compiler specifics

set(CMAKE_SYSTEM_NAME Generic)
set(CMAKE_SYSTEM_PROCESSOR arm)

set(CMAKE_CXX_COMPILER clang++)
set(CMAKE_CXX_COMPILER_TARGET clang++)

# utilities
set(OBJCOPY llvm-objcopy)
set(OBJDUMP llvm-objdump)
set(SIZE llvm-size)

# setup C++17 required compiler standard
set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED on)
set(CMAKE_CXX_EXTENSIONS off)

function (setup_custom_compiler_flags)
    set(NRTI_FLAGS "-fno-rtti -fno-exceptions -fno-unwind-tables")
    set(CLANG_FLAGS "-target thumbv7em-unkown-none-eabi")
    set(ARCH_FLAGS "${CLANG_FLAGS} -march=armv7e-m -mcpu=cortex-m4")
    set(TARGET_CFLAGS "${ARCH_FLAGS} -nostdinc -g")
    set(TARGET_FLAGS "-mlittle-endian -nostdlib -fno-common -fno-pic")
    set(COMMON_FLAGS "${NRTI_FLAGS} ${TARGET_FLAGS} ${TARGET_CFLAGS}")

    set(WARN_FLAGS "-Wall -Wextra")
    set(OPTIMIZE_FLAGS "-ffreestanding -fomit-frame-pointer")

    set(EXTEND_FLAGS "${WARN_FLAGS} ${OPTIMIZE_FLAGS}")

    set(CMAKE_CXX_FLAGS "${COMMON_FLAGS} ${EXTEND_FLAGS}"
        CACHE INTERNAL "cxx compiler flags")
endfunction()

function (setup_custom_linker_flags LINKER_SCRIPT TARGET)
    get_filename_component(SCRIPT_PATH "${LINKER_SCRIPT}" PATH)
    set(CMAKE_CXX_LINK_FLAGS
        "-L${SCRIPT_PATH} -Wl,-T${LINKER_SCRIPT} -Wl,-Map,${TARGET}.map"
        CACHE INTERNAL "cxx linker flags")
endfunction()

function (setup_custom_target_properties TARGET)
    set(BIN_FILE ${TARGET}.bin)
    add_custom_command(TARGET ${TARGET} POST_BUILD
        COMMAND ${OBJCOPY} -O binary $<TARGET_FILE:${TARGET}> ${BIN_FILE}
        COMMENT "BUILDING ${BIN_FILE}"
        COMMAND ${OBJDUMP} -triple=thumbv7em -disassemble $<TARGET_FILE:${TARGET}> > ${TARGET}.dis
        COMMENT "CREATING ${TARGET}.dis"
        COMMAND ${SIZE} $<TARGET_FILE:${TARGET}>
    )
endfunction()