Variables not updating in a loop

hi all,

i'm trying write program flash led's attached wheel on half revolution , off half revolution.  revolutions detected interrupt attached hall effect sensor , works.  in other programs have current mph displayed on led's (i.e. 1 led = 1mph etc), driven interrupt.

the idea code timing of led on/off governed variables updated every 5 seconds or speed changes timing changes maintain half on, half off behavior.

i set initial vales flash every 128 milliseconds , when start code , spin wheel flash correctly aren't changing speed of flashing time elapses.  i've tested code firing every 5 seconds increasing pixeldelay value 1 each time , behaved expected , flashing slowed down every 5 seconds.

i don't understand why delay variables aren't updating.

any appreciated , have been of such great assistance far in project.

below pertinent code:

[font=courier]volatile int revcount;
int duration;
float onerevduration;
float pixeldelay;

void setup() {
 //set pins output because addressed in main loop
 pinmode(latchpin, output);
 pinmode(2, input);      // make digital 2 input
 digitalwrite(2, high);  // enable pull resistor
 attachinterrupt(0, rpmfun, falling);
 revcount = 0;
 duration = 0;
 onerevduration = 256.0;
 pixeldelay = 1.0;
}


void loop() {
 
 if (duration > 5000) {
    onerevduration = duration / revcount;
    pixeldelay = onerevduration / 256;
    duration =0;
    revcount = 0;
 }
 
 else {
   
 digitalwrite(latchpin, 0);
   shiftout(datapin, clockpin, 255);  
   shiftout(datapin, clockpin, 255);
 digitalwrite(latchpin, 1);
 
 delay((int)(pixeldelay * 128));
 duration = (int)(duration + (pixeldelay * 128));
 
 digitalwrite(latchpin, 0);
   shiftout(datapin, clockpin, 0);  
   shiftout(datapin, clockpin, 0);
 digitalwrite(latchpin, 1);
 
 delay((int)(pixeldelay * 128));
 duration = (int)(duration + (pixeldelay * 128));
}
}

void rpmfun()
{
  revcount++;
}
[/font]

i've been playing around think line problem lies:

[font=courier]onerevduration = duration / revcount;[/font]

still no idea how fix it!

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