What precautions should be taken when implementing an interrupt routine with write access to a global variable?

What precautions should be taken when implementing an interrupt routine with write access to a global variable?

Use static globals as much as possible so that the variable is only in scope in that particular source file. Use static variables declared in functions that use them for even better isolation. Use volatile for all variables used in both Interrupt routines and main code loop.

How do I enable global interrupt in AVR?

Steps to configure the Interrupts:

1. Set INT1 and INT0 bits in the General Interrupt Control Register (GICR)
2. Configure MCU Control Register (MCUCR) to select interrupt type.
3. Set Global Interrupt(I-bit) Enable bit in the AVR Status Register(SREG)
4. Handle the interrupt in the Interrupt Service Routine code.

Why we should not use global variable frequently?

Using global variables causes very tight coupling of code. Using global variables causes namespace pollution. This may lead to unnecessarily reassigning a global value. Testing in programs using global variables can be a huge pain as it is difficult to decouple them when testing.

Is global variable bad in Python?

While in many or most other programming languages variables are treated as global if not declared otherwise, Python deals with variables the other way around. They are local, if not otherwise declared. The driving reason behind this approach is that global variables are generally bad practice and should be avoided.

What are interrupts AVR?

AVR® devices provide several different interrupt sources including internal and external interrupts. Interrupts can stop the main program from executing to perform a separate interrupt service routine (ISR).

Is using global variables bad?

Global variables are declared and defined outside any function in the program. Non-const global variables are evil because their value can be changed by any function. Using global variables reduces the modularity and flexibility of the program. It is suggested not to use global variables in the program.

Why are global variables evil?

Non-const global variables are evil because their value can be changed by any function. Using global variables reduces the modularity and flexibility of the program. It is suggested not to use global variables in the program. Instead of using global variables, use local variables in the program.

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 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.

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!