-
Notifications
You must be signed in to change notification settings - Fork 630
Things You Should Know
(Timer callbacks happen from IRQ context)
A number of these functions take a 'reschedule' parameter, which must
be false when called from IRQ context. If your interrupt handler takes
action which will wake a thread and you want to ensure it wakes now
(provided priority is high enough) rather than when the next quantum
expires, return INT_RESCHEDULE
instead of INT_NO_RESCHEDULE
. This
will cause the kernel to invoke the scheduler before returning to
thread context.
The follow actions are IRQ-safe:
-
Signal an event with
event_signal()
. -
Reprogram a timer with
timer_set_oneshot()
,timer_set_periodic()
, ortimer_cancel()
. -
Timer reprogramming is safe even from within that timer’s callback.
-
Using spinlocks.
-
Wake threads on wait queues with
wake_queue_wake_one()
orwake_queue_wake_all()
, provided you hold the thread lock while doing so (useful for building new synchronization primitives).
Things are slightly different on Cortex-M platforms. IRQ handlers there have
no return value. They must call arm_cm_irq_entry()
before doing any work
and arm_cm_irq_exit(bool resched)
before returning. The resched parameter
to the exit function causes a reschedule on IRQ return if true, similar to
returning INT_RESCHEDULE
on other platforms.
This unsigned type is used by kernel functions involving timers,
timeouts, etc, and is in units of milliseconds. The maximum value
(defined as INFINITE_TIME
) is used to specify a timeout that will
never expire. The value 0 passed as a timeout parameter always means ``return immediately if you would have to wait.''
ERR_TIMED_OUT
is the status returned by a function taking a timeout
value, if the timeout expires before the requested action can be
accomplished.
The largest timestamp lk_time_t can hold is 2^32 milliseconds which translates to ~50 days. For a timer which does not rollover after 50 days use lk_bigtime_t. As unsigned type which is in units of microseconds, whose largest timestamp is 2^64 microseconds.