RealtimeThreads - Revision history

Suhridk at 22:17, 3 October 2012

2012-10-03T22:17:40Z

Suhridk: /* Periodic RT Thread */

2012-01-10T19:33:37Z

Periodic RT Thread

Suhridk: /* WFNP Semantics */

2012-01-02T02:47:47Z

WFNP Semantics

Suhridk: /* DL Handler Priority */

2012-01-02T02:40:19Z

DL Handler Priority

Suhridk: /* DL Handler Priority */

2012-01-02T02:38:59Z

DL Handler Priority

Suhridk: /* WFNP Semantics */

2012-01-02T02:37:08Z

WFNP Semantics

Suhridk: /* WFNP Semantics */

2012-01-02T02:25:16Z

WFNP Semantics

Suhridk: /* WFNP Semantics */

2012-01-02T02:02:31Z

WFNP Semantics

Suhridk: /* DL Miss */

2012-01-02T01:38:26Z

DL Miss

Suhridk: /* SO States */

2012-01-02T01:36:11Z

SO States

← Older revision		Revision as of 22:17, 3 October 2012
Line 155:		Line 155:
	* '''It is currently not possible for the RTSJ to detect either deadline miss or cost overruns for these activities, as there is no notion of a release event.'''		* '''It is currently not possible for the RTSJ to detect either deadline miss or cost overruns for these activities, as there is no notion of a release event.'''
	* Indeed, programmers are best advised to use Async Event handlers to represent non-periodic activities.		* Indeed, programmers are best advised to use Async Event handlers to represent non-periodic activities.
		+
		+	[[Category:RealtimeJava]]

← Older revision		Revision as of 19:33, 10 January 2012
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	* waitForNextPeriod() : Causes the current real-time thread to be suspended until the beginning of the next period. Each time it is called this method will block until the start of the next period unless the thread is in a deadline miss condition. In that case the operation of waitForNextPeriod is controlled by this thread's scheduler. Returns True (when the thread is next released ) when the thread is not in a deadline miss condition. Otherwise the return value is governed by this thread's scheduler.		* waitForNextPeriod() : Causes the current real-time thread to be suspended until the beginning of the next period. Each time it is called this method will block until the start of the next period unless the thread is in a deadline miss condition. In that case the operation of waitForNextPeriod is controlled by this thread's scheduler. Returns True (when the thread is next released ) when the thread is not in a deadline miss condition. Otherwise the return value is governed by this thread's scheduler.
		+	** Suppose a thread starts running (first release) at time t=0 and has a period of time 10 units. Then the next period is due at time t=20. '''The release events are separated by 10 time units irrespective of when the thread finishes.'''
	* The deschedulePeriodic() method will cause the associated thread to block (to be descheduled) at the end of its current release (when it calls waitForNextPeriod). It will then remain descheduled until schedulerPeriodic() is called.		* The deschedulePeriodic() method will cause the associated thread to block (to be descheduled) at the end of its current release (when it calls waitForNextPeriod). It will then remain descheduled until schedulerPeriodic() is called.

@@ Line 87: / Line 87: @@
 * If missCount is > 0 then the Misscount is decremented.
-** If lastReturn from wFNP is true - previous release has not missed its DL. Then wFNP returns false '''immediately.''' This situation indicates current release has not met its deadline.
+** If lastReturn from wFNP is true - previous release has not missed its DL. Then wFNP returns false '''immediately.''' This situation indicates that the current release has missed its deadline. At this point, the ''' current release is still active''' (this means the current bud- get is unaltered).
 * ELSE
-** If lastreturn from wFNP is false - then a previous DL has been missed as well and the current DL too because missCount > 0
+** If lastreturn from wFNP is false, This situation indicates that the next release time has already passed and the next deadline has already been missed. At this point, the current release has completed and the next release is active (and if it has not been allocated already, a new budget of cost is allocated). TODO: How ?
-*** PendingRelease decremented, and false returned again. (next release has already missed its DL ) - TODO
+*** PendingRelease decremented, and false returned again. (next release has already missed its DL)
 * When a DL Miss handler is released, and DL miss count = 0. (When thread exceeds DL, DL Handler is automatically released and DL Miss count is decremented), then thread calls wFNP.
-wFNP now deschedules the thread until a call to schedulePeriodic occurs. Once schedulePeriodic returns, wFNP returns true.
+wFNP now deschedules the thread until a call to schedulePeriodic occurs. Once schedulePeriodic returns, wFNP returns true. At this point, the next release is active (and a new budget of cost is allocated).
-* When the deadlineMiss count = 0 and no deadline has been missed on the current release and the time for the next release has passed (maybe thread was pre-empted by another thread), then wFNP returns true immediately.
+* When the deadlineMiss count = 0 and no deadline has been missed on the current release and the time for the next release has passed (maybe thread was pre-empted by another thread), then wFNP returns true immediately. At this point, the next release is active (and a new budget of cost is allocated).
 * When the deadlineMiss count equals zero and no deadline has been missed on the current release and the time for the next release has not passed, (all is well case) wFNP returns true at the next release time.
 * If descheduled is true
@@ Line 104: / Line 105: @@
 *** pendingRelease decremented.
 *** lastReturn is set to true and true is returned.
 * If descheduled is false

@@ Line 119: / Line 119: @@
 * Consequently, it will compete with its associated schedulable object according to their priority. Hence, for the handler to have an impact on the errant realtime thread it must have a priority higher than the thread.
 * If the priority is lower, it will not run until the errant thread blocks. For e.g. RTThread can miss deadline, at which point the DL Handler is called. It can keep working till the next call to wFNP. The DL Handler will not be able to take corrective action because of its low priority.
 == Cost Overruns ==

@@ Line 118: / Line 118: @@
 * The deadline miss handler is a schedulable object.
 * Consequently, it will compete with its associated schedulable object according to their priority. Hence, for the handler to have an impact on the errant realtime thread it must have a priority higher than the thread.
-* If the priority is lower, it will not run until the errant thread blocks. [TODO: But isnt RTThread automatically blocked-for-reschedule when DL miss happens and a DL Handler is defined ?]
+* If the priority is lower, it will not run until the errant thread blocks. For e.g. RTThread can miss deadline, at which point the DL Handler is called. It can keep working till the next call to wFNP. The DL Handler will not be able to take corrective action because of its low priority.
 == Cost Overruns ==

@@ Line 109: / Line 109: @@
 ** pendingReleases <= 0 : thread becomes blocked for release event.
 ** pendingRelease > 0. Decrement pendingRelease and true is returned.
 == DL Handler Priority ==

@@ Line 62: / Line 62: @@
 == DL Miss ==
 * On each DL miss:
 ** '''If the thread has a DL Miss Handler'''

@@ Line 54: / Line 54: @@
 ** Eligible for Execution: SO's state can be changed to executing.
 ** Executing: means SO is running.
 == DL Miss ==