Compiling external CPP modules

[steoj]

Have been reading the docs on this and it seems there are two paths on buliding external C/C++ micropython modules: Make and CMake.
Trying to compile a c++ module for a port/esp8266 it seems the module is not included unless using
make USER_C_MODULES=../../examples/usercmodule
But then I get the error message:

In file included from lib/micropython/examples/usercmodule/cppexample/example.cpp:2:0:
lib/micropython/examples/usercmodule/cppexample/examplemodule.h:2:24: fatal error: py/runtime.h: No such file or directory
 #include "py/runtime.h"

Am I missing something, or is it just not possible to compile C++ modules as external modules for esp8266 port?

Using USER_C_MODULES=../../examples/usercmodule/micropython.cmake does not include any of the example modules at all.

[jimmo]

there are two paths on buliding external C/C++ micropython modules: Make and CMake.

@steoj Make or CMake is entirely dependent on which microcontroller you're using (because we match the vendor's SDK). For ESP8266 you must use Make.

is it just not possible to compile C++ modules as external modules for esp8266 port?

Yeah this looks like when C++ support was added, the ESP8266 port was missed, and the C++ compilation is not inheriting the right flags (which is why it's not getting the correct include paths). You need to add something like this to ports/esp8266/Makefile:

CXXFLAGS += $(filter-out -Wmissing-prototypes -Wold-style-definition -std=gnu99,$(CFLAGS))

Put it just above the line:

# Options for mpy-cross
MPY_CROSS_FLAGS += -march=xtensa

[jimmo]

Raised #14178 to fix.

[steoj]

Thank you. Got a little further:

LINK  build/firmware.elf
xtensa-lx106-elf-ld: cannot find -lstdc++
make[1]: *** [Makefile:210: build/firmware.elf] Error 1
make[1]: Leaving directory 'lib/micropython/ports/esp8266'
make: *** [Makefile:38: firmware] Error 2

Seems like the lib/micropython/examples/usercmodule/cppexample/micropython.mk contains the line:

LDFLAGS_USERMOD += -lstdc++

Removing this seems to fix the problem and I can load, run and test the cpp function:

>>> import cppexample
>>> cppexample.cppfunc(2,3)
(5, 'hellocpp')
>>> 

Context: I have made a Makefile at the root of the project I'm working on and this makefile includes the esp8266 port make as well.

USER_C_MODULES ?= $(abspath lib/micropython/examples/usercmodule)

is defined in this makefile

[jimmo]

@steoj How are you setting up the ESP8266 toolchain? I didn't run into this issue.

FWIW, I use the process described in the "Building with a local toolchain" section of ports/esp8266/README.md.

[steoj]

Using the same instructions but running the docker image:

docker run --rm -v $HOME:$HOME -u $UID -w $PWD larsks/esp-open-sdk make v=1  -j BOARD=ESP8266_GENERIC

Im on a Mack M3 Pro, and installing the Espressif toolchain proves to be a little difficult. Standard Setup of Toolchain for Mac OS kinda works, but the compiler is throwing

xtensa-lx106-elf-gcc: error: unrecognized command line option '-mforce-l32'; did you mean '--force-link'?
-e See https://github.com/micropython/micropython/wiki/Build-Troubleshooting

at me. The troubleshooting does not give me much.

[dpgeorge]

You need a custom version of the xtensa-lx106-elf-gcc compiler, which supports the command -mforce=l32.

I'm not sure exactly how to get this all working on a Mac, using a Docker image is probably the easiest way to do it. In that case you can try installing the custom compiler using the commands from tools/ci.sh:

function ci_esp8266_setup {
    sudo pip install pyserial esptool==3.3.1
    wget https://github.com/jepler/esp-open-sdk/releases/download/2018-06-10/xtensa-lx106-elf-standalone.tar.gz
    zcat xtensa-lx106-elf-standalone.tar.gz | tar x
    # Remove this esptool.py so pip version is used instead
    rm xtensa-lx106-elf/bin/esptool.py
}