esp-pacs VS esp-storage

The no-std ecosystem follows the same layering approach that exists within embedded Rust. In embedded Rust, there are several levels of abstraction that are introduced on top of microcontroller hardware as shown in the figure below. The first level is the peripheral access crate (PAC) which gives us access to low-level microcontroller registers at the bit level. It's also worth noting that the PAC is specific to a particular microcontroller series. For ESP devices the different PACs are captured in the esp-pacs repository. The microarchitecture crate is at a similar abstraction level to the PAC but specific to processor core (Ex. RISC-V) functions.

Among these several abstractions, we can program a microcontroller device at any level we like. Additionally, we can develop code with a mix of low-level and high-level abstractions. Obviously, to make code more portable it's better to stick to higher-level abstractions. Also in addition to the above, there exists other crates supporting other functions in no-std development. These include wifi services in the esp-wifi repository, heap allocators in the esp-alloc repository, logging features in the esp-println repository, exception handlers in the esp-backtrace repository, and finally embedded storage traits in the esp-storage repository.