Arduino MKR ZERO - Original Board with Atmel SAMD21 for IoT - Bus I2S and SD - 5 V - 32,768 Khz - 48 Mhz - ABX00012 ("ABX00012", "ABX00012-R","ABX00012","ARD-0131","1050-1137-ND","2830993","2275551","30101961")
Omzlo: Programming the SAMD21 using Atmel ICE with OpenOCD (updated)
Atmel SamD21 Xplained pro board pin out. - Microcontrollers - Arduino Forum
Custom Arduino SAMD21 bootloader with Atmel Studio – Projects blog Erik Henneberg