code: def load_fw(path):
      
      fname = os.path.realpath(path)
      exists = os.path.isfile(fname)
      if not exists or not os.access(fname, os.R_OK):
          _LOGGER.error(
              'Firmware path %s does not exist or is not readable',
              path)
          return None
      try:
          intel_hex = IntelHex()
          with open(path, 'r') as file_handle:
              intel_hex.fromfile(file_handle, format='hex')
          return intel_hex.tobinstr()
      except (IntelHexError, TypeError, ValueError) as exc:
          _LOGGER.error(
              'Firmware not valid, check the hex file at %s: %s', path, exc)
          return None
docs: Open firmware file and return a binary string.