code: def _get_useful_callpoint_name():
      
      if not _setting_slower_but_more_descriptive_tmps:
          return None
  
      import inspect
      loc = None
      frame_stack = inspect.stack()
      try:
          for frame in frame_stack:
              modname = inspect.getmodule(frame[0]).__name__
              if not modname.startswith('pyrtl.'):
                  full_filename = frame[0].f_code.co_filename
                  filename = full_filename.split('/')[-1].rstrip('.py')
                  lineno = frame[0].f_lineno
                  loc = (filename, lineno)
                  break
      except:
          loc = None
      finally:
          del frame_stack
      return loc
docs: Attempts to find the lowest user-level call into the pyrtl module
      :return (string, int) or None: the file name and line number respectively
  
      This function walks back the current frame stack attempting to find the
      first frame that is not part of the pyrtl module.  The filename (stripped
      of path and .py extention) and line number of that call are returned.
      This point should be the point where the user-level code is making the
      call to some pyrtl intrisic (for example, calling "mux").   If the
      attempt to find the callpoint fails for any reason, None is returned.