Example
As an example, consider the following Verilog code fragment:
val = 41; $increment(val); $display("After $increment, val=%d", val); Suppose the increment system task increments its first parameter by one. Using C and the VPI mechanism, the increment task can be implemented as follows:
// Implements the increment system taskstaticintincrement(char*userdata){vpiHandlesystfref,args_iter,argh;structt_vpi_valueargval;intvalue;// Obtain a handle to the argument listsystfref=vpi_handle(vpiSysTfCall,NULL);args_iter=vpi_iterate(vpiArgument,systfref);// Grab the value of the first argumentargh=vpi_scan(args_iter);argval.format=vpiIntVal;vpi_get_value(argh,&argval);value=argval.value.integer;vpi_printf("VPI routine received %d\n",value);// Increment the value and put it back as first argumentargval.value.integer=value+1;vpi_put_value(argh,&argval,NULL,vpiNoDelay);// Cleanup and returnvpi_free_object(args_iter);return0;}Also, a function that registers this system task is necessary. This function is invoked prior to elaboration or resolution of references when it is placed in the externally visible vlog_startup_routines[] array.
// Registers the increment system taskvoidregister_increment(){s_vpi_systf_datadata={vpiSysTask,0,"$increment",increment,0,0,0};vpi_register_systf(&data);}// Contains a zero-terminated list of functions that have to be called at startupvoid(*vlog_startup_routines[])()={register_increment,0};The C code is compiled into a shared object that will be used by the Verilog simulator. A simulation of the earlier mentioned Verilog fragment will now result in the following output:
VPI routine received 41 After $increment, val=42
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