METHOD FOR CONTROLLING STACK POINTER

PURPOSE:To hold response and to reduce the number of stand-by stack areas by forming an interruption processing stack area and a preserving working area for presurving the contents of a stack pointer in addition to the stack areas at every task. CONSTITUTION:When any one tasks A2, B3, C4 generates an interruption during traveling, a real time operating system 1 decides whether the stack pointer SP is switched to an interrupting stack area 25 or not. When the decided result is NO, a temporary work area 26 is secured in the stack area 22, 23, or 24 of the relevant task, the contents of the preserving working area 21 are transferred to the secured area 26 and the SP contents of the stack area of the task concerned are transferred to the area 21. Then, the SP contents are switched to the area 25, and after ending the interruption processing, the SP contents are returned to the contents preserved in the area 21. Since the SP contents can be switched without forming an interruption inhibiting state, the response can be held and the number of stand-by stack areas can be reduced.