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When to use volatile?
Volatile is usually applied to a variable when we are declaring it. The main reason behind using volatile keyword is that it is used to prevent optimizations on objects in our source code. Therefore, an object declared as volatile can’t be optimized because its value can be easily changed by the code.
How you can declare the variable volatile?
To declare a variable volatile, include the keyword volatile before or after the data type in the variable definition.
What do you use the volatile keyword for?
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. The volatile keyword can be used either with primitive type or objects.
Is ROM a volatile memory?
ROM is non-volatile memory, which means the information is permanently stored on the chip. Turning off the computer does not have any effect on ROM.
Can a variable be both const and volatile?
Yes a C++ variable be both const and volatile. It is used in situations like a read-only hardware register, or an output of another thread. Volatile means it may be changed by something external to the current thread and Const means that you do not write to it (in that program that is using the const declaration).
Is Typedef a keyword in C?
typedef is a reserved keyword in the programming languages C and C++. It is used to create an additional name (alias) for another data type, but does not create a new type, except in the obscure case of a qualified typedef of an array type where the typedef qualifiers are transferred to the array element type.
What happens when volatile variable is not declared?
When a volatile variable is not declared as volatile, the compiler assumes that its value cannot be modified from outside the scope that it is defined in. Therefore, the compiler might perform unwanted optimizations. This problem can manifest itself in various ways: Code might become stuck in a loop while polling hardware.
How to use delay with a global variable?
I have tried to use _delay_ms () function with global variable, declared like this: volatile uint16_t pulse_width=1000. If I use a number as an argument to delay, everything works fine. Why a variable can not be used as an argument?
How to use delay with variable in ISR?
The problem seems to be that retrieving the volatile global variable has so much more overhead compared to short delay demand. See below. Using a local variable in ISR works fine. Assigning global variable to local will be optimised away. Or can this be forced somehow, without touching to the optimising parameters?
How to use delay with variable in AVR?
You can see the generated code via Studio. This is far more use to you than speculation. If you want to control several servos, you could synchronise them all. You just have to control several mark/space ratios in a constant frame. You can use the AVR timer hardware. Or just poll the timing loop and do the compare value yourself.