I've got native OCaml code running! It seems to pass all the runtime tests, and as I fixed some GC segfaults I'm now pretty confident in the backend code. It's not optimized at all, but you can now experiment with OCaml on ESP32 MCUs.
# OCaml cross-compiler installation
Switch opam to OCaml version 4.06 or a 4.07 as only these two versions are supported, using the
opam switch command.
Add my cross-compilation repository in opam, with:
opam repo add cross-esp32 https://github.com/TheLortex/opam-cross-esp32.git
After that, you'll be able to install the cross-compiler, with:
opam install ocaml-esp32
You now have an OCaml cross-compiler for esp32 installed in
# Cross-compiling OCaml libraries
Your favorite build system can already cross-compile code. You can either use
jbuilder build -x esp32 ...
ocamlfind -toolchain esp32 ...
env OCAMLFIND_TOOLCHAIN=esp32 ocamlbuild ...to build libraries.
The libraries used by these build systems are located in
~/.opam/<switch>/esp32-sysroot/lib/. A good thing to know is that jbuilder automatically makes the difference between host code and target code, hence enabling the use of ppx tools.
# Building an ESP32 application
To build an esp32 application, you'll need to link native code with the ESP-Iot Development Framework which contains libraries, bootloader code and linker scripts.
Hello caml is an example of project structure using jbuilder that builds a flashable binary for esp32.
Basically, it's not complicated:
- Build and ship OCaml code into a single object:
- using the
-output-complete-objoption on the native compiler
jbuilder build -x esp32 _build/default.esp32/main.exe.othat will automatically use the option.
- using the
- This object file's entry point is
caml_main. So the next thing to do is create a
startup-c.cfile that defines a function
- Then everything needs to be linked together, and the ESP32 framework takes the lead to create the final binary.