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Computer Organization - Chapter 7
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- 1Three categories of external devices:Human readable
Machine readable
Communication - 2The major functions for an I/O module fall into the following categories:Control and timing
Processor communication
Device communication
Data buffering - 3Three techniques are possible for I/O operations:Programmed I/O
Interrupt-driven I/O
Direct memory access (DMA) - 4There are four types of I/O commands that an I/O module may receive when it is addressed by a processor:Control
Test
Read
Write - 5Two design issues arise in implementing interrupt I/O:With multiple I/O modules how does the processor determine which device issued the interrupt?
If multiple interrupts have occurred how does the processor decide which one to
process? - 6Device identification techniques:Multiple interrupt lines
Software poll
Daisy chain
Bus arbitration - 7Drawbacks of Programmed and Interrupt-Driven I/O1) The I/O transfer rate is limited by the speed with which the processor can test and service a device
2) The processor is tied up in managing an I/O transfer; a number of instructions must be executed for each I/O transfer - 8Control and timingCoordinates the flow of traffic between internal resources and external devices
- 9Processor communicationInvolves command decoding, data, status reporting, address recognition
- 10Device communicationInvolves commands, status information, and data
- 11Data bufferingPerforms the needed buffering operation to balance device and memory speeds
- 12Error detectionDetects and reports transmission errors
- 13Programmed I/OData exchanged between CPU and I/O module. CPU executes a program that gives it direct control of the I/O operation.
When CPU issues a command it must wait until I/O operation is complete
If CPU is faster than the I/O module is wasteful of processor time - 14Interrupt-driven I/OProcessor issues an I/O command, continues to execute other instructions, and is interrupted by the I/O module when the latter has completed its work
- 15Direct memory access (DMA)The I/O module and main memory exchange data directly without processor involvement
- 16Controlused to activate a peripheral and tell it what to do
- 17Testused to test various status conditions associated with an I/O module and its peripherals
- 18Readcauses the I/O module to obtain an item of data from the peripheral and place it in an internal buffer
- 19Writecauses the I/O module to take an item of data from the data bus and subsequently transmit that data item to the peripheral
- 20Multiple Interrupt LinesBetween the processor and the I/O modules. Most straightforward approach to the problem. Consequently even if multiple lines are used, it is likely that each line will have multiple I/O modules attached to it
- 21Software PollWhen processor detects an interrupt it branches to an interrupt-service routine whose job is to poll each I/O module to determine which module caused the interrupt.
Time consuming. - 22Daisy ChainThe interrupt acknowledge line is daisy chained through the modules.
Vectored interrupt – processor uses the vector as a pointer to the appropriate device-service routine, avoiding the need to execute a general interrupt-service routine first. - 23Bus ArbitrationI/O module first gains control of the bus then raises the interrupt request line.
When the processor detects the interrupt it responds on the interrupt acknowledge line.
Then the requesting module places its vector on the data lines.
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- Fichas sobre Computer Organization - Chapter 7, creado por M KB el 23/02/2018.
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- M KB
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