void USB_c_irq_handler( void )
{
бла-бла
}

то устанавливается он так

	AT91F_AIC_Init( AT91C_BASE_AIC, AT91C_ID_UDP, usbINTERRUPT_PRIORITY, AT91C_AIC_SRCTYPE_INT_LEVEL_SENSITIVE, USB_c_irq_handler );

где

unsigned int AT91F_AIC_Init
	(
	AT91PS_AIC pAic,  // \arg pointer to the AIC registers
	unsigned int irq_id,     // \arg interrupt number to initialize
	unsigned int priority,   // \arg priority to give to the interrupt
	unsigned int src_type,   // \arg activation and sense of activation
	void (*newHandler) (void)// \arg address of the interrupt handler
    )
{
	unsigned int oldHandler;
    unsigned int mask;
    oldHandler = pAic->AIC_SVR[ irq_id ];
    mask = 0x1 << irq_id;
    //* Disable the interrupt on the interrupt controller
    pAic->AIC_IDCR = mask;
    //* Save the interrupt handler routine pointer and the interrupt priority
    pAic->AIC_SVR[ irq_id ] = (unsigned int) newHandler;
    //* Store the Source Mode Register
    pAic->AIC_SMR[ irq_id ] = src_type | priority;
    //* Clear the interrupt on the interrupt controller
    pAic->AIC_ICCR = mask;
	return( oldHandler );
}