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          void  OSCtxSw (void)
          {
              Save all CPU registers;                         (1)
              OSTCBCurPtr->StkPtr = SP;                       (2)
              OSTaskSwHook();                                 (3)
              OSPrioCur           = OSPrioHighRdy;            (4)
              OSTCBCurPtr         = OSTCBHighRdyPtr;          (5)
              SP                  = OSTCBHighRdyPtr->StkPtr;  (6)
              Restore all CPU registers;                      (7)
              Return from interrupt;                          (8)
          }

(1) OSCtxSw() must save all of the CPU registers onto the current task’s stack. OSCtxSw() is called from the context of the task being switched out. Therefore, the CPU stack pointer is pointing to the proper stack. The user must save all of the registers in the same order as if an ISR started and all the CPU registers were saved on the stack. The stacking order should therefore match that of OSTaskStkInit().

(2) The current task’s stack pointer is then saved into the current task’s OS_TCB.

(3) Next, OSCtxSw() must call OSTaskSwHook().

(4) OSPrioHighRdy is copied to OSPrioCur.

(5) OSTCBHighRdyPtr is copied to OSTCBCurPtr since the current task is now the task being switched in.

(6) The stack pointer of the new task is restored from the OS_TCB of the new task.

(7) All the CPU registers from the new task’s stack are restored.

(8) Finally, OSCtxSw() must execute a return from interrupt instruction.