wait_us_auto.py

00001 """
00002 mbed SDK
00003 Copyright (c) 2011-2013 ARM Limited
00004 
00005 Licensed under the Apache License, Version 2.0 (the "License");
00006 you may not use this file except in compliance with the License.
00007 You may obtain a copy of the License at
00008 
00009     http://www.apache.org/licenses/LICENSE-2.0
00010 
00011 Unless required by applicable law or agreed to in writing, software
00012 distributed under the License is distributed on an "AS IS" BASIS,
00013 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
00014 See the License for the specific language governing permissions and
00015 limitations under the License.
00016 """
00017 
00018 from time import time
00019 
00020 class WaitusTest ():
00021     """ This test is reading single characters from stdio
00022         and measures time between their occurrences.
00023     """
00024     TICK_LOOP_COUNTER = 13
00025     TICK_LOOP_SUCCESSFUL_COUNTS = 10
00026     DEVIATION = 0.10    # +/-10%
00027 
00028     def test(self, selftest):
00029         test_result = True
00030         # First character to start test (to know after reset when test starts)
00031         if selftest.mbed.set_serial_timeout(None) is None:
00032             return selftest.RESULT_IO_SERIAL
00033         c = selftest.mbed.serial_read(1)
00034         if c is None:
00035             return selftest.RESULT_IO_SERIAL
00036         if c == '$': # target will printout TargetID e.g.: $$$$1040e649d5c09a09a3f6bc568adef61375c6
00037             #Read additional 39 bytes of TargetID
00038             if selftest.mbed.serial_read(39) is None:
00039                 return selftest.RESULT_IO_SERIAL
00040             c = selftest.mbed.serial_read(1) # Re-read first 'tick'
00041             if c is None:
00042                 return selftest.RESULT_IO_SERIAL
00043         start_serial_pool = time()
00044         start = time()
00045 
00046         success_counter = 0
00047 
00048         for i in range(0, self.TICK_LOOP_COUNTER ):
00049             c = selftest.mbed.serial_read(1)
00050             if c is None:
00051                 return selftest.RESULT_IO_SERIAL
00052             delta = time() - start
00053             deviation = abs(delta - 1)
00054             # Round values
00055             delta = round(delta, 2)
00056             deviation = round(deviation, 2)
00057             # Check if time measurements are in given range
00058             deviation_ok = True if delta > 0 and deviation <= self.DEVIATION  else False
00059             success_counter = success_counter+1 if deviation_ok else 0
00060             msg = "OK" if deviation_ok else "FAIL"
00061             selftest.notify("%s in %.2f sec (%.2f) [%s]"% (c, delta, deviation, msg))
00062             start = time()
00063             if success_counter >= self.TICK_LOOP_SUCCESSFUL_COUNTS :
00064                 break
00065         measurement_time = time() - start_serial_pool
00066         selftest.notify("Consecutive OK timer reads: %d"% success_counter)
00067         selftest.notify("Completed in %.2f sec" % (measurement_time))
00068         test_result = True if success_counter >= self.TICK_LOOP_SUCCESSFUL_COUNTS  else False
00069         return selftest.RESULT_SUCCESS if test_result else selftest.RESULT_FAILURE