MGMT 1040 Lecture Notes - Lecture 13: Opcode
8 May 2018
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MGMT 1040 Tutorial 13 Notes – Power Line Monitor
Introduction
• A power line monitor that connects to the interrupt facility provides this capability.
• The interrupt routine will save the status of programs that are in memory, close open
files
• Perform other housekeeping operations that will allow the computer to restart without
any loss of data.
• It will then halt the computer.
• Another important application of the abnormal event interrupt is when a program
attempts to execute an illegal instruction such as a divide by 0 or a nonexistent op code,
or when a hardware error is detected, such as a memory parity error.
• When the error occurs it is not possible to complete the executing program.
• Yet it is important that the system attempt to recover from the error and that the
appropriate personnel be notified.
• It is not acceptable simply to halt the computer.
• Particularly in modern multitasking computer systems this would be undesirable
• Since it would also stop other executing programs that might not be affected by the
error and would affect other users if the system is a multiuser system.
• Instead, an interrupt routine can notify the user of the error and return control of the
CPU to the operating system program.
• You should notice that these interrupts are actually generated from inside the CPU
• Whereas the other interrupts that we have discussed so far are generated externally.
• Internal interrupts are sometimes called traps or exceptions.
• EXAMPLE
• Most modern computers have a set of instructions known as privileged instructions.
• These instructions are intended for use by an operating system program.
• The HALT instruction generally is a privileged instruction.
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