Can you tell me what do you look for in a interview? How does a candidate with no experience shows you that he know how to program embedded systems?
A candidate with no experience, by definition, doesn't know how to program embedded systems. Just because you don't have
professional experience doesn't mean you have no experience--lots of people have plenty of experience doing embedded programming as a hobby. As a hiring manager, I'd certainly consider hiring someone with hobby-level experience, but I would certainly question them closely to try and get an idea of how much they really know and how much is just BS. I've interviewed plenty of people who's only experience with a language, for example, was reading "Learn XX in 24 Hours" the night before the interview. It doesn't take an experienced interviewer long to root out these candidates and show them the door.
Here are some of the things I ask candidates for embedded software positions:
1. What's the difference between re-entrant, thread-safe, and position-independent code?
2. How would you write a bootloader for a microcontroller with only a single FLASH region?
3. What does the C keyword "volatile" do and when/how is it used? Same for "const" and "static".
4. Draw the state diagram for a simple FSM on the whiteboard (a 4-way traffic signal is a good starting place).
5. What is interrupt latency and why is it important?
6. What's the difference between a semaphore and a mutex and when would you use them?
7. What is a critical section and how would you implement one?
8. Have you used an oscilloscope? A logic analyser? Give me examples of how you've used them.
9. What is a pull-up resistor used for? How about a pull-down resistor?
10. What's the difference between a successive approximation ADC and a Sigma-Delta ADC?
11. What are the differences between SPI and I2C?
12. How fast do you have to sample a 10 kHz signal to faithfully reproduce it?