AVR Freaks

"I check whether the distance has been lesser than a specified value for atleast 5 times, checked every 0.01 seconds. "

How is that "without delay"?

See the recent topic I made in 'Site Feedback'.

First:

1). Variable names with less than 3 letters are hard to read. Longer names can be easily searched for and highligheded in a decent IDE which makes it a lot easier for other people to scan the code for where a particular variable is used.

2). Where does your "distance" come from? How and how often is it updated?

3). Do not use "magic values" in your code. What does "40" mean? What if you want to change "40 to 38 ?

4). Manual "unrolling" of loops is tedious and error prone and has a big code size. Use loops to clear arrays, check values etc. (Speed penalty for a loop is minimal, FLASH is precious in a small uC).

5). Always, I mean *** ALWAYS *** use braces around compound statements, even if blocks of 1 line. This prevents nasty bugs from creaping into your code while editing. It is only allowed to not use braces with single line statements for historical compatibility reasons, but it is bad practice nontheless.

Designing good algorithms is a very dificult task and completely separate from learning a programming language.

You start your code with:

if(distance<40)    

And then fill an array with values < 40, and check that 5 times ???

Those values will always be < 40.

So this does not check 5 consecutive samples, but only if there have ever been a totoal of 5 samples < 40.

A better way would be to turn your array in a circular buffer like structure, and write a value into it, then check for all 5 indices of the array.

Untested code:

#define ARRAY_SIZE 5
#define MIN_DISTANCE 40

uint16_t sv[ARRAY_SIZE];
uint8_t p;
uint8_t index;
uint8_t cnt;

if( Time_Interval_Elapsed) {
	if( ++p >= ARRAY_SIZE) {	// Calc new "p" index.
		p = 0;
	}

	sv[p] = distance;	// Store next measured distance at new index.

	for( index = 0, cnt = 0; index <= ARRAY_ZIZE, ++index) {  // Check all indices for size.
		if( sv[ index] < MIN_DISTANCE) {
			++cnt;
		}
	}

	if( cnt >= ARRAY_SIZE) {
		// Counted 5 small values...
	}
}

But it can be simplified. You do not need to save all those distances in an array, you only have to know if a distance is or is not within the intended range.

Something like:

#define COUNTER 5
#define MIN_DISTANCE 40

bool check_distance( uint16_t);

void main( void) {

	for( ;;) {
		if( Time_Interval_Elapsed) {
			if( check_distance( distance)) {
				// Found small distance
			}
		}
	}
}

bool check_distance( uint16_t distance) {
	static uint8_t cnt;

	if( distance < MIN_DISTANCE) {
		cnt++
	}
	else {
		cnt = 0;
	}

	if ( cnt >= COUNTER) {
		cnt = COUNTER	// Prevent overflow / wrap around.
		// Found COUNTER consecuttive small distances.
		return true;
	}
	return false;
}

Also:

Designing algorithms it is much easier to do on a PC.

You can have (a bunch of) arrays with test distances, and you can feed those test distances into your distance check algorithm and use printf to print all kind of intermediate values, or tables to clarify what your algorithm is doing.

Those test distances are known in advance, and can be easily made for specific test data.

You can also use single stepping, breakpoints or watching variables without having to buy Atmel / Microchip debug hardware.

Your code has 3 or more tabs on most lines, which is unexpected indentation. It also makes your text so wide that it gets wrapped in my web browser.

This probably is a left over from a cut & paste operation, but if you want to intice others to look at your code, then put some effort in it to make it easier to read.

If you copied / pasted to an empty edit window in your IDE and reformatted it those tabs would have been gone, and you would have had a check for matching braces.