Replace wait_us with nu_busy_wait_us in lp_ticker since wait_us is not allowed in sleep test
which would suspend us ticker layer on which wait_us relies. nu_busy_wait_us is implemented
by calling us ticker HAL API directly rather than relying on us ticker layer.
If us_ticker/lp_ticker is scheduled and then the interrupt is disabled, the originally scheduled
interrupt may still become pending. If this occurs, then an interrupt will fire twice on the next
call to us_ticker_set_interrupt/lp_ticker_set_interrupt - once immediately and then a second time
at the appropriate time.
This patch prevents the first interrupt by clearing interrupts in
us_ticker_set_interrupt/lp_ticker_set_interrupt before calling NVIC_EnableIRQ.
1. Introduce S/W interrupt enable/disable to reduce calls to TIMER_EnableInt/TIMER_DisableInt.
2. Allow dummy interrupt because clear interrupt flag is not synchronized.
3. Enable LPTICKER_DELAY_TICKS to make lp_ticker_set_interrupt non-blocking.
Originally, we use 2 H/W timers for us_ticker/lp_ticker, one for counting and the other for alarm.
With H/W timer running in continuous mode, we could use just one H/W timer for counting/alarm simultaneously.
The rework includes the following:
1. Remove ticker overflow handling because upper layer (mbed_ticker_api.c) has done with it.
This makes us_ticker/lp_ticker implementation more succinct and avoids potential error.
2. Refine timer register access with low-power clock source
fire_interrupt function should be used for events in the past. As we have now
64bit timestamp, we can figure out what is in the past, and ask a target to invoke
an interrupt immediately. The previous attemps in the target HAL tickers were not ideal, as it can wrap around easily (16 or 32 bit counters). This new
functionality should solve this problem.
set_interrupt for tickers in HAL code should not handle anything but the next match interrupt. If it was in the past is handled by the upper layer.
It is possible that we are setting next event to the close future, so once it is set it is already in the past. Therefore we add a check after set interrupt to verify it is in future.
If it is not, we fire interrupt immediately. This results in
two events - first one immediate, correct one. The second one might be scheduled in far future (almost entire ticker range),
that should be discarded.
The specification for the fire_interrupts are:
- should set pending bit for the ticker interrupt (as soon as possible),
the event we are scheduling is already in the past, and we do not want to skip
any events
- no arguments are provided, neither return value, not needed
- ticker should be initialized prior calling this function (no need to check if it is already initialized)
All our targets provide this new functionality, removing old misleading if (timestamp is in the past) checks.
Martin Kojtal
ccli8
Bartek Szatkowski
Martin Kojtal
Christopher Haster