clean up

Author: hathach

cores/nRF5/usb/usb.c

@@ -63,6 +63,8 @@ void usb_init(void)
 
   nrfx_power_usbevt_enable();
 
+  // Priorities 0, 1, 4 (nRF52) are reserved for SoftDevice
+  // 2 is highest for application
   NVIC_SetPriority(USBD_IRQn, 2);
 
   // USB power may already be ready at this time -> no event generated