📄 00001.html
字号:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN">
<html>
<head>
<title>10.2 任务</title>
<meta http-equiv="Content-Type" content="text/html; charset=GB2312" />
<meta name="generator" content="Doc-O-Matic" />
<meta http-equiv="Content-Style-Type" content="text/css" />
<link rel="STYLESHEET" href="default.css" type="text/css" />
<script type="text/javascript" src="scripts.js"></script>
</head>
<body class="Element700" onload="onBodyLoadEx('systemverilog31a.html', 'topic', '00001.html');" onmousedown="onBodyMouseDown();">
<!-- Begin Popups -->
<div class="Element801" id="popup00177">
<div class="Element800">
<div class="Element14">
链接</div>
<div class="Element11">
<div class="Element10">
<a href="00873.html" target="topic">第十章 任务与函数</a></div>
</div>
</div>
</div>
<!-- End Popups -->
<!-- Begin Page Header -->
<div class="Element710" id="areafixed">
<div class="Element92">
<table width="100%" cellspacing="0" cellpadding="0">
<tr><td width="33%">
<div class="Element1">
<a href="#" onmousedown="showPopup(this, 'popup00177');"><img src="seealsolink.png" border="0" alt="" title=""></a> SystemVerilog 3.1a语言参考手册</div>
</td><td width="34%">
<div class="Element2">
</div>
</td><td width="33%">
<div class="Element90">
<a href="00000.html" target="topic"><img src="btn_prev_lightblue.gif" border="0" alt="Previous" title="Previous" onmouseover="switchImage(this, 'btn_prev_lightblue_hover.gif');" onmouseout="switchImage(this, 'btn_prev_lightblue.gif');"></a><a href="00873.html" target="topic"><img src="btn_up_lightblue.gif" border="0" alt="Up" title="Up" onmouseover="switchImage(this, 'btn_up_lightblue_hover.gif');" onmouseout="switchImage(this, 'btn_up_lightblue.gif');"></a><a href="00002.html" target="topic"><img src="btn_next_lightblue.gif" border="0" alt="Next" title="Next" onmouseover="switchImage(this, 'btn_next_lightblue_hover.gif');" onmouseout="switchImage(this, 'btn_next_lightblue.gif');"></a></div>
</td></tr></table><div class="Element5">
10.2 任务</div>
</div>
</div>
<!-- End Page Header -->
<!-- Begin Client Area -->
<div class="Element720" id="areascroll">
<div class="Element721">
<!-- Begin Page Content -->
<div class="Element58">
<a name="描述"></a><div class="Element11">
<div class="Element10">
<div class="Element170">
<a href="#" onclick="CopyElementToClipboard('code00312');">Copy Code</a></div>
<div class="Element13"><div class="Element12" id="code00312"><pre class="Element12">task_declaration ::= <strong><span style="color: #FF0000">task</span></strong> [lifetime] task_body_declaration <span style="color: #008000">// 引用自附录A.2.7</span>
task_body_declaration ::=
[interface_identifier<strong><span style="color: #FF0000">.</span></strong>|class_scope] task_identifier<strong><span style="color: #FF0000">;</span></strong>
{tf_item_declaration}
{statement_or_null}
<strong><span style="color: #FF0000">endtask</span></strong> [<strong><span style="color: #FF0000">:</span></strong> task_identifier]
| [interface_identifier<strong><span style="color: #FF0000">.</span></strong>|class_scope] task_identifier <strong><span style="color: #FF0000">(</span></strong>[tf_port_list]<strong><span style="color: #FF0000">);</span></strong>
{block_item_declaration}
{statement_or_null}
<strong><span style="color: #FF0000">endtask</span></strong> [<strong><span style="color: #FF0000">:</span></strong> task_identifier]
tf_item_declaration ::=
block_item_declaration
| tf_port_declaration
tf_port_list ::=
tf_port_item {<strong><span style="color: #FF0000">,</span></strong> tf_port_item}
tf_port_item ::=
{attribute_instance}
[tf_port_direction] data_type_or_implicit
port_identifier variable_dimension [<strong><span style="color: #FF0000">= </span></strong>expression]
tf_port_direction ::= port_direction | <strong><span style="color: #FF0000">const ref</span></strong>
tf_port_declaration ::=
{attribute_instance} tf_port_direction data_type_or_implicit list_of_tf_variable_identifiers<strong><span style="color: #FF0000">;</span></strong>
lifetime ::= <strong><span style="color: #FF0000">static</span></strong> | <strong><span style="color: #FF0000">automatic </span><span style="color: #008000"></strong>// 引用自附录A.2.1</span>
signing ::= <strong><span style="color: #FF0000">signed</span></strong> | <strong><span style="color: #FF0000">unsigned </span><span style="color: #008000"></strong>// 引用自附录A.2.2.1</span>
data_type_or_implicit ::=
data_type
| [signing] {packed_dimension}</pre></div></div>
<p class="Element10" style="text-align: center">
<strong>语法 10-1 — 任务语法（摘录自附录A）</strong></p><p class="Element10">
</p>
<p class="Element10">
Verilog任务声明或者在圆括号（向ANSI C一样）中，或者在声明和方向中具有形式参数。 </p><div class="Element170">
<a href="#" onclick="CopyElementToClipboard('code00313');">Copy Code</a></div>
<div class="Element13"><div class="Element12" id="code00313"><pre class="Element12"><span style="color: #0000FF">task</span> mytask1 <span style="color: #800080">(</span><span style="color: #0000FF">output int</span> x<span style="color: #800080">,</span> <span style="color: #0000FF">input logic</span> y<span style="color: #800080">);</span>
...
<span style="color: #0000FF">endtask</span>
<span style="color: #0000FF">task</span> mytask2<span style="color: #800080">;</span>
<span style="color: #0000FF">output</span> x<span style="color: #800080">;</span>
<span style="color: #0000FF">input</span> y<span style="color: #800080">;</span>
<span style="color: #0000FF">int</span> x<span style="color: #800080">;</span>
<span style="color: #0000FF">logic</span> y<span style="color: #800080">;</span>
...
<span style="color: #0000FF">endtask</span></pre></div></div>
<p class="Element10">
每一个形式参数可以具有下列之一的方向： </p><div class="Element170">
<a href="#" onclick="CopyElementToClipboard('code00314');">Copy Code</a></div>
<div class="Element13"><div class="Element12" id="code00314"><pre class="Element12"><span style="color: #0000FF">input</span> <span style="color: #008000">// 在开始的时候拷贝值</span>
<span style="color: #0000FF">output</span> <span style="color: #008000">// 在结束的时候拷贝值</span>
<span style="color: #0000FF">inout</span> <span style="color: #008000">// 在开始的时候拷贝，在结束的时候输出</span>
<span style="color: #0000FF">ref</span> <span style="color: #008000">// 传递引用（参见</span><a href="00007.html" target="topic">10.4.2节</a><span style="color: #008000">）</span></pre></div></div>
<p class="Element10">
在SystemVerilog中，如果没有指定参数的方向，那么它的缺省方向是输入。一旦指定了一个方向，那么它就成为后续参数的缺省方向。在下面的例子中，形式参数<i>a</i>和<i>b</i>缺省为输入，<i>u</i>和<i>v</i>都是输出。 </p><div class="Element170">
<a href="#" onclick="CopyElementToClipboard('code00315');">Copy Code</a></div>
<div class="Element13"><div class="Element12" id="code00315"><pre class="Element12"><span style="color: #0000FF">task</span> mytask3<span style="color: #800080">(</span>a<span style="color: #800080">,</span> b<span style="color: #800080">,</span> <span style="color: #0000FF">output logic</span> <span style="color: #800080">[</span><span style="color: #FF0000">15</span><span style="color: #800080">:</span><span style="color: #FF0000">0</span><span style="color: #800080">]</span> u<span style="color: #800080">,</span> v<span style="color: #800080">);</span>
...
<span style="color: #0000FF">endtask</span></pre></div></div>
<p class="Element10">
每一个形式参数都具有一个数据类型，它或者显式声明，或者从一个缺省类型继承。SystemVerilog中任务参数的缺省类型为logic。 </p>
<p class="Element10">
</p>
<p class="Element10">
SystemVerilog允许将一个数组声明为任务的形式参数。例如： </p><div class="Element170">
<a href="#" onclick="CopyElementToClipboard('code00316');">Copy Code</a></div>
<div class="Element13"><div class="Element12" id="code00316"><pre class="Element12"><span style="color: #008000">// b的声明结果为input [3:0][7:0] b[3:0]</span>
<span style="color: #0000FF">task</span> mytask4<span style="color: #800080">(</span><span style="color: #0000FF">input</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><span style="color: #FF0000">7</span><span style="color: #800080">:</span><span style="color: #FF0000">0</span><span style="color: #800080">]</span> a<span style="color: #800080">,</span> b<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> <span style="color: #0000FF">output</span> <span style="color: #FF0000">3</span><span style="color: #800080">:</span><span style="color: #FF0000">0</span><span style="color: #800080">][</span><span style="color: #FF0000">7</span><span style="color: #800080">:</span><span style="color: #FF0000">0</span><span style="color: #800080">]</span> y<span style="color: #800080">[</span><span style="color: #FF0000">1</span><span style="color: #800080">:</span><span style="color: #FF0000">0</span><span style="color: #800080">]);</span>
...
<span style="color: #0000FF">endtask</span></pre></div></div>
<p class="Element10">
Verilog-2001允许将任务声明成自动的，因此所有的形式参数和本地变量都被存储在堆栈当中。SystemVerilog扩展了这种能力，它允许在一个静态任务中将特定的形式参数和本地变量声明成自动的，或者，它也允许在一个自动任务内将特定的形式参数和本地变量声明成静态的。 </p>
<p class="Element10">
</p>
<p class="Element10">
在SystemVerilog中，多条语句可以在任务声明和<span style="color: #0000FF">endtask</span>之间被写入，这也就意味着<span style="color: #0000FF">begin</span>...<span style="color: #0000FF">end</span>可以被忽略。如果<span style="color: #0000FF">begin</span>...<span style="color: #0000FF">end</span>被忽略，这些语句顺序地执行，这与它们被包含在<span style="color: #0000FF">begin</span>...<span style="color: #0000FF">end</span>组中是一样的。任务中没有任何语句也是合法的。 </p>
<p class="Element10">
</p>
<p class="Element10">
在Verilog中，当任务到达<span style="color: #0000FF">endtask</span>的时候任务退出。而对于SystemVerilog，在<span style="color: #0000FF">endtask</span>关键字之前可以使用<span style="color: #0000FF">return</span>语句退出任务。</p></div>
</div>
<a name="Group"></a><div class="Element14">
<a onclick="toggleVisibilityStored('Group');" class="a_Element14"><img src="sectionminus.png" border="0" alt="" title="" id="imgGroup">Group</a></div>
<div id="divGroup">
<div class="Element11">
<div class="Element10">
<p class="Element10">
<a href="00873.html" target="topic">第十章 任务与函数</a></p></div>
</div>
</div>
<a name="Links"></a><div class="Element14">
<a onclick="toggleVisibilityStored('链接');" class="a_Element14"><img src="sectionminus.png" border="0" alt="" title="" id="img链接">链接</a></div>
<div id="div链接">
<div class="Element11">
<div class="Element10">
<a href="00873.html" target="topic">第十章 任务与函数</a></div>
</div>
</div>
</div>
<!-- End Page Content -->
<!-- Begin Page Footer -->
<hr width="98%" align="center" size="1" color="#CCCCCC" />
<table align="center" cellpadding="0" cellspacing="0" border="0">
<tbody>
<tr height="10">
<td></td>
</tr>
<tr align="center">
<td>
<script type="text/javascript"><!--
google_ad_client = "pub-5266859600380184";
google_ad_width = 468;
google_ad_height = 60;
google_ad_format = "468x60_as";
google_ad_type = "text_image";
google_ad_channel ="";
google_page_url = document.location;
//--></script>
<script type="text/javascript"
src="http://pagead2.googlesyndication.com/pagead/show_ads.js">
</script>
</td>
</tr>
<tr height="15">
<td></td>
</tr>
<tr align="center">
<td>
<font size=2>除非特别声明，原文版权归作者所有，如有转摘请注明原作者以及译者（<a href="http://www.fpgatech.net/" target="_blank">FPGA技术网</a>）信息。<br />
如果您对本主题有何建议或意见，请登陆<a href="http://www.fpgatech.net/forum/forumdisplay.php?fid=18" target="_blank">FPGA开发者家园</a>提交，您的参与是我们前进的动力。</font>
<script language="javascript" type="text/javascript" src="http://js.users.51.la/195685.js"></script>
<noscript><a href="http://www.51.la/?195685" target="_blank"><img alt="我要啦免费统计" src="http://img.users.51.la/195685.asp" style="border:none" /></a></noscript>
</td>
</tr>
</tbody>
</table>
<!-- End Page Footer -->
</div>
</div>
<!-- End Client Area -->
</body></html>⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -