I/O MODULE FUNCTIONS

 I/O   MODULE FUNCTIONS

·       Control & Timing.

·       CPU Communication

·       Device Communication

·       Data Buffering

·       Error Detection

I/O  steps

•         CPU checks I/O module device status

•         I/O module returns status

•         If ready, CPU requests data transfer

•         I/O module gets data from device

•         I/O module transfers data to CPU

A)  Input Output Techniques :

         1)   Programmed  I/O

2)   Interrupt driven  I/O

3)Direct Memory Access (DMA)

1)      Programmed I/O

·       CPU  has direct control over I/O for :

·       Sensing status

·       Read/write commands.

·       Transferring data

·          CPU waits for  I/O module to complete operation.

·          Wastes CPU time.

-> Programmed  I/O in  detail

•         CPU requests I/O operation

•         I/O module performs operation

•         I/O module sets status bits

•         CPU checks status bits periodically

•         I/O module does not inform CPU directly

•         I/O module does not interrupt CPU

•         CPU may wait or come back later

-> I/O Commands

·       Control - telling module what to do. (e.g. spin up disk)

·       Test - check status

·       Read/Write

2)      Interrupt  Driven I/O 

      ·       Overcomes CPU waiting

      ·       No repeated CPU checking of device

      ·       I/O module interrupts when ready

-> Interrupt  Driven  I/O in detail

•         CPU  issues read command

•         I/O module gets data from peripheral while  CPU does other work

•         I/O module interrupts CPU

•         CPU requests data

•         I/O module transfers data

CPU Viewpoint

•         Issue read command

•         Do other work

•         Check for interrupt at end of each instruction cycle

•         If  interrupted:-

—  Save context (registers)

—  Process interrupt

–      Fetch data & store

1)      Direct Memory Access :

•         Interrupt driven and  programmed  I/O require active CPU intervention , because

·       Transfer  rate is limited

·       CPU  is tied up

DMA Function

•         Additional Module (hardware) on bus.

•         DMA controller takes over from CPU for I/O

DMA Operation

•         CPU tells DMA controller:-

—  Read/Write

—  Device address

—  Starting address of memory block for data

—  Amount of data to be transferred

•         CPU carries on with other work

•         DMA controller deals with transfer

•         DMA controller sends interrupt when finished

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About DP

HI FRIENDS I AM DHANESH. I ADD THIS BLOG FOR AN EDUCATION PURPOSE

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