Code:

 */
#if USB_CFG_CLOCK_KHZ==16500
#define USB_CFG_HAVE_MEASURE_FRAME_LENGTH   1
#include "osccal.h"
#else
#define USB_CFG_HAVE_MEASURE_FRAME_LENGTH   0
#endif
/* define this macro to 1 if you want the function usbMeasureFrameLength()
 * compiled in. This function can be used to calibrate the AVR's RC oscillator.
 */

Code:

#ifndef __ASSEMBLER__
#include <avr/interrupt.h>  // for sei()
extern void calibrateOscillator(void);
#endif
#define USB_RESET_HOOK(resetStarts)  if(!resetStarts){cli(); calibrateOscillator(); sei();}

Code:

/* -----------------------------------------------------------------------------*/
static void calibrateOscillator(void)
{
uchar       step = 128;
uchar       trialValue = 0, optimumValue;
int         x, optimumDev, targetValue = (unsigned)(1499 * (double)F_CPU / 10.5e6 + 0.5);
 
    /* do a binary search: */
    do{
        OSCCAL = trialValue + step;
        x = usbMeasureFrameLength();    // proportional to current real frequency
        if(x < targetValue)             // frequency still too low
            trialValue += step;
        step >>= 1;
    }while(step > 0);
    /* We have a precision of +/- 1 for optimum OSCCAL here */
    /* now do a neighborhood search for optimum value */
    optimumValue = trialValue;
    optimumDev = x; // this is certainly far away from optimum
    for(OSCCAL = trialValue - 1; OSCCAL <= trialValue + 1; OSCCAL++){
        x = usbMeasureFrameLength() - targetValue;
        if(x < 0)
            x = -x;
        if(x < optimumDev){
            optimumDev = x;
            optimumValue = OSCCAL;
        }
    }
    OSCCAL = optimumValue;
}
 
/* ------------------------------------------------------------------------- */

int main(void)
{
uchar   i;
uchar   calibrationValue;
    
   wdt_enable(WDTO_1S);
    


    calibrationValue = eeprom_read_byte(0); /* calibration value from last time */
    if(calibrationValue != 0xff){
        OSCCAL = calibrationValue;
    }
   
   /* Even if you don't use the watchdog, turn it off here. On newer devices,
     * the status of the watchdog (on/off, period) is PRESERVED OVER RESET!
     */
    //DBG1(0x00, 0, 0);       /* debug output: main starts */
    /* RESET status: all port bits are inputs without pull-up.
     * That's the way we need D+ and D-. Therefore we don't need any
     * additional hardware initialization.
     */
    //odDebugInit();
    usbInit();
    usbDeviceDisconnect();  /* enforce re-enumeration, do this while interrupts are disabled! */
    i = 250;
    while(--i){             /* fake USB disconnect for > 250 ms */
        wdt_reset();
        _delay_ms(1);
    }
   usbDeviceConnect();
    sei();
    //DBG1(0x01, 0, 0);       /* debug output: main loop starts */
    for(;;){                /* main event loop */
      //  DBG1(0x02, 0, 0);   /* debug output: main loop iterates */
        wdt_reset();
        usbPoll();
    }
    return 0;
}

/* ------------------------------------------------------------------------- */