typus_fugit

typus_fugit provides a comprehensive library of Duration and Instant for the handling of time in embedded systems, using compile-time types to represent values.

This library began as a fork of fugit, which is, in turn, a heavily inspired of std::chrono's Duration from C++ which does all it can at compile time.

The decision to fork was due to the desire to replace const-generics values represented in the type system. This provides:

• Specification of legal values within the type system
• Evaluation of values within the type system
• Erasure of machine representation of values until needed at execution time

Initial implementation uses typenum for type-level values and evaluation. There is an intent to migrate to type_eval when it's ready.

Should I use typus_fugit over fugit?

I cannot escape the fact that forking fugit fractures the ecosystem. Please do not use, or depend, on this crate, unless the topics of values at the type-level is of interest to you. This crate is, in significant part, motivated by assessing the reality of what a migration from const-generics to type-vals would look like.

Aims

• Try to stay in sync with fugit
  • If users wish to switch between the two, the process should be low-friction and relatively reliable
  • If fugit decides to migrate to types instead of consts, the result should not look very different to typus_fugit
• no_std library with goals of user-friendliness and performance first
  • Priority placed on type-level evaluation
  • When type-level evaluation isn't available, use const fn where the possible.
  • All timebase operations performed using type-level evaluation
• Support for both u32 and u64 backing storage with efficient instruction lowering on MCUs
  • On Cortex-M3 and up: no soft-impls pulled in for both u32 and u64 except when changing base on u64
  • Comparisons on u32 and u64 do not use division, only changing base with all constants calculated at compile time
• Selection of base happens at compile time, within the type-system.
  • A common problem is that run time changing of base robs us of a lot of optimization opportunities, but since types are used here, bases are evaluated at compile time.

Name

The original fugit name, as I understand it, comes from the latin phrase "tempus fugit", i.e. "time flies".

typus_fugit is a pun coming from said understanding.