docs: def load_routing_table_entries(self, entries, x, y, app_id):
          """Allocate space for and load multicast routing table entries into the
          router of a SpiNNaker chip.
  
          .. note::
              This method only loads routing table entries for a single chip.
              Most users should use :py:meth:`.load_routing_tables` which loads
              routing tables to multiple chips.
  
          Parameters
          ----------
          entries : [:py:class:`~rig.routing_table.RoutingTableEntry`, ...]
              List of :py:class:`rig.routing_table.RoutingTableEntry`\ s.
  
          Raises
          ------
          rig.machine_control.machine_controller.SpiNNakerRouterError
              If it is not possible to allocate sufficient routing table entries.
          """
          count = len(entries)
  
          # Try to allocate room for the entries
          rv = self._send_scp(
              x, y, 0, SCPCommands.alloc_free,
              (app_id << 8) | consts.AllocOperations.alloc_rtr, count
          )
          rtr_base = rv.arg1  # Index of the first allocated entry, 0 if failed
  
          if rtr_base == 0:
              raise SpiNNakerRouterError(count, x, y)
  
          # Determine where to write into memory
          buf = self.read_struct_field("sv", "sdram_sys", x, y)
  
          # Build the data to write in, then perform the write
          data = bytearray(16 * len(entries))
          for i, entry in enumerate(entries):
              # Build the route as a 32-bit value
              route = 0x00000000
              for r in entry.route:
                  route |= 1 << r
  
              struct.pack_into(consts.RTE_PACK_STRING, data, i*16,
                               i, 0, route, entry.key, entry.mask)
          self.write(buf, data, x, y)
  
          # Perform the load of the data into the router
          self._send_scp(
              x, y, 0, SCPCommands.router,
              (count << 16) | (app_id << 8) | consts.RouterOperations.load,
              buf, rtr_base
          )