Using nanopb in configurable library outside of application folder

[asteriskSF]

I am working on a project with multiple build variations off a common code base. All of the build variations use protobuf with nanopb but some of the protobuf files do not apply to some of the build variations. As an example there are multiple boards supported, each with multiple applications such as a manufacturing test application, and various customer-focused applications for different markets.

The general approach has been to place all these configurable library/modules into a folder where the CmakeLists.txt is conditionally included based on a Kconfig boolean flag such as CONFIG_LIB_OPTIONAL_PROTOBUF_COMPONENT1 Each of these conditional directories builds its files in a zephyr library, so the cmake usually has:

zephyr_include_directories(include)
zephyr_library()
zephyr_library_sources(library_source_file1.c)

The nanopb integration seems to be focused solely on protobuf files found directly in the application folder. This doesn't work in my application because the .proto files are share across multiple applications. In addition, they are actually placed into a submodule so the proto files can be shared with the mobile app developers.

I'm looking for advise on how to craft the configurable library's cmake file to:

• run protoc to convert the .proto into *.c and *.h
• compile *.c into a the zephyr_library()
• add the current directory into the include list

Also what should I have in the application cmake to trigger building the common nanopb files, although there are not any application specific protobuf files.

thanks for any help!

[asteriskSF]

@pdgendt Maybe you can give me some help, I see you have some experience with the nanopb targets!

[pdgendt]

Take a look at tests/modules/nanopb/lib/CMakeLists.txt, it demonstrates using the generated headers in a library.

[asteriskSF]

@pdgendt Thanks for your response..

From what I see, that example doesn't match what I'm trying to create.

I have multiple application folders. I also have multiple library folders with .proto files For maintainability, the code is structured with lib, boards, drivers folders outside of the application folder. This is based on the zephyr example_application: https://github.com/zephyrproject-rtos/example-application

I'm trying to create a structure like this;

lib/CMakeLIsts.txt
lib/Kconfig
lib/schemas/CMakeLIsts.txt
lib/schemas/Kconfig
lib/schemas/schema1/CMakeLists.txt
lib/schemas/schema1/Kconfig
lib/schemas/schema1/schema1.proto
lib/schemas/schema1/schema1.pb.c //generated files
lib/schemas/schema1/schema1.pb.h //generated files
lib/schemas/schema2/CMakeLists.txt
lib/schemas/schema2/Kconfig
lib/schemas/schema2/schema2.proto
lib/schemas/schema2/schema2.pb.c //generated files
lib/schemas/schema2/schema2.pb.h //generated files

The application directories are parallel to the lib/schema folders:

applications/mfg_app/CMakeLists.txt
applications/mfg_app/prj.conf
applications/mfg_app/src
applications/product_app/CMakeLists.txt
application/product_app/CmakeLists.txt

The application/prj.conf would only have a single additional line:
CONFIG_SCHEMA1=y
which would cause schema1 proto/c/h files to be automatically added into the build.

How do I add proto targets to generate the .c and .h files in the lib/schemas/schema1/CMakeLists.txt?

Perhaps we could make a PR to add a nanopb library to the example_application repo?

a*

[pdgendt]

I think you want to add the following in lib/schemas/schema1/CMakeLists.txt (and similar for schema2)

zephyr_library() # this creates a schema1 library target

# Make sure the c/h files are generated
zephyr_nanopb_sources(schema1
  schema1.proto
)

# Add the path of the generated header file to the global includes
zephyr_include_directories($CMAKE_CURRENT_BINARY_DIR)

In any of the application CMake files make sure to add a dependency on nanopb generated headers (so you can include them), e.g.

cmake_minimum_required(VERSION 3.20.0)

find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
project(mfg_app)

list(APPEND CMAKE_MODULE_PATH ${ZEPHYR_BASE}/modules/nanopb)
include(nanopb)

FILE(GLOB app_sources src/*.c)
target_sources(app PRIVATE ${app_sources})

if(CONFIG_SCHEMA1)
  # Make sure the headers are generated before building app
  add_dependencies(app nanopb_generated_headers)

  add_subdirectory(lib/schemas/schema1)
  target_link_libraries(app PRIVATE schema1)
endif()

[asteriskSF]

@pdgendt This is helping, I made some progress but not quite there yet.

I did have to make a change, the library name from zephyr_library is complicated but its available from a variable $ZEPHYR_CURRENT_LIBRARY.

I put this is the lib/schema1/CMakeLists.txt:

zephyr_include_directories($CMAKE_CURRENT_BINARY_DIR)
zephyr_nanopb_sources(${ZEPHYR_CURRENT_LIBRARY} schema1.proto)

I also put this in the app/CMakeLists.txt

project(app LANGUAGES C)

list(APPEND CMAKE_MODULE_PATH ${ZEPHYR_BASE}/modules/nanopb)
include(nanopb)

target_sources(app PRIVATE src/main.c)

add_dependencies(app nanopb_generated_headers)

I didn't put the CONFIG_SCHEMA1 in the app directory since that is included from lib\CMakeLists.txt based on a Kconfig from lib\schema1\Kconfig

However I still have a problem.

I have an additional library we'll call it lib1, which provides functions using schema1. Its header file lib1.h includes schema1.pb.h..

When I compile main.c which include lib1.h and schema1.h

In file included from XXX/app/src/main.c:16:
XXX/lib/lib1/include/lib1.h:14:10: fatal error: schema1.pb.h: No such file or directory
14 | #include "schema1.pb.h"
| ^~~~~~~~~~~~~~~~~~
compilation terminated.

It seems like main.c is compiled before hud_control.pb.h is generated or possibly the include directory is not setup correctly.

I did find the schema1.pb.h is generated in the build directory
find ./ -name "schema1*" -print
./build/modules/app.git/lib/schema1
./build/modules/app.git/lib/schema1/schema1.pb.c
./build/modules/app.git/lib/schema1/schema1.pb.h

Any ideas?

[pdgendt]

Any CMake target that includes a generated nanopb header needs to add

add_dependencies(<target> nanopb_generated_headers)

That should ensure that the headers are generated before compiling any source in the target. Also note that zephyr_include_directories works for zephyr targets, but not for "vanilla" CMake targets.

You could try to add the following in schema1/CMakeLists.txt instead

include_directories($CMAKE_CURRENT_BINARY_DIR)

[asteriskSF]

I think I have it working now.

In the lib/schema1/CMakeLists.txt I have:

list(APPEND CMAKE_MODULE_PATH ${ZEPHYR_BASE}/modules/nanopb)
include(nanopb)

zephyr_library()
zephyr_include_directories(${CMAKE_CURRENT_BINARY_DIR})
zephyr_nanopb_sources(${ZEPHYR_CURRENT_LIBRARY} schema1.proto)

In my previous code I had forgotten the braces around CMAKE_CURRENT_BINARY_DIR

[pdgendt]

Hey @asteriskSF, if you think this is fixed, can you close the discussion?

[asteriskSF]

I have it working, thanks for the help!