Contents
- 1 What happens to global variables during an interrupt?
- 2 What happens when a variable is read during an interrupt?
- 3 Can a global variable be declared volatile in C?
- 4 When do you need to use a global variable?
- 5 What happens to a 16 bit variable during an interrupt?
- 6 How are variables saved in a micro controller?
What happens to global variables during an interrupt?
When the interrupts is triggered the execution of the main code stops, the current working variables are saved, a preassigned function is executed and then the main code picks back up where it left off. Because the interrupt is a stand alone function that can trigger at any time nothing can be passed into or out of the function.
What happens when a variable is read during an interrupt?
If the interrupt fires in between you will have corrupted 16-bit data because only half of the variable has been read. The first 8bit before the ISR and the other 8bit after the ISR returns. This is bad data which can cause huge problems if pointers are involved rather than just passing a ADC data value for example.
Can a volatile variable be shared between Main and ISR?
Note that being volatile does NOT mean that you are “safely” sharing this variable between the ISR and main code. It is NOT guaranteed to be Atomic access which is when the variable is accessed with a single CPU instruction. For instance a 16-bit variable on an 8 bit micro will take multiple read instructions to read the value.
Why is a new thread created for each interrupt request?
A new thread is created for each interrupt request. It is important to consider each individual request as a separate thread because local variables and registers used in the interrupt service routine are unique and separate from one interrupt event to the next interrupt.
Can a global variable be declared volatile in C?
In single-threaded code, and in the C and C++ standards, “and then” is defined by sequence points, of which there are plenty in the code given. No. Global variables should not always be declared volatile.
When do you need to use a global variable?
Globals are only “evil” when you have too many and are accessing them back and forth over many files. It just gets very messy and you can easily create another variable that has the same name as another existing global. Not good. Thanks for contributing an answer to Stack Overflow!
How often does an interrupt occur in an ISR?
The interrupt may occur at different times every time. Instead it is common to write global variables in the ISR. For this you have to consider some points: Global variables, that may be changed during an ISR, has to be declared (additionally to the type) as volatile.
Which is the correct description of an interrupt?
Interrupt Concepts An interrupt is the automatic transfer of software execution in response to a hardware event that is asynchronous with the current software execution. This hardware event is called a trigger .
What happens to a 16 bit variable during an interrupt?
For instance a 16-bit variable on an 8 bit micro will take multiple read instructions to read the value. If the interrupt fires in between you will have corrupted 16-bit data because only half of the variable has been read. The first 8bit before the ISR and the other 8bit after the ISR returns.
How are variables saved in a micro controller?
The micro controller is equipped with interrupts. An interrupt is an event triggered externally in hardware. When the interrupts is triggered the execution of the main code stops, the current working variables are saved, a preassigned function is executed and then the main code picks back up where it left off.
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