Cargo Features

EFR32xG1 has no features set by default.

efr32xg1 = { version = "0.2.1", features = ["rt"] }

Enables device of cortex-m-rt ^0.6.5

Features from optional dependencies

In crates that don't use the dep: syntax, optional dependencies automatically become Cargo features. These features may have been created by mistake, and this functionality may be removed in the future.

as suggested by svd2rust 0.14 documentation:

cortex-m-rt rt?

Enables cortex-m-rt ^0.6.5