code: def scan_chain_len(self, scan_chain):
          
          res = self._dll.JLINKARM_MeasureSCLen(scan_chain)
          if res < 0:
              raise errors.JLinkException(res)
          return res
docs: Retrieves and returns the number of bits in the scan chain.
  
          Args:
            self (JLink): the ``JLink`` instance
            scan_chain (int): scan chain to be measured
  
          Returns:
            Number of bits in the specified scan chain.
  
          Raises:
            JLinkException: on error.