EMBEDDED C INTERVIEW QUESTIONS

Q1. Describe the function  of the volatile keyword in embedded C?

A1. It’s job is to tell the compiler that a variable should not be optimised.

• It should be used only when there can be sudden change of the value of that particular variable.
• Quite useful for the registers that are memory mapped.

Q2. Is it possible to declare a variable as both a constant and a volatile variable?

A2. Yes it woul bd make sense that the compiler wants to keep the volatile variable constant.

• However the value can be altered through external intervention.

Q3. Describe what is a null pointer?

A3. It is one of the popular macros used in c programming.

• It does not indicate any valid memory location.Hence it is used to find out whether a particular memory address is valid or not.

Q4,. State the size of integer, pointer, and their corresponding pointers?

A4. The corresponding sizes are as follows:-

1. Integer – 4 bytes
2. Character – 1 byte
3. Integer pointer – 8 bytes on 64 bit machine and 4 bytes on 32 bit machine
4. Character pointer – 8 bytes on 64 bit machine and 4 bytes  on 32 bit machine.

Q5. Describe what is an ISR in Embedded C?

A5. It is essentially a subroutine that is activated whenever an interrupt is encountered in the main program.

Q6. Is the printf statement applicable within the interrupt routine?

A6. It is not employed within a service routine as it is thread damaging, and employs dynamic memory location.

• It could have a negative effect on the time of ISR and even latency.

Q7. Describe what are inline functions?

A7. These function are usually used in the ARM architecture.

• They are essentially small functions with small definitions.
• Function body takes effect in each call to inline function.

Q8.Describe whats is an RTOS?

A8. It is a.k.a Real time Operating System.

• It comprises of an useful component known as the scheduler:- It organises which process to be executed on the processor based on priorities assigned by the user.
• Multitasking is efficient based on the number of cores of processor and optimisation.

Main features:

• Kernel preemption should be available.
• The dispatch latency of the interrupt should be shortened
• The latency taken for switching context must be short
• The multiple  processes taking place within the RTOS  should be both reliable as well as time efficient.

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