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27.1.1 Tasks and functions</div>
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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. </p>
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It is also possible to perform task enables across the language boundary. Foreign code can call SystemVerilog tasks, and native Verilog code can call imported tasks. An imported task has the same semantics as a native Verilog task: It never returns a value, and it can block and consume simulation time. </p>
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All functions used in DPI are assumed to complete their execution instantly and consume 0 (zero) simulation time, just as normal SystemVerilog functions. DPI provides no means of synchronization other than by data exchange and explicit transfer of control. </p>
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Every imported task and function needs to be declared. A declaration of an imported task or function is referred to as an import declaration. Import declarations are very similar to SystemVerilog task and function declarations. Import declarations can occur anywhere where SystemVerilog task and function definitions are permitted. An import declaration is considered to be a definition of a SystemVerilog task or function with a foreign language implementation. The same foreign task or function can be used to implement multiple SystemVerilog tasks and functions (this can be a useful way of providing differing default argument values for the same basic task or function), but a given SystemVerilog name can only be defined once per scope. Imported task and functions can have zero or more formal input, output, and inout arguments. Imported tasks always return a void value, and thus can only be used in statement context. Imported functions can return a result or be defined as void functions. </p>
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DPI is based entirely upon SystemVerilog constructs. The usage of imported functions is identical as for native </p>
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SystemVerilog functions. With few exceptions imported functions and native functions are mutually </p>
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exchangeable. Calls of imported functions are indistinguishable from calls of SystemVerilog functions. This </p>
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facilitates ease-of-use and minimizes the learning curve. Similar interchangeable semantics exist between </p>
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native SystemVerilog tasks and imported tasks.</p></div>
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