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E.8 Context tasks and functions</div>
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Some DPI imported tasks and functions require that the context of their call is known. For example, those calls can be associated with instances of C models that have a one-to-one correspondence with instances of SystemVerilog modules that are making the calls. Alternatively, a DPI imported task or function might need to access or modify simulator data structures using PLI or VPI calls, or by making a call back into SystemVerilog via an export task or function. Context knowledge is required for such calls to function properly. It can take special instrumentation of their call to provide such context. </p>
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To avoid any unnecessary overhead, imported task and function calls in SystemVerilog code are not instrumented unless the imported task or function is specified as context in its SystemVerilog import declaration. A small set of DPI utility functions are available to assist programmers when working with context tasks or functions (see Annex E.8.3). If those utility functions are used with any non-context function, a system error shall result.</p></div>
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<a href="00789.html" target="topic">E.8.1 Overview of DPI and VPI context</a> </div></td><td class="Element206" valign="top" width="50%">
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Both DPI task and functions and VPI/PLI functions might need to understand their context. However, the meaning of the term is different for the two categories of task and functions.<br><br>DPI imported tasks and functions are essentially proxies for native SystemVerilog tasks and functions. Native SystemVerilog tasks and functions always operate in the scope of their declaration site. For example, a native SystemVerilog function f() can be declared in a module m which is instantiated as top.i1_m. The top.i1_m instance of f() can be called via hierarchical reference from code in a distant design region. Function f() is said to... <a href="00789.html" target="topic">more</a> </div></td></tr><tr>
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<a href="00790.html" target="topic">E.8.2 Context of imported and export tasks and functions</a> </div></td><td class="Element206" valign="top" width="50%">
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DPI imported and export tasks and functions can be declared anywhere a normal SystemVerilog task or function can be declared. Specifically, this means that they can be declared in module, program, interface, or generate declarative scope.<br><br>A context imported task or function executes in the context of the instantiated scope surrounding its declaration. This means that such tasks and functions can see other variables in that scope without qualification. As explained in Annex E.8.1, this should not be confused with the context of the task’s or function’s call site, which can actually be anywhere in the SystemVerilog design hierarchy. The... <a href="00790.html" target="topic">more</a> </div></td></tr><tr>
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<a href="00791.html" target="topic">E.8.3 Working with DPI context tasks and functions in C code</a> </div></td><td class="Element206" valign="top" width="50%">
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DPI defines a small set of functions to help programmers work with DPI context tasks and functions. The term scope is used in the task or function names for consistency with other SystemVerilog terminology. The terms scope and context are equivalent for DPI tasks and functions.<br><br>There are functions that allow the user to retrieve and manipulate the current operational scope. It is an error to use these functions with any C code that is not executing under a call to a DPI context imported task or function.<br><br>There are also functions that provide users with the power to set... <a href="00791.html" target="topic">more</a> </div></td></tr><tr>
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<a href="00792.html" target="topic">E.8.4 Example 1 — Using DPI context functions</a> </div></td><td class="Element206" valign="top" width="50%">
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<a href="00793.html" target="topic">E.8.5 Relationship between DPI and VPI/PLI interfaces</a> </div></td><td class="Element206" valign="top" width="50%">
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DPI allows C code to run in the context of a SystemVerilog simulation, thus it is natural for users to consider using VPI/PLI C code from within imported tasks and functions.<br><br>There is no specific relationship defined between DPI and the existing Verilog programming interfaces (VPI and PLI). Programmers must make no assumptions about how DPI and the other interfaces interact. In particular, note that a vpiHandle is not equivalent to an svOpenArrayHandle, and the two must not be interchanged and passed between functions defined in two different interface standards.<br><br>If a user wants to call VPI or PLI functions... <a href="00793.html" target="topic">more</a> </div></td></tr></table></div></div>
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