Two phone interviews for the same job position.

First interview:

Asked me questions on my project listed on my resume. Basic questions in C like the difference between & and &&, and memory regions such as stack, heap, text, and data segments.

OS concepts: What is mutual exclusion? What is the difference between semaphores and mutexes?

Asked me to code (in C) a function that takes the bit number of an output port as an argument and toggles it.

Second interview:

Did not discuss my resume at all. Dived straight into tech questions: What are interrupts, and if you have fewer external interrupt pins on a processor, how do you interface multiple interrupts?

How do breakpoints in a C program work? How does a debugger work?

Asked me to write a program (in C) to remove duplicate continuous characters in a string. Another way to find the sizeof and data type without using sizeof()?

The second interview was a bit difficult, and I didn't think I would make it. Sure enough, I received an email from their HR stating they want to hire someone who more closely matches the job description, so I was not invited to the on-site interview.

The unexpected last question asked how to find the size of a data type without using the sizeof() function. I Googled later on how to do this and discovered it had something to do with null pointers. I would not have thought of that at the time.