Advanced Operating Systems: Lecture 35 - Mr. Farhan Zaidi

CS703 ­ Advanced 
Operating Systems
By Mr. Farhan Zaidi


Lecture No. 
35


Overview of today’s lecture
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Goals of I/O software
Layers of I/O software
Direct Vs memory mapped I/O
Interrupt driven I/O
Polled I/O
Direct Memory Access (DMA)


Principles of I/O Software
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Goals of I/O Software
Device independence

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Uniform naming

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handle as close to the hardware as possible

Synchronous vs. asynchronous transfers
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name of a file or device a string or an integer not depending
on which machine
Error handling

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programs can access any I/O device without specifying
device in advance (floppy, hard drive, or CD-ROM)

blocked transfers vs. interrupt-driven

Buffering

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data coming off a device cannot be stored in final destination
immediately


Device Controllers
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I/O devices have components:
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The electronic component is the device controller
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mechanical component
electronic component

may be able to handle multiple devices

Controller's tasks
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convert serial bit stream to block of bytes
perform error correction as necessary
make available to main memory


Layers of the I/O system and the main 
functions of each layer


Memory mapped I/O Vs Direct I/O
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Memory mapped I/O
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Device controller’s registers and internal memory
are directly mapped into the processor’s address
space

Direct I/O
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Device controller’s registers and internal memory
is accessible via special instructions in the
assembly language instruction set. The
arguments to these instructions are usually called
ports.

Programmed I/O 

Writing a string to the printer using programmed I/O


Interrupt­Driven I/O

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Writing a string to the printer using interrupt-driven I/O

a. Code executed when print system call is made
b. Interrupt service procedure


A Typical Hardware System
CPU chip
register file
ALU
system bus

memory bus

main
memory

I/O
bridge

bus interface

I/O bus
USB
controller
mouse keyboard

graphics
adapter

disk
controller

monitor
disk

Expansion slots for
other devices such
as network adapters.


Reading a Disk Sector: Step 1
CPU chip
register file
ALU

CPU initiates a disk read by writing a
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command, logical block number, and
destination memory address to a port

(address) associated with disk controller.

main
memory

bus interface

I/O bus

USB
controller
mouse keyboard

graphics
adapter

disk
controller

monitor
disk


Reading a Disk Sector: Step 2
CPU chip
register file
ALU

Disk controller reads the sector and
performs a direct memory access (DMA)

transfer into main memory.

main
memory

bus interface

I/O bus

USB
controller
mouse keyboard

graphics
adapter

disk
controller

monitor
disk


Reading a Disk Sector: Step 3
CPU chip
register file
ALU

When the DMA transfer completes, the
disk controller notifies the CPU with an

interrupt (i.e., asserts a special “interrupt”
pin on the CPU)

main
memory

bus interface

I/O bus

USB
controller
mouse keyboard

graphics
adapter

disk
controller

monitor
disk


Direct Memory Access (DMA)

Operation of a DMA transfer


I/O Using DMA



Printing a string using DMA

a. code executed when the print system call is made
b. interrupt service procedure