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SeptemberOS
Software Timers
SeptemberOS provides installable software timers. Timers may be used by
any code in the OS: application, system or driver. Application timers
use main system timer interrupt and may be installed with timeout being
any multiple of system timer tick.
Timers are called when their timeout value expires in context of system
timer's interrupt. This way timers reporting presicion is fairly good,
as it doesn't need a task switch, doesn't allow additional
interrupts interfere with the timer handler's code and doesn't risk
being preempted. However care should be taken in order to use only very
short (time-wise) processing code, in particular not to overlap the
next timer tick interrupt, as it may cause the system behave
incorrectly (this particularly means using debug printouts to serial
port from a timer handler ONLY in development/experimental code (taking
into account that the system may misbehave) and NEVER in production
code.
A timer may be installed as periodic (will auto-reinstall itself after
being handled) or as one-shot (will be removed after being handled). If
some condition changed, the timer may be canceled
(and removed) at any time, including from within its
own handler.
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