The CMSIS-RTOS library provides a scheduler to run concurrently multiple threads of execution and methods for the exchange of data among these threads.

CMSIS-RTOS Library URL: http://mbed.org/projects/libraries-testing/svn/rtos

Thread¶

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Mutex¶

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Semaphore¶

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Signals¶

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Message Queue¶

Memory Pool¶

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Mail Queue¶

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Timer¶

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Interrupt Service Routines¶

The same CMSIS-RTOS can be used in ISR. The only two warnings are:

• Mutexes can not be used.
• Wait in ISR is not allowed: all the timeouts in method parameters have to be set to 0 (no wait).

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Stack Configuration¶

The stack configuration is very dependent from the underling CMSIS-RTOS implementation.

As first reference implementation we are using RTX. One of the limitation of the RTX implementation is that it requires to statically configure the maximum number of threads and the size of the memory pool for their stacks.

Our initial RTX configuration choices are likely to change in response to the mbed users feedback:

Status and Error Codes¶

The Status and Error Codes section lists all the return values that the CMSIS-RTOS functions will return:

• osOK: function completed; no event occurred.
• osEventSignal: function completed; signal event occurred.
• osEventMessage: function completed; message event occurred.
• osEventMail: function completed; mail event occurred.
• osEventTimeout: function completed; timeout occurred.
• osErrorParameter: parameter error: a mandatory parameter was missing or specified an incorrect object.
• osErrorResource: resource not available: a specified resource was not available.
• osErrorTimeoutResource: resource not available within given time: a specified resource was not available within the timeout period.
• osErrorISR: not allowed in ISR context: the function cannot be called from interrupt service routines.
• osErrorISRRecursive: function called multiple times from ISR with same object.
• osErrorPriority: system cannot determine priority or thread has illegal priority.
• osErrorNoMemory: system is out of memory: it was impossible to allocate or reserve memory for the operation.
• osErrorValue: value of a parameter is out of range.
• osErrorOS: unspecified RTOS error: run-time error but no other error message fits.

osEvent¶

The osEvent data structure is returned by get methods of Queue and Mail objects. This data structure contains both an error code and a pointer to the actual data:

  * status       [osStatus    ]: status code (event or error information)

union: either {
  * value
    * v          [uint32_t    ]: message as 32-bit value 
    * p          [void *      ]: message or mail as void pointer 
} or {
  * def
    * mail_id    [osMailQId   ]: mail id obtained by osMailCreate 
    * message_id [osMessageQId]: message id obtained by osMessageCreate
}