MGMT 1040 Lecture Notes - Lecture 17: Jargon, Program Counter, Interrupt Handler
8 May 2018
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MGMT 1040 Tutorial 17 Notes – Chain Interrupt
Introduction
• The daisy chain interrupt line can be used for this purpose: the highest-priority devices
are placed closest to the CPU and block the signals of lower-priority devices that are
farther down the line.
• In other systems, priorities are established by assigning a priority number to each
interrupt.
• Most interrupts can be temporarily disabled by program instructions when a program is
performing a critical task that would be negatively affected if an interrupt were to occur.
• This is particularly true of time-sensitive tasks.
• In many systems, interrupts are mask able.
• That is, they can be selectively disabled.
• Certain interrupts, such as power failure, that are never disabled are sometimes
referred to as non-mask able interrupts.
• Most modern computer systems save interrupts that occur when interrupts are disabled
• So that when the interrupts are re-enabled, the pending interrupts will be processed.
• EXAMPLE
• In the IBM System z architecture, interrupts are divided into six classes, with the
priorities shown
• All the different interrupts within each class are handled by the interrupt service routine
for that class.
• Each interrupt class has two vectored addresses permanently associated with it.
• The first of these is a space reserved for the Program Status Word of the current
program, known in IBM jargon as the OLD PSW.
• The Program Status Word is a 64-bit word that includes the program counter and other
significant information about the program.
• The second vectored address contains a pointer to the interrupt routine.
• This address is known as the NEW PSW.
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