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This chapter highlights the Direct Programming Interface and provides a detailed description of the SystemVerilog layer of the interface. The C layer is defined in Annex E.

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27.1 概述	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... more
27.2 Two layers of the DPI	DPI consists of two separate layers: the SystemVerilog layer and a foreign language layer. The SystemVerilog layer does not depend on which programming language is actually used as the foreign language. Although different programming languages can be supported and used with the intact SystemVerilog layer, SystemVerilog 3.1 defines a foreign language layer only for the C programming language. Nevertheless, SystemVerilog code shall look identical and its semantics shall be unchanged for any foreign language layer. Different foreign languages can require that the SystemVerilog implementation shall use the appropriate function call protocol, argument passing and linking mechanisms. This shall be, however,... more
27.3 Global name space of imported and exported functions	Every task or function imported to SystemVerilog must eventually resolve to a global symbol. Similarly, every task or function exported from SystemVerilog defines a global symbol. Thus the tasks and functions imported to and exported from SystemVerilog have their own global name space of linkage names, different from compilation- unit scope name space. Global names of imported and exported tasks and functions must be unique (no overloading is allowed ) and shall follow C conventions for naming; specifically, such names must start with a letter or underscore, and can be followed by alphanumeric characters or underscores. Exported and imported tasks... more
27.4 导入的任务和函数	导入函数的使用与SystemVerilog原生函数类似。
27.5 Calling imported functions	The usage of imported functions is identical as for native SystemVerilog functions., hence the usage and syntax for calling imported functions is identical as for native SystemVerilog functions. Specifically, arguments with default values can be omitted from the call; arguments can be passed by name, if all formal arguments are named.
27.6 Exported functions	DPI allows calling SystemVerilog functions from another language. However, such functions must adhere to the same restrictions on argument types and results as are imposed on imported functions. It is an error to export a function that does not satisfy such constraints. SystemVerilog functions that can be called from foreign code need to be specified in export declarations. Export declarations are allowed to occur only in the scope in which the function being exported is defined. Only one export declaration per function is allowed in a given scope. Note that class member functions cannot be exported, but all other SystemVerilog... more
27.7 Exported tasks	SystemVerilog allows tasks to be called from a foreign language, similar to functions. Such tasks are termed “exported tasks”. All aspects of exported functions described above in Section 27.6 apply to exported tasks. This includes legal declaration scopes as well as usage of the optional c_identifier. It is never legal to call an exported task from within an imported function. These semantics are identical to native SystemVerilog semantics, in which it is illegal for a function to perform a task enable. It is legal for an imported task to call an exported task only if the imported task is declared... more
27.8 Disabling DPI tasks and functions	It is possible for a disable statement to disable a block that is currently executing a mixed language call chain. When a DPI import task or function is disabled, the C code is required to follow a simple disable protocol. The protocol gives the C code the opportunity to perform any necessary resource cleanup, such as closing open file handles, closing open VPI handles, or freeing heap memory. An imported task or function is said to be in the disabled state when a disable statement somewhere in the design targets either it or a parent for disabling. Note that the... more

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