Interoperability between Rust and C code is always dependent on transforming data between the two languages. For this purposes there are two dedicated modules in the stdlib called std::ffi and std::os::raw.

std::os::raw deals with low-level primitive types that can be converted implicitly by the compiler because the memory layout between Rust and C is similar enough or the same.

std::ffi provides some utility for converting more complex types such as Strings, mapping both &str and String to C-types that are easier and safer to handle.

Neither of these modules are available in core, but you can find a #![no_std] compatible version of std::ffi::{CStr,CString} in the cstr_core crate, and most of the std::os::raw types in the cty crate.

As mentioned above, primitive types can be converted by the compiler implicitly.

unsafe fn foo(num: u32) {
    let c_num: c_uint = num;
    let r_num: u32 = c_num;
}

A common requirement for including Rust in your embedded project is combining Cargo with your existing build system, such as make or cmake.

We are collecting examples and use cases for this on our issue tracker in issue #61.

Integrating Rust with an RTOS such as FreeRTOS or ChibiOS is still a work in progress; especially calling RTOS functions from Rust can be tricky.

We are collecting examples and use cases for this on our issue tracker in issue #62.