MGMT 1040 Lecture 15: MGMT 1040 Tutorial 15 Notes
8 May 2018
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MGMT 1040 Tutorial 15 Notes – Multiple Interrupts
Introduction
• Programs can access these routines simply by executing the INT instruction with the
appropriate parameter.
• An important application for software interrupts is to centralize I/O operations.
• One way to assure that multiple programs do not unintentionally alter another
progra’s files or iter igle priter output is to provide a sigle path for I/O to each
device.
• Generally, the I/O paths are interrupt routines that are a part of the operating system
software.
• Software interrupts are used by each program to request I/O from the operating system
software.
• As an example, a software interrupt was used to initiate printing.
• As you have now seen, there may be many different input and output devices and event
indicators connected to interrupt lines.
• This means that there may be many different events vying for attention.
• Inevitably, multiple interrupts will occur from time to time.
• There are two questions that must be answered when an interrupt occurs.
• First, are there other interrupts already awaiting service.
• If so, how does the computer determine the order in which the interrupts get serviced?
• And, second, how does the computer identify the interrupting device?
• Two different processing methods are commonly used for determining which device
initiated the interrupt.
• Some computers use a method known as vectored interrupt, in which the address of the
interrupting device is included as part of the interrupt.
• Another method provides a general interrupt that is shared by all devices.
• The computer identifies the interrupting device by polling each device.
• These two methods are illustrated respectively.
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