Update the low power ticker wrapper code so it does not violate any
properties of the ticker specification. In specific this patch fixes
the following:
- Prevent spurious interrupts
- Fire interrupt only when the ticker times increments to or past the
value set by ticker_set_interrupt
- Disable interrupts when ticker_init is called
Some low power tickers take multiple cycles of the low power clock
to set a compare value. Because of this if the compare value is set
twice back-to-back these implementations will block until that time
has passed. This can cause system stability issues since interrupts
are disabling for this time.
To gracefully support this kind of hardware this patch adds code
to prevent back-to-back writes to the hardware. It does this by
recording the low power clock cycle of the initial write. If any
writes come in too soon after this initial write the microsecond
ticker is used to schedule the new write in the future when the
hardware is ready to accept a new value.
To enable this feature on a target the macro LOWPOWERTIMER_DELAY_TICKS
must be set to the number of low power clock cycles that must elapse
between writes to the low power timer.
This API is added primarily for testing purposes, to be able to test HAL drivers without using upper layers to handle ticker interrupt.
By default IRQ handler is set to ticker_irq_handler() for us ticker and lp ticker - original one.
Usage example (setting custom ticker irq handler):
void my_irq_handler(const ticker_data_t *const) {
// handle interrupt
}
ticker_irq_handler_type old_handler = set_us_ticker_irq_handler(my_irq_handler);
Respectively for lp timer set_lp_ticker_irq_handler() API should be used.
Allow tickers to specify their native frequency and number of bits.
This allows the conversion to happen in common code rather than in
each vendor's implementation.
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.
Russ Butler
Przemyslaw Stekiel
Martin Kojtal
jeromecoutant
Bartek Szatkowski
Martin Kojtal
Vincent Coubard
Sam Grove
Christopher Haster