text: """
  mbed SDK
  Copyright (c) 2011-2013 ARM Limited
  
  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at
  
      http://www.apache.org/licenses/LICENSE-2.0
  
  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
  """
  
  from time import time
  
  class WaitusTest(object):
      """ This test is reading single characters from stdio
          and measures time between their occurrences.
      """
      TICK_LOOP_COUNTER = 13
      TICK_LOOP_SUCCESSFUL_COUNTS = 10
      DEVIATION = 0.10    # +/-10%
  
      def test(self, selftest):
          test_result = True
          # First character to start test (to know after reset when test starts)
          if selftest.mbed.set_serial_timeout(None) is None:
              return selftest.RESULT_IO_SERIAL
          c = selftest.mbed.serial_read(1)
          if c is None:
              return selftest.RESULT_IO_SERIAL
          if c == '$': # target will printout TargetID e.g.: $$$$1040e649d5c09a09a3f6bc568adef61375c6
              #Read additional 39 bytes of TargetID
              if selftest.mbed.serial_read(39) is None:
                  return selftest.RESULT_IO_SERIAL
              c = selftest.mbed.serial_read(1) # Re-read first 'tick'
              if c is None:
                  return selftest.RESULT_IO_SERIAL
          start_serial_pool = time()
          start = time()
  
          success_counter = 0
  
          for i in range(0, self.TICK_LOOP_COUNTER):
              c = selftest.mbed.serial_read(1)
              if c is None:
                  return selftest.RESULT_IO_SERIAL
              delta = time() - start
              deviation = abs(delta - 1)
              # Round values
              delta = round(delta, 2)
              deviation = round(deviation, 2)
              # Check if time measurements are in given range
              deviation_ok = True if delta > 0 and deviation <= self.DEVIATION else False
              success_counter = success_counter+1 if deviation_ok else 0
              msg = "OK" if deviation_ok else "FAIL"
              selftest.notify("%s in %.2f sec (%.2f) [%s]"% (c, delta, deviation, msg))
              start = time()
              if success_counter >= self.TICK_LOOP_SUCCESSFUL_COUNTS:
                  break
          measurement_time = time() - start_serial_pool
          selftest.notify("Consecutive OK timer reads: %d"% success_counter)
          selftest.notify("Completed in %.2f sec" % (measurement_time))
          test_result = True if success_counter >= self.TICK_LOOP_SUCCESSFUL_COUNTS else False
          return selftest.RESULT_SUCCESS if test_result else selftest.RESULT_FAILURE
  