编写测试代码是验证HDL设计的主要手段_算法_其他

<html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta charset="utf-8"> <meta name="generator" content="pdf2htmlEX"> <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"> <link rel="stylesheet" href="https://static.pudn.com/base/css/base.min.css"> <link rel="stylesheet" href="https://static.pudn.com/base/css/fancy.min.css"> <link rel="stylesheet" href="https://static.pudn.com/prod/directory_preview_static/62631b034c65f41259957c23/raw.css"> <script src="https://static.pudn.com/base/js/compatibility.min.js"></script> <script src="https://static.pudn.com/base/js/pdf2htmlEX.min.js"></script> <script> try{ pdf2htmlEX.defaultViewer = new pdf2htmlEX.Viewer({}); }catch(e){} </script> <title></title> </head> <body> <div id="sidebar" style="display: none"> <div id="outline"> </div> </div> <div id="pf1" class="pf w0 h0" data-page-no="1"><div class="pc pc1 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="https://static.pudn.com/prod/directory_preview_static/62631b034c65f41259957c23/bg1.jpg"><div class="t m0 x1 h2 y1 ff1 fs0 fc0 sc0 ls0 ws0">W<span class="_ _0"></span>riting Efficient T<span class="_ _1"></span>estbenches </div><div class="t m0 x2 h3 y2 ff2 fs1 fc1 sc0 ls1 ws1">原文作者：<span class="ff3 ls2 ws2">Mujtaba Hamid </span></div><div class="t m0 x3 h3 y3 ff2 fs1 fc1 sc0 ls1 ws1">翻译：<span class="ff3 ls3">phixcoco@freecity<span class="_ _2"></span>.cn</span></div><div class="t m0 x4 h3 y4 ff3 fs2 fc1 sc0 ls1 ws1">(<span class="ff2">浙江大学飘渺水云间论坛</span>)<span class="fs1"> </span></div><div class="t m0 x5 h4 y5 ff3 fs2 fc1 sc0 ls1 ws1"> </div><div class="t m0 x5 h4 y6 ff3 fs2 fc1 sc0 ls1 ws1">[<span class="ff2">请阅读文档最后的说明</span><span class="ls4">] </span></div><div class="t m0 x5 h5 y7 ff2 fs2 fc1 sc1 ls5 ws1">摘要：<span class="ff1 sc0 ls1"> </span></div><div class="t m0 x5 h4 y8 ff2 fs2 fc1 sc0 ls1 ws1">本应用笔记是专门为没有测试编写经验并对<span class="_ _3"> </span><span class="ff3 ls6">HDL<span class="_"> </span></span>验证流程陌生的逻辑设计者而编写的。<span class="ff3"> </span></div><div class="t m0 x5 h4 y9 ff2 fs2 fc1 sc0 ls1 ws1">编写测试代码是验证<span class="_ _3"> </span><span class="ff3 ls6">HDL<span class="_"> </span></span>设计的主要手段。<span class="_ _1"></span>本应用笔记为创建或构建有效的测试设计提供了准则。<span class="_ _1"></span>同时给</div><div class="t m0 x5 h4 ya ff2 fs2 fc1 sc0 ls1 ws1">出了一个为任何设计开发自检测测试的算法。<span class="ff3"> </span></div><div class="t m0 x5 h4 yb ff2 fs2 fc1 sc0 ls1 ws1">涉及的所有设计文件可以从以下的站点获得：<span class="ff3"> </span></div><div class="t m0 x5 h4 yc ff3 fs2 fc1 sc0 ls7 ws1">PC: <span class="fc2">ftp://ftp.xilinx.com/pub/ap<span class="ls8">plications/xapp/xapp199.zip</span></span></div><div class="t m0 x6 h4 yd ff3 fs2 fc1 sc0 ls1 ws1"> </div><div class="t m0 x5 h4 ye ff3 fs2 fc1 sc0 ls9 ws1">UNIX: <span class="fc2 ls8">ftp://ftp.xilinx.com/pub/applications/xapp/xapp199.tar<span class="_ _2"></span>.gz</span></div><div class="t m0 x7 h4 yf ff3 fs2 fc1 sc0 ls1 ws1"> </div><div class="t m0 x5 h3 y10 ff3 fs1 fc1 sc0 ls1 ws1"> </div><div class="t m0 x5 h6 y11 ff1 fs3 fc0 sc0 ls1 ws1">1<span class="_"> </span><span class="ff2 sc2 lsa">简介</span><span class="ff3 fs1 fc1"> </span></div><div class="t m0 x5 h7 y12 ff2 fs1 fc1 sc0 ls1 ws1">由于设计的规模越来越大和越来越复杂，<span class="_ _4"></span>数字设计的验证已经成为一个日益困难和繁琐的任</div><div class="t m0 x5 h7 y13 ff2 fs1 fc1 sc0 ls1 ws1">务。<span class="_ _5"></span>验证工程师们运用多种验证工具和方法来应对挑战。<span class="_ _5"></span>对于大的系统，<span class="_ _5"></span>如几百万门的设计，</div><div class="t m0 x5 h7 y14 ff2 fs1 fc1 sc0 ls1 ws1">工程师们通常使用一系列完善的验证工具。<span class="_ _1"></span>当然，<span class="_ _6"></span>对于一些小的设计，<span class="_ _1"></span>设计工程师常常发现</div><div class="t m0 x5 h3 y15 ff2 fs1 fc1 sc0 ls1 ws1">能编写测试设计的<span class="_ _7"> </span><span class="ff3 lsb">hdl<span class="_"> </span></span>仿真器就可以做得很好。<span class="ff3"> </span></div><div class="t m0 x5 h3 y16 ff2 fs1 fc1 sc0 ls1 ws1">测试设计已经成为一个验证高级语言<span class="_ _7"> </span><span class="ff3 lsc ws3">HLL<span class="_ _0"></span> (High-Level Language)<span class="ff2 ls1 ws1">描述的设计的标准方法。<span class="ff3"> </span></span></span></div><div class="t m0 x5 h3 y17 ff2 fs1 fc1 sc0 ls1 ws1">典型的，测试设计完成以下任务：<span class="ff3"> </span></div><div class="t m0 x5 h3 y18 ff2 fs1 fc1 sc0 ls1 ws1">·<span class="ff3"> <span class="_ _8"> </span></span>在测试中实例化设计模块<span class="_ _7"> </span><span class="ff3 lsd ws4">Design Under T<span class="_ _2"></span>est<span class="ff2 ls1 ws1">（<span class="ff3 lse">DUT</span>）<span class="_ _9"></span>；<span class="ff3"> </span></span></span></div><div class="t m0 x5 h3 y19 ff2 fs1 fc1 sc0 ls1 ws1">·<span class="ff3"> <span class="_ _8"> </span></span>向要进行测试的模块（<span class="ff3 lse">DUT</span>）输入测试向量进行仿真；<span class="ff3"> </span></div><div class="t m0 x5 h3 y1a ff2 fs1 fc1 sc0 ls1 ws1">·<span class="ff3"> <span class="_ _8"> </span></span>仿真通过使用模块的测试向量来仿真测试设计；<span class="ff3"> </span></div><div class="t m0 x5 h3 y1b ff2 fs1 fc1 sc0 ls1 ws1">·<span class="ff3"> <span class="_ _8"> </span></span>仿真结果输出到终端或波形窗口以观察结果；<span class="ff3"> </span></div><div class="t m0 x5 h3 y1c ff2 fs1 fc1 sc0 ls1 ws1">·<span class="ff3"> <span class="_ _8"> </span></span>将实际结果和预期结果进行比较（可选步骤）<span class="_ _9"></span>。<span class="ff3"> </span></div><div class="t m0 x5 h3 y1d ff2 fs1 fc1 sc0 ls1 ws1">一般测试使用工业标准的<span class="_ _7"> </span><span class="ff3 lse">VHDL<span class="_"> </span></span>或<span class="_ _7"> </span><span class="ff3 lsf">V<span class="_ _2"></span>erilog<span class="_"> </span><span class="ff2 ls1">硬件<span class="_ _0"></span>描述语言来编写。<span class="_ _2"></span>测试中调用功能设计，<span class="_ _2"></span>然</span></span></div><div class="t m0 x5 h7 y1e ff2 fs1 fc1 sc0 ls1 ws1">后仿真。<span class="_ _4"></span>复杂的测试设计完成一些附加的功能――如它们包含逻辑模块来为设计产生适当的</div><div class="t m0 x5 h3 y1f ff2 fs1 fc1 sc0 ls1 ws1">激励或者将实际结果与预期结果做比较。<span class="ff3"> </span></div><div class="t m0 x5 h7 y20 ff2 fs1 fc1 sc0 ls1 ws1">后续的章节说明了一个优良的测试设计的结构，<span class="_ _4"></span>并提供了一个自检测测试的例子――用以自</div><div class="t m0 x5 h3 y21 ff2 fs1 fc1 sc0 ls1 ws1">动化地比较实际结果和测试设计的预期结果。<span class="ff3"> </span></div><div class="t m0 x5 h3 y22 ff2 fs1 fc1 sc0 ls1 ws1">图<span class="_ _a"> </span><span class="ff3">1<span class="_ _a"> </span></span><span class="ls10">给出了符合上述步骤的一个标<span class="_ _0"></span>准的<span class="_ _b"> </span><span class="ff3 lse">HDL<span class="_ _a"> </span></span>验证流程。由于测试设计使用<span class="_ _b"> </span><span class="ff3 lse">VHDL<span class="_ _a"> </span></span><span class="ls1">或</span></span></div><div class="t m0 x5 h3 y23 ff3 fs1 fc1 sc0 ls11 ws1">V<span class="_ _2"></span>erilo<span class="_ _0"></span>gHDL<span class="_"> </span><span class="ff2 ls1">编写，<span class="_ _c"></span>因此测试设计的验证流程可以在各平台或各公司提供的软件工具间移植。</span></div><div class="t m0 x5 h3 y24 ff2 fs1 fc1 sc0 ls1 ws1">另外，由于<span class="_ _7"> </span><span class="ff3 lse">VHDL<span class="_"> </span></span>或<span class="_ _7"> </span><span class="ff3 ls11">V<span class="_ _2"></span>erilogHDL<span class="_"> </span><span class="ff2 ls1">是公开化的标准语言，用<span class="_ _7"> </span></span><span class="lse">VHDL<span class="_"> </span><span class="ff2 ls1">或<span class="_ _7"> </span></span></span>V<span class="_ _6"></span>erilogHDL<span class="_"> </span><span class="ff2 ls1">编写的验</span></span></div><div class="t m0 x5 h3 y25 ff2 fs1 fc1 sc0 ls1 ws1">证测试包可以方便地以后的设计中重用。<span class="ff3"> </span></div></div><div class="pi" data-data='{"ctm":[1.611639,0.000000,0.000000,1.611639,0.000000,0.000000]}'></div></div> </body> </html>

<div id="pf2" class="pf w0 h0" data-page-no="2"><div class="pc pc2 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="https://static.pudn.com/prod/directory_preview_static/62631b034c65f41259957c23/bg2.jpg"><div class="t m0 x8 h3 y26 ff3 fs1 fc1 sc0 ls1 ws1"> </div><div class="t m0 x9 h4 y27 ff2 fs2 fc1 sc0 ls1 ws1">图<span class="_ _3"> </span><span class="ff3">1<span class="_"> </span></span>使用测试设计的<span class="_ _3"> </span><span class="ff3 ls6">HDL<span class="_"> </span></span>测试验证流程<span class="ff3"> </span></div><div class="t m0 x5 h3 y28 ff3 fs1 fc1 sc0 ls1 ws1"> </div><div class="t m0 x5 h6 y29 ff1 fs3 fc0 sc0 ls1 ws1">2<span class="_"> </span><span class="ff2 sc2 lsa">构建测试设计</span><span class="ff3 fs1 fc1"> </span></div><div class="t m0 x5 h3 y2a ff2 fs1 fc1 sc0 ls1 ws1">测试设计可以用<span class="_ _7"> </span><span class="ff3 lse">VHDL<span class="_"> </span></span>或<span class="_ _7"> </span><span class="ff3 ls12">V<span class="_ _2"></span>erilogHDL<span class="_"> </span><span class="ff2 ls1">编写。<span class="_ _2"></span>因为测试设计只用来进行仿真，<span class="_ _6"></span>不需要受综合</span></span></div><div class="t m0 x5 h3 y2b ff2 fs1 fc1 sc0 ls1 ws1">中仅能使用<span class="_ _d"> </span><span class="ff3 ls13">RT<span class="_ _e"></span>L<span class="_ _f"> </span></span>语言子集这样的语法约束。因此它可以使用所有的行为级结构。从而测试</div><div class="t m0 x5 h3 y2c ff2 fs1 fc1 sc0 ls1 ws1">可以编写地更为通用，从而方便维护。<span class="ff3"> </span></div><div class="t m0 x5 h3 y2d ff2 fs1 fc1 sc0 ls1 ws1">所有的测试设计都包含了如表<span class="_ _7"> </span><span class="ff3">1<span class="_"> </span></span>的基本程序段。<span class="_ _10"></span>正如上面所提到的，<span class="_ _10"></span>测试设计一般也可以包</div><div class="t m0 x5 h3 y2e ff2 fs1 fc1 sc0 ls1 ws1">含更多的附加功能，如在终端上显示可视化的结果以及内建的错误检测。<span class="ff3"> </span></div><div class="t m0 xa h3 y2f ff3 fs1 fc1 sc0 ls1 ws1"> </div><div class="t m0 xb h4 y30 ff2 fs2 fc1 sc0 ls1 ws1">表<span class="_ _3"> </span><span class="ff3">1 <span class="_"> </span></span>测试设计的基本程序段<span class="ff3"> </span></div><div class="t m0 x5 h3 y31 ff2 fs1 fc1 sc0 ls1 ws1">下面的例子给出了常用的测试设计的模块。<span class="ff3"> </span></div><div class="t m0 x5 h3 y32 ff3 fs1 fc1 sc0 ls14 ws1"> </div><div class="t m0 x5 h8 y33 ff1 fs4 fc0 sc0 ls1 ws1">2.1<span class="_"> </span><span class="ff2 sc2 ls15">产生时钟信号</span> </div><div class="t m0 x5 h7 y34 ff2 fs1 fc1 sc0 ls1 ws1">使用系统时钟控制逻辑工作的时序逻辑设计必然需要一个时钟。<span class="_ _4"></span>重复的时钟信号可以很容易</div><div class="t m0 x5 h3 y35 ff2 fs1 fc1 sc0 ls1 ws1">地用<span class="_ _7"> </span><span class="ff3 lse">VHDL<span class="_"> </span></span>或<span class="_ _7"> </span><span class="ff3 ls16">Ve<span class="_"> </span>r<span class="_ _11"></span>i<span class="_ _11"></span>l<span class="_"> </span>o<span class="_ _11"></span>g<span class="_ _d"> </span></span>代码实现。以下是<span class="_ _7"> </span><span class="ff3 lse">VHDL<span class="_"> </span></span>和<span class="_ _7"> </span><span class="ff3 ls16">Ve<span class="_"> </span>r<span class="_ _11"></span>i<span class="_"> </span>l<span class="_ _11"></span>o<span class="_"> </span>g<span class="_ _d"> </span></span>编写的时钟产生器的示例。<span class="ff3"> </span></div><div class="t m0 x5 h9 y36 ff1 fs1 fc1 sc0 ls17 ws1">VHDL </div><div class="t m0 x5 ha y37 ff4 fs2 fc1 sc0 ls18 ws1">-- Declare a clock period constant. </div><div class="t m0 x5 ha y38 ff4 fs2 fc1 sc0 ls18 ws1">Constant ClockPeriod : TIME := 10 ns; </div><div class="t m0 x5 ha y39 ff4 fs2 fc1 sc0 ls18 ws1">-- Clock Generation method 1: </div><div class="t m0 x5 ha y3a ff4 fs2 fc1 sc0 ls18 ws1">Clock <= not Clock after ClockPeriod / 2; </div><div class="t m0 x5 ha y3b ff4 fs2 fc1 sc0 ls18 ws1">-- Clock Generation method 2: </div><div class="t m0 x5 ha y3c ff4 fs2 fc1 sc0 ls18 ws1">GENERATE CLOCK: process </div><div class="t m0 x5 ha y3d ff4 fs2 fc1 sc0 ls18 ws1">begin </div><div class="t m0 x5 ha y3e ff4 fs2 fc1 sc0 ls18 ws1">wait for (ClockPeriod / 2) </div><div class="t m0 x5 ha y3f ff4 fs2 fc1 sc0 ls18 ws1">Clock <= ’1’; </div><div class="t m0 x5 ha y40 ff4 fs2 fc1 sc0 ls18 ws1">wait for (ClockPeriod / 2) </div><div class="t m0 x5 ha y41 ff4 fs2 fc1 sc0 ls18 ws1">Clock <= ’0’; </div><div class="t m0 x5 ha y42 ff4 fs2 fc1 sc0 ls18 ws1">end process; </div><div class="t m0 x5 h9 y43 ff1 fs1 fc1 sc0 ls19 ws1">V<span class="_ _2"></span>erilog </div><div class="t m0 x5 ha y44 ff4 fs2 fc1 sc0 ls18 ws1">// Declare a clock period constant. </div></div><div class="pi" data-data='{"ctm":[1.611639,0.000000,0.000000,1.611639,0.000000,0.000000]}'></div></div>

<div id="pf3" class="pf w0 h0" data-page-no="3"><div class="pc pc3 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="https://static.pudn.com/prod/directory_preview_static/62631b034c65f41259957c23/bg3.jpg"><div class="t m0 x5 ha y45 ff4 fs2 fc1 sc0 ls18 ws1">Parameter ClockPeriod = 10; </div><div class="t m0 x5 ha y46 ff4 fs2 fc1 sc0 ls18 ws1">// Clock Generation method 1: </div><div class="t m0 x5 ha y47 ff4 fs2 fc1 sc0 ls18 ws1">initial begin </div><div class="t m0 x5 ha y48 ff4 fs2 fc1 sc0 ls18 ws1">forever Clock = #(ClockPeriod / 2) ~ Clock; </div><div class="t m0 x5 ha y49 ff4 fs2 fc1 sc0 ls18 ws1">end </div><div class="t m0 x5 ha y4a ff4 fs2 fc1 sc0 ls18 ws1">// Clock Generation method 2: </div><div class="t m0 x5 ha y4b ff4 fs2 fc1 sc0 ls18 ws1">initial begin </div><div class="t m0 x5 ha y4c ff4 fs2 fc1 sc0 ls18 ws1">always #(ClockPeriod / 2) Clock = ~Clock; </div><div class="t m0 x5 ha y4d ff4 fs2 fc1 sc0 ls18 ws1">end </div><div class="t m0 x5 h8 y4e ff1 fs4 fc0 sc0 ls1 ws1"> </div><div class="t m0 x5 h8 y4f ff1 fs4 fc0 sc0 ls1 ws1">2.2<span class="_"> </span><span class="ff2 sc2 ls15">准备激励信号</span> </div><div class="t m0 x5 h7 y50 ff2 fs1 fc1 sc0 ls1 ws1">要得到测试验证的结果，<span class="_ _1"></span>就要为测试的设计模块提供激励。<span class="_ _6"></span>必要时，<span class="_ _1"></span>需要在测试设计中使用</div><div class="t m0 x5 h7 y51 ff2 fs1 fc1 sc0 ls1 ws1">并行的激励程序块。<span class="_ _1"></span>通常采用两种方式给出激励：<span class="_ _6"></span>绝对时间激励和相对时间激励。<span class="_ _1"></span>第一种方</div><div class="t m0 x5 h7 y52 ff2 fs1 fc1 sc0 ls1 ws1">式，<span class="_ _1"></span>仿真激励的数值是以对应于仿真时刻零点的绝对时间的形式列出。<span class="_ _6"></span>相比而言，<span class="_ _1"></span>相对时间</div><div class="t m0 x5 h7 y53 ff2 fs1 fc1 sc0 ls1 ws1">激励首先给出激励的初始值，<span class="_ _9"></span>然后等待事件触发然后赋予激励新的数值。<span class="_ _9"></span>根据设计者的需要，</div><div class="t m0 x5 h3 y54 ff2 fs1 fc1 sc0 ls1 ws1">两种方式可以在测试设计中组合使用。<span class="ff3"> </span></div><div class="t m0 x5 h3 y55 ff2 fs1 fc1 sc0 ls1 ws1">表<span class="_ _7"> </span><span class="ff3">2<span class="_"> </span></span>和表<span class="_ _7"> </span><span class="ff3">3<span class="_"> </span></span>用<span class="_ _7"> </span><span class="ff3 lse">VHDL<span class="_"> </span></span>和<span class="_ _7"> </span><span class="ff3 lsf">V<span class="_ _2"></span>erilog<span class="_"> </span><span class="ff2 ls1">分别<span class="_ _0"></span>给出了一段绝对时间激励和相对时间激励的代码。<span class="ff3"> </span></span></span></div><div class="t m0 xa h3 y56 ff3 fs1 fc1 sc0 ls1 ws1"> </div><div class="t m0 xc h3 y57 ff2 fs2 fc1 sc0 ls1 ws1">表<span class="_ _3"> </span><span class="ff3">2<span class="_"> </span></span>绝对时间激励<span class="ff3 fs1"> </span></div><div class="t m0 xd h3 y58 ff3 fs1 fc1 sc0 ls1 ws1"> </div><div class="t m0 xc h4 y59 ff2 fs2 fc1 sc0 ls1 ws1">表<span class="_ _3"> </span><span class="ff3">3<span class="_"> </span></span>相对时间激励<span class="ff3"> </span></div><div class="t m0 x5 h3 y5a ff3 fs1 fc1 sc0 lse ws1">VHDL<span class="_ _12"> </span><span class="ff2 ls1">进程块和<span class="_ _7"> </span></span><span class="ls14">V<span class="_ _2"></span>erilog<span class="_"> </span><span class="ff2 ls1">初始块与设计文件中的其他的进程块或初始块并行执行。然而，在</span></span></div><div class="t m0 x5 h7 y5b ff2 fs1 fc1 sc0 ls1 ws1">每一个进程块或初始块中，<span class="_ _10"></span>事件是按照代码书写的顺序依次执行的。<span class="_ _10"></span>就是说各个模块是在仿</div></div><div class="pi" data-data='{"ctm":[1.611639,0.000000,0.000000,1.611639,0.000000,0.000000]}'></div></div>

<div id="pf4" class="pf w0 h0" data-page-no="4"><div class="pc pc4 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="https://static.pudn.com/prod/directory_preview_static/62631b034c65f41259957c23/bg4.jpg"><div class="t m0 x5 h7 y5c ff2 fs1 fc1 sc0 ls1 ws1">真的零时刻同时启动的。<span class="_ _4"></span>我们应该将复杂的激励序列分解为多个模块来编写以保障代码的可</div><div class="t m0 x5 h3 y5d ff2 fs1 fc1 sc0 ls1 ws1">读性和易于维护性。<span class="ff3"> </span></div><div class="t m0 x5 h3 y5e ff3 fs1 fc1 sc0 ls1 ws1"> </div><div class="t m0 x5 h8 y5f ff1 fs4 fc0 sc0 ls1 ws1">2.2<span class="_"> </span><span class="ff2 sc2 ls15">显示结果</span> </div><div class="t m0 x5 h3 y60 ff2 fs1 fc1 sc0 ls1 ws1">在<span class="_ _13"> </span><span class="ff3 ls16">Ve<span class="_ _11"></span>r<span class="_"> </span>i<span class="_ _11"></span>l<span class="_"> </span>o<span class="_ _11"></span>g<span class="_ _f"> </span></span>中我们使用关键字<span class="ff3 ls1a">$display <span class="_"> </span></span>和<span class="ff3 ls1b ws5"> $monitor </span>显示结果。虽然<span class="_ _12"> </span><span class="ff3 lse">VHDL<span class="_ _d"> </span></span>没有等效的显示</div><div class="t m0 x5 h3 y61 ff2 fs1 fc1 sc0 ls1 ws1">指令，<span class="_ _10"></span>它提供了<span class="_ _7"> </span><span class="ff3 ls1c">std_textio<span class="_"> </span></span>标准文本输入输出程序包。<span class="_ _10"></span>它允许文件的<span class="_ _3"> </span><span class="ff3 ls1d">i/o<span class="_"> </span></span>重定向到显示终端窗</div><div class="t m0 x5 h3 y62 ff2 fs1 fc1 sc0 ls1 ws1">口（这个技术的一个示例，参看后面的自检测测试设计）<span class="ff3"> </span></div><div class="t m0 x5 h3 y63 ff2 fs1 fc1 sc0 ls1 ws1">下面是<span class="_ _7"> </span><span class="ff3 ls16">Ve<span class="_ _11"></span>r<span class="_"> </span>i<span class="_ _11"></span>l<span class="_"> </span>o<span class="_ _11"></span>g<span class="_ _d"> </span></span>示例<span class="ff3">,</span>它将在终端屏幕上显示数值。<span class="ff3"> </span></div><div class="t m0 x5 ha y64 ff4 fs2 fc1 sc0 ls18 ws1">// pipes the ASCII results to the terminal or text editor </div><div class="t m0 x5 ha y65 ff4 fs2 fc1 sc0 ls18 ws1">initial begin </div><div class="t m0 x5 ha y66 ff4 fs2 fc1 sc0 ls18 ws1">$timeformat(-9,1,"ns",12); </div><div class="t m0 x5 ha y67 ff4 fs2 fc1 sc0 ls18 ws1">$display(" Time Clk Rst Ld SftRg Data Sel"); </div><div class="t m0 x5 ha y68 ff4 fs2 fc1 sc0 ls18 ws1">$monitor("%t %b %b %b %b %b %b", $realtime, <span class="_ _2"></span> </div><div class="t m0 xe ha y69 ff4 fs2 fc1 sc0 ls18 ws1">clock, reset, load, shiftreg, data, sel); </div><div class="t m0 x5 ha y6a ff4 fs2 fc1 sc0 ls18 ws1">end </div><div class="t m0 x5 h3 y2c ff2 fs1 fc1 sc0 ls1 ws1">关键字<span class="ff3 ls1e ws6"> $display<span class="_ _7"> </span></span>在终端屏幕上输出用<span class="ff3 ls12">(“</span>…<span class="ff3 ls1f">”)</span>括起的附加的文字。关键字<span class="ff3 ls1a">$monitor<span class="_"> </span></span>操作不同，</div><div class="t m0 x5 h3 y2d ff2 fs1 fc1 sc0 ls1 ws1">它的输出是由事件驱动的。<span class="_ _2"></span>例子中的变量<span class="ff3 ls20">$realtime<span class="_ _2"></span><span class="ff2 ls1">（用户用于赋值以当前的仿真时间）<span class="_ _14"></span>用于</span></span></div><div class="t m0 x5 h3 y2e ff2 fs1 fc1 sc0 ls1 ws1">触发信号列表中各个值的显示。<span class="_ _9"></span>信号表由变量<span class="ff3 ls3 ws7"> $realtime<span class="_ _7"> </span></span>开始，<span class="_ _9"></span>随后是需要显示的信号<span class="_ _4"></span>（<span class="ff3 ls21">clock, </span></div><div class="t m0 x5 h3 y6b ff3 fs1 fc1 sc0 lsf ws8">reset, load<span class="_"> </span><span class="ff2 ls22 ws1">等）<span class="_ _9"></span><span class="ls1">。起头的一<span class="_ _0"></span>连串<span class="ff3 ls23">“%”</span>关键字是一些格式标识符，用来控制信号列表中的数值以</span></span></div><div class="t m0 x5 h7 y6c ff2 fs1 fc1 sc0 ls1 ws1">何种格式显示。<span class="_ _4"></span>格式列表是有位置关系的――每个格式标识符对应于信号列表中的相应位置</div><div class="t m0 x5 h3 y6d ff2 fs1 fc1 sc0 ls1 ws1">的信号。<span class="_ _15"></span>比如<span class="ff3 lsf">%t<span class="_"> </span></span>标识符规定了<span class="ff3 ls3">$realtime<span class="_"> </span></span>的值以时间<span class="_ _0"></span>格式给出，<span class="_ _15"></span>而第一个<span class="ff3 lsf">%b<span class="_"> </span></span>标识符规定<span class="_ _7"> </span><span class="ff3 ls24">clock</span></div><div class="t m0 x5 h3 y6e ff2 fs1 fc1 sc0 ls1 ws1">信号的值以二进制形式给出。<span class="_ _16"></span><span class="ff3 ls16">Ve<span class="_ _11"></span>r<span class="_"> </span>i<span class="_ _11"></span>l<span class="_"> </span>o<span class="_ _11"></span>g<span class="_ _d"> </span><span class="ff2 ls1">还提供其它的一些格式标识符，<span class="_ _16"></span>比如<span class="ff3 lsf">%h<span class="_"> </span></span>说明十六进制，</span></span></div><div class="t m0 x5 h3 y6f ff3 fs1 fc1 sc0 lsf ws1">%d<span class="_ _d"> </span><span class="ff2 ls1">说明十进制，</span>%c<span class="_ _17"> </span><span class="ff2 ls1">说明显示为八进制。<span class="_ _9"></span>（参见<span class="_ _d"> </span><span class="ff3 lsf">V<span class="_ _6"></span>erilog<span class="_ _17"> </span><span class="ff2 ls1">参考手册以了解完整的关键字及格</span></span></span></div><div class="t m0 x5 h3 y70 ff2 fs1 fc1 sc0 ls1 ws1">式标识符）<span class="ff3"> </span></div><div class="t m0 x5 h3 y71 ff2 fs1 fc1 sc0 ls1 ws1">格式化的输出结果如图<span class="_ _7"> </span><span class="ff3">2<span class="_"> </span></span>所示。<span class="ff3"> </span></div><div class="t m0 xf h3 y72 ff3 fs1 fc1 sc0 ls1 ws1"> </div><div class="t m0 x10 h4 y73 ff2 fs2 fc1 sc0 ls1 ws1">图<span class="_ _3"> </span><span class="ff3">2<span class="_"> </span></span>仿真结果返回结果<span class="ff3"> </span></div><div class="t m0 x5 h3 y74 ff3 fs1 fc1 sc0 ls1 ws1"> </div><div class="t m0 x5 h6 y75 ff1 fs3 fc0 sc0 ls1 ws1">3<span class="_"> </span><span class="ff2 sc2 lsa">简单的测试设计</span> </div><div class="t m0 x5 h7 y76 ff2 fs1 fc1 sc0 ls1 ws1">简单的测试设计就是实例化用户设计，<span class="_ _10"></span>然后向它提供激励。<span class="_ _10"></span>测试的输出可以图形化地显示在</div><div class="t m0 x5 h7 y77 ff2 fs1 fc1 sc0 ls1 ws1">仿真器的波形窗口中或者以文本的方式显示在用户终端或者是管道重定向输出到文本中。</div><div class="t m0 x11 h6 y78 ff1 fs3 fc0 sc0 ls1 ws1"> </div><div class="t m0 x5 h3 y79 ff2 fs1 fc1 sc0 ls1 ws1">以下是一个简单的用<span class="_ _7"> </span><span class="ff3 lsf">V<span class="_ _6"></span>e<span class="_ _18"></span>rilog<span class="_"> </span><span class="ff2 ls1">实现的设计，它实现了一个移位寄存器的功能。<span class="ff3"> </span></span></span></div><div class="t m0 x5 ha y7a ff4 fs2 fc1 sc0 ls18 ws1">module shift_reg (clock, reset, load, sel, data, shiftreg); </div><div class="t m0 x5 ha y7b ff4 fs2 fc1 sc0 ls18 ws1">input clock; </div><div class="t m0 x5 ha y7c ff4 fs2 fc1 sc0 ls18 ws1">input reset; </div><div class="t m0 x5 ha y7d ff4 fs2 fc1 sc0 ls18 ws1">input load; </div></div><div class="pi" data-data='{"ctm":[1.611639,0.000000,0.000000,1.611639,0.000000,0.000000]}'></div></div>

<div id="pf5" class="pf w0 h0" data-page-no="5"><div class="pc pc5 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="https://static.pudn.com/prod/directory_preview_static/62631b034c65f41259957c23/bg5.jpg"><div class="t m0 x5 ha y45 ff4 fs2 fc1 sc0 ls18 ws1">input [1:0] sel; </div><div class="t m0 x5 ha y46 ff4 fs2 fc1 sc0 ls18 ws1">input [4:0] data; </div><div class="t m0 x5 ha y47 ff4 fs2 fc1 sc0 ls18 ws1">output [4:0] shiftreg; </div><div class="t m0 x5 ha y48 ff4 fs2 fc1 sc0 ls18 ws1">reg [4:0] shiftreg; </div><div class="t m0 x5 ha y49 ff4 fs2 fc1 sc0 ls18 ws1">always @ (posedge clock) </div><div class="t m0 x5 ha y4a ff4 fs2 fc1 sc0 ls18 ws1">begin </div><div class="t m0 xe ha y4b ff4 fs2 fc1 sc0 ls18 ws1">if (reset) </div><div class="t m0 x12 ha y4c ff4 fs2 fc1 sc0 ls18 ws1">shiftreg = 0; </div><div class="t m0 xe ha y4d ff4 fs2 fc1 sc0 ls18 ws1">else if (load) </div><div class="t m0 x12 ha y7e ff4 fs2 fc1 sc0 ls18 ws1">shiftreg = data; </div><div class="t m0 xe ha y7f ff4 fs2 fc1 sc0 ls18 ws1">else </div><div class="t m0 x12 ha y80 ff4 fs2 fc1 sc0 ls18 ws1">case (sel) </div><div class="t m0 x12 ha y81 ff4 fs2 fc1 sc0 ls18 ws1">2’b00 : shiftreg = shiftreg; </div><div class="t m0 x12 ha y82 ff4 fs2 fc1 sc0 ls18 ws1">2’b01 : shiftreg = shiftreg << 1; </div><div class="t m0 x12 ha y83 ff4 fs2 fc1 sc0 ls18 ws1">2’b10 : shiftreg = shiftreg >> 1; </div><div class="t m0 x12 ha y84 ff4 fs2 fc1 sc0 ls18 ws1">default : shiftreg = shiftreg; </div><div class="t m0 xe ha y85 ff4 fs2 fc1 sc0 ls18 ws1">endcase </div><div class="t m0 x5 ha y86 ff4 fs2 fc1 sc0 ls18 ws1">end </div><div class="t m0 x5 ha y87 ff4 fs2 fc1 sc0 ls18 ws1">endmodule </div><div class="t m0 x5 h3 y88 ff2 fs1 fc1 sc0 ls1 ws1">以下是实例化了移位寄存器的一个简单的测试设计<span class="ff3"> </span></div><div class="t m0 x5 h9 y89 ff1 fs1 fc1 sc0 ls1 ws1"> </div><div class="t m0 x5 h9 y8a ff1 fs1 fc1 sc0 ls1c ws1">V<span class="_ _2"></span>erilog<span class="_"> </span><span class="ff2 sc1 ls25">示例<span class="_ _0"></span><span class="ff1 sc0 ls1"> </span></span></div><div class="t m0 x5 ha y8b ff4 fs2 fc1 sc0 ls18 ws1">module testbench; // declare testbench name </div><div class="t m0 x5 ha y8c ff4 fs2 fc1 sc0 ls18 ws1">reg clock; </div><div class="t m0 x5 ha y8d ff4 fs2 fc1 sc0 ls18 ws1">reg load; </div><div class="t m0 x5 ha y8e ff4 fs2 fc1 sc0 ls18 ws1">reg reset; // declaration of signals </div><div class="t m0 x5 ha y8f ff4 fs2 fc1 sc0 ls18 ws1">wire [4:0] shiftreg; </div><div class="t m0 x5 ha y90 ff4 fs2 fc1 sc0 ls18 ws1">reg [4:0] data; </div><div class="t m0 x5 ha y91 ff4 fs2 fc1 sc0 ls18 ws1">reg [1:0] sel; </div><div class="t m0 x5 ha y92 ff4 fs2 fc1 sc0 ls18 ws1">// instantiation of the shift_reg design below </div><div class="t m0 x5 ha y93 ff4 fs2 fc1 sc0 ls18 ws1">shift_reg dut( <span class="_ _12"> </span>.clock (clock), </div><div class="t m0 x13 ha y94 ff4 fs2 fc1 sc0 ls18 ws1">.load (load), </div><div class="t m0 x13 ha y95 ff4 fs2 fc1 sc0 ls18 ws1">.reset (reset), </div><div class="t m0 x13 ha y96 ff4 fs2 fc1 sc0 ls18 ws1">.shiftreg (shiftreg), </div><div class="t m0 x13 ha y97 ff4 fs2 fc1 sc0 ls18 ws1">.data (data), </div><div class="t m0 x13 ha y98 ff4 fs2 fc1 sc0 ls18 ws1">.sel (sel)); </div><div class="t m0 x5 ha y99 ff4 fs2 fc1 sc0 ls18 ws1">//this process block sets up the free running clock </div><div class="t m0 x5 ha y9a ff4 fs2 fc1 sc0 ls18 ws1">initial begin </div><div class="t m0 xe ha y9b ff4 fs2 fc1 sc0 ls18 ws1">clock = 0; </div><div class="t m0 xe ha y9c ff4 fs2 fc1 sc0 ls18 ws1">forever #50 clock = ~clock; </div><div class="t m0 x5 ha y9d ff4 fs2 fc1 sc0 ls18 ws1">end </div><div class="t m0 x5 ha y9e ff4 fs2 fc1 sc0 ls18 ws1">initial begin// this process block specifies the stimulus. </div><div class="t m0 xe ha y9f ff4 fs2 fc1 sc0 ls18 ws1">reset = 1; </div><div class="t m0 xe ha ya0 ff4 fs2 fc1 sc0 ls18 ws1">data = 5’b00000; </div></div><div class="pi" data-data='{"ctm":[1.611639,0.000000,0.000000,1.611639,0.000000,0.000000]}'></div></div>