// 从流中删除包</span></pre></div></div>
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下面的例子使用位流强制类型转换来建模在字节流上传输数据包： </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00099"><pre class="Element12"><span style="color: #0000FF">typedef struct</span> <span style="color: #800080">{</span>
    <span style="color: #0000FF">byte</span> length<span style="color: #800080">;</span>
    <span style="color: #0000FF">shortint</span> address<span style="color: #800080">;</span>
    <span style="color: #0000FF">byte</span> payload<span style="color: #800080">[];</span>
    <span style="color: #0000FF">byte</span> chksum<span style="color: #800080">;</span>
<span style="color: #800080">}</span> Packet<span style="color: #800080">;</span></pre></div></div>
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上面的类型定义了一个普通的数据包，它的净荷的尺寸存储在<i>length</i>域。下面的函数随机地初始化包并产生校验和。 </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00100"><pre class="Element12"><span style="color: #0000FF">function</span> Packet genPkt<span style="color: #800080">();</span>
    Packet p<span style="color: #800080">;</span>
    <span style="color: #0000FF">void</span><span style="color: #800080">'(</span><span style="color: #0000FF">randomize</span><span style="color: #800080">(</span>p<span style="color: #800080">.</span>address<span style="color: #800080">,</span> p<span style="color: #800080">.</span>length<span style="color: #800080">,</span> p<span style="color: #800080">.</span>payload<span style="color: #800080">)</span>
    <span style="color: #0000FF">with</span> <span style="color: #800080">{</span>p<span style="color: #800080">.</span>length<span style="color: #800080">&gt;</span><span style="color: #FF0000">1</span> <span style="color: #800080">&amp;&amp;</span> p<span style="color: #800080">.</span>payload<span style="color: #800080">.</span><span style="color: #0000FF">size</span> <span style="color: #0000FF">==</span> p<span style="color: #800080">.</span>length<span style="color: #800080">});</span>
        p<span style="color: #800080">.</span>chksum <span style="color: #800080">=</span> p<span style="color: #800080">.</span>payload<span style="color: #800080">.</span><span style="color: #0000FF">xor</span><span style="color: #800080">();</span>
    <span style="color: #0000FF">return</span> p<span style="color: #800080">;</span>
<span style="color: #0000FF">endfunction</span></pre></div></div>
<p class="Element10">
字节流使用一个队列建模，一个位流强制类型转换被用来在流上发送包。 </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00101"><pre class="Element12"><span style="color: #0000FF">typedef byte</span> channel_type<span style="color: #800080">[</span><span style="color: #FF0000">$</span><span style="color: #800080">];</span>
channel_type channel<span style="color: #800080">;</span>
channel <span style="color: #800080">= {</span>channel<span style="color: #800080">,</span> channel_type<span style="color: #800080">'(</span>genPkt<span style="color: #800080">())};</span></pre></div></div>
<p class="Element10">
下面的代码用来接收包。 </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00102"><pre class="Element12">Packet p<span style="color: #800080">;</span>
<span style="color: #0000FF">int</span> size<span style="color: #800080">;</span>
size <span style="color: #800080">=</span> channel<span style="color: #800080">[</span><span style="color: #FF0000">0</span><span style="color: #800080">]</span> <span style="color: #800080">+</span> <span style="color: #FF0000">4</span><span style="color: #800080">;</span>
p <span style="color: #800080">=</span> Packet<span style="color: #800080">'(</span>channel<span style="color: #800080">[</span><span style="color: #FF0000">0</span><span style="color: #800080">:</span>size<span style="color: #800080">-</span><span style="color: #FF0000">1</span><span style="color: #800080">]);</span> <span style="color: #008000">// 将流转换成包</span>
channel <span style="color: #800080">=</span> channel<span style="color: #800080">[</span>size<span style="color: #800080">,</span> $]<span style="color: #800080">;</span>     <span style="color: #008000">// 从流中删除包</span></pre></div></div>
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<a href="00863.html" target="topic">第三章 数据类型</a></p></div>
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<a href="00863.html" target="topic">第三章 数据类型</a></div>
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