ATmega32U4 USB Init

//-------------------------

int16_t    usb_init (void)

//-------------------------

{

  ATOMIC_BLOCK(ATOMIC_RESTORESTATE)

  {

    UHWCON |= (1 << UVREGE);                        // Enable USB Pads Regulator

    // configure PLL interface

    PLLCSR = 0;

    PLLFRQ = 0;

    PLLFRQ  =   0b00001010;                          // 96MHz

    PLLFRQ  |=  (1 << PLLUSB);                        // /2 = 48MHz USB clock

    PLLCSR  |=  (1 << PINDIV);                        // external 16MHz source

    // enable PLL

    PLLCSR |= (1 << PLLE);

    // check PLL lock

    while (!(PLLCSR & (1 << PLOCK)));

    USBCON    |=  (1 << USBE) | (1 << OTGPADE);              // Enable USB Controller and USB power pads

    USBCON    &= ~(1 << FRZCLK);                      // Unfreeze the clock

    UDCON    &= ~(1 << LSM);                        // FULL SPEED MODE

    UDCON    &= ~(1 << DETACH);                      // Attach USB Controller to the data bus

    UDINT     = 0;

    UDIEN    |=  (1 << EORSTE) | (1 << SOFE);              // Re-enable the EORSTE (End Of Reset) Interrupt so we know when we can configure the control endpoint  usb_config_status = 0;

  }

  return 0;

}

//--------------------

ISR    (USB_GEN_vect)

//--------------------

{

  uint8_t      USB_InterruptSource;

  USB_InterruptSource    = UDINT;

  UDINT = 0;

  DDRD    |= 1;

  PORTD   |= 1;

  _delay_ms (1);

  PORTD  &= 254;

  return;