This lists the technical data of CMSIS-FreeRTOS.

Limitations

The following list briefly describes the limitations and unsupported features of the CMSIS-RTOS2 wrapper for FreeRTOS:

• Static memory allocation will only work if all memory (from attributes structure) is provided statically. In order to allocate object memory statically, you need to:
  • provide the memory for control blocks and stack in the osThreadAttr_t structure for threads.
  • provide the memory for control blocks and message data in the osMessageQueueAttr_t structure for memory queues.
  • provide the memory for control blocks for other objects in the object's attributes structure.
• Each timer object requires additional 8 bytes of memory:
  • to allocate all memory statically, provide the memory for control block of size (sizeof(StaticTimer_t) + 8 bytes)
  • otherwise, additional 8 bytes of dynamic memory will be used
• osKernelSuspend and osKernelResume are not supported.
• osThreadDetach, osThreadJoin() and attribute osThreadJoinable are not supported (osThreadNew returns NULL when osThreadJoinable attribute is specified).
• osThreadGetStackSize is not implemented.
• Event flags are limited to 24 bits.
• osEventFlagsGetName is not implemented.
• osEventFlagsWait cannot be called from an ISR.
• Priority inherit protocol is used as default mutex behavior (osMutexNew creates priority inherit mutex object by default and ignores osMutexPrioInherit attribute when specified).
• Robust mutex objects are not supported (osMutexNew returns NULL when osMutexRobust attribute is specified).
• osMutexGetName is not implemented and always returns NULL.
• osSemaphoreGetName is not implemented and always returns NULL.
• osMessageQueueGetName is not implemented and always returns NULL.
• osMessageQueuePut and osMessageQueueGet always ignore message priority.

CMSIS-RTOS validation suite results

CMSIS provides a validation suite that can be used to test a real-time operating system for compliance to the standard. The test suite has been run successfully on the CMSIS-FreeRTOS implementation with the following exceptions:

TC_ThreadParam:

• Reason: unsupported feature
• Test attempts to test osThreadJoin and osThreadDetach functions for invalid parameter input. These two functions are not implemented.

TC_ThreadInterrupts:

• Reason: unsupported feature
• Test attempts to call osThreadJoin and osThreadDetach from the ISR. These two functions are not implemented.

TC_EventFlagsInterrupts:

• Reason: unsupported feature
• Test attempts to call osEventFlagsWait from the ISR. Wrapper implementation does not allow function osEventFlagsWait to be called from interrupts.

TC_MutexRobust:

• Reason: unsupported feature
• Test attempts to create robust mutex. FreeRTOS implementation does not support robust mutexes.

TC_MutexOwnership:

• Reason: unsupported feature
• Test attempts to release a mutex from a thread which is not the mutex owner. Test fails, because FreeRTOS implementation does not verify ownership on mutex release.