RTOS Interview Preparation Guide

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RTOS might be having 10k memory, might not fragmentation
problem, and the largest hole available to user might be
lesser than 5k, this condition might be one of the reason
for NULL error.

Not sure what this question is. But looks like the question
is: Why 4GB addressing space available in Linux. Well, the
simple answer is it can address so much of memory with
available 32 address lines. 2 ^ 32 = 4 GB.

a) Use Atomic Instructions
b) Remember to enable interrupts
c) Make the critical section code as small as possible.
(Prefer not more than 20 instructions)
d) Prefer not to call other functions from the critical
section. if u r calling, see that there is no critical
section in the other function too. Critical section is
bounded by Disable Interrupt and Enable Interrupt.
Check the example below.
fnA()
{
/* Critical Section Start */
Disable_Interrupt();
Some Instructions A ....
Call FnB();
/* do Something B */
Some Instructions B ....
/* Critical Section End */
}


fnB()
{
/* Critical Section Start */
Disable_Interrupt();
Some Instructions ..
Enable_Interrupts();
/* Critical Section End */
}


Now the Enable_Interrupts in fnB() will enable the
interrupts and hence "Some Instructions B .." in fnA()
which should have been in critical section will no more be
in critical section because the interrupts are already
enabled!!

Please check if this condition is handled by the Enable and
Disable functions. If you want suggestions on how to solve
this problem, do revert back

Adv:
1) Supports various types of processor platforms
2) Possible to Customize the Kernel and can reduce its size
(upto ~300KB kernel size)
3) Especially for the embedded device platforms

Disadv:
1) Process limits, max. 32 process at a time in WinCE 5.0
2) Limited space allocation for each processes, 32MB/each
process

Well there is nothing to related with limited H/w I believe,
Because MFC is just a collection classes designed using the
Windows APIs , to provide ease of use.
So the proper answer may Be...
To design any application on mobile.. We have very limited
APIs which user can directly used. Generally in Embedded
system (even in Soft RTOS also ) , if application design
using less ( comfort )layer like MFC ( and other if it is
there :) ),then your aplication would be more efficient.
That's why even today's era... The application written in
Assembly is the most efficient application then others.

speciality in the sense ...
1) number of processes supported by wince 5.0 is more
than wince 4.0
2) memory mapping might be varying.

there are four levels in Win CE architecture.
They are
1)Hardware layer
2)OEM layer
3)OS layer
4)Application layer

MSFT standard SDK's are,

1. Windows Mobile for Smartphone = Windows Mobile Standard.
2. Windows Mobile for Pocket PC = Windows Mobile Classic.
3. Windows Mobile for Pocket PC Phone Edition = Windows
Mobile Professional.

Normal OS wince
drivers runs under User space(part of device manager)
kernel space

cannot be customized customized for embedded application
for embedded application like mobile phones,thin client...
(exception linux)

kernel - monolithic kernel- micro kernel

In the name "Windows CE," the letters "CE" are not an
abbreviation for anything, but rather they imply a number
of the precepts around which Windows CE is designed,
including "Compact," Connectable,"
Compatible," "Companion," and "Efficient."