由于笔者没学过Linux等系统，对make文件所知甚少，本节分析可能有大量错误，只提供参考，随着技术积累，以后会回过头改正错误的地方，也非常欢迎提出指导意见。
其中分析大多数参考网上解释，加上自己的理解，对make源码逐行阅读并做了相关注释和分析。
统一规定：红字是注释分析；代码部分左边是程序，右边是注释。
下面开始分析
首先打开ardupilot/Arducopter/makefile
include ../mk/apm.mk 引用其他mk所以去看看apm.mk是什么
# find the mk/ directory, which is where this makefile fragment
# lives. (patsubst strips the trailing slash.)
SYSTYPE := $(shell uname) 系统环境是win还是Linux？
下述程序是为了根据系统的类型确定不同的工作目录MK_DIR
我们始终需要记住一件事，那就是我们在哪个目录编译，以及我们的编译命令。编译目录为： ardupilot/ArduCopter，编译命令我们用的是“make px4”，但我们也可以改变命令编译我们需要的。
ifneq ($(findstring CYGWIN, $(SYSTYPE)),) ifeq (<arg1>, <arg2>)比较参数“arg1”和“arg2”的值是否相同，
(判断系统环境是否不为CYGWIN) 不同为真；ifneq (<arg1>, <arg2>)，相同为真
$(findstring find,in)
$(findstring a,a b c) $(findstring a,b c) 结果分别为‘a’ and ‘’
MK_DIR := $(shell cygpath -m ../mk) cygpath用于转换Unix和Windows的格式路径
-m, --mixed like --windows, but with regular slashes (C:/WINNT)
-w, --windows print Windows form of NAMEs (C:\WINNT)
else
MK_DIR := $(patsubst %/,%,$(dir $(lastword $(MAKEFILE_LIST)))) $应该是取值的意思
根据gnu make定义，gnu make 会自动将所有读取的makefile路径都会加入到MAKEFILE_LIST变量中，
而且是按照读取的先后顺序添加。例如
#If a makefile named Makefile has this content:
name1 := $(lastword $(MAKEFILE_LIST))
include inc.mk
name2 := $(lastword $(MAKEFILE_LIST))
all:
@echo name1 = $(name1)
@echo name2 = $(name2)
#then you would expect to see this output:
#name1 = Makefile
#name2 = inc.mk
格式：$(patsubst ,,)
名称：模式字符串替换函数——patsubst
功能：查找中的单词（单词以“空格”、“Tab”或“回车”“换行”分隔）是否符合模式，如果匹配的话，则以替换。这里，可以包括通配符“%”，表示任意长度的字串。如果中也包含“%”，那么，中的这个“%”将是中的那个“%”所代表的字串。（可以用“\”来转义，以“\%”来表示真实含义的“%”字符）
返回：函数返回被替换过后的字符串。
示例：
$(patsubst %.c,%.o,x.c.c bar.c)
把字串“x.c.c bar.c”符合模式[%.c]的单词替换成[%.o]，返回结果是“x.c.o bar.o”
而dir是提取路径
$(dir src/foo.c hacks)
#produces the result ‘src/ ./’.
所以$(patsubst%/,%,$(dir $(lastword $(MAKEFILE_LIST))))返回了当前的mk路径，到这里也就得出了 MK_DIR 信息。
endif
include $(MK_DIR)/environ.mk 添加environ.mk文件，关键的环境变量在里面实现
# short-circuit build for the configure target
ifeq ($(MAKECMDGOALS),configure) 如果编译参数是configure，则添加configure.mk
include $(MK_DIR)/configure.mk configure.mk的内容为
configure:
else @echo "make configure is no longer required"
所以可以直接执行下面的程序
# short-circuit build for the help target
include $(MK_DIR)/help.mk 添加help.mk help.mk的内容主要是打印一些信息，对理解pixhawk程序有点帮助
# common makefile components 添加常用makefile
include $(MK_DIR)/targets.mk 添加targets.mk
include $(MK_DIR)/sketch_sources.mk 添加sketch_sources.mk
ifneq ($(MAKECMDGOALS),clean) 判断命令不为clean是否为真
# board specific includes 根据板子添加相应的.mk文件
ifeq ($(HAL_BOARD),HAL_BOARD_SITL)
include $(MK_DIR)/board_native.mk
endif
ifeq ($(HAL_BOARD),HAL_BOARD_LINUX)
include $(MK_DIR)/board_linux.mk
endif
ifeq ($(HAL_BOARD),HAL_BOARD_PX4)
include $(MK_DIR)/board_px4.mk
endif
ifeq ($(HAL_BOARD),HAL_BOARD_VRBRAIN)
include $(MK_DIR)/board_vrbrain.mk
endif
ifeq ($(HAL_BOARD),HAL_BOARD_FLYMAPLE)
include $(MK_DIR)/board_flymaple.mk
endif
ifeq ($(HAL_BOARD),HAL_BOARD_QURT)
include $(MK_DIR)/board_qurt.mk
endif
endif
endif
这个时候可能我们会很迷惑， $(HAL_BOARD)的值到底是多少？
但其实我们在执行“make px4”命令编译的时候会有一行信息：
HAL_BOARD=HAL_BOARD_PX4HAL_BOARD_SUBTYPE= TOOLCHAIN=NATIVEEXTRAFLAGS=-DGIT_VERSION="b6d361a3" -DNUTTX_GIT_VERSION="eba6b56f"-DPX4_GIT_VERSION="cf208916"
这行信息非常清楚地告诉了我们用的是“$(MK_DIR)/board_px4.mk”文件。
所以apm.mk根据各种判断，添加environ.mk文件(关键的环境变量在里面实现), 添加help.mk(打印相关信息)，添加targets.mk，添加sketch_sources.mk，添加board_px4.mk
接下来就分别分析environ.mk，targets.mk，sketch_sources.mk，board_px4.mk
environ.mk 关键的环境变量在里面实现
windows下的环境变量简单来说就是将某些数据，文件或文件夹设置为系统默认值，这样你调用的时候就不用给出完整路径和地址或进行设置，直接用名字就可以了。
这里实现的是查找 SKETCHBOOK 的位置，根据源文件路径判断 SKETCH 名称， 算出要 build 的哪里，建立 BUILDROOT 目录，根据编译参数确定 HAL_BOARD 类型，等等为系统实现做基础工作。
以下是部分代码分析：
GIT_VERSION := $(shell git rev-parse HEAD | cut -c1-8) 获得git 版本
#
# Locate the sketch sources based on the initial Makefile's path
#
SRCROOT := $(realpath $(dir $(firstword $(MAKEFILE_LIST)))) 通过判断是否有libraries来获取当前
ifneq ($(findstring CYGWIN, $(SYSTYPE)),) make的真实路径，不存在则返回为空
# Workaround a $(realpath ) bug on Cygwin libraries下的测试 makefile都是指向apm
ifeq ($(SRCROOT),)
SRCROOT := $(shell cygpath -m ${CURDIR})
$(warning your realpath function is not working)
$(warning > setting SRCROOT to $(SRCROOT))
endif
endif
#
# We need to know the location of the sketchbook. If it hasn't been overridden,
# try the parent of the current directory. If there is no libraries directory
# there, assume that we are in a library's examples directory and try backing up
# further. 通过判断是否有libraries来获取当前SKETCHBOOK的位置
# 查找SKETCHBOOK的位置
ifeq ($(SKETCHBOOK),) wildcard通配符，如：列出该目录下所有的C文件为$(wildcard *.c)
SKETCHBOOK := $(shell cd $(SRCROOT)/.. && pwd)
ifeq ($(wildcard $(SKETCHBOOK)/libraries),) 此位置为该项目的根目录
SKETCHBOOK := $(shell cd $(SRCROOT)/../.. && pwd)
endif
ifeq ($(wildcard $(SKETCHBOOK)/libraries),)
SKETCHBOOK := $(shell cd $(SRCROOT)/../../.. && pwd)
endif
ifeq ($(wildcard $(SKETCHBOOK)/libraries),)
SKETCHBOOK := $(shell cd $(SRCROOT)/../../../.. && pwd)
endif
ifeq ($(wildcard $(SKETCHBOOK)/libraries),)
$(error ERROR: cannot determine sketchbook location - please specify on the commandline with SKETCHBOOK=<path>)
endif
else
ifeq ($(wildcard $(SKETCHBOOK)/libraries),)
$(warning WARNING: sketchbook directory $(SKETCHBOOK) contains no libraries)
endif
endif
ifneq ($(findstring CYGWIN, $(SYSTYPE)),) 如果是在win平台，转换为win格式的路径
# Convert cygwin path into a windows normal path
SKETCHBOOK := $(shell cygpath ${SKETCHBOOK})
endif
ifneq ($(wildcard $(SKETCHBOOK)/config.mk),) 如果config.mk不是空，include他
$(info Reading $(SKETCHBOOK)/config.mk)
include $(SKETCHBOOK)/config.mk
endif
ifneq ($(wildcard $(SKETCHBOOK)/developer.mk),) 如果developer.mk不是空，include他
$(info Reading $(SKETCHBOOK)/developer.mk)
include $(SKETCHBOOK)/developer.mk
endif
#
# Work out the sketch name from the name of the source directory.
#找出是哪个sketch，他的名字
SKETCH := $(lastword $(subst /, ,$(SRCROOT))) 根据源文件路径判断SKETCH名称
# Workaround a $(lastword ) bug on Cygwin subst是将源文件路径中所有的/替换为空格。
ifeq ($(SKETCH),)
WORDLIST := $(subst /, ,$(SRCROOT))
SKETCH := $(word $(words $(WORDLIST)),$(WORDLIST))
Endif
#
# Work out where we are going to be building things
#算出哪是我们要build的事
TMPDIR ?= /tmp
ifneq ($(findstring px4, $(MAKECMDGOALS)),)
# when building px4 we need all sources to be inside the sketchbook directory
# as the NuttX build system relies on it
BUILDROOT := $(SKETCHBOOK)/Build.$(SKETCH) 建立BUILDROOT目录：根据编译目标$(MAKECMDGOALS)建
Endif 立相关目录，如果编译目标不匹配，建立临时目录。
ifneq ($(findstring vrbrain, $(MAKECMDGOALS)),)
# when building vrbrain we need all sources to be inside the sketchbook directory
# as the NuttX build system relies on it
BUILDROOT := $(SKETCHBOOK)/Build.$(SKETCH)
endif
ifneq ($(findstring vrubrain, $(MAKECMDGOALS)),)
# when building vrbrain we need all sources to be inside the sketchbook directory
# as the NuttX build system relies on it
BUILDROOT := $(SKETCHBOOK)/Build.$(SKETCH)
endif
ifneq ($(findstring vrhero, $(MAKECMDGOALS)),)
# when building vrbrain we need all sources to be inside the sketchbook directory
# as the NuttX build system relies on it
BUILDROOT := $(SKETCHBOOK)/Build.$(SKETCH)
Endif
ifneq ($(APPDIR),)
# this is a recusive PX4 build
HAL_BOARD = HAL_BOARD_PX4
endif
# handle target based overrides for board type根据编译参数确定HAL_BOARD类型。
ifneq ($(findstring px4, $(MAKECMDGOALS)),)
HAL_BOARD = HAL_BOARD_PX4
endif
ifneq ($(findstring sitl, $(MAKECMDGOALS)),)
HAL_BOARD = HAL_BOARD_SITL
HAL_BOARD_SUBTYPE = HAL_BOARD_SUBTYPE_NONE
endif
ifneq ($(findstring linux, $(MAKECMDGOALS)),)
HAL_BOARD = HAL_BOARD_LINUX
HAL_BOARD_SUBTYPE = HAL_BOARD_SUBTYPE_LINUX_NONE
endif
board_px4.mk文件代码：
TOOLCHAIN = NATIVE
include $(MK_DIR)/find_tools.mk
include $(MK_DIR)/px4_targets.mk
find_tools.mk就是寻找编译工具
FIND_TOOL = $(firstword $(wildcard $(addsuffix /$(1),$(TOOLPATH)))) 快速查找
px4_targets.mk
部分代码分析
NUTTX_GIT_VERSION := $(shell cd $(NUTTX_SRC) && git rev-parse HEAD | cut -c1-8) 获取NUTTX_GIT_VERSION
PX4_GIT_VERSION:= $(shell cd $(PX4_ROOT) && git rev-parse HEAD | cut -c1-8) 及PX4_GIT_VERSION版本
EXTRAFLAGS += -DNUTTX_GIT_VERSION="\"$(NUTTX_GIT_VERSION)\"" 添加EXTRAFLAGS
EXTRAFLAGS += -DPX4_GIT_VERSION="\"$(PX4_GIT_VERSION)\"" = 是最基本的赋值 := 是覆盖之前的值
EXTRAFLAGS += -DUAVCAN=1 ?= 是如果没有被赋值过就赋予等号后面的值
+= 是添加等号后面的值
PX4_V2_CONFIG_FILE=$(MK_DIR)/PX4/config_px4fmu-v2_APM.mk 更新PX4_V2_CONFIG_FILE配置文件
在这里又调用了px4_common.mk，这是一个很重要的东西；如定义了ROMFS_ROOT，定义了BUILTIN_COMMANDS，其中strip为去除空格；
SKETCHFLAGS=$(SKETCHLIBINCLUDES) -DARDUPILOT_BUILD -DTESTS_MATHLIB_DISABLE -DCONFIG_HAL_BOARD=HAL_BOARD_PX4 -DSKETCHNAME="\\\"$(SKETCH)\\\"" -DSKETCH_MAIN=ArduPilot_main -DAPM_BUILD_DIRECTORY=APM_BUILD_$(SKETCH)
WARNFLAGS = -Wall -Wextra -Wlogical-op -Werror -Wno-unknown-pragmas -Wno-redundant-decls -Wno-psabi -Wno-packed -Wno-error=double-promotion -Wno-error=unused-variable -Wno-error=reorder -Wno-error=float-equal -Wno-error=pmf-conversions -Wno-error=missing-declarations -Wno-error=unused-function
OPTFLAGS = -fsingle-precision-constant
定义SKETCHFLAGS/WARNFLAGS/OPTFLAGS，其中-D表示为define，-I为添加库
PYTHONPATH=$(SKETCHBOOK)/mk/PX4/Tools/genmsg/src:$(SKETCHBOOK)/mk/PX4/Tools/gencpp/src确定PYTHONPATH路径
PX4_MAKE = $(v)+ GIT_SUBMODULES_ARE_EVIL=1 ARDUPILOT_BUILD=1 $(MAKE) -C $(SKETCHBOOK) -f $(PX4_ROOT)/Makefile.make EXTRADEFINES="$(SKETCHFLAGS) $(WARNFLAGS) $(OPTFLAGS) "'$(EXTRAFLAGS)' APM_MODULE_DIR=$(SKETCHBOOK) SKETCHBOOK=$(SKETCHBOOK) CCACHE=$(CCACHE) PX4_ROOT=$(PX4_ROOT) NUTTX_SRC=$(NUTTX_SRC) MAXOPTIMIZATION="-Os" UAVCAN_DIR=$(UAVCAN_DIR)
PX4_MAKE_ARCHIVES = $(MAKE) -C $(PX4_ROOT) -f $(PX4_ROOT)/Makefile.make NUTTX_SRC=$(NUTTX_SRC) CCACHE=$(CCACHE) archives MAXOPTIMIZATION="-Os"
定义PX4_MAKE及PX4_MAKE_ARCHIVES
$(MAKE) –C 表示进入指定文件夹执行
$(PX4_ROOT)/Makefile.make 编译PX4原生代码的
HASHADDER_FLAGS += --ardupilot "$(SKETCHBOOK)" 添加HASHADDER_FLAGS
ifneq ($(wildcard $(PX4_ROOT)),)
HASHADDER_FLAGS += --px4 "$(PX4_ROOT)"
endif
ifneq ($(wildcard $(NUTTX_SRC)/..),)
HASHADDER_FLAGS += --nuttx "$(NUTTX_SRC)/.."
endif
HASHADDER_FLAGS += --uavcan "$(UAVCAN_DIR)"
.PHONY: module_mk
module_mk: 生成module_mk
$(v) echo "Building $(SKETCHBOOK)/module.mk"
$(RULEHDR)
$(v) echo "# Auto-generated file - do not edit" > $(SKETCHBOOK)/module.mk.new
$(v) echo "MODULE_COMMAND = ArduPilot" >> $(SKETCHBOOK)/module.mk.new
$(v) echo "SRCS = $(wildcard $(SRCROOT)/*.cpp) $(SKETCHLIBSRCSRELATIVE)" >>$(SKETCHBOOK)/module.mk.new
$(v) echo "MODULE_STACKSIZE = 4096" >> $(SKETCHBOOK)/module.mk.new
$(v) echo "EXTRACXXFLAGS = -Wframe-larger-than=1300" >> $(SKETCHBOOK)/module.mk.new
$(v) cmp $(SKETCHBOOK)/module.mk $(SKETCHBOOK)/module.mk.new 2>/dev/null || mv $(SKETCHBOOK)/module.mk.new $(SKETCHBOOK)/module.mk
$(v) rm -f $(SKETCHBOOK)/module.mk.new
px4-v2: $(BUILDROOT)/make.flags CHECK_MODULES $(MAVLINK_HEADERS) 最后建立px4的相关目标$(PX4_ROOT)/Archives/px4fmu-v2.export $(SKETCHCPP) module_mk px4-io-v2
$(RULEHDR) 注意：px4-v2的依赖条件中包含了$(SKETCHCPP)，从这里调用该工程下的源文件；
$(v) cp $(PX4_V2_CONFIG_FILE) $(PX4_ROOT)/makefiles/nuttx/ cp 复制copy
$(PX4_MAKE) px4fmu-v2_APM
$(v) arm-none-eabi-size $(PX4_ROOT)/Build/px4fmu-v2_APM.build/firmware.elf
$(v) cp $(PX4_ROOT)/Images/px4fmu-v2_APM.px4 $(SKETCH)-v2.px4
$(v) $(SKETCHBOOK)/Tools/scripts/add_git_hashes.py $(HASHADDER_FLAGS) "$(SKETCH)-v2.px4" "$(SKETCH)-v2.px4"
$(v) echo "PX4 $(SKETCH) Firmware is in $(SKETCH)-v2.px4"这个步骤就是编译 px4fmu-v2_APM的过程，仔细分析这段代码
首先 通过 echo 命令将 $(xxx) 真正意思打印出来，分别用 1 到 7 对应起来echo "1$(BUILDROOT) 2$(MAVLINK_HEADERS) 3$(PX4_ROOT) 4$(PX4_V2_CONFIG_FILE)5$(PX4_MAKE) 6$(SKETCH) 7$(SKETCHBOOK)"
1/c/ardupilot/Build.ArduCopter 2/c/ardupilot/Build.ArduCopter/libraries/GCS_MAVLink/include/mavlink/v1.0/ardupilotmega/mavlink.h
3/c/ardupilot/modules/PX4Firmware
4../mk/PX4/config_px4fmu-v2_APM.mk
5@+ GIT_SUBMODULES_ARE_EVIL=1 ARDUPILOT_BUILD=1 make -C /c/ardupilot -f /c/ardupilot/modules/PX4Firmware/Makefile.make EXTRADEFINES=-I/c/ardupilot/libraries/ -I/c/ardupilot/Build.ArduCopter/libraries/ -I/c/ardupilot/Build.ArduCopter/libraries/GCS_MAVLink/ -DARDUPILOT_BUILD -DTESTS_MATHLIB_DISABLE -DCONFIG_HAL_BOARD=HAL_BOARD_PX4 -DSKETCHNAME=\"ArduCopter\" -DSKETCH_MAIN=ArduPilot_main -DAPM_BUILD_DIRECTORY=APM_BUILD_ArduCopter -Wall -Wextra -Wlogical-op -Werror -Wno-unknown-pragmas -Wno-redundant-decls -Wno-psabi -Wno-packed -Wno-error=double-promotion -Wno-error=unused-variable -Wno-error=reorder -Wno-error=float-equal -Wno-error=pmf-conversions -Wno-error=missing-declarations -Wno-error=unused-function -fsingle-precision-constant '-DGIT_VERSION="3c5287e8" -I/c/ardupilot/libraries/AP_Common/missing -DNUTTX_GIT_VERSION="579e82d4" -DPX4_GIT_VERSION="55491083" -DUAVCAN=1 -DHAVE_STD_NULLPTR_T=0 -I/c/ardupilot/Build.ArduCopter/libraries/GCS_MAVLink/include/mavlink' APM_MODULE_DIR=/c/ardupilot SKETCHBOOK=/c/ardupilot CCACHE= PX4_ROOT=/c/ardupilot/modules/PX4Firmware NUTTX_SRC=/c/ardupilot/modules/PX4NuttX/nuttx/ MAXOPTIMIZATION=-Os UAVCAN_DIR=/c/ardupilot/modules/uavcan/
6ArduCopter
7/c/ardupilot
然后根据脚本的语法，可知主要是$(PX4_MAKE)px4fmu-v2_APM完成编译任务
$(PX4_MAKE)真正意思对应上面第5条，再根据脚本基本语法可知
make-C /c/ardupilot -f /c/ardupilot/modules/PX4Firmware/Makefile.make主要完成编译任务
-D是定义、-I是添加库、=是赋值
由此可定位到/c/ardupilot/modules/PX4Firmware/Makefile.make
但是Makefile.make文件里没有px4fmu-v2_APM的目标，说明目标被处理过了。于是只好去看编译输出信息了
%%%%
%%%% Building px4fmu-v2_APM in /c/ardupilot/modules/PX4Firmware/Build/px4fmu-v2_APM.build/
%%%%
通过这串信息，匹配到了这样一个目标
#
# Generate FIRMWARES.
#
.PHONY: $(FIRMWARES)
$(BUILD_DIR)%.build/firmware.px4: config = $(patsubst $(BUILD_DIR)%.build/firmware.px4,%,$@)
$(BUILD_DIR)%.build/firmware.px4: work_dir = $(BUILD_DIR)$(config).build/
$(FIRMWARES): $(BUILD_DIR)%.build/firmware.px4: generateuorbtopicheaders checksubmodules
@$(ECHO) %%%%
@$(ECHO) %%%% Building $(config) in $(work_dir)
@$(ECHO) %%%%
$(Q) $(MKDIR) -p $(work_dir)
$(Q)+ $(MAKE) -r -C $(work_dir) \ 从这开始，完成编译工作
-f $(PX4_MK_DIR)firmware.mk \ 语句尾部“\”表示语句连接
CONFIG=$(config) \
WORK_DIR=$(work_dir) \
$(FIRMWARE_GOAL)
$(PX4_MK_DIR)firmware.mk的真正意思是/c/ardupilot/modules/PX4Firmware/makefiles/firmware.mk
这样就定位到firmware.mk文件 此处主要分析px4_targets.mk，firmware.mk文件内容较多，下节再分析。
px4-io-v2: $(PX4_ROOT)/Archives/px4io-v2.export
$(v)+ $(MAKE) -C $(PX4_ROOT) -f $(PX4_ROOT)/Makefile.make px4io-v2_default EXTRADEFINES="-DARDUPILOT_BUILD"
$(v) cp $(PX4_ROOT)/Images/px4io-v2_default.bin px4io-v2.bin
$(v) cp $(PX4_ROOT)/Build/px4io-v2_default.build/firmware.elf px4io-v2.elf
$(v) mkdir -p $(MK_DIR)/PX4/ROMFS/px4io/ mkdir 创建目录
$(v) cp px4io-v2.bin $(MK_DIR)/PX4/ROMFS/px4io/px4io.bin
$(v) mkdir -p $(MK_DIR)/PX4/ROMFS/bootloader/
$(v) cp $(SKETCHBOOK)/mk/PX4/bootloader/px4fmuv2_bl.bin $(MK_DIR)/PX4/ROMFS/bootloader/fmu_bl.bin
$(v) echo "PX4IOv2 Firmware is in px4io-v2.bin"实际的内容是
make -C /e/ardupilot/modules/PX4Firmware px4io-v2_default 编译firmware基本文件
/bin/rm -f px4io-v2.bin
cp /e/ardupilot/modules/PX4Firmware/Build/px4io-v2_default.build/firmware.bin px4io-v2.bin
cp /e/ardupilot/modules/PX4Firmware/Images/px4io-v2_default.bin px4io-v2.bin
cp /e/ardupilot/modules/PX4Firmware/Build/px4io-v2_default.build/firmware.elf px4io-v2.elf
mkdir -p ../mk/PX4/ROMFS/px4io/
rm -f ../mk/PX4/ROMFS/px4io/px4io.bin
cp px4io-v2.bin ../mk/PX4/ROMFS/px4io/px4io.bin
mkdir -p ../mk/PX4/ROMFS/bootloader/
rm -f ../mk/PX4/ROMFS/bootloader/fmu_bl.bin
cp /c/ardupilot/mk/PX4/bootloader/px4fmuv2_bl.bin ../mk/PX4/ROMFS/bootloader/fmu_bl.bin
PX4IOv2 Firmware is in px4io-v2.bin
生成.bin .elf 文件
.NOTPARALLEL: \
$(PX4_ROOT)/Archives/px4fmu-v1.export \
$(PX4_ROOT)/Archives/px4fmu-v2.export \
$(PX4_ROOT)/Archives/px4fmu-v4.export \
$(PX4_ROOT)/Archives/px4io-v1.export \
$(PX4_ROOT)/Archives/px4io-v2.export
px4_targets.mk
px4_common.mk添加驱动、系统命令等模块
firmware.mk 注释：GenericMakefile for PX4 firmware images. 通用MakefilePX4固件镜像。
include $(MK_DIR)/setup.mk /c/ardupilot/modules/PX4Firmware/makefiles/setup.mk
目的是Get path and tool config 即设置路径和tool
include $(PX4_MK_DIR)/$(PX4_TARGET_OS).mk /c/ardupilot/modules/PX4Firmware/makefiles/nuttx.mk
目的是Rules and definitions related to handling the NuttX export archives when building firmware.
即Nuttx输出的相关规则和定义
# Make a list of the object files we expect to build from modules
# Note that this path will typically contain a double-slash at the WORK_DIR boundary; this must be
# preserved as it is used below to get the absolute path for the module.mk file correct.
#
MODULE_OBJS := $(foreach path,$(dir $(MODULE_MKFILES)),$(WORK_DIR)$(path)module.pre.o)
# rules to build module objects
.PHONY: $(MODULE_OBJS)
$(MODULE_OBJS): relpath = $(patsubst $(WORK_DIR)%,%,$@)
$(MODULE_OBJS): mkfile = $(patsubst %module.pre.o,%module.mk,$(relpath))
$(MODULE_OBJS): workdir = $(@D)
$(MODULE_OBJS): $(GLOBAL_DEPS) $(NUTTX_CONFIG_HEADER)
$(Q) $(MKDIR) -p $(workdir)
$(Q)+ $(MAKE) -r -f $(PX4_MK_DIR)module.mk \
-C $(workdir) \
MODULE_WORK_DIR=$(workdir) \
MODULE_OBJ=$@ \
MODULE_MK=$(mkfile) \
MODULE_NAME=$(lastword $(subst /, ,$(workdir))) \
Module
这段是module的obj文件生成规则，规定了module的路径、makefile文件路径、工作目录等，并生成obj文件
# make a list of phony clean targets for modules
MODULE_CLEANS := $(foreach path,$(dir $(MODULE_MKFILES)),$(WORK_DIR)$(path)/clean)
# rules to clean modules
.PHONY: $(MODULE_CLEANS)
$(MODULE_CLEANS): relpath = $(patsubst $(WORK_DIR)%,%,$@)
$(MODULE_CLEANS): mkfile = $(patsubst %clean,%module.mk,$(relpath))
$(MODULE_CLEANS):
@$(ECHO) %% cleaning using $(mkfile)
$(Q)+ $(MAKE) -r -f $(PX4_MK_DIR)module.mk \
MODULE_WORK_DIR=$(dir $@) \
MODULE_MK=$(mkfile) \
Clean
这段是clean module的规则，清除的路径、makefile的路径。
# Make a list of the archive files we expect to build from libraries
# Note that this path will typically contain a double-slash at the WORK_DIR boundary; this must be
# preserved as it is used below to get the absolute path for the library.mk file correct.
#
LIBRARY_LIBS := $(foreach path,$(dir $(LIBRARY_MKFILES)),$(WORK_DIR)$(path)library.a)
# rules to build module objects
.PHONY: $(LIBRARY_LIBS)
$(LIBRARY_LIBS): relpath = $(patsubst $(WORK_DIR)%,%,$@)
$(LIBRARY_LIBS): mkfile = $(patsubst %library.a,%library.mk,$(relpath))
$(LIBRARY_LIBS): workdir = $(@D)
$(LIBRARY_LIBS): $(GLOBAL_DEPS) $(NUTTX_CONFIG_HEADER)
$(Q) $(MKDIR) -p $(workdir)
$(Q)+ $(MAKE) -r -f $(PX4_MK_DIR)library.mk \
-C $(workdir) \
LIBRARY_WORK_DIR=$(workdir) \
LIBRARY_LIB=$@ \
LIBRARY_MK=$(mkfile) \
LIBRARY_NAME=$(lastword $(subst /, ,$(workdir))) \
Library
这段是库的obj文件生成规则，规定了库的路径、makefile文件路径、工作目录等，并生成obj文件
# make a list of phony clean targets for modules
LIBRARY_CLEANS := $(foreach path,$(dir $(LIBRARY_MKFILES)),$(WORK_DIR)$(path)/clean)
# rules to clean modules
.PHONY: $(LIBRARY_CLEANS)
$(LIBRARY_CLEANS): relpath = $(patsubst $(WORK_DIR)%,%,$@)
$(LIBRARY_CLEANS): mkfile = $(patsubst %clean,%library.mk,$(relpath))
$(LIBRARY_CLEANS):
@$(ECHO) %% cleaning using $(mkfile)
$(Q)+ $(MAKE) -r -f $(PX4_MK_DIR)library.mk \
LIBRARY_WORK_DIR=$(dir $@) \
LIBRARY_MK=$(mkfile) \
clean
这段是clean 库的规则，清除的路径、makefile的路径。
以下是直接复制的，主要实现相关的编译功能，有相应的注释。
################################################################################
# Builtin command list generation
################################################################################
#
# Builtin commands can be generated by the configuration, in which case they
# must refer to commands that already exist, or indirectly generated by modules
# when they are built.
#
# The configuration supplies builtin command information in the BUILTIN_COMMANDS
# variable. Applications make empty files in $(WORK_DIR)/builtin_commands whose
# filename contains the same information.
#
# In each case, the command information consists of four fields separated with a
# period. These fields are the command's name, its thread priority, its stack size
# and the name of the function to call when starting the thread.
#
# BUILTIN_COMMANDS
# Contains a list of built-in commands not explicitly provided
# by modules / libraries. Each entry in this list is formatted
# as <command>.<priority>.<stacksize>.<entrypoint>
BUILTIN_CSRC = $(WORK_DIR)builtin_commands.c
# command definitions from modules (may be empty at Makefile parsing time...)
MODULE_COMMANDS = $(subst COMMAND.,,$(notdir $(wildcard $(WORK_DIR)builtin_commands/COMMAND.*)))
# We must have at least one pre-defined builtin command in order to generate
# any of this.
#
ifneq ($(BUILTIN_COMMANDS),)
# (BUILTIN_PROTO,<cmdspec>,<outputfile>)
define BUILTIN_PROTO
$(ECHO) 'extern int $(word 4,$1)(int argc, char *argv[]);' >> $2;
endef
# (BUILTIN_DEF,<cmdspec>,<outputfile>)
define BUILTIN_DEF
$(ECHO) ' {"$(word 1,$1)", $(word 2,$1), $(word 3,$1), $(word 4,$1)},' >> $2;
endef
# Don't generate until modules have updated their command files
$(BUILTIN_CSRC): $(GLOBAL_DEPS) $(MODULE_OBJS) $(MODULE_MKFILES) $(BUILTIN_COMMAND_FILES)
@$(ECHO) "CMDS: $@"
$(Q) $(ECHO) '/* builtin command list - automatically generated, do not edit */' > $@
$(Q) $(ECHO) '#include <nuttx/config.h>' >> $@
$(Q) $(ECHO) '#include <nuttx/binfmt/builtin.h>' >> $@
$(Q) $(foreach spec,$(BUILTIN_COMMANDS),$(call BUILTIN_PROTO,$(subst ., ,$(spec)),$@))
$(Q) $(foreach spec,$(MODULE_COMMANDS),$(call BUILTIN_PROTO,$(subst ., ,$(spec)),$@))
$(Q) $(ECHO) 'const struct builtin_s g_builtins[] = {' >> $@
$(Q) $(foreach spec,$(BUILTIN_COMMANDS),$(call BUILTIN_DEF,$(subst ., ,$(spec)),$@))
$(Q) $(foreach spec,$(MODULE_COMMANDS),$(call BUILTIN_DEF,$(subst ., ,$(spec)),$@))
$(Q) $(ECHO) ' {NULL, 0, 0, NULL}' >> $@
$(Q) $(ECHO) '};' >> $@
$(Q) $(ECHO) 'const int g_builtin_count = $(words $(BUILTIN_COMMANDS) $(MODULE_COMMANDS));' >> $@
SRCS += $(BUILTIN_CSRC)
EXTRA_CLEANS += $(BUILTIN_CSRC)
endif
endif
################################################################################
# Default SRCS generation
################################################################################
#
# If there are no SRCS, the build will fail; in that case, generate an empty
# source file.
#
ifeq ($(SRCS),)
EMPTY_SRC = $(WORK_DIR)empty.c
$(EMPTY_SRC):
$(Q) $(ECHO) '/* this is an empty file */' > $@
SRCS += $(EMPTY_SRC)
endif
################################################################################
# Build rules
################################################################################
ifeq ($(PX4_TARGET_OS),nuttx)
#
# What we're going to build.
#
PRODUCT_BUNDLE = $(WORK_DIR)firmware.px4
PRODUCT_BIN = $(WORK_DIR)firmware.bin
PRODUCT_ELF = $(WORK_DIR)firmware.elf
PRODUCT_PARAMXML = $(WORK_DIR)/parameters.xml
.PHONY: firmware
firmware: $(PRODUCT_BUNDLE)
endif
#
# Object files we will generate from sources
#
OBJS := $(foreach src,$(SRCS),$(WORK_DIR)$(src).o)
#
# SRCS -> OBJS rules 将源文件编译成obj文件
#
$(OBJS): $(GLOBAL_DEPS)
$(filter %.c.o,$(OBJS)): $(WORK_DIR)%.c.o: %.c $(GLOBAL_DEPS)
$(call COMPILE,$<,$@)
$(filter %.cpp.o,$(OBJS)): $(WORK_DIR)%.cpp.o: %.cpp $(GLOBAL_DEPS)
$(call COMPILEXX,$<,$@)
$(filter %.S.o,$(OBJS)): $(WORK_DIR)%.S.o: %.S $(GLOBAL_DEPS)
$(call ASSEMBLE,$<,$@)
ifeq ($(PX4_TARGET_OS),nuttx)
#
# Built product rules
#
$(PRODUCT_BUNDLE): $(PRODUCT_BIN)
@$(ECHO) %% Generating $@
ifdef GEN_PARAM_XML
$(Q) $(PYTHON) $(PX4_BASE)/Tools/px_process_params.py --src-path $(PX4_BASE)/src --board CONFIG_ARCH_BOARD_$(CONFIG_BOARD) --xml
$(Q) $(MKFW) --prototype $(IMAGE_DIR)/$(BOARD).prototype \
--git_identity $(PX4_BASE) \
--parameter_xml $(PRODUCT_PARAMXML) \
--image $< > $@
else
$(Q) $(MKFW) --prototype $(IMAGE_DIR)/$(BOARD).prototype \
--git_identity $(PX4_BASE) \
--image $< > $@
endif
$(PRODUCT_BIN): $(PRODUCT_ELF)
$(call SYM_TO_BIN,$<,$@)
$(PRODUCT_ELF): $(OBJS) $(MODULE_OBJS) $(LIBRARY_LIBS) $(GLOBAL_DEPS) $(LINK_DEPS) $(MODULE_MKFILES)
$(call LINK,$@,$(OBJS) $(MODULE_OBJS) $(LIBRARY_LIBS))
#
# Utility rules 实用的规则
#
.PHONY: upload
upload: $(PRODUCT_BUNDLE) $(PRODUCT_BIN)
$(Q) $(MAKE) -f $(PX4_MK_DIR)/upload.mk \
METHOD=serial \
CONFIG=$(CONFIG) \
BOARD=$(BOARD) \
BUNDLE=$(PRODUCT_BUNDLE) \
BIN=$(PRODUCT_BIN)
.PHONY: clean
clean: $(MODULE_CLEANS)
@$(ECHO) %% cleaning
$(Q) $(REMOVE) $(PRODUCT_BUNDLE) $(PRODUCT_BIN) $(PRODUCT_ELF)
$(Q) $(REMOVE) $(OBJS) $(DEP_INCLUDES) $(EXTRA_CLEANS)
$(Q) $(RMDIR) $(NUTTX_EXPORT_DIR)
endif
# Include the OS specific build rules
# The rules must define the "firmware" make target
#
ifeq ($(PX4_TARGET_OS),nuttx)
# TODO
# Move above nuttx specific rules to $(MK_DIR)/nuttx_romfs.mk
endif
ifeq ($(PX4_TARGET_OS),posix)
include $(MK_DIR)/posix_elf.mk
endif
ifeq ($(PX4_TARGET_OS),qurt)
include $(MK_DIR)/qurt_elf.mk
endif
#
# DEP_INCLUDES is defined by the toolchain include in terms of $(OBJS)
#
-include $(DEP_INCLUDES)
通过firmware.mk文件阅读，终于知道.px4是如何编译出来的了，如何添加lib、module，从而用于裁剪程序。其实.mk文件只是将ccs或者kile等软件的编译工作完成，自行设置编译规则、编译什么文件、分配芯片占用空间等等。至于具体程序的裁剪，若在.mk文件中去掉lib或者module，最后下载进板子的程序就不会有这部分内容，就没法运行；若.mk添加了，但在rcS、Rc.APM中不启动，只是占有了板子内存，并没有运行。
targets.mk，sketch_sources.mk 暂时先放着如果您觉得此文对您的发展有用，请随意打赏。
您的鼓励将是笔者书写高质量文章的最大动力^_^!!
