ocaml-bare-esp32

Bare metal, ESP-IDF free, OCaml running on ESP32 devices.

esp_bootloader: libboot.a

Contains the entry point in bootloader_start.c. This is taken from ESP-IDF because I don't know much about what's needed and what's not in ESP32 hardware initialization. It then calls OCaml runtime's entry point caml_startup provided by libasmrun.a.

libm.a libgcc.a

Provided with xtensa gcc toolchain.

ocaml-freestanding: libnolibc.a

Minimal standard library.

ocaml-esp32: libasmrun.a

OCaml runtime.

app: payload.o

OCaml application payload.

Installation

• git clone --recursive --depth 1 https://github.com/well-typed-lightbulbs/ocaml-baremetal-esp32: clone this repo and submodules.
• opam switch create mirage-32 ocaml-variants.4.07.1+32bit: need a 32-bit compiler switch for OCaml to build on esp32. The name is hardcoded in app/Makefile.
• opam remote add esp https://github.com/well-typed-lightbulbs/opam-cross-esp32: opam repository containing ESP32 cross-compilation tools.
• opam install gcc-toolchain-esp32 ocaml-esp32: GCC toolchain and OCaml cross-compiler for ESP32.

Compilation/execution

• make: builds app.elf.
• make flash: converts app.elf to app.bin and flashes it to the board -- you can tweak ESP32_PORT in Makefile.
• make monitor: opens the serial port -- Ctrl+] to leave.

Debugging

ESP32 has a JTAG interface that you can use to debug the processor with gdb. For ESP-WROVER kits it's JTAG over USB, so you don' need another cable. For more information: https://docs.espressif.com/projects/esp-idf/en/latest/api-guides/jtag-debugging/

Binary size

• payload: 79676

• nolibc: 41548

• asmrun: 86462

• libcc: 24241

• libm: 119727

• app.elf: 167814 (with --gc-sections)