For both implementation, RTC and LPTIM, there is some delay in the
set_interrupt function due to HW constraints.
Value has been set to 4 for STM32L0,
because SystemClock is slower than other families.
When both tickless and LPTICKER_DELAY_TICKS are enabled some ST
devices randomly get stuck sleeping forever. This is because the
wake up time passed to the rtc is ignored if the previous match is
about to occur. This causes the device to get stuck in sleep.
This patch prevents matches from getting dropped by the rtc by
deactivating the rtc wake up timer before setting a new value.
Events leading up to this failure for the RTC:
-1st call to lp_ticker_set_interrupt
-delay until ticker interrupt is about to fire
-2nd call to lp_ticker_set_interrupt
-interrupt for 1st call fires and match time for 2nd call is dropped
-LowPowerTickerWrapper gets ticker interrupt but treats it as a
spurious interrupt and drops it since it comes in too early
-device enters sleep without a wakeup source and locks up
There is no problem with this test during the morph, but some issue has been noticed while testing new Jenkins CI in Oulu on NRF52_DK.
I was able to reproduce the issue locally. The difference between morph and local run is that CPU statistics are enabled on morph. This makes the difference and test passes.
The sleep test case perform sleep for 100 us, 200 us, ... ,1000 us in loop (us ticker wakes the board) and verifies if sleep time matches the assumption.
I got the following results:
sleep wake-up after
100 us ~100 us ok
200 us ~200 us ok
300 us ~300 us ok
400 us ~400 us ok
500 us ~14 us (??)
When requested sleep time is equal to 500 us some unexpected interrupt occurs which wakeup the board and force the test to fail.
Register state just after exit from sleep:
Control and State Register: 0x00400000 (ISRPENDING - Interrupt pending flag is set).
NVIC Interrupt Set-pending Register[0]: 0x00000004 (UARTE0_UART0_IRQn) or 0x00000200 (TIMER1_IRQn - timer used by us ticker).
UART interrupt is generated because of green-tea transmission. We know that it is performed while test is executed since we need to wait before going into deep-sleep since otherwise the transmission will be broken. So to take care of UART interrupt we need to wait before sleep test in the same way like it is done in deep-sleep test.
Heap statistics are used for analysing heap stats, but it doesn't tell anything
about real heap usage or malloc overheads. Adding `overhead_size` element
will help users to get the real heap usage.