Question

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.

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.

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.