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<a href="00871.html" target="topic">第十五章 时钟控制块</a></div>
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15.2 时钟控制块声明</div>
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时钟控制块的声明语法如下： </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00530"><pre class="Element12">clocking_declaration ::= <span style="color: #008000">// 引用自附录A.6.11</span>
[<strong><span style="color: #FF0000">default</span></strong>] <strong><span style="color: #FF0000">clocking</span></strong> [clocking_identifier] clocking_event<strong><span style="color: #FF0000">;</span></strong>
{clocking_item}
<strong><span style="color: #FF0000">endclocking</span></strong> [<strong><span style="color: #FF0000">:</span></strong> clocking_identifier]
clocking_event ::=
<strong><span style="color: #FF0000">@</span></strong> identifier
| <strong><span style="color: #FF0000">@</span></strong> <strong><span style="color: #FF0000">(</span></strong>event_expression<strong><span style="color: #FF0000">)</span></strong>
clocking_item :=
<strong><span style="color: #FF0000">default</span></strong> default_skew<strong><span style="color: #FF0000">;</span></strong>
| clocking_direction list_of_clocking_decl_assign<strong><span style="color: #FF0000">;</span></strong>
| {attribute_instance} concurrent_assertion_item_declaration
default_skew ::=
<strong><span style="color: #FF0000">input</span></strong> clocking_skew
| <strong><span style="color: #FF0000">output</span></strong> clocking_skew
| <strong><span style="color: #FF0000">input</span></strong> clocking_skew <strong><span style="color: #FF0000">output</span></strong> clocking_skew
clocking_direction ::=
<strong><span style="color: #FF0000">input</span></strong> [clocking_skew]
| <strong><span style="color: #FF0000">output</span></strong> [clocking_skew]
| <strong><span style="color: #FF0000">input</span></strong> [clocking_skew] <strong><span style="color: #FF0000">output</span></strong> [clocking_skew]
| <strong><span style="color: #FF0000">inout</span></strong>
list_of_clocking_decl_assign ::= clocking_decl_assign {<strong>,</strong> clocking_decl_assign}
clocking_decl_assign ::= signal_identifier [<strong><span style="color: #FF0000">=</span></strong> hierarchical_identifier]
clocking_skew ::=
edge_identifier [delay_control]
| delay_control
edge_identifier ::= <strong><span style="color: #FF0000">posedge</span></strong> | <strong><span style="color: #FF0000">negedge </span><span style="color: #008000"></strong>// 引用自附录A.7.4</span>
delay_control ::= <span style="color: #008000">// 引用自附录A.6.5</span>
<strong><span style="color: #FF0000">#</span></strong> delay_value
| <strong><span style="color: #FF0000">#</span></strong> <strong><span style="color: #FF0000">(</span></strong>mintypmax_expression<strong><span style="color: #FF0000">)</span></strong></pre></div></div>
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<strong>语法 15-1—时钟控制块语法（摘录自附录A）</strong></p><p class="Element10">
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<span class="Element146">delay_control</span>必须是一个时间文本或者一个可以计算成一个正的整数值的常量表达式。 </p>
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<span class="Element146">clocking_identifier</span>了指定所声明的时钟控制块的名字。 </p>
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<span class="Element146">signal_identfier</span>标识一个位于包围时钟控制块声明的作用范围内的信号，并且声明了时钟控制块中一个信号的名字。除非使用了一个<span class="Element146">hierarchical_expression</span>，无论是这个信号还是<span class="Element146">clocking_item</span>的名字都应该是相同的。 </p>
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