How to resolve my Timer Interrupt issue

Question

I am trying to work with arduino timer1 interrupts to make an led blink every bit on an 8 bit number, depending on whether its a 1 or 0. However, im trying to make a basic blinking program, and it does not seem to be working.

#include "TimerOne.h"
bool val=0;
void setup()
{
 pinMode(13, OUTPUT);
 Timer1.initialize(500000); // initialize timer1, and set a 1/2 second period
 Timer1.attachInterrupt(callback); // attaches callback() as a timer overflow interrupt
}
void callback()
{
 val=1;
}
void loop()
{
 digitalWrite(13,val);
 while(!val);
 val=0;
}

The LED doesnt blink at all! Any help would be appreceitated! thanks!

Answer 1

Try this instead.

#include "TimerOne.h"
bool val=0;
void setup()
{
 pinMode(13, OUTPUT);
 Timer1.initialize(500000); // initialize timer1, and set a 1/2 second period
 Timer1.attachInterrupt(callback); // attaches callback() as a timer overflow interrupt
}
void callback()
{
 val=!val;
}
void loop()
{
 digitalWrite(13,val);
}

Answer 2

I'm not surprised the LED doesn't blink - the entirety of your logic in the loop() function is so bizarre as to elicit the question:

WTF?

Let's take a look at it line by line:

digitalWrite(13,val);

Set the LED to whatever val is - val starts as 0, so the LED is off.

while(!val);

While val is not anything except 0, so while val is zero, do nothing. (The interrupt would escape you from this if your val was volatile)

val=0;

Set val to 0.

So how can val be anything except 0 when you do the digitalWrite?