Howto power off usb devices

[bashrules]

Under FreeBSD, I can power off a usb device with usbconfig's "power_off" option. How can I do that under NetBSD?

# usbstats 
Controller /dev/usb0:
      1069 control
         0 isochronous
 154806725 bulk
   8954336 interrupt
Controller /dev/usb1:
       375 control
         0 isochronous
  33390421 bulk
         2 interrupt

# usbdevs 
addr 1: EHCI root hub, NetBSD
 addr 2: Rate Matching Hub, Intel
  addr 5: External USB 3.0, Toshiba
  addr 3: USB Optical Mouse, Primax Electronics
  addr 4: Kensington U+P Keyboard, NOVATEK
addr 1: EHCI root hub, NetBSD
 addr 2: Rate Matching Hub, Intel
  addr 3: USB2.0-CRW, Generic

I want to power off (and later on) External USB 3.0, Toshiba, which I believe is at usb0, addr 5.