Deprecated Dependencies

[KuangjuX]

Hi!
I try to import this library into my project, but the rust compiler throw a compilation error:

 |
5 | #![feature(const_fn)]
  |            ^^^^^^^^ feature has been removed
  |
  = note: split into finer-grained feature gates

I check dependencies of this library and find that the register library has been deprecated, and this library use tock-registers which have a const_fn feature. const_fn has been removed in PR77136. So this library can't be compiled in rust 2021.