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The following list provides a brief overview of all CMSIS-RTOS functions. Functions marked with $ are optional. A specific CMSIS-RTOS implementation may not provide all functions, but this is clearly indicated with osFeatureXXXX defines.

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Note: Functions that are not supported by the RTX Implementation, are marked with a (*).

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Kernel Information and Control
- osKernelInitialize : Initialize the RTOS kernel.
- osKernelStart : Start the RTOS kernel.
- osKernelRunning : Query if the RTOS kernel is running.
- osKernelSysTick : Get RTOS kernel system timer counter.
- osKernelSysTickFrequency : RTOS kernel system timer frequency in Hz.
- osKernelSysTickMicroSec : Convert microseconds value to RTOS kernel system timer value.
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Thread Management
- osThreadCreate : Start execution of a thread function.
- osThreadTerminate : Stop execution of a thread function.
- osThreadYield : Pass execution to next ready thread function.
- osThreadGetId : Get the thread identifier to reference this thread.
- osThreadSetPriority : Change the execution priority of a thread function.
- osThreadGetPriority : Obtain the current execution priority of a thread function.
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Generic Wait Functions
- osDelay : Wait for a specified time.
- osWait : Wait for any event of the type Signal, Message, or Mail.(*)
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Timer Management
- osTimerCreate : Define attributes of the timer callback function.
- osTimerStart : Start or restart the timer with a time value.
- osTimerStop : Stop the timer.
- osTimerDelete : Delete a timer.
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Signal Events
- osSignalSet : Set signal flags of a thread.
- osSignalClear : Reset signal flags of a thread.
- osSignalWait : Suspend execution until specific signal flags are set.
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Mutexes
- osMutexCreate : Define and initialize a mutex.
- osMutexWait : Obtain a mutex or Wait until it becomes available.
- osMutexRelease : Release a mutex.
- osMutexDelete : Delete a mutex.
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Semaphores
- osSemaphoreCreate : Define and initialize a semaphore.
- osSemaphoreWait : Obtain a semaphore token or Wait until it becomes available.
- osSemaphoreRelease : Release a semaphore token.
- osSemaphoreDelete : Delete a semaphore.
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Memory Pool
- osPoolCreate : Define and initialize a fix-size memory pool.
- osPoolAlloc : Allocate a memory block.
- osPoolCAlloc : Allocate a memory block and zero-set this block.
- osPoolFree : Return a memory block to the memory pool.
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Message Queue
- osMessageCreate : Define and initialize a message queue.
- osMessagePut : Put a message into a message queue.
- osMessageGet : Get a message or suspend thread execution until message arrives.
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Mail Queue
- osMailCreate : Define and initialize a mail queue with fix-size memory blocks.
- osMailAlloc : Allocate a memory block.
- osMailCAlloc : Allocate a memory block and zero-set this block.
- osMailPut : Put a memory block into a mail queue.
- osMailGet : Get a mail or suspend thread execution until mail arrives.
- osMailFree : Return a memory block to the mail queue.
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RTX Specific Functions
- os_idle_demon : System thread running when no other thread is ready to run.
- os_suspend : Suspend the RTX task scheduler.
- os_resume : Resume the RTX task scheduler.
- os_tick_init : Initialize an alternative hardware timer as RTX kernel timer.
- os_tick_val : Get alternative hardware timer's current value.
- os_tick_ovf : Get alternative hardware timer's overflow flag.
- os_tick_irqack : Acknowledge alternative hardware timer interrupt.
- os_error : Called when a runtime error is detected.
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+Timout Value

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The timeout value specifies the number of timer ticks until a timeout or time delay elapses. The value is an upper bound and depends on the actual time elapsed since the last timer tick.

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For a value of 1 the system waits until the next timer tick occurs. That means that the actual timeout value can be one timer tick less than the specified timeout value.

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+Timer Values

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+Calls from Interrupt Service Routines

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The following CMSIS-RTOS functions can be called from threads and Interrupt Service Routines (ISR):

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osKernelRunning
osSignalSet
osSemaphoreRelease
osPoolAlloc, osPoolCAlloc, osPoolFree
osMessagePut, osMessageGet
osMailAlloc, osMailCAlloc, osMailGet, osMailPut, osMailFree

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Functions that cannot be called from an ISR are verifying the interrupt status and return, in case they are called from an ISR context, the status code osErrorISR. In some implementations, this condition might be caught using the HARD FAULT vector.

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Some CMSIS-RTOS implementations support CMSIS-RTOS function calls from multiple ISRs at the same time. If this is impossible, the CMSIS-RTOS rejects calls by nested ISR functions with the status code osErrorISRRecursive.

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