Optional Headers

Application app_opthdr requires module lib_mod0, and lib_mod0 supports an optional header file.

Optional headers are a module feature which allows module code to be conditionally compiled based on the presence of a header file in the application or another module. One use for this feature is to allow an application to override the definitions of constants in the module.

Directory structure

sandbox/
       |-- lib_mod0/
       |           |-- lib_mod0/
       |                       |-- api/
       |                       |-- lib_build_info.cmake
       |                       |-- src/
       |-- sw_opthdr/
                    |-- app_opthdr/
                                  |-- CMakeLists.txt
                                  |-- src/
                                         |-- mod0_conf.h
                                         |-- main.c

CMake file contents

sandbox/sw_opthdr/app_opthdr/CMakeLists.txt

cmake_minimum_required(VERSION 3.21)
include($ENV{XMOS_CMAKE_PATH}/xcommon.cmake)
project(opthdr)

set(APP_HW_TARGET XCORE-AI-EXPLORER)
set(APP_DEPENDENT_MODULES "lib_mod0")

XMOS_REGISTER_APP()

sandbox/lib_mod0/lib_mod0/lib_build_info.cmake

set(LIB_NAME lib_mod0)
set(LIB_VERSION 1.0.0)
set(LIB_INCLUDES api)
set(LIB_OPTIONAL_HEADERS mod0_conf.h)
set(LIB_DEPENDENT_MODULES "")

XMOS_REGISTER_MODULE()

Files in lib_mod0 (source or headers) can now conditionally compile code using preprocessor directives like

#ifdef __mod0_conf_h_exists__

For example, mod0_conf.h could be conditionally included into files in lib_mod0, so that the application can define or override constants in module lib_mod0.

Build instructions

Commands to configure and build the app, from working directory sandbox/sw_opthdr/app_opthdr:

cmake -G "Unix Makefiles" -B build
cd build
xmake