Most useful VPI code blocks

1. Register a system call
void hello_register()
{
　s_vpi_systf_data tf_data;

　tf_data.type = vpiSysTask;
　tf_data.tfname = "$hello";
　tf_data.calltf = hello;
　tf_data.compiletf = NULL;
　tf_data.sizetf = NULL;
　vpi_register_systf(&tf_data);
}

2. Obtain system task arguments

　vpiHandle systf_handle, arg_iterator, arg_handle, net_handle;
　s_vpi_value current_value;

　/* obtain a handle to the system task instance */
　systf_handle = vpi_handle(vpiSysTfCall, NULL);

　/* obtain handle to system task argument */
　arg_iterator = vpi_iterate(vpiArgument, systf_handle);
　net_handle = vpi_scan(arg_iterator);
　vpi_free_object(arg_iterator); /* free iterator memory */