📄 00778.html
字号:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN">
<html>
<head>
<title>E.7 Argument passing modes</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', '00778.html');" onmousedown="onBodyMouseDown();">
<!-- Begin Popups -->
<div class="Element801" id="popup00787">
<div class="Element800">
<div class="Element14">
链接</div>
<div class="Element11">
<div class="Element10">
<a href="00883.html" target="topic">附录E DPI C-layer</a>, <a href="01036.html" target="topic">主题</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, 'popup00787');"><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="00777.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="00883.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="00779.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">
E.7 Argument passing modes</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">
<p class="Element10">
This section defines the ways to pass arguments in the C-layer of the Direct Programming Interface.</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="00883.html" target="topic">附录E DPI C-layer</a></p></div>
</div>
</div>
<a name="主题"></a><div class="Element14">
<a onclick="toggleVisibilityStored('主题');" class="a_Element14"><img src="sectionminus.png" border="0" alt="" title="" id="img主题">主题</a></div>
<div id="div主题">
<div class="Element11">
<div class="Element10">
<div class="Element212">
<div class="TableDiv">
<table cellspacing="0" class="Table0">
<tr>
<td class="Element200" valign="top" width="50%">
<div class="Element201">
主题 </div></td><td class="Element204" valign="top" width="50%">
<div class="Element205">
描述 </div></td></tr><tr>
<td class="Element202" valign="top" width="50%">
<div class="Element203">
<a href="00779.html" target="topic">E.7.1 Overview</a> </div></td><td class="Element206" valign="top" width="50%">
<div class="Element207">
Imported and exported function arguments are generally passed by some form of a reference, with the exception of small values of SystemVerilog input arguments (see Annex E.11.7), which are passed by value. Similarly, the function result, which is restricted to small values, is passed by value, i.e., directly returned.<br><br>Actual arguments passed by reference typically are passed without changing their representation from the one used by a simulator. There is no inherent copying of arguments (other than any copying resulting from coercing).<br><br>Access to packed arrays via canonical representation involves copying arguments and does incur some overhead, however. Alternatively, for... <a href="00779.html" target="topic">more</a> </div></td></tr><tr>
<td class="Element202" valign="top" width="50%">
<div class="Element203">
<a href="00780.html" target="topic">E.7.2 Calling SystemVerilog tasks and functions from C</a> </div></td><td class="Element206" valign="top" width="50%">
<div class="Element207">
There is no difference in argument passing between calls from SystemVerilog to C and calls from C to System- Verilog. Tasks and functions exported from SystemVerilog cannot have open arrays as arguments. Apart from this restriction, the same types of formal arguments can be declared in SystemVerilog for exported tasks and functions and imported tasks and functions. A task or function exported from SystemVerilog shall have the same function header in C as would an imported function with the same function result type and same formal argument list. In the case of arguments passed by reference, an actual argument to... <a href="00780.html" target="topic">more</a> </div></td></tr><tr>
<td class="Element202" valign="top" width="50%">
<div class="Element203">
<a href="00781.html" target="topic">E.7.3 Argument passing by value</a> </div></td><td class="Element206" valign="top" width="50%">
<div class="Element207">
Only small values of formal input arguments (see Annex E.11.7) are passed by value. Function results are also directly passed by value. The user needs to provide the C-type equivalent to the SystemVerilog type of a formal argument if an argument is passed by value. </div></td></tr><tr>
<td class="Element202" valign="top" width="50%">
<div class="Element203">
<a href="00782.html" target="topic">E.7.4 Argument passing by reference</a> </div></td><td class="Element206" valign="top" width="50%">
<div class="Element207">
For arguments passed by reference, their original simulator-defined representation shall be used and a reference (a pointer) to the actual data object is passed. The actual argument is usually allocated by a caller. The caller can also pass a reference to an object already allocated somewhere else, for example, its own formal argument passed by reference.<br><br>If an argument of type T is passed by reference, the formal argument shall be of type T*. However, packed arrays can also be passed using generic pointers void* (typedefed accordingly to svBitPackedArrRef or svLogicPackedArrRef). </div></td></tr><tr>
<td class="Element202" valign="top" width="50%">
<div class="Element203">
<a href="00783.html" target="topic">E.7.5 Allocating actual arguments for SystemVerilog-specific types</a> </div></td><td class="Element206" valign="top" width="50%">
<div class="Element207">
This is relevant only for calling exported SystemVerilog functions from C code. The caller is responsible for allocating any actual arguments that are passed by reference.<br><br>Static allocation requires knowledge of the relevant data type. If such a type involves SystemVerilog packed arrays, their actual representation needs to be known to C code; thus, the file svdpi_src.h needs to be included, which makes the C code implementation-dependent and not binary compatible.<br><br>Sometimes binary compatibility can be achieved by using dynamic allocation functions. The functions svSizeOfLogicPackedArr() and svSizeOfBitPackedArr() provide the size of the actual representation of a packed array, which can... <a href="00783.html" target="topic">more</a> </div></td></tr><tr>
<td class="Element202" valign="top" width="50%">
<div class="Element203">
<a href="00784.html" target="topic">E.7.6 Argument passing by handle—open arrays</a> </div></td><td class="Element206" valign="top" width="50%">
<div class="Element207">
Arguments specified as open (unsized) arrays are always passed by a handle, regardless of direction of the SystemVerilog formal argument, and are accessible via library functions. The actual implementation of a handle is simulator-specific and transparent to the user. A handle is represented by the generic pointer void * (typedefed to svOpenArrayHandle). Arguments passed by handle shall always have a const qualifier, because the user shall not modify the contents of a handle. </div></td></tr><tr>
<td class="Element202" valign="top" width="50%">
<div class="Element203">
<a href="00785.html" target="topic">E.7.7 input arguments</a> </div></td><td class="Element206" valign="top" width="50%">
<div class="Element207">
input arguments of imported functions implemented in C shall always have a const qualifier.<br><br>input arguments, with the exception of open arrays, are passed by value or by reference, depending on the size. ‘Small’ values of formal input arguments are passed by value. The following data types are considered small:
<ul class="Element630">
<li class="Element600">byte, shortint, int, longint, real, shortreal</li>
<li class="Element600">chandle, string</li>
<li class="Element600">bit (i.e., 2-state) packed arrays up to 32 bits (canonical representation shall be used, like for a function result; thus a small packed bit array shall be represented as const svBitVec32) input arguments of other types are passed by reference.</li>
</ul>If an... <a href="00785.html" target="topic">more</a> </div></td></tr><tr>
<td class="Element202" valign="top" width="50%">
<div class="Element203">
<a href="00786.html" target="topic">E.7.8 inout and output arguments</a> </div></td><td class="Element206" valign="top" width="50%">
<div class="Element207">
inout and output arguments, with the exception of open arrays, are always passed by reference. Specifically, packed arrays are passed, accordingly, as svBitPackedArrRef or svLogicPackedArrRef. The same rules about unused bits apply as in Annex E.11.7. </div></td></tr><tr>
<td class="Element202" valign="top" width="50%">
<div class="Element203">
<a href="00787.html" target="topic">E.7.9 Function result</a> </div></td><td class="Element206" valign="top" width="50%">
<div class="Element207">
Types of a function result are restricted to the following SystemVerilog data types (see Table E-1 for the corresponding C type):
<ul class="Element630">
<li class="Element600">byte, shortint, int, longint, real, shortreal, chandle, string</li>
<li class="Element600">packed bit arrays up to 32 bits</li>
<li class="Element600">scalar values of type bit and logic</li>
</ul>Encodings for bit and logic are given in file svdpi.h. Refer to Annex E.9.1.1.<br><br>If the function result type is a packed bit array, the returned value shall be represented using the canonical representation svBitVec32. If a packed bit array is smaller than 32 bits, the most significant bits are unused and their contents are undetermined. </div></td></tr></table></div></div>
</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="00883.html" target="topic">附录E DPI C-layer</a>, <a href="01036.html" target="topic">主题</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 + -