in the past you have to deal heavily with registers to enable the deep sleep mode on the SAMD21 while still wanting to "listen" to pin interrupts,
see for example here --> External interruption not being triggered with CHANGE, RISING or FALLING while on standby (sleep) mode. · Issue #142 · arduino/ArduinoCore-samd · GitHub
or here --> Interrupt modes not working - #5 by GabrielNotman - Arduino Zero - Arduino Forum
on gitub @sandeepmistry wrote on June'16 "We'll need to figure out a plan to incorporate low power into the core ..."
are there any new core functions regarding the sleep modes of the SAMD21
or is there some kind of "low-power library" available for that ?