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HREF="node16.html">Understanding Canfestival</A>
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HREF="node19.html">CanFestival CAN interfaces</A>
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<B> <A NAME="tex2html393"
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<H2><A NAME="SECTION00054000000000000000">
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CanFestival events scheduling</A>
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</H2>
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A CanOpen node must be able to take delayed actions.
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<P>
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As exemples, periodic sync emission, heartbeat production or SDO timeout
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need to set some alarms that will be called later and do the job.
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<P>
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µC generaly do not have enough free timers to handle all the
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CanOpen needs directly. Moreover, CanFestival internal data may be
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corrupt by reentrant calls.
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<P>
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CanFestival implement a micro-scheduler (timer.c). It uses only one
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timer to mimic many timers. It manage an alarm table, and call alarms
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at desired time.
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<P>
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Scheduler can handle short clock value ranges limitation found on some
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µC. As an example, value range for a 16bit clock counter with
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4µs tick is crossed within 0.26 seconds... Long alarms must be
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segmented.
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<P>
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Chronogram illustrate a long alarm (A) and a short periodic alarm (B),
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with a A value > clock range > B value.
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Values t0...t8 are successive setTimer call parameter values. t1
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illustrates an intermediate call to TimeDispatch, caused by a delay
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longer than clock range. Because of long alarm segmentation, at the end
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of t1, TimeDispatch call will not trig any alarm callback.
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<B> Next:</B> <A NAME="tex2html395"
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HREF="node21.html">Linux Target</A>
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<B> Up:</B> <A NAME="tex2html391"
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HREF="node16.html">Understanding Canfestival</A>
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<B> Previous:</B> <A NAME="tex2html387"
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HREF="node19.html">CanFestival CAN interfaces</A>
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<B> <A NAME="tex2html393"
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HREF="node1.html">Contents</A></B> </DIV>
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epimerde
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2007-06-06
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