From http://code.google.com/p/leaflabs/issues/detail?id=7 Reported by Okie "PWM outputs are always zero on 0.0.8 on windows xp on my computer. everything is fine with 0.0.6."

audioshield_comb.pde

#define AIN1 18
#define AIN2 19
#define AOUT1 6
#define AOUT2 7
#define POT1 16
#define POT2 17
#define SAMPLETIME 10 // in microseconds
#define KNOBSAMPLETIME 21
#define SYSTICK_CSR 0xE000E010

void createSample(void);
void measureKnobs(void);
uint16 comb(int signalin, int tap, int feedback);

uint16 knob1 = 0;
uint16 knob2 = 0;
uint16 signalin = 0;
uint16 signalout = 0;
int comb_index = 0;
uint16 outputbuffer[8192];

void setup(){
  pinMode(AIN1, INPUT_ANALOG);
  pinMode(AIN2, INPUT_ANALOG);
  pinMode(AOUT1, PWM);
  pinMode(AOUT2, PWM);
  pinMode(POT1, INPUT_ANALOG);
  pinMode(POT2, INPUT_ANALOG);

  // PWM timers
  Timer1.setPrescaleFactor(1);
  Timer1.setOverflow(0x00FF);
  
  // timer for I/0 measurement and calculation
  Timer2.setChannel1Mode(TIMER_OUTPUTCOMPARE);
  Timer2.setPeriod(SAMPLETIME); // in microseconds
  Timer2.setCompare1(1);      // overflow might be small
  Timer2.attachCompare1Interrupt(createSample);

  // timer for reading potentiometers
  Timer3.setChannel1Mode(TIMER_OUTPUTCOMPARE);
  Timer3.setPeriod(KNOBSAMPLETIME); // in microseconds
  Timer3.setCompare1(1);      // overflow might be small
  Timer3.attachCompare1Interrupt(measureKnobs);
}

void loop(){

}

void createSample(void){
  pwmWrite(AOUT1, (signalout)%256);
  pwmWrite(AOUT2, (signalout)/256);
  signalin = 0;
  for(int i=0; i<8; i++){
    signalin = signalin + analogRead(AIN1) + analogRead(AIN2);
  }
  signalout = comb(signalin, knob1, knob2);
}

void measureKnobs(void){
  knob1 = analogRead(POT1);
  knob2 = analogRead(POT2);
  knob1 = knob1 + analogRead(POT1);
  knob2 = knob2 + analogRead(POT2);
}

uint16 comb(int signalin, int tap, int feedback){
  outputbuffer[comb_index%8192] = (8192-feedback)*signalin/8192 + ((feedback-1)%8192)*outputbuffer[(comb_index+tap+1)%8192]/8192;
  return outputbuffer[(comb_index++)%8192];
}