lbuild module: modm:board:samd21-mini

The SAMD21 MINI board is a small breakout board for the ATSAMD21G18 ARM Cortex-M0 processor, clocked at 48 MHz and at 3.3V logic.

See: https://robotdyn.com/samd21-m0-mini.html

It can be bought for little cost from well known Chinese online stores.