|
|
|
Modern Operating Systems by Herbert Bos and Andrew S. Tanenb...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf
Showing 425 out of 1137
Modern Operating Systems by Herbert Bos and Andrew...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 425
394
INPUT/OUTPUT
CHAP. 5
an occasional missed deadline. Being 10
μ
sec late from time to time is often better
than having interrupts eat up 35% of the CPU.
Of course, there will be periods when there are no system calls, TLB misses, or
page faults, in which case no soft timers will go off. To put an upper bound on
these intervals, the second hardware timer can be set to go off, say, every 1 msec.
If the application can live with only 1000 activations per second for occasional in-
tervals, then the combination of soft timers and a low-frequency hardware timer
may be better than either pure interrupt-driven I/O or pure polling.
5.6 USER INTERFACES: KEYBOARD, MOUSE, MONITOR
Every general-purpose computer has a keyboard and monitor (and sometimes a
mouse) to allow people to interact with it. Although the keyboard and monitor are
technically separate devices, they work closely together.
On mainframes, there are
frequently many remote users, each with a device containing a keyboard and an at-
tached display as a unit. These devices have historically been called
terminals
.
People frequently still use that term, even when discussing personal computer
keyboards and monitors (mostly for lack of a better term).
5.6.1 Input Software
User input comes primarily from the keyboard and mouse (or somtimes touch
screens), so let us look at those.
On a personal computer, the keyboard contains an
embedded microprocessor which usually communicates through a specialized
serial port with a controller chip on the parentboard (although increasingly
keyboards are connected to a USB port).
An interrupt is generated whenever a key
is struck and a second one is generated whenever a key is released. At each of
these keyboard interrupts, the keyboard driver extracts the information about what
happens from the I/O port associated with the keyboard. Everything else happens
in software and is pretty much independent of the hardware.
Most of the rest of this section can be best understood when thinking of typing
commands to a shell window (command-line interface). This is how programmers
commonly work. We will discuss graphical interfaces below. Some devices, in
particular touch screens, are used for input
and
output. We have made an (arbi-
trary) choice to discuss them in the section on output devices. We will discuss
graphical interfaces later in this chapter.
Keyboard Software
The number in the I/O register is the key number, called the
scan code
, not the
ASCII code. Normal keyboards have fewer than 128 keys, so only 7 bits are need-
ed to represent the key number.
The eighth bit is set to 0 on a key press and to 1 on
Ace your assessments! Get Better Grades
Browse thousands of Study Materials & Solutions from your Favorite Schools
Concordia University
Concordia_University
School:
Operating_Systems
Course:
Great resource for chem class. Had all the past labs and assignments
Leland P.
Santa Clara University
Introducing Study Plan
Using AI Tools to Help you understand and remember your course concepts better and faster than any other resource.
Find the best videos to learn every concept in that course from Youtube and Tiktok without searching.
Save All Relavent Videos & Materials and access anytime and anywhere
Prepare Smart and Guarantee better grades
Know more
Students also viewed documents
lab 18.docx
lab_18.docx
Course
Course
3
Module5QuizSTA2023.d...
Module5QuizSTA2023.docx.docx
Course
Course
10
Week 7 Test Math302....
Week_7_Test_Math302.docx.docx
Course
Course
30
Chapter 1 Assigment ...
Chapter_1_Assigment_Questions.docx.docx
Course
Course
5
Week 4 tests.docx.do...
Week_4_tests.docx.docx
Course
Course
23
Week 6 tests.docx.do...
Week_6_tests.docx.docx
Course
Course
106
