USBDevice_::detach() empty function?

I am trying to understand 32U4 USB core code in Arduino IDE 1.6.5-r5 with atmel's doc on 32u4.

In USBCore.cpp:

void USBDevice_::attach()
	_usbConfiguration = 0;
	UHWCON = 0x01;						// power internal reg
	USBCON = (1<<USBE)|(1<<FRZCLK);		// clock frozen, usb enabled
#if F_CPU == 16000000UL
	PLLCSR = 0x12;						// Need 16 MHz xtal
#elif F_CPU == 8000000UL
	PLLCSR = 0x02;						// Need 8 MHz xtal
	while (!(PLLCSR & (1<<PLOCK)))		// wait for lock pll

	// Some tests on specific versions of macosx (10.7.3), reported some
	// strange behaviuors when the board is reset using the serial
	// port touch at 1200 bps. This delay fixes this behaviour.

	USBCON = ((1<<USBE)|(1<<OTGPADE));	// start USB clock
	UDIEN = (1<<EORSTE)|(1<<SOFE);		// Enable interrupts for EOR (End of Reset) and SOF (start of frame)
	UDCON = 0;							// enable attach resistor

void USBDevice_::detach()

As you can see, there is no code in detach(). How would I detach then? Going back to atmel doc? This reminds me when arduino IDE has only .begin() for so many things but not a single .end() to complete the loop. Are we looking at this again, all assuming best-case scenario? Thanks.

As far as my studies, I know that one should reset USEN bit in USBCON but that's probably not enough for detach.

Maybe this explains:

//	Check for interrupts
//	TODO: VBUS detection

Arduino IDE 1.8.4 has fancier defs for different chips but still won't check VBUS to see whether usb insertion happened or not, just turn them hardware on!!! :slight_smile: