Nuttx編譯系統

配置

Nuttx在編譯之前需要先進行配置，而Nuttx是一個高度可配置的RTOS，Nuttx的配置檔案使用kconfig-frontends 工具來維護，配置工具將使用Kconfig 檔案，而Kconfig 檔案在Nuttx的程式碼資料夾中隨處可見。每一個Kconfig 檔案包含了配置變數的宣告，而每一個配置變數又給Nuttx提供了一種配置選擇，Nuttx的最終配置都由這些Kconfig 檔案決定。

一般進行Nuttx配置的時候，都可以在Nuttx根目錄中通過make menuconfig 命令來操作，前提是在根目錄中需要有.config 檔案存在，而.config 檔案是從某個特定的開發板中的某個路徑下拷貝過來的。

Copy configs/<board-name>/[<config-dir>/]Make.defs to ${TOPDIR}/Make.defs
Copy configs/<board-name>/[<config-dir>/]defconfig to ${TOPDIR}/.config

每個特定的開發板資料夾中都有兩個檔案Make.defs 和defconfig 檔案來描述該開發板的配置。

Tools: CC, LD, AR, NM, OBJCOPY, OBJDUMP
Tools options: CFLAGS, LDFLAGS

defconfig

defconfig 檔案中包含一些如CONFIG_VARIABLE=value 形式的定義，它拷貝至$(TOPDIR) 路徑下後，在編譯時會被其他Makefile 所包含，並且會用它來生成include/nuttx/config.h 檔案，這個檔案在很多C檔案中會用到。

編譯

大概的目錄組織如下：

build
|-nuttx
||
|- Makefile
|-apps
||
|- Makefile

講這麼多，還是直接從Makefile開始入手跟蹤吧。在$(TOPDIR) 目錄中，Makefile 內容如下：

...
-include .config#將.config檔案包含進來，其中`-`表示如果.config檔案不存在，Makefile也不會報錯，並繼續執行
ifeq ($(CONFIG_WINDOWS_NATIVE),y)
include Makefile.win
else
include Makefile.unix#根據編譯環境，選擇對應的Makefile，真正的入口
endif

下面將分別介紹上面講到的檔案，核心是圍繞Makefile.unix 檔案。

.config

整個.config 檔案內容格式如下所示，用來定義配置選項，在編譯時需要用到。

...
# Build Setup
#
# CONFIG_EXPERIMENTAL is not set
# CONFIG_DEFAULT_SMALL is not set
CONFIG_HOST_LINUX=y
# CONFIG_HOST_OSX is not set
# CONFIG_HOST_WINDOWS is not set
# CONFIG_HOST_OTHER is not set

#
# Build Configuration
#
CONFIG_APPS_DIR="../apps"
CONFIG_BUILD_FLAT=y
# CONFIG_BUILD_2PASS is not set
...

tools/Config.mk

在Config.mk 檔案中，定義瞭如PREPROCESS, COMPILE, COMPILEXX, ASSEMBLE, ARCHIVE, DELFILE 等通用巨集，在其他檔案中將使用$(call XXX, in-file, out-file) 形式來使用，其中XXX 表示定義的這些巨集。

# These are configuration variables that are quoted by configuration tool
# but which must be unquoated when used in the build system.

# 調整架構相關巨集的值，其中patsubst為Makefile匹配與替換函式，strip為去空格函式
CONFIG_ARCH:= $(patsubst "%",%,$(strip $(CONFIG_ARCH)))
CONFIG_ARCH_CHIP:= $(patsubst "%",%,$(strip $(CONFIG_ARCH_CHIP)))
CONFIG_ARCH_BOARD := $(patsubst "%",%,$(strip $(CONFIG_ARCH_BOARD)))

# Some defaults just to prohibit some bad behavior if for some reason they
# are not defined

OBJEXT ?= .o
LIBEXT ?= .a

# DELIM - Path segment delimiter character
#
# Depends on this settings defined in board-specific defconfig file installed
# at $(TOPDIR)/.config:
#
#CONFIG_WINDOWS_NATIVE - Defined for a Windows native build
# 定義DELIM分隔符
ifeq ($(CONFIG_WINDOWS_NATIVE),y)
DELIM = $(strip \)
else
DELIM = $(strip /)
endif

# INCDIR - Convert a list of directory paths to a list of compiler include
#directirves
# Example: CFFLAGS += ${shell $(INCDIR) [options] "compiler" "dir1" "dir2" "dir2" ...}
#
# Note that the compiler string and each directory path string must quoted if
# they contain spaces or any other characters that might get mangled by the
# shell
#
# Depends on this setting passed as a make commaond line definition from the
# toplevel Makefile:
#
#TOPDIR - The path to the top level NuttX directory in the form
#appropriate for the current build environment
#
# Depends on this settings defined in board-specific defconfig file installed
# at $(TOPDIR)/.config:
#
#CONFIG_WINDOWS_NATIVE - Defined for a Windows native build

ifeq ($(CONFIG_WINDOWS_NATIVE),y)
INCDIR = "$(TOPDIR)\tools\incdir.bat"
else
INCDIR = "$(TOPDIR)/tools/incdir.sh"
endif

# PREPROCESS - Default macro to run the C pre-processor
# Example: $(call PREPROCESS, in-file, out-file)
#
# Depends on these settings defined in board-specific Make.defs file
# installed at $(TOPDIR)/Make.defs:
#
#CPP - The command to invoke the C pre-processor
#CPPFLAGS - Options to pass to the C pre-processor
# 預處理巨集
define PREPROCESS
@echo "CPP: $1->$2"
$(Q) $(CPP) $(CPPFLAGS) $1 -o $2
endef

# COMPILE - Default macro to compile one C file
# Example: $(call COMPILE, in-file, out-file)
#
# Depends on these settings defined in board-specific Make.defs file
# installed at $(TOPDIR)/Make.defs:
#
#CC - The command to invoke the C compiler
#CFLAGS - Options to pass to the C compiler

define COMPILE
@echo "CC: $1"
$(Q) $(CC) -c $(CFLAGS) $1 -o $2
endef

# COMPILEXX - Default macro to compile one C++ file
# Example: $(call COMPILEXX, in-file, out-file)
#
# Depends on these settings defined in board-specific Make.defs file
# installed at $(TOPDIR)/Make.defs:
#
#CXX - The command to invoke the C++ compiler
#CXXFLAGS - Options to pass to the C++ compiler

define COMPILEXX
@echo "CXX: $1"
$(Q) $(CXX) -c $(CXXFLAGS) $1 -o $2
endef

# ASSEMBLE - Default macro to assemble one assembly language file
# Example: $(call ASSEMBLE, in-file, out-file)
#
# NOTE that the most common toolchain, GCC, uses the compiler to assemble
# files because this has the advantage of running the C Pre-Processor against
# the assembly language files.This is not possible with other toolchains;
# platforms using those other tools should define AS and over-ride this
# definition in order to use the assembler directly.
#
# Depends on these settings defined in board-specific Make.defs file
# installed at $(TOPDIR)/Make.defs:
#
#CC - By default, the C compiler is used to compile assembly language
#files
#AFLAGS - Options to pass to the C+compiler

define ASSEMBLE
@echo "AS: $1"
$(Q) $(CC) -c $(AFLAGS) $1 -o $2
endef

# MOVEOBJ - Default macro to move an object file to the correct location
# Example: $(call MOVEOBJ, prefix, directory)
#
# This is only used in directories that keep object files in sub-directories.
# Certain compilers (ZDS-II) always place the resulting files in the the
# directory where the compiler was invoked with not option to generate objects
# in a different location.

define MOVEOBJ
endef

# ARCHIVE - Add a list of files to an archive
# Example: $(call ARCHIVE, archive-file, "file1 file2 file3 ...")
#
# Note: The fileN strings may not contain spaces orcharacters that may be
# interpreted strangely by the shell
#
# Depends on these settings defined in board-specific Make.defs file
# installed at $(TOPDIR)/Make.defs:
#
#AR - The command to invoke the archiver (includes any options)
#
# Depends on this settings defined in board-specific defconfig file installed
# at $(TOPDIR)/.config:
#
#CONFIG_WINDOWS_NATIVE - Defined for a Windows native build

ifeq ($(CONFIG_WINDOWS_NATIVE),y)
define ARCHIVE
@echo AR: $2
$(Q) $(AR) $1 $(2)
endef
else
define ARCHIVE
@echo "AR: $2"
$(Q) $(AR) $1 $(2) || { echo "$(AR) $1 FAILED!" ; exit 1 ; }
endef
endif

# PRELINK - Prelink a list of files
# This is useful when files were compiled with fvisibility=hidden.
# Any symbol which was not explicitly made global is invisible outside the
# prelinked file.
#
# Example: $(call PRELINK, prelink-file, "file1 file2 file3 ...")
#
# Note: The fileN strings may not contain spaces orcharacters that may be
# interpreted strangely by the shell
#
# Depends on these settings defined in board-specific Make.defs file
# installed at $(TOPDIR)/Make.defs:
#
#LD - The command to invoke the linker (includes any options)
#OBJCOPY - The command to invoke the object cop (includes any options)
#
# Depends on this settings defined in board-specific defconfig file installed
# at $(TOPDIR)/.config:
#
#CONFIG_WINDOWS_NATIVE - Defined for a Windows native build

ifeq ($(CONFIG_WINDOWS_NATIVE),y)
define PRELINK
@echo PRELINK: $1
$(Q) $(LD) -Ur -o $1 $2 && $(OBJCOPY) --localize-hidden $1
endef
else
define PRELINK
@echo "PRELINK: $1"
$(Q) $(LD) -Ur -o $1 $2 && $(OBJCOPY) --localize-hidden $1
endef
endif

# DELFILE - Delete one file

ifeq ($(CONFIG_WINDOWS_NATIVE),y)
define DELFILE
$(Q) if exist $1 (del /f /q $1)
endef
else
define DELFILE
$(Q) rm -f $1
endef
endif

# DELDIR - Delete one directory

ifeq ($(CONFIG_WINDOWS_NATIVE),y)
define DELDIR
$(Q) if exist $1 (rmdir /q /s $1)
endef
else
define DELDIR
$(Q) rm -rf $1
endef
endif

# MOVEFILE - Move one file

ifeq ($(CONFIG_WINDOWS_NATIVE),y)
define MOVEFILE
$(Q) if exist $1 (move /Y $1 $2)
endef
else
define MOVEFILE
$(Q) mv -f $1 $2
endef
endif

# CLEAN - Default clean target

ifeq ($(CONFIG_WINDOWS_NATIVE),y)
define CLEAN
$(Q) if exist *$(OBJEXT) (del /f /q *$(OBJEXT))
$(Q) if exist *$(LIBEXT) (del /f /q *$(LIBEXT))
$(Q) if exist *~ (del /f /q *~)
$(Q) if exist (del /f /q.*.swp)
endef
else
define CLEAN
$(Q) rm -f *$(OBJEXT) *$(LIBEXT) *~ .*.swp
endef
endif

Make.defs

Make.defs 中定義了一些板級相關的巨集定義。

# 包含需要依賴的檔案
include ${TOPDIR}/.config 
include ${TOPDIR}/tools/Config.mk 
include ${TOPDIR}/arch/arm/src/arm/Toolchain.defs

ifeq ($(WINTOOL),y)
# Windows-native toolchains
DIRLINK = $(TOPDIR)/tools/copydir.sh
DIRUNLINK = $(TOPDIR)/tools/unlink.sh
MKDEP = $(TOPDIR)/tools/mkwindeps.sh
ARCHINCLUDES = -I. -isystem "${shell cygpath -w $(TOPDIR)/include}"
ARCHXXINCLUDES = -I. -isystem "${shell cygpath -w $(TOPDIR)/include}" -isystem "${shell cygpath -w $(TOPDIR)/include/cxx}"
ARCHSCRIPT = -T "${shell cygpath -w $(TOPDIR)/configs/$(CONFIG_ARCH_BOARD)/scripts/ld.script}"
else
# Linux/Cygwin-native toolchain在Linux環境下使用的工具鏈
MKDEP = $(TOPDIR)/tools/mkdeps$(HOSTEXEEXT)
ARCHINCLUDES = -I. -isystem $(TOPDIR)/include
ARCHXXINCLUDES = -I. -isystem $(TOPDIR)/include -isystem $(TOPDIR)/include/cxx -isystem $(TOPDIR)/include/uClibc++
ARCHSCRIPT = -T$(TOPDIR)/configs/<board-name>/$(CONFIG_ARCH_BOARD)/scripts/ld.script
endif

# 定義工具，其中$(CROSSDEV)在$(TOPDIR)/arch/arm/src/arm/Toolchain.defs檔案中定義
CC = $(CROSSDEV)gcc
CXX = $(CROSSDEV)g++
CPP = $(CROSSDEV)gcc -E
LD = $(CROSSDEV)ld
AR = $(CROSSDEV)ar rcs
NM = $(CROSSDEV)nm
OBJCOPY = $(CROSSDEV)objcopy
OBJDUMP = $(CROSSDEV)objdump

# 編譯器版本
ARCHCCVERSION = ${shell $(CC) -v 2>&1 | sed -n '/^gcc version/p' | sed -e 's/^gcc version \([0-9\.]\)/\1/g' -e 's/[-\ ].*//g' -e '1q'}
ARCHCCMAJOR = ${shell echo $(ARCHCCVERSION) | cut -d'.' -f1}

ifeq ($(CONFIG_DEBUG_SYMBOLS),y)
ARCHOPTIMIZATION = -g
ARCHOPTIMIZATION += -fno-omit-frame-pointer -mapcs -mno-sched-prolog
endif

ifneq ($(CONFIG_DEBUG_NOOPT),y)
ARCHOPTIMIZATION += $(MAXOPTIMIZATION) -fno-strict-aliasing -fno-strength-reduce -fomit-frame-pointer
endif

ifeq ($(ARCHCCMAJOR),4)
ARCHCPUFLAGS = -mtune=arm9tdmi -march=armv5te -mfloat-abi=soft -fno-builtin
else
ARCHCPUFLAGS = -mapcs-32 -mtune=arm9tdmi -march=armv5te -msoft-float -fno-builtin
endif

ARCHCFLAGS = -fno-builtin
ARCHCXXFLAGS = -fno-builtin -fno-exceptions -fcheck-new-fpermissive -fno-rtti
ARCHWARNINGS = -Wall -Wstrict-prototypes -Wshadow -Wundef
ARCHWARNINGSXX = -Wall -Wshadow -Wundef
ARCHDEFINES =
ARCHPICFLAGS = -fpic -msingle-pic-base -mpic-register=r10

# 定義所有編譯時的FLAG選項
CFLAGS = $(ARCHCFLAGS) $(ARCHWARNINGS) $(ARCHOPTIMIZATION) $(ARCHCPUFLAGS) $(ARCHINCLUDES) $(ARCHDEFINES) $(EXTRADEFINES) -pipe
CPICFLAGS = $(ARCHPICFLAGS) $(CFLAGS)
CXXFLAGS = $(ARCHCXXFLAGS) $(ARCHWARNINGSXX) $(ARCHOPTIMIZATION) $(ARCHCPUFLAGS) $(ARCHXXINCLUDES) $(ARCHDEFINES) $(EXTRADEFINES) -std=c++11 -pipe
CXXPICFLAGS = $(ARCHPICFLAGS) $(CXXFLAGS)
CPPFLAGS = $(ARCHINCLUDES) $(ARCHDEFINES) $(EXTRADEFINES)
AFLAGS = $(CFLAGS) -D__ASSEMBLY__

NXFLATLDFLAGS1 = -r -d -warn-common
NXFLATLDFLAGS2 = $(NXFLATLDFLAGS1) -T$(TOPDIR)/binfmt/libnxflat/gnu-nxflat-gotoff.ld -no-check-sections
LDNXFLATFLAGS = -e main -s 2048

# 定義檔案字尾
ASMEXT = .S
OBJEXT = .o
LIBEXT = .a
EXEEXT =

ifneq ($(CONFIG_ARM_TOOLCHAIN),BUILDROOT)
LDFLAGS += -nostartfiles -nodefaultlibs
endif
ifeq ($(CONFIG_DEBUG_SYMBOLS),y)
LDFLAGS += -g
endif

# 定義Host的編譯器
HOSTCC = gcc
HOSTINCLUDES = -I.
HOSTCFLAGS = -Wall -Wstrict-prototypes -Wshadow -Wundef -g -pipe
HOSTLDFLAGS =

Directories.mk

Directories.mk主要 定義了NUTTX_ADDONS 和USER_ADDONS ，其中NUTTX_ADDONS 包含了一系列資料夾，最終將編譯進Nuttx核心中，而USER_ADDONS 包含了一系列資料夾，最終會編譯進Apps中。Directories.mk 將Nuttx核心中的資料夾都包含了進來。

# All add-on directories.
#
# NUTTX_ADDONS is the list of directories built into the NuttX kernel.
# USER_ADDONS is the list of directories that will be built into the user
#application

NUTTX_ADDONS :=
USER_ADDONS :=

# In the protected build, the applications in the apps/ directory will be
# into the userspace; in the flat build, the applications will b built into
# the kernel space.But in the kernel build, the applications will not be
# built at all by this Makefile.

ifeq ($(CONFIG_BUILD_PROTECTED),y)
USER_ADDONS += $(APPDIR)
else
ifneq ($(CONFIG_BUILD_KERNEL),y)
NUTTX_ADDONS += $(APPDIR)
endif
endif

# Lists of build directories.
#
# FSDIRS depend on file descriptor support; NONFSDIRS do not (except for parts
#of FSDIRS).We will exclude FSDIRS from the build if file descriptor
#support is disabled.NOTE that drivers, in general, depends on file
#descriptor support but is always built because there are other components
#in the drivers directory that are needed even if file descriptors are not
#supported.
# CONTEXTDIRS include directories that have special, one-time pre-build
#requirements.Normally this includes things like auto-generation of
#configuration specific files or creation of configurable symbolic links
# USERDIRS - When NuttX is build is a monolithic kernel, this provides the
#list of directories that must be built
# OTHERDIRS - These are directories that are not built but probably should
#be cleaned to prevent garbage from collecting in them when changing
#configurations.

NONFSDIRS = sched drivers configs $(ARCH_SRC) $(NUTTX_ADDONS)
FSDIRS = fs binfmt
CONTEXTDIRS = configs $(APPDIR)
USERDIRS =
OTHERDIRS = lib

ifeq ($(CONFIG_BUILD_PROTECTED),y)

USERDIRS += libc mm $(USER_ADDONS)
ifeq ($(CONFIG_HAVE_CXX),y)
USERDIRS += libxx
endif

else
ifeq ($(CONFIG_BUILD_KERNEL),y)

USERDIRS += libc mm
ifeq ($(CONFIG_HAVE_CXX),y)
USERDIRS += libxx
endif

else

NONFSDIRS += libc mm
OTHERDIRS += $(USER_ADDONS)
ifeq ($(CONFIG_HAVE_CXX),y)
NONFSDIRS += libxx
else
OTHERDIRS += libxx
endif

endif
endif

ifeq ($(CONFIG_LIB_SYSCALL),y)
NONFSDIRS += syscall
CONTEXTDIRS += syscall
USERDIRS += syscall
else
OTHERDIRS += syscall
endif

ifeq ($(CONFIG_LIB_ZONEINFO_ROMFS),y)
CONTEXTDIRS += libc
endif

ifeq ($(CONFIG_NX),y)
NONFSDIRS += graphics libnx
CONTEXTDIRS += graphics libnx
else
OTHERDIRS += graphics libnx
endif

ifeq ($(CONFIG_AUDIO),y)
NONFSDIRS += audio
else
OTHERDIRS += audio
endif

ifeq ($(CONFIG_DRIVERS_WIRELESS),y)
NONFSDIRS += wireless
else
OTHERDIRS += wireless
endif

# CLEANDIRS are the directories that will clean in.These are
#all directories that we know about.
# KERNDEPDIRS are the directories in which we will build target dependencies.
#If NuttX and applications are built separately (CONFIG_BUILD_PROTECTED or
#CONFIG_BUILD_KERNEL), then this holds only the directories containing
#kernel files.
# USERDEPDIRS. If NuttX and applications are built separately (CONFIG_BUILD_PROTECTED),
#then this holds only the directories containing user files. If
#CONFIG_BUILD_KERNEL is selected, then applications are not build at all.

CLEANDIRS= $(NONFSDIRS) $(FSDIRS) $(USERDIRS) $(OTHERDIRS)
KERNDEPDIRS = $(NONFSDIRS)
USERDEPDIRS = $(USERDIRS)

# Add file system directories to KERNDEPDIRS (they are already in CLEANDIRS)

ifeq ($(CONFIG_NFILE_DESCRIPTORS),0)
ifeq ($(CONFIG_NET),y)
ifneq ($(CONFIG_NSOCKET_DESCRIPTORS),0)
KERNDEPDIRS += fs
endif
KERNDEPDIRS += drivers
endif
else
KERNDEPDIRS += $(FSDIRS)
endif

# Add networking directories to KERNDEPDIRS and CLEANDIRS

ifeq ($(CONFIG_NET),y)
KERNDEPDIRS += net
endif
CLEANDIRS += net

ifeq ($(CONFIG_CRYPTO),y)
KERNDEPDIRS += crypto
endif
CLEANDIRS += crypto

FlatLibs.mk

記憶體配置在Flat模式情況下，會使用FlatLibs.mk 檔案，該檔案主要定義NUTTXLIBS 和USERLIBS ，其中NUTTXLIBS 包含了一系列的庫檔案，最終用於特定處理器來編譯Nuttx Image ，USERLIBS 包含一系列庫檔案用於使用者層的Apps。此外，還定義了EXPORTLIBS ，用於在make export 時，生成庫檔案。

# NUTTXLIBS is the list of NuttX libraries that is passed to the
#processor-specific Makefile to build the final NuttX target.
#Libraries in FSDIRS are excluded if file descriptor support
#is disabled.
# USERLIBS is the list of libraries used to build the final user-space
#application
# EXPORTLIBS is the list of libraries that should be exported by
#'make export' is

NUTTXLIBS = lib$(DELIM)libsched$(LIBEXT)
USERLIBS =

# Driver support.Generally depends on file descriptor support but there
# are some components in the drivers directory that are needed even if file
# descriptors are not supported.

NUTTXLIBS += lib$(DELIM)libdrivers$(LIBEXT)

# Add libraries for board support

NUTTXLIBS += lib$(DELIM)libconfigs$(LIBEXT)

# Add libraries for syscall support.

NUTTXLIBS += lib$(DELIM)libc$(LIBEXT) lib$(DELIM)libmm$(LIBEXT)
NUTTXLIBS += lib$(DELIM)libarch$(LIBEXT)
ifeq ($(CONFIG_LIB_SYSCALL),y)
NUTTXLIBS += lib$(DELIM)libstubs$(LIBEXT)
USERLIBS+= lib$(DELIM)libproxies$(LIBEXT)
endif

# Add libraries for C++ support.CXX, CXXFLAGS, and COMPILEXX must
# be defined in Make.defs for this to work!

ifeq ($(CONFIG_HAVE_CXX),y)
NUTTXLIBS += lib$(DELIM)libcxx$(LIBEXT)
endif

# Add library for application support.

ifneq ($(APPDIR),)
NUTTXLIBS += lib$(DELIM)libapps$(LIBEXT)
endif

# Add libraries for network support

ifeq ($(CONFIG_NET),y)
NUTTXLIBS += lib$(DELIM)libnet$(LIBEXT)
endif

# Add libraries for Crypto API support

ifeq ($(CONFIG_CRYPTO),y)
NUTTXLIBS += lib$(DELIM)libcrypto$(LIBEXT)
endif

# Add libraries for file system support

ifeq ($(CONFIG_NFILE_DESCRIPTORS),0)
ifneq ($(CONFIG_NSOCKET_DESCRIPTORS),0)
NUTTXLIBS += lib$(DELIM)libfs$(LIBEXT)
endif
else
NUTTXLIBS += lib$(DELIM)libfs$(LIBEXT) lib$(DELIM)libbinfmt$(LIBEXT)
endif

# Add libraries for the NX graphics sub-system

ifeq ($(CONFIG_NX),y)
NUTTXLIBS += lib$(DELIM)libgraphics$(LIBEXT)
NUTTXLIBS += lib$(DELIM)libnx$(LIBEXT)
endif

# Add libraries for the Audio sub-system

ifeq ($(CONFIG_AUDIO),y)
NUTTXLIBS += lib$(DELIM)libaudio$(LIBEXT)
endif

# Add libraries for the Wireless sub-system

ifeq ($(CONFIG_WIRELESS),y)
NUTTXLIBS += lib$(DELIM)libwireless$(LIBEXT)
endif

# Add C++ library

ifeq ($(CONFIG_HAVE_CXX),y)
NUTTXLIBS += lib$(DELIM)libcxx$(LIBEXT)
endif

# Export all libraries

EXPORTLIBS = $(NUTTXLIBS)

tools/

tools 目錄下包含了各種各樣的指令碼和Host C程式，這些都是Nuttx編譯系統的必要的部分。README.txt 有詳盡的介紹。

Makefile.unix

Makefile.unix 才是我們的核心，上述所介紹的檔案，最終都要為它所用，直接看程式碼吧。

TOPDIR := ${shell pwd | sed -e 's/ /\\ /g'}
-include $(TOPDIR)/.config
include $(TOPDIR)/tools/Config.mk
-include $(TOPDIR)/Make.defs

# 可以通過“make V=1”的形式來選擇不同的編譯方式，其中V=1/2時，會使能命令的回顯，而在Makefile中“@”可以控制命令不回顯。
# Control build verbosity
#
#V=1,2: Enable echo of commands
#V=2:Enable bug/verbose options in tools and scripts

ifeq ($(V),1)
export Q :=
else
ifeq ($(V),2)
export Q :=
else
export Q := @
endif
endif

# Default tools

# 定義符號連結和斷開連結的巨集
ifeq ($(DIRLINK),)
DIRLINK = $(TOPDIR)/tools/link.sh
DIRUNLINK = $(TOPDIR)/tools/unlink.sh
endif

# This define is passed as EXTRADEFINES for kernel-mode builds.It is also passed
# during PASS1 (but not PASS2) context and depend targets.

KDEFINE = ${shell $(TOPDIR)/tools/define.sh "$(CC)" __KERNEL__}

# Process architecture and board-specific directories

#架構和板級相關的目錄巨集定義
ARCH_DIR = arch/$(CONFIG_ARCH)
ARCH_SRC = $(ARCH_DIR)/src
ARCH_INC = $(ARCH_DIR)/include

ifeq ($(CONFIG_ARCH_BOARD_CUSTOM),y)
ifeq ($(CONFIG_ARCH_BOARD_CUSTOM_DIR_RELPATH),y)
BOARD_DIR = $(TOPDIR)$(DELIM)$(CONFIG_ARCH_BOARD_CUSTOM_DIR)
else
BOARD_DIR = $(CONFIG_ARCH_BOARD_CUSTOM_DIR)
endif
else
BOARD_DIR = $(TOPDIR)$(DELIM)configs/hobot$(DELIM)$(CONFIG_ARCH_BOARD)
endif

# CONFIG_APPS_DIR can be over-ridden from the command line or in the .config file.
# The default value of CONFIG_APPS_DIR is ../apps.Ultimately, the application
# will be built if APPDIR is defined.APPDIR will be defined if a directory containing
# a Makefile is found at the path provided by CONFIG_APPS_DIR

#當在CONFIG_APPS_DIR路徑中存在Makefile時，APPDIR才會被定義
ifeq ($(CONFIG_APPS_DIR),)
CONFIG_APPS_DIR = ../apps
endif
APPDIR := ${shell if [ -r $(CONFIG_APPS_DIR)/Makefile ]; then echo "$(CONFIG_APPS_DIR)"; fi}

# Add-on directories.These may or may not be in place in the
# NuttX source tree (they must be specifically installed)
#
# NUTTX_ADDONS is the list of directories built into the NuttX kernel.
# USER_ADDONS is the list of directories that will be built into the user
#application
#
# FSDIRS depend on file descriptor support; NONFSDIRS do not (except for parts
#of FSDIRS).We will exclude FSDIRS from the build if file descriptor
#support is disabled
# CONTEXTDIRS include directories that have special, one-time pre-build
#requirements.Normally this includes things like auto-generation of
#configuration specific files or creation of configurable symbolic links
# USERDIRS - When NuttX is build is a monolithic kernel, this provides the
#list of directories that must be built
# OTHERDIRS - These are directories that are not built but probably should
#be cleaned to prevent garbage from collecting in them when changing
#configurations.
#
# CLEANDIRS are the directories that will clean in.These are
#all directories that we know about.
# KERNDEPDIRS are the directories in which we will build target dependencies.
#If NuttX and applications are built separately (CONFIG_BUILD_PROTECTED or
#CONFIG_BUILD_KERNEL), then this holds only the directories containing
#kernel files.
# USERDEPDIRS. If NuttX and applications are built separately (CONFIG_BUILD_PROTECTED),
#then this holds only the directories containing user files. If
#CONFIG_BUILD_KERNEL is selected, then applications are not build at all.

# 定義了一系列資料夾相關的巨集
include Directories.mk

#
# Extra objects used in the final link.
#
# Pass 1 1ncremental (relative) link objects should be put into the
# processor-specific source directory (where other link objects will
# be created).If the pass1 object is an archive, it could go anywhere.

ifeq ($(CONFIG_BUILD_2PASS),y)
EXTRA_OBJS += $(CONFIG_PASS1_OBJECT)
endif

# Library build selections
#
# NUTTXLIBS is the list of NuttX libraries that is passed to the
#processor-specific Makefile to build the final NuttX target.
#Libraries in FSDIRS are excluded if file descriptor support
#is disabled.
# USERLIBS is the list of libraries used to build the final user-space
#application
# EXPORTLIBS is the list of libraries that should be exported by
#'make export' is

ifeq ($(CONFIG_BUILD_PROTECTED),y)
include ProtectedLibs.mk
else
ifeq ($(CONFIG_BUILD_KERNEL),y)
include KernelLibs.mk
else
include FlatLibs.mk
endif
endif

# LINKLIBS derives from NUTTXLIBS and is simply the same list with the
#subdirectory removed

#LINKLIBS連結庫和NUTTXLIBS是一樣的，只是通過patsubst將子目錄lib去掉了而已
LINKLIBS = $(patsubst lib/%,%,$(NUTTXLIBS))

# Export tool definitions

#用於'make export'
MKEXPORT= tools/mkexport.sh
MKEXPORT_ARGS = -w$(WINTOOL) -t "$(TOPDIR)"

ifeq ($(CONFIG_BUILD_PROTECTED),y)
MKEXPORT_ARGS += -u
else
ifeq ($(CONFIG_BUILD_KERNEL),y)
MKEXPORT_ARGS += -u
endif
endif

ifeq ($(V),2)
MKEXPORT_ARGS += -d
endif

# This is the name of the final target (relative to the top level directorty)

NUTTXNAME = nuttx
BIN= $(NUTTXNAME)$(EXEEXT)

#編譯的最終目標：nuttx, .PHONY用來宣告偽目標
all: $(BIN)
.PHONY: dirlinks context clean_context check_context export subdir_clean clean subdir_distclean distclean apps_clean apps_distclean

#標頭檔案：math.h、float.h、stdarg.h，在不同的平臺中可能有不同的實現
# Target used to copy include/nuttx/lib/math.h.If CONFIG_ARCH_MATH_H is
# defined, then there is an architecture specific math.h header file
# that will be included indirectly from include/math.h.But first, we
# have to copy math.h from include/nuttx/. to include/.Logic within
# include/nuttx/lib/math.h will hand the redirection to the architecture-
# specific math.h header file.
#
# If the CONFIG_LIBM is defined, the Rhombus libm will be built at libc/math.
# Definitions and prototypes for the Rhombus libm are also contained in
# include/nuttx/lib/math.h and so the file must also be copied in that case.
#
# If neither CONFIG_ARCH_MATH_H nor CONFIG_LIBM is defined, then no math.h
# header file will be provided.You would want that behavior if (1) you
# don't use libm, or (2) you want to use the math.h and libm provided
# within your toolchain.

ifeq ($(CONFIG_ARCH_MATH_H),y)
NEED_MATH_H = y
else
ifeq ($(CONFIG_LIBM),y)
NEED_MATH_H = y
endif
endif

ifeq ($(NEED_MATH_H),y)
include/math.h: include/nuttx/lib/math.h
$(Q) cp -f include/nuttx/lib/math.h include/math.h
else
include/math.h:
endif

# The float.h header file defines the properties of your floating point
# implementation.It would always be best to use your toolchain's float.h
# header file but if none is available, a default float.h header file will
# provided if this option is selected.However there is no assurance that
# the settings in this float.h are actually correct for your platform!

ifeq ($(CONFIG_ARCH_FLOAT_H),y)
include/float.h: include/nuttx/lib/float.h
$(Q) cp -f include/nuttx/lib/float.h include/float.h
else
include/float.h:
endif

# Target used to copy include/nuttx/lib/stdarg.h.If CONFIG_ARCH_STDARG_H is
# defined, then there is an architecture specific stdarg.h header file
# that will be included indirectly from include/lib/stdarg.h.But first, we
# have to copy stdarg.h from include/nuttx/. to include/.

ifeq ($(CONFIG_ARCH_STDARG_H),y)
include/stdarg.h: include/nuttx/lib/stdarg.h
$(Q) cp -f include/nuttx/lib/stdarg.h include/stdarg.h
else
include/stdarg.h:
endif

# Targets used to build include/nuttx/version.h.Creation of version.h is
# part of the overall NuttX configuration sequence. Notice that the
# tools/mkversion tool is built and used to create include/nuttx/version.h

# 先編譯mkversion工具，再用該工具來建立version.h檔案。下行make命令中，-C後邊指定需要執行make的路徑，此處指tools目錄，
# -f指定Makefile檔案，此處指Makefile.host，並將TOPDIR這個巨集的值傳遞給Makefile.unix，make的目標是mkversion$(HOSTEXEEXT)
# 當make命令中帶有多個引數時，注意'-'和'='等特殊符號，沒特殊符號約束的就是make的目標，比如此處的mkversion$(HOSTEXEEXT)
tools/mkversion$(HOSTEXEEXT):
$(Q) $(MAKE) -C tools -f Makefile.host TOPDIR="$(TOPDIR)"mkversion$(HOSTEXEEXT)

# 檢視是否存在.version檔案
$(TOPDIR)/.version:
$(Q) if [ ! -f .version ]; then \
echo "No .version file found, creating one"; \
tools/version.sh -v 0.0 -b 0 .version; \
chmod 755 .version; \
fi

# 建立version.h檔案
include/nuttx/version.h: $(TOPDIR)/.version tools/mkversion$(HOSTEXEEXT)
$(Q) tools/mkversion $(TOPDIR) > include/nuttx/version.h

# ROMFS，其中rcS.template為啟動指令碼，nsh_romfsimg.h是根據這個啟動指令碼而產生的頭部資訊
arch/arm/include/board/nsh_romfsimg.h:
ifeq ($(CONFIG_NSH_ARCHROMFS),y)
$(Q) if [ ! -f $(BOARD_DIR)/include/rcS.template ]; then \
echo "No rcS.template file create it!!!!!"; \
fi
$(Q) cp -f $(BOARD_DIR)/include/rcS.template $(TOPDIR)/rcS.template

$(Q) tools/mkromfsimg.sh $(TOPDIR)
$(Q) if [ ! -f $(TOPDIR)/nsh_romfsimg.h ]; then \
echo "No nsh_romfsimg.h file create !!!!!"; \
fi
$(Q) cp -f nsh_romfsimg.h arch/arm/include/board/
$(Q) rm -f $(TOPDIR)/rcS.template $(TOPDIR)/nsh_romfsimg.h
else
$(Q) echo "use nsh defalut nsh_romfsimg.h for romfs"
endif

# Targets used to build include/nuttx/config.h.Creation of config.h is
# part of the overall NuttX configuration sequence. Notice that the
# tools/mkconfig tool is built and used to create include/nuttx/config.h

# 建立config.h檔案
tools/mkconfig$(HOSTEXEEXT):
$(Q) $(MAKE) -C tools -f Makefile.host TOPDIR="$(TOPDIR)"mkconfig$(HOSTEXEEXT)

include/nuttx/config.h: $(TOPDIR)/.config tools/mkconfig$(HOSTEXEEXT)
$(Q) tools/mkconfig $(TOPDIR) > include/nuttx/config.h

# Targets used to create dependencies

# 編譯Host上建立dependency的工具
tools/mkdeps$(HOSTEXEEXT):
$(Q) $(MAKE) -C tools -f Makefile.host TOPDIR="$(TOPDIR)" mkdeps$(HOSTEXEEXT)

tools/cnvwindeps$(HOSTEXEEXT):
$(Q) $(MAKE) -C tools -f Makefile.host TOPDIR="$(TOPDIR)" cnvwindeps$(HOSTEXEEXT)

# dirlinks, and helpers
#
# Directories links.Most of establishing the NuttX configuration involves
# setting up symbolic links with 'generic' directory names to specific,
# configured directories.

# Make.defs:
#$(Q) echo "No Make.defs file found, creating one"
#$(Q) echo "include $(TOPDIR)$(DELIM).config" > Make.defs
#$(Q) echo "include $(TOPDIR)$(DELIM)tools$(DELIM)Config.mk" >> Make.defs

# tools/initialconfig$(HOSTEXEEXT):
#$(Q) $(MAKE) -C tools -f Makefile.host TOPDIR="$(TOPDIR)" initialconfig$(HOSTEXEEXT)
#
# .config: tools/initialconfig$(HOSTEXEEXT)
#$(Q) echo "No .config file found, creating one"
#$(Q) tools/initialconfig$(HOSTEXEEXT)

# Link the arch/<arch-name>/include directory to include/arch

include/arch: .config
@echo "LN: include/arch to $(ARCH_DIR)/include"
$(Q) $(DIRLINK) $(TOPDIR)/$(ARCH_DIR)/include include/arch

# Link the configs/<board-name>/include directory to include/arch/board

include/arch/board: include/arch
@echo "LN: include/arch/board to $(BOARD_DIR)/include"
$(Q) $(DIRLINK) $(BOARD_DIR)/include include/arch/board

# Link the configs/<board-name>/src dir to arch/<arch-name>/src/board

$(ARCH_SRC)/board: .config
@echo "LN: $(ARCH_SRC)/board to $(BOARD_DIR)/src"
$(Q) $(DIRLINK) $(BOARD_DIR)/src $(ARCH_SRC)/board

# Link arch/<arch-name>/include/<chip-name> to arch/<arch-name>/include/chip

$(ARCH_SRC)/chip: .config
ifneq ($(CONFIG_ARCH_CHIP),)
@echo "LN: $(ARCH_SRC)/chip to $(ARCH_SRC)/$(CONFIG_ARCH_CHIP)"
$(Q) $(DIRLINK) $(TOPDIR)/$(ARCH_SRC)/$(CONFIG_ARCH_CHIP) $(ARCH_SRC)/chip
endif

# Link arch/<arch-name>/src/<chip-name> to arch/<arch-name>/src/chip

include/arch/chip: include/arch
ifneq ($(CONFIG_ARCH_CHIP),)
@echo "LN: include/arch/chip to $(ARCH_INC)/$(CONFIG_ARCH_CHIP)"
$(Q) $(DIRLINK) $(TOPDIR)/$(ARCH_INC)/$(CONFIG_ARCH_CHIP) include/arch/chip
endif

# 根據依賴關係建立連結，進入nuttx/configs目錄中，執行make dirlinks；進入apps/目錄中，執行make dirlinks
dirlinks: include/arch include/arch/board include/arch/chip $(ARCH_SRC)/board $(ARCH_SRC)/chip
$(Q) $(MAKE) -C configs dirlinks TOPDIR="$(TOPDIR)"
$(Q) $(MAKE) -C $(CONFIG_APPS_DIR) dirlinks TOPDIR="$(TOPDIR)"

# context
#
# The context target is invoked on each target build to assure that NuttX is
# properly configured.The basic configuration steps include creation of the
# the config.h and version.h header files in the include/nuttx directory and
# the establishment of symbolic links to configured directories.

# CONTEXTDIRS在Directories.mk中定義
context: check_context include/nuttx/config.h include/nuttx/version.h include/math.h include/float.h include/stdarg.h dirlinks arch/arm/include/board/nsh_romfsimg.h
$(Q) for dir in $(CONTEXTDIRS) ; do \
$(MAKE) -C $$dir TOPDIR="$(TOPDIR)" context; \
done

# clean_context
#
# This is part of the distclean target.It removes all of the header files
# and symbolic links created by the context target.

clean_context:
$(Q) $(MAKE) -C configs TOPDIR="$(TOPDIR)" clean_context
$(call DELFILE, include/nuttx/config.h)
$(call DELFILE, include/nuttx/version.h)
$(call DELFILE, arch/arm/include/board/nsh_romfsimg.h)
$(call DELFILE, include/math.h)
$(call DELFILE, include/stdarg.h)
$(Q) $(DIRUNLINK) include/arch/board
$(Q) $(DIRUNLINK) include/arch/chip
$(Q) $(DIRUNLINK) include/arch
$(Q) $(DIRUNLINK) $(ARCH_SRC)/board
$(Q) $(DIRUNLINK) $(ARCH_SRC)/chip

# 檢查Nuttx是否已經被配置好
# check_context
#
# This target checks if NuttX has been configured.NuttX is configured using
# the script tools/configure.sh.That script will install certain files in
# the top-level NuttX build directory.This target verifies that those
# configuration files have been installed and that NuttX is ready to be built.

check_context:
$(Q) if [ ! -e ${TOPDIR}/.config -o ! -e ${TOPDIR}/Make.defs ]; then \
echo "" ; echo "Nuttx has not been configured:" ; \
echo "cd tools; ./configure.sh <target>" ; echo "" ; \
exit 1 ; \
fi

# Archive targets.The target build sequence will first create a series of
# libraries, one per configured source file directory.The final NuttX
# execution will then be built from those libraries.The following targets
# build those libraries.

#包含各種庫檔案
include LibTargets.mk

# pass1 and pass2
#
# If the 2 pass build option is selected, then this pass1 target is
# configured to built before the pass2 target.This pass1 target may, as an
# example, build an extra link object (CONFIG_PASS1_OBJECT) which may be an
# incremental (relative) link object, but could be a static library (archive);
# some modification to this Makefile would be required if CONFIG_PASS1_OBJECT
# is an archive.Exactly what is performed during pass1 or what it generates
# is unknown to this makefile unless CONFIG_PASS1_OBJECT is defined.

# PASS1為apps部分
pass1deps: pass1dep $(USERLIBS)

# 如果定義了CONFIG_BUILD_2PASS，則需要先編譯PASS1
pass1: pass1deps
ifeq ($(CONFIG_BUILD_2PASS),y)
$(Q) if [ -z "$(CONFIG_PASS1_BUILDIR)" ]; then \
echo "ERROR: CONFIG_PASS1_BUILDIR not defined"; \
exit 1; \
fi
$(Q) if [ ! -d "$(CONFIG_PASS1_BUILDIR)" ]; then \
echo "ERROR: CONFIG_PASS1_BUILDIR does not exist"; \
exit 1; \
fi
$(Q) if [ ! -f "$(CONFIG_PASS1_BUILDIR)/Makefile" ]; then \
echo "ERROR: No Makefile in CONFIG_PASS1_BUILDIR"; \
exit 1; \
fi
$(Q) $(MAKE) -C $(CONFIG_PASS1_BUILDIR) TOPDIR="$(TOPDIR)" LINKLIBS="$(LINKLIBS)" USERLIBS="$(USERLIBS)" "$(CONFIG_PASS1_TARGET)"
endif

# PASS2為nuttx部分
pass2deps: pass2dep $(NUTTXLIBS)

pass2: pass2deps
$(Q) $(MAKE) -C $(ARCH_SRC) TOPDIR="$(TOPDIR)" EXTRA_OBJS="$(EXTRA_OBJS)" LINKLIBS="$(LINKLIBS)" EXTRADEFINES=$(KDEFINE) $(BIN)
$(Q) if [ -w /tftpboot ] ; then \
cp -f $(BIN) /tftpboot/$(BIN).${CONFIG_ARCH}; \
fi
ifeq ($(CONFIG_RRLOAD_BINARY),y)
@echo "MK: $(NUTTXNAME).rr"
$(Q) $(TOPDIR)/tools/mkimage.sh --Prefix $(CROSSDEV) $(BIN) $(NUTTXNAME).rr
$(Q) if [ -w /tftpboot ] ; then \
cp -f $(NUTTXNAME).rr /tftpboot/$(NUTTXNAME).rr.$(CONFIG_ARCH); \
fi
endif
ifeq ($(CONFIG_INTELHEX_BINARY),y)
@echo "CP: $(NUTTXNAME).hex"
$(Q) $(OBJCOPY) $(OBJCOPYARGS) -O ihex $(BIN) $(NUTTXNAME).hex
endif
ifeq ($(CONFIG_MOTOROLA_SREC),y)
@echo "CP: $(NUTTXNAME).srec"
$(Q) $(OBJCOPY) $(OBJCOPYARGS) -O srec $(BIN) $(NUTTXNAME).srec
endif
ifeq ($(CONFIG_RAW_BINARY),y)#生成RAW格式檔案，並生成nuttx.bin檔案
@echo "CP: $(NUTTXNAME).bin"
$(Q) $(OBJCOPY) $(OBJCOPYARGS) -O binary $(BIN) $(NUTTXNAME).bin
endif
ifeq ($(CONFIG_UBOOT_UIMAGE),y)
@echo "MKIMAGE: uImage"
$(Q) mkimage -A arm -O linux -C none -T kernel -a $(CONFIG_UIMAGE_LOAD_ADDRESS) \
-e $(CONFIG_UIMAGE_ENTRY_POINT) -n $(BIN) -d $(NUTTXNAME).bin uImage
$(Q) if [ -w /tftpboot ] ; then \
cp -f uImage /tftpboot/uImage; \
fi
endif

# $(BIN)
#
# Create the final NuttX executable in a two pass build process.In the
# normal case, all pass1 and pass2 dependencies are created then pass1
# and pass2 targets are built.However, in some cases, you may need to build
# pass1 dependencies and pass1 first, then build pass2 dependencies and pass2.
# in that case, execute 'make pass1 pass2' from the command line.

$(BIN): pass1deps pass2deps pass1 pass2

# download
#
# This is a helper target that will rebuild NuttX and download it to the target
# system in one step.The operation of this target depends completely upon
# implementation of the DOWNLOAD command in the user Make.defs file.It will
# generate an error an error if the DOWNLOAD command is not defined.

download: $(BIN)
$(call DOWNLOAD, $<)

# pass1dep: Create pass1 build dependencies
# pass2dep: Create pass2 build dependencies

# 建立pass1的依賴關係，make depend後，將會生成Make.dep檔案
pass1dep: context tools/mkdeps$(HOSTEXEEXT) tools/cnvwindeps$(HOSTEXEEXT)
$(Q) for dir in $(USERDEPDIRS) ; do \
$(MAKE) -C $$dir TOPDIR="$(TOPDIR)" depend ; \
done

# 建立pass2的依賴關係，make depend後，將會生成Make.dep檔案
pass2dep: context tools/mkdeps$(HOSTEXEEXT) tools/cnvwindeps$(HOSTEXEEXT)
$(Q) for dir in $(KERNDEPDIRS) ; do \
$(MAKE) -C $$dir TOPDIR="$(TOPDIR)" EXTRADEFINES=$(KDEFINE) depend; \
done

# Configuration targets
#
# These targets depend on the kconfig-frontends packages.To use these, you
# must first download and install the kconfig-frontends package from this
# location: http://ymorin.is-a-geek.org/projects/kconfig-frontends.See
# README.txt file in the NuttX tools GIT repository for additional information.

# 配置目標
do_config: dirlinks apps_preconfig
$(Q) APPSDIR=${CONFIG_APPS_DIR} kconfig-conf Kconfig

config: do_config clean_context

do_oldconfig: dirlinks apps_preconfig
$(Q) APPSDIR=${CONFIG_APPS_DIR} kconfig-conf --oldconfig Kconfig

oldconfig: do_oldconfig clean_context

do_olddefconfig: dirlinks apps_preconfig
$(Q) APPSDIR=${CONFIG_APPS_DIR} kconfig-conf --olddefconfig Kconfig

olddefconfig: do_olddefconfig clean_context

do_menuconfig: dirlinks apps_preconfig
$(Q) APPSDIR=${CONFIG_APPS_DIR} kconfig-mconf Kconfig

menuconfig: do_menuconfig clean_context

do_qconfig: dirlinks apps_preconfig
$(Q) APPSDIR=${CONFIG_APPS_DIR} kconfig-qconf Kconfig

qconfig: do_qconfig clean_context

do_gconfig: dirlinks apps_preconfig
$(Q) APPSDIR=${CONFIG_APPS_DIR} kconfig-gconf Kconfig

gconfig: do_gconfig clean_context

# export
#
# The export target will package the NuttX libraries and header files into
# an exportable package.Caveats: (1) These needs some extension for the KERNEL
# build; it needs to receive USERLIBS and create a libuser.a). (2) The logic
# in tools/mkexport.sh only supports GCC and, for example, explicitly assumes
# that the archiver is 'ar'

# 'make export'將生成一個打包檔案，將nuttx核心中的庫及標頭檔案放置在一起
export: pass2deps
$(Q) MAKE=${MAKE} $(MKEXPORT) $(MKEXPORT_ARGS) -l "$(EXPORTLIBS)"

# General housekeeping targets:dependencies, cleaning, etc.
#
# depend:Create both PASS1 and PASS2 dependencies
# clean:Removes derived object files, archives, executables, and
#temporary files, but retains the configuration and context
#files and directories.
# distclean: Does 'clean' then also removes all configuration and context
#files.This essentially restores the directory structure
#to its original, unconfigured stated.

# 生成依賴關係
depend: pass1dep pass2dep

subdir_clean:
$(Q) for dir in $(CLEANDIRS) ; do \
if [ -e $$dir/Makefile ]; then \
$(MAKE) -C $$dir TOPDIR="$(TOPDIR)" clean ; \
fi \
done
$(Q) $(MAKE) -C tools -f Makefile.host TOPDIR="$(TOPDIR)" clean
ifeq ($(CONFIG_BUILD_2PASS),y)
$(Q) $(MAKE) -C $(CONFIG_PASS1_BUILDIR) TOPDIR="$(TOPDIR)" clean
endif

# make clean，將目錄中生成的檔案都刪除掉
clean: subdir_clean
$(call DELFILE, $(BIN))
$(call DELFILE, nuttx.*)
$(call DELFILE, *.map)
$(call DELFILE, _SAVED_APPS_config)
$(call DELFILE, nuttx-export*)
$(call DELFILE, nuttx_user*)
$(call CLEAN)

subdir_distclean:
$(Q) for dir in $(CLEANDIRS) ; do \
if [ -e $$dir/Makefile ]; then \
$(MAKE) -C $$dir TOPDIR="$(TOPDIR)" distclean ; \
fi \
done

# make distclean，將目錄中生成的檔案，以及配置項都刪除掉
distclean: clean subdir_distclean clean_context
ifeq ($(CONFIG_BUILD_2PASS),y)
$(Q) $(MAKE) -C $(CONFIG_PASS1_BUILDIR) TOPDIR="$(TOPDIR)" distclean
endif
$(call DELFILE, Make.defs)
$(call DELFILE, .config)
$(call DELFILE, .config.old)

# Application housekeeping targets.The APPDIR variable refers to the user
# application directory.A sample apps/ directory is included with NuttX,
# however, this is not treated as part of NuttX and may be replaced with a
# different application directory.For the most part, the application
# directory is treated like any other build directory in this script.However,
# as a convenience, the following targets are included to support housekeeping
# functions in the user application directory from the NuttX build directory.
#
# apps_preconfig: Prepare applications to be configured
# apps_clean:Perform the clean operation only in the user application
#directory
# apps_distclean: Perform the distclean operation only in the user application
#directory.

# 針對apps目錄下的配置及清除工作

apps_preconfig:
ifneq ($(APPDIR),)
$(Q) $(MAKE) -C "$(TOPDIR)/$(APPDIR)" TOPDIR="$(TOPDIR)" preconfig
endif

apps_clean:
ifneq ($(APPDIR),)
$(Q) $(MAKE) -C "$(TOPDIR)/$(APPDIR)" TOPDIR="$(TOPDIR)" clean
endif

apps_distclean:
ifneq ($(APPDIR),)
$(Q) $(MAKE) -C "$(TOPDIR)/$(APPDIR)" TOPDIR="$(TOPDIR)" distclean
endif

頂層目錄中的Makefile，通過make -C逐層進入子目錄中，執行相應的編譯動作，最終找到所有的依賴關係，生成nuttx 及nuttx.bin 檔案。

apps目錄中的編譯方式也類似，從apps/Makefile開始分析即可。