IotTaskPool_CreateSystemTaskPool() calls synchronisation primitives, so cannot be called before the scheduler starts. Add a configASSERT() to ensure the scheduler is running when it executes.
IotTaskPool_CreateSystemTaskPool() can conceivably be called from multiple different libraries that depend on the thread pool. In this version _IotSystemTaskPool.running can be used to check the system task pool has not already been created. If the task pool has been created simply return from IotTaskPool_CreateSystemTaskPool() instead of re-creating it (which would leak memory and leave orphaned tasks).
Call taskENTER_CRITICAL() and taskEXIT_CRITICAL() directly in place of mapping them to TASKPOOL_ENTER_CRITICAL() and TASKPOOL_EXIT_CRITICAL() in the same file.
Rename _timerThread() _timerCallback(), as it is a callback function and not a thread.
Remove the unused flags parameter from _scheduleInternal().
Richard Barry