USBB17RX78K4-XXX NEC Electronics, USBB17RX78K4-XXX Datasheet - Page 23

• Manufacturer Part Number: USBB17RX78K4-XXX
• Description: 78K/4 series realtime OS
• Manufacturer: NEC Electronics

2.3.2 Semaphore
currently usable resources exist, or manage the number of resources.
semaphore is fixed to 1.
“wai_sem”, “preq_sem”. If the number of resources is 1 or more, the number of resources of the semaphore is
decremented by one.
is not placed in the WAIT state, an error code is returned (preq_sem). If the task does not need the resource any
more, it executes resource return manipulation (V instruction) by issuing system call “sig_sem”. As a consequence,
the number of resources of the semaphore is incremented by one. If there are tasks waiting for a resource at this
time, the task first placed in the WAIT state is released. A task waits for a semaphore on a FIF0 basis only.
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A semaphore is used to mutually exclude tasks. The semaphore is a measurement that can check whether
The number of requested resources of the wait manipulation (P) and signal manipulation (V) instructions for a
If a task needs a resource, it performs resource acquisition manipulation (P instruction) by issuing system call
If the number of resources is 0, the resource requesting task is placed in the WAIT state (wai_sem), or if the task
CHAPTER 2
BASIC FUNCTIONS OF RX78K/IV