User guide

22-52
SystemVerilog Design Constructs
• The context keyword enables, in this case, the C or C++
language function to call the user-defined task in the
SystemVerilog code. (This keyword also has other uses in the
DPI.)
• The task keyword also enables the C or C++ language function
to call the user-defined task in the SystemVerilog code. We are
calling it a task even thought there are no tasks in C or C++.
You must include both keywords.
The SystemVerilog IEEE Std 1800-2005, Section 26.1.1 "Tasks and
functions", specifies the following:
“All functions used in DPI are assumed to complete their execution
instantly and consume 0 (zero) simulation time, just as normal
SystemVerilog functions.”
So imported C functions that call time-consuming user-defined tasks
must be declared to be tasks.
The SystemVerilog IEEE Std 1800-2005, Section 26.7 "Exported
tasks", specifies the following:
• “It is never legal to call an exported task from within an imported
function.”
• “It is legal for an imported task to call an exported task only if the
imported task is declared with the context property.”
Next comes the user-defined task:
task task_in_SV(inout int i);
#5 i = i/2;
endtask