Can keep a DIE routine from receiving control. If a clock required by a DIE routine's TQE fails while the TQE is on the real time queue, timer supervision leaves the TQE on the queue, thereby denying control to the DIE routine. To permit the DIE routine to receive control, a properly functioning TOD clock and clock comparator must be varied online. For this remedy to work, the DIE routine must be in resident or fixed storage as long as its TQE is on the real time queue. These storage locations make the DIE routine available to the system from any address space.
When the DIE routine gains control under these circumstances, the clock comparator value in TQEVAL could be behind the TOD clock. If the DIE routine re-enqueues the TQE on each successive entry and adds a new interval to TQEVAL, then the DIE routine gains control each time, immediately upon enablement of the external interruptions. This sequence continues until the value in TQEVAL is equal to the TOD clock value. To avoid this synchronization loop, the DIE routine can calculate the new TQEVAL as the sum of the new interval plus the current TOD clock value. This method, however, requires that the DIE routine contain error recovery code in case the STCK instruction fails due to a bad TOD clock in the executing processor.