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INTERVIEW QUESTIONS HARDWARE EMBEDDED SYSTEMS DETAILS
Question :
Can you have constant volatile variable?
Category Embedded Systems Interview Questions
Rating (3.9) By 37 users
Added on 7/6/2010
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Answers:



yes we can have constant volatile variable.

In this current context of code will not change the value of the variable but out side of the program i.e. hardware registers can change it.



Posted by: rajkumar

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In some scenarios expressions having volatile variables cant be optimized by a compiler.



Posted by: shashank vimal

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precisely volatile variable warns the compiler that the value of the variable may change at any time without the knowledge of the compiler, to the code currently executed.
volatile int * const port_add = 0x400;



Posted by: Murali Prasath

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Volatile type tell the compiler , this variable can be changed by any external tasks, So do not optimize while compiling and linking final executable.
Here is Example:


In Embedded system System Timer is one of the most important.

func()
{
TIME* time;
time = GetSystime();

for ( 1000 times )
{
some expressions;
}
time = GetSystime();
}

In the above function , time is a structure which gets the time before and after FOR loop.
At these two instances time is definitely different, because of FOR loop. If you go for an embedded system compiler, generally it optimizes the "time = GetSystime();" expression. because it thought that, code is redundant no need to load the getsystime value again from memory , if u dont use VOLATILE. to avoid this kind of things use Volatile.



Posted by: Jay

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