Pulse Width Modulated waveform using Timer/Counter0
    The bits of the two control registers TCCR0 and OCR0 are manipulated to generate the PWM. PB3 should be set as output by setting the corresponding bit in DDRB

setReg(DDRB, 8)      # set PB3 as output
WGM01=3
WGM00=6
COM01=5
setReg( TCCR0 , (1 << WGM01) | (1 << WGM00) | (1 << COM01)  |  1)
setReg(OCR0 ,  64)