This pull request includes BinSem, CountSem, and MutSem, wrappers for the three types of synchronization primitive provided by OSAL, as well as wrappers for CFE_ES_CreateChildTask and CFE_ES_ExitChildTask.

Adding just the latter part was my original intent, but my desire for a more idiomatic interface to CFE_ES_CreateChildTask led to me needing the former.

In the places we're using S: AsRef<CStr>, we only ever deal with references to S.

The implicit Sized bound is thus unnecessarily restrictive (and in some contexts, actively obstructive), so this PR removes it.

Now that Rust 1.64.0 has landed, the C FFI types we need in n2o4 and cfs-sys are available in core::ffi on stable Rust.

This pull request has the following effects:

• Switches from using libc::c_* to core::ffi::c_*, removing the need for the libc crate as a dependency
• Genericizes (null-terminated) string parameters beyond just printf_wrap::NullString to any implementer of AsRef<CStr> (as CStr's available in #[no_std] land now)

Resolves #3.

Issue BlackCAT-CubeSat/printf-wrap#1 should make the printf-wrap crate unconditionally #[no_std] on Rust ≥1.64.0 and remove the dependency on the libc crate. Once that comes out, we should propagate those changes to n2o4 and cfs-sys.

Relevant bits include Cargo.toml as well as stuff scattered throughout the Rust source (idea: change NullString arguments to be AsRef<CStr> instead?).

This PR includes three additions:

• A consuming constructor for CStrBuf
• Splitting the "absolute time" and "time delta" roles of cfe::time::SysTime into separate types (SysTime and DeltaTime, respectively)
• Implementing operations on SysTime and DeltaTime

The latter two are of use for current development of an internal app; the first should be useful for some future bindings work.

Each Rust-based cFS app is compiled separately. Often, they have many of the same dependencies (n2o4, bindgen, etc.), and it would be nice to leverage that to speed up compilation.

Need to find out how to do that safely.

As a crate which isn't being released on crates.io currently, we don't just get online docs for free from docs.rs. Hand-maintaining generation is tedious and prone to errors of omission; as such, we should probably set up a GitHub workflow for building the docs upon an update of the main branch, generating the HTML and pushing it onto the gh-pages branch.

Right now, with the use of printf-wrap, n2o4 has decent support for printf(3)-type formatting with syslog entries and events. However, Rust has its own string-formatting system. It would be good to support using that instead when making syslog entries or events for a more Rustic experience.

Some things that may come in handy when creating that:

core::write core::fmt::Write core::format_args

In particular, implementing Write for a "[u8; N] plus index-into-buffer" type would allow all this to be done without heap allocations.

Currently, the n2o4 and cfs-sys crates only support a specific version of cFE and OSAL:

• cFE tag v7.0.0-rc4
• OSAL tag v6.0.0-rc4

As these are the versions of the respective libraries we're using in the BlackCAT flight software, this has been OK for development so far. However, n2o4 should ideally be usable on as wide a range of setups as possible, and that means being able to support other versions of cFE and OSAL.

Right now, it's not clear to me how to modify the current system to support multiple library versions. cfs-sys just tries to bindgen everything it can (with some manual additions), with no awareness of what versions of cFE and OSAL it's working with. n2o4 does no version detection whatsoever, and manually trying to track which APIs are available in which versions of {cFE, OSAL} (and with which signatures) sounds like it would be tedious and error-prone.

So, are there good ways to automate or semi-automate this?