OS_EnterRegion() Indicates to the OS the beginning of a critical region.
A critical region counter (OS_RegionCnt), which is 0 by default, is incremented so that the routine can be nested.
Interrupts < Fast Interrupt and Normal Interrupt > are not disabled using OS_EnterRegion();
however, disabling interrupts will disable preemptive task switches.
Fast Interrupt : High priority interrupts - May not call embOS API functions
embOS does never disable high priority interrupts
Normal Interrupt : Low priority interrupts - May call embOS API functions
OS_LeaveRegion() Indicates to the OS the end of a critical region.
A critical region counter (OS_RegionCnt), which is 0 by default, is decremented.
If this counter reaches 0 again, the critical region ends.