delay() runs super fast unless I remove a while loop that never runs

Question

I'm working on a small game on arduino but I'm facing some really odd behavior. When I run this code all of my leds flash on and off in less than a second even though delay(10000); should stop them for 10 seconds. However if I remove the while(game_running) block they go back to flashing every 10 seconds even though that block of code never actually runs.

int yellow = 12;
int green = 10;
int red = 9;
int blue = 11;
int debug = 13;
int sequence[1000];
int level = 0;
int game_running = false;
void setup() { 
 pinMode(yellow, OUTPUT);
 pinMode(blue, OUTPUT);
 pinMode(green, OUTPUT);
 pinMode(red, OUTPUT);
 pinMode(debug, OUTPUT);
}
void loop() {
 // Pre Game light flash
 digitalWrite(yellow, HIGH);
 digitalWrite(green, HIGH);
 digitalWrite(red, HIGH);
 digitalWrite(blue, HIGH);
 digitalWrite(debug,HIGH);
 delay(10000);
 digitalWrite(debug,LOW);
 digitalWrite(yellow, LOW);
 digitalWrite(green, LOW);
 digitalWrite(red, LOW);
 digitalWrite(blue, LOW);
 delay(10000);
 game_running = false;
 level = 0;
 while(game_running) {
 sequence[level] = random(4); // Select next color
 // Blink LEDs
 for (int i=0; i < level; i++) {
 if(sequence[i] == 0) {
 digitalWrite(yellow, HIGH);
 delay(1000); 
 digitalWrite(yellow, LOW);
 delay(1000);
 } else if(sequence[i] == 1) {
 digitalWrite(green, HIGH);
 delay(1000); 
 digitalWrite(green, LOW);
 delay(1000);
 } else if(sequence[i] == 2) {
 digitalWrite(red, HIGH);
 delay(1000); 
 digitalWrite(red, LOW);
 delay(1000);
 } else {
 digitalWrite(blue, HIGH);
 delay(1000); 
 digitalWrite(blue, LOW);
 delay(1000);
 }
 }
 level += 1;
 } 
}

• lemontwist: You're using the Uno? Your array sequence with 1000 entries eats up 2,000 bytes of RAM. (To say nothing of your other variables.) It might be causing some issues.
• lemontwist: I have no problems running your code on my board, of course I changed the sequence array to have just 100 entries. Maybe that was a problem?
• Qwertie: @lemontwistI changed the 1000 to 100 and now it runs as expected. Guess it run out of memory and removing the extra code freed some up?
• lemontwist: Probably was the case. Memory management is very important. Microcontrollers have much more limited memory than PCs!

Answer 1

I will add an official answer just so that others can see it if they run into similar problems.

The issue is with the int sequence[1000] array, which eats up 2,000 bytes of data memory. The Uno only has 2,048 bytes of data memory so the instability is due to this memory hog of an array. Use a smaller number of array entries or switch to char (if you can) to use half the bytes of an int.

• Jot: Compiler output: Sketch uses 1724 bytes (5%) of program storage space. Maximum is 32256 bytes. Global variables use 2017 bytes (98%) of dynamic memory, leaving 31 bytes for local variables. Maximum is 2048 bytes. Low memory available, stability problems may occur.

Answer 2

offtopic (but cannot put it in a comment):

I do not see any problem with your code (maybe it's in the circuit?)

You can rewrite the 10 s pregame flash as:

// Pre Game light flash
setAllLights(HIGH);
setAllLights(LOW);
void setAllLight(int state)
{
 digitalWrite(yellow, state);
 digitalWrite(green, state);
 digitalWrite(red, state);
 digitalWrite(blue, state);
 digitalWrite(debug, state);
 delay(10000);
}

You can even optimize this further by creating an array:

int[] lights = { yellow, green, red, blue, debug}
void SetAllLights(int state)
{
 for (int color = 0; color < sizeof(lights) / sizeof(int); color++)
 {
 digitalWrite(lights[color], state);
 }
}

You can rewrite the inside of the loop like:

switch (sequence[i]):
 case 0:
 flash(yellow);
 break;
 case 1:
 flash(green);
 break;
 case 2:
 flash(red);
 break;
 default:
 flash(blue);
 break;
}
void flash(int colorPin)
{
 digitalWrite(colorPin, HIGH);
 delay(1000); 
 digitalWrite(colorPin, LOW);
 delay(1000);
}