Chapter 6 - OpenVMS AXP Exceptions, Interrupts, and Machine Checks (II–A)

Abstract

At certain times during the operation of a system, events within the system require the execution of software outside the explicit flow of control. When such an exceptional event occurs, an Alpha AXP processor forces a change in control flow from that indicated by the current instruction stream. The notification process for such events is of one of three types: (1) exceptions, (2) interrupts, and (3) machine checks. For all such events, the change in flow of control involves changing the Program Counter (PC), possibly changing the execution mode and/or interrupt priority level (IPL) in the Processor Status (PS), and saving the old values of the PC and PS. The old values are saved on the target stack as part of an exception, interrupt, or machine check stack frame. This chapter discusses these events in detail and highlights the differences among them.