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<a href="00851.html" target="topic">第二十七章 直接编程接口（DPI）</a>, <a href="00975.html" target="topic">主题</a></div>
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27.1 概述</div>
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Direct Programming Interface (DPI) is an interface between SystemVerilog and a foreign programming language. It consists of two separate layers: the SystemVerilog layer and a foreign language layer. Both sides of DPI are fully isolated. Which programming language is actually used as the foreign language is transparent and irrelevant for the SystemVerilog side of this interface. Neither the SystemVerilog compiler nor the foreign language compiler is required to analyze the source code in the other’s language. Different programming languages can be used and supported with the same intact SystemVerilog layer. For now, however, SystemVerilog 3.1 defines a foreign language layer only for the C programming language. See Annex E for more details. </p>
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The motivation for this interface is two-fold. The methodological requirement is that the interface should allow a heterogeneous system to be built (a design or a testbench) in which some components can be written in a language (or more languages) other than SystemVerilog, hereinafter called the foreign language. On the other hand, there is also a practical need for an easy and efficient way to connect existing code, usually written in C or C++, without the knowledge and the overhead of PLI or VPI. </p>
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DPI follows the principle of a black box: the specification and the implementation of a component is clearly separated and the actual implementation is transparent to the rest of the system. Therefore, the actual programming language of the implementation is also transparent, though this standard defines only C linkage semantics. The separation between SystemVerilog code and the foreign language is based on using functions as the natural encapsulation unit in SystemVerilog. By and large, any function can be treated as a black box and implemented either in SystemVerilog or in the foreign language in a transparent way, without changing its calls.</p></div>
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<a href="00297.html" target="topic">27.1.1 Tasks and functions</a> </div></td><td class="Element206" valign="top" width="50%">
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DPI allows direct inter-language function calls between the languages on either side of the interface. Specifically, functions implemented in a foreign language can be called from SystemVerilog; such functions are referred to as imported functions. SystemVerilog functions that are to be called from a foreign code shall be specified in export declarations (see Section 27.6 for more details). DPI allows for passing SystemVerilog data between the two domains through function arguments and results. There is no intrinsic overhead in this interface.<br><br>It is also possible to perform task enables across the language boundary. Foreign code can call SystemVerilog tasks, and... <a href="00297.html" target="topic">more</a> </div></td></tr><tr>
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<a href="00298.html" target="topic">27.1.2 Data types</a> </div></td><td class="Element206" valign="top" width="50%">
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SystemVerilog data types are the sole data types that can cross the boundary between SystemVerilog and a foreign language in either direction (i.e., when an imported function is called from SystemVerilog code or an exported SystemVerilog function is called from a foreign code). It is not possible to import the data types or directly use the type syntax from another language. A rich subset of SystemVerilog data types is allowed for formal arguments of import and export functions, although with some restrictions and with some notational extensions. Function result types are restricted to small values, however (see Section 27.4.5).<br><br>Formal... <a href="00298.html" target="topic">more</a> </div></td></tr></table></div></div>
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