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Firmware Engineering Interview Questions


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How to swap the values in 2 variables without using a temporary variable.

5 Answers

a=a^b b=b^a a=a^b

but it should say swap two integers! because this XOR won't work with float for example

This works for floats: a = a+b b = a-b a = a-b But you might overflow on a+b.

If you have two devices that can interrupt your program and you want to give priority and atomicity to one of the processes over the other, but you cannot use a semaphore or mutex, how would you do it?

3 Answers

Write a c functions that takes two bit indices and an int, and reverses the bits in the int between the two indices.

9 Answers

How to invert all the bits in a byte? e.g. 0x55 should be changed to 0xAA.

3 Answers

Name a few different types of registers.

2 Answers

Puzzles 1: You have rope that take 60 min to burn. Speed of burning is not uniform. Example: it doesn't take 30 min to burn half Using two ropes, how would you get 45 min? Answer: First Rope. Burn both ends at same time Second Rope: Burn only one side. when First rope is totally burn, it's been 30 min, now burn the rest of second rope both ends. Which should take additional 15 min. 30 + 15 = 45 min. Puzzle 2: There is a guy in a boat holding a rope that's tight to a Top of pole in the shore. He keep pulling the rope until he reach the shore. What is the speed relationship between amount of rope he pulls, vs horizonal speed? Which speed is higher? Answer: Horizonal speed is faster than the amount of rope he pulls. (Horizonal distance he travel is higher than amount of rope he pulls, by triangle theory where sum of two sides must be greater than 3rd side) Puzzle 3: in Analog Clock, It's exacly 3:00 Clock. What time would the Hour hand, and Min hand would overlap each other?

4 Answers

They were looking for someone to write firmware in C++ and had a small program as part of test for this. Since I had indicated my experience in this are was from many years ago and not very long in duration, I did not believe they would test me and I did not prepare for this.

1 Answer

Describe the two different uses of the "volatile" keywork in C.

2 Answers

What techniques would you use to reduce power consumption in an embedded system?

2 Answers

What kind of data structure would you use to store data from a serial receive line?

2 Answers
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