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Signals
If a thread calls PostSemaphore() from within an unscheduled region,
where the scheduler is disabled, the highest-priority thread moved to the
ready queue runs (see Figure 4-5).
Thread Domain/Unscheduled Region
PostSemaphore()
Ready Queue
Order threads by
priority, then FIFO
Semaphore's List of
Pending Threads
Order by priority, then FIFO
...
...
...
Thread 1
Thread 1 runs
Block
The highest-priority thread
Figure 4-5. Thread Domain/Unscheduled Region: Posting a Semaphore
Posting from the Interrupt Domain. Interrupt subroutines can also post
semaphores. Figure 4-6 illustrates the process of posting a semaphore from
the interrupt domain.
Interrupt Domain
1). RTI
Ready Queue
Order threads by
priority, then FIFO
VDK_ISR_POST_SEMAPHORE_()
2). The low-priority ISR runs
3). Scheduler runs
1). Set the low-priority ISR
2). Invoke Scheduler
ISR 1
ISR 2
The
highest-priorityThread
thread
Highest-Priority
ISR 3
1). Switch out the
interrupted thread
Yes
The interrupted
thread runs
Is the
interrupted
thread of the
highest
priority?
No
Figure 4-6. Interrupt Domain: Posting a Semaphore
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VisualDSP++ Kernel (VDK) User’s Guide
2). Switch in the highestpriority pending thread