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When should we use volatile qualifier in embedded firmware development?
If even one bit can change unexpectedly, the entire register must be declared volatile. The register must also be declared volatile if it’s write only since the optimizer may optimize out the first write in a two-write operation, and optimize out all writes when a subsequent read isn’t done.
When should I use volatile in C?
The volatile keyword is intended to prevent the compiler from applying any optimizations on objects that can change in ways that cannot be determined by the compiler. Objects declared as volatile are omitted from optimization because their values can be changed by code outside the scope of current code at any time.
When should the volatile modifier be used?
A variable should be declared volatile whenever its value could change unexpectedly. In practice, only three types of variables could change: Memory-mapped peripheral registers. Global variables modified by an interrupt service routine.
What is the use of volatile keyword in C?
A volatile keyword in C is nothing but a qualifier that is used by the programmer when they declare a variable in source code. It is used to inform the compiler that the variable value can be changed any time without any task given by the source code. Volatile is usually applied to a variable when we are declaring it.
Can const and volatile be used together?
Yes. A variable can be declared as both volatile and constant in C. Const modifier does not allow changing the value of the variable by internal program. But, it does not mean that value of const variable should not be changed by external code.
Where the volatile variables are stored in memory?
There’s no reason for a volatile variable to be stored in any “special” section of memory. It is normally stored together with any other variables, including non-volatile ones. If some compiler decides to store volatile variables in some special section of memory – there’s nothing to prevent it from doing so.
Can we use static and volatile together in C?
static volatile: Even if the static variables are shared variables, but in different thread there can be different values for a static variable in the local cache of a thread. To make it consistent for all threads, just declare it as static volatile . So each time it will fetch from main memory.
Why is volatile needed?
The volatile field is needed to make sure that multiple threads always see the newest value, even when the cache system or compiler optimizations are at work. Reading from a volatile variable always returns the latest written value from this variable.
What is the difference between volatile and const volatile?
In C, const and volatile are type qualifiers and these two are independent. Basically, const means that the value isn’t modifiable by the program. And volatile means that the value is subject to sudden change (possibly from outside the program).
What is the purpose of a volatile variable?
Volatile keyword is used to modify the value of a variable by different threads. It is also used to make classes thread safe. It means that multiple threads can use a method and instance of the classes at the same time without any problem.
What is difference between volatile and static?
A static variable refers to a class variable that’s shared among all instances. volatile: Volatile variables are those which are read and written to main memory. They aren’t stored in local cache and are always fetched from main memory.
Can we use static volatile?
Even if the static variables are shared variables, but in different thread there can be different values for a static variable in the local cache of a thread. To make it consistent for all threads, just declare it as static volatile . So each time it will fetch from main memory.