Question

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.

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.

If a user wants to call VPI or PLI functions from within an imported task or function, the imported task or function must be flagged with the context qualifier.

Not all VPI or PLI functionality is available from within DPI context imported tasks and functions. For example, a SystemVerilog imported task or function is not a system task, and thus making the following call from within an imported task or function would result in an error:

/* Get handle to system task call site in preparation for argument scan */
vpiHandle myHandle = vpi_handle(vpiSysTfCall, NULL);

Similarly, receiving misctf callbacks and other activities associated with system tasks are not supported inside DPI imported tasks and functions. Users should use VPI or PLI if they wish to accomplish such actions.

However, the following kind of code is guaranteed to work from within DPI context imported tasks and functions:

/* Prepare to scan all top level modules */
vpiHandle myHandle = vpi_iterate(vpiModule, NULL);