MGMT 1040 Lecture Notes - Lecture 16: Backplane, Interrupt
8 May 2018
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MGMT 1040 Tutorial 16 Notes – Prioritization
Introduction
• Requires additional hardware to implement.
• Some systems use different interrupt lines for each interrupt
• Others use a ethod called daisy chaiig, which places the iterrupts oto a sigle
interrupt line to the CPU in such a way that highest priorities are recognized first.
• Multiple interrupts can be handled by assigning priorities to each interrupt.
• In general, multiple interrupts will be handled top priority first.
• A higher-priority interrupt will be allowed to interrupt an interrupt of lower priority
• A lower-priority interrupt will have to wait until a higher-priority interrupt is completed.
• This leads to a hierarchy of interrupts, in which higher-priority interrupts can interrupt
other interrupts of lower priority, back and forth
• Eventually returning control to the original program that was running.
• Although this sounds complicated, this situation is actually quite common, and is fairly
easy to implement.
• A simple example of this situation.
• Interrupt routine C is the highest priority, followed by B and A.
• Most computer systems allow the system manager to establish priorities for the various
interrupts.
• Priorities are established in a logical way.
• The highest priorities are reserved for time-sensitive situations, such as power failure or
external events that are being time measured.
• Keyboard events are also usually considered high-priority events, since data loss can
occur if the keyboard input is not read quickly.
• Task completion interrupts usually take lower priorities, since the delay will not affect
the integrity of the data under normal conditions.
• Depending on the system, priorities may be established with software or with hardware.
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