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<H2><A NAME="SECTION00054000000000000000">
CanFestival events scheduling</A>
</H2>
A CanOpen node must be able to take delayed actions.
<P>
As exemples, periodic sync emission, heartbeat production or SDO timeout
need to set some alarms that will be called later and do the job.
<P>
µC generaly do not have enough free timers to handle all the
CanOpen needs directly. Moreover, CanFestival internal data may be
corrupt by reentrant calls.
<P>
CanFestival implement a micro-scheduler (timer.c). It uses only one
timer to mimic many timers. It manage an alarm table, and call alarms
at desired time.
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<P>
Scheduler can handle short clock value ranges limitation found on some
µC. As an example, value range for a 16bit clock counter with
4µs tick is crossed within 0.26 seconds... Long alarms must be
segmented.
<P>
Chronogram illustrate a long alarm (A) and a short periodic alarm (B),
with a A value > clock range > B value.
Values t0...t8 are successive setTimer call parameter values. t1
illustrates an intermediate call to TimeDispatch, caused by a delay
longer than clock range. Because of long alarm segmentation, at the end
of t1, TimeDispatch call will not trig any alarm callback.
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2007-06-08
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