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Critical Sections
Measuring the scheduler lock time adds measurement artifacts and thus increases the
amount of time the scheduler is actually locked. However, measurement overhead is
accounted for and the measured value represents the actual scheduler lock time as if the
measurement was not present.
4-3 μC/OS-III FEATURES WITH LONGER CRITICAL SECTIONS
Table 4-1 shows several μC/OS-III features that have potentially longer critical sections.
Knowledge of these will help the user decide whether to direct μC/OS-III to use one critical
section over another.
Feature
Multiple tasks at the same priority
Event Flags
Chapter 14, “Synchronization” on page 251
Pend on multiple objects
Chapter 16, “Pending On Multiple Objects” on
page 313
Broadcast on Post calls
See OSSemPost() and OSQPost() descriptions in
Appendix A, “μC/OS-III API Reference Manual” on
page 375.
Reason
Although this is an important feature of μC/OS-III, multiple
tasks at the same priority create longer critical sections.
However, if there are only a few tasks at the same priority,
interrupt latency would be relatively small.
If multiple tasks are not created at the same priority, use the
interrupt disable method.
If multiple tasks are waiting on different events, going through
all of the tasks waiting for events requires a fair amount of
processing time, which means longer critical sections.
If only a few tasks (approximately one to five) are waiting on
an event flag group, the critical section would be short
enough to use the interrupt disable method.
Pending on multiple objects is probably the most complex
feature provided by μC/OS-III, requiring interrupts to be
disabled for fairly long periods of time should the interrupt
disable method be selected. If pending on multiple objects, it
is highly recommended that the user select the
scheduler-lock method.
If the application does not use this feature, the interrupt
disable method is an alternative.
μC/OS-III disables interrupts while processing a post to
multiple tasks in a broadcast.
When not using the broadcast option, you can use the
interrupt disable method.
Table 4-1 Disabling interrupts or locking the Scheduler
73
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