Test inserts event into the TimerEvent object which is scheduled 50 ms in the future. Then test thread hangs on the semaphore for 51 ms and after that time we expect that event handler has been executed. This test fails sometimes on NRF51_DK, NRF52_DK since different clocks are used for event handling and delay. TimerEvent class uses fast us ticker and semaphores are based on lp ticker (NRF51_DK) or System Tick Timer (NRF52_DK).
We assume that ticker measurement error is 10% and our 1 [ms] extra corresponds to 2% error. I suggest to increase delay to 2 [ms] (4%). This should be enough for all boards at this moment.
Since now us ticker is disabled in deep-sleep mode and tests-mbed_drivers-timerevent verifies TimerEvent class which uses us ticker then deep-sleep mode needs to be disabled during the test execution.
Martin Kojtal
Przemyslaw Stekiel
Filip Jagodzinski