keyboard interrupt at 54 if so it has found a critical instruction and immediately exits the timer interrupt service routine and performs the high speed exit routine at 60 to be subsequently described if the instruction is not an interrupt the process will verify whether the instruction is one of the critical instructions at 56 that is one that might be used in an operation for which performance is critical if the instruction is critical the process immediately exits the timer interrupt routine and runs the high speed exit routine 60 if neither critical condition is present the process loops back to step 52 to continue stepping back one instruction at time after is has stepped back a predetermined number of instructions as compared at 58 it steps forward a similar number of instructions at steps 62 checking for interrupts at step 64 critical instructions at step 66 and looping as in the step back procedure if after evaluating all of these instructions the process locates no interrupts or critical instructions it increments the inactivity counter at 70 and checks the counter for its predetermined critical value at 72 if the critical value has not been achieved the program ends the interrupt service routine at 74 if the critical value has been reached the program issues an instruction to trigger the low speed latch at 76 then exits the interrupt service routine at 74 if the critical value has been exceeded the program decrements the inactivity.