code: public void addCommandPolling(final String commandName, final int pollingPeriod) throws DevFailed {
          checkPollingLimits(commandName, pollingPeriod, minCommandPolling);
          final CommandImpl command = CommandGetter.getCommand(commandName, commandList);
          if (!command.getName().equals(DeviceImpl.INIT_CMD) && command.getInType().equals(CommandTangoType.VOID)) {
              command.configurePolling(pollingPeriod);
              if (command.getName().equals(DeviceImpl.STATE_NAME) || command.getName().equals(DeviceImpl.STATUS_NAME)) {
                  // command is also set as polled
                  final AttributeImpl attribute = AttributeGetterSetter.getAttribute(command.getName(), attributeList);
                  attribute.configurePolling(pollingPeriod);
                  pollAttributes.put(attribute.getName().toLowerCase(Locale.ENGLISH), pollingPeriod);
                  cacheManager.startStateStatusPolling(command, attribute);
                  pollAttributes.put(attribute.getName().toLowerCase(Locale.ENGLISH), pollingPeriod);
                  savePollingConfig();
              } else {
                  cacheManager.startCommandPolling(command);
              }
          }
  
      }
docs: Add command polling. Init command cannot be polled. Only command with
  parameter void can be polled
  
  @param commandName   the command to poll
  @param pollingPeriod the polling period
  @throws DevFailed