[Ilugc] REAL TIME EMBEDDED SYSTEM
- From: girishvenkatachalam@xxxxxxxxx (Girish Venkatachalam)
- Date: Wed, 25 Apr 2012 10:48:43 +0530
On Wed, Apr 25, 2012 at 9:36 AM, Vignesh Rajendran
<vickylinuxer at gmail.com> wrote:
On Thu, Apr 19, 2012 at 3:24 PM, Amirtharaja Alankaram <
amirtharajaa at yahoo.co.in> wrote:
HI Friends
? ? ? ? ? ?I am one among the member of this group right now i am doing my
ME in MIIT chennai,,if anyone could help me for knowing the basics of real
time embedded system in open source or any pdf files about this topic or
any wireless networks configuration in linux environment please help me
regarding this...im eagerly waiting for your reply
In LUG we are very familiar with people eagerly waiting to do student
projects, completing office deadlines and doing small projects.
But the real joy of intellectual labor is when we solve real life
problems in real life
settings for businesses where networking problems will solve his
business issues
, give him peace of mind and also get you some cash in the bargain.
There are very few such questions concerning work that is challenging, real life
and long term.
Anyway I will now proceed to answer your questions:
You ask two things:
1) Real time embedded systems
2) Wireless configuration in Linux
I only know little bit about wireless and Linux.
Real time embedded systems are basically divided into two:
1) hard real time
2) soft real time
Hard real time embedded systems are mission critical and used in
surgical equipment, life saving equipment, rocket launching and plane cockpits.
Soft real time embedded systems are used in routers, switches and networking
equipment where a delay in performing a programming task will not
endanger a life.
There are two types of CPU scheduling broadly speaking.
Pre emptive multi tasking and non pre emptive multitasking.
In pre emptive multi tasking, the running process is forcibly
jettisoned to replace with
a new process to ensure fair allocation of resources to waiting
processes in the Q.
In non pre emptive multi tasking a long running process can starve
others since it
may be a rogue.
In other words non pre emtive multi tasking is democracy in which
rules are lenient.
How does this relate to real time embedded systems?
In embedded systems , say hard real time, you have pre emptive multitasking.
Then there is priority queuing in which the mission critical
processes like disk I/O, network
interrupt processing when you receive packets are run at a higher
importance than
say some music playing or handling user interface.
A real time OS also has other characteristics like low CPU, memory,
secondary storage, no swap,
usually no MMU(which means not multi processing based), and it will
have power saving needs
which are usually built into wireless antenna management software.
Now let us talk about wireless.
A wireless transceiver works based on certain characteristics:
1) What is the arbitration protocol for transmitting? Bus arbitration
similar to CSMA/CD on ethernet
or inside a computer , how the control bus interfaces the peripherals
like memory, CPU, keyboard
and so on
2) What is the encoding in wireless to transfer data? Say, CDMA(spread
spectrum), QPSK and so on
3) The topology of the network, bus, star, mesh and so on
Okay now the various wireless protocols in vogue are:
1) WiFi 802.11a to i
2) Bluetooth
3) WiMAX
4) IrDA
5) USB wireless for keyboard and mouse interfacing
6) Others like Zigbee probably are built on top of the above
Bluetooth is low speed wireless and WiFi is the fastest.
Usually wireless is unreliable and fixed wireless between satellite
and earth station and
between two line of sight microwave towers are the best.
All other wireless technologies suffer from throughput issues.
-Girish
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