Some questions that were asked(may not be exact question, but rather as I understood or remember them):
Q: Explain or share knowledge of RTOS(Real-Time Operating System)
A: I didn't know what they were, but was offered a brief explanation.
Q: Now that you know what RTOS is, given a printer, would you rather use a RTOS or a regular operating system such as, windows or linux in it.
A: No correct answer, but rather the interviewer wished to see my train of thought.
Q: Have you heard of an Interrupt before?
A: I didn't know but they shared with me what it was. Google it up, Interrupt handler.
Q: Given a function:
int func(int *x)
{
int t;
t = *x * *x;
return t;
}
A: I think ths is simple enough, it's a function which squares the value at the given memory location.
Q: And here's the relatively tough one. You are given a microprocessor and a square clock wave entering it. The clock wave has a maximum frequency of 250hz. Within a tolerance of 25%-75%, design a function within the microprocessor which interates at a certain interval, x, which will calculate the average frequency of the input clock wave.
A: At first I didn't get the answer but after some illustration, the picture became clearer. What you want to do is store the previous state recorded, and then check it with current state(whether it be 0 or 1) then execute a +1 to a counter if previous state = 0 and current state = 1. Answer I gave was something like this:
void loop()
{
static int prev, counter, freq, x;
int curr;
if(prev==0 && curr = 1)
{
counter++;
}
x++;
freq = counter/(x)(t);
}
x counts the number of times the function iterates regardless of whether it has detected a change in state. t on the other hand is the timing of the loop function, found by converting the 250hz into seconds(4ms) and then taking the value of 25% - 75% of that 4ms.