上一节成功点亮了led的，但是，它是裸机程序，还没有真正的开始，真正的开始应该是运行u-boot所以本节主要解决以下问题：
1 uboot怎么下载
2 uboot怎么生成BL1(u-boot-spl.bin)
3 uboot怎么样生成BL2(u-boot.bin)
一 下载源码
u-boot的源码，一般下载下来的都是压缩格式，ftp://ftp.denx.de/pub/u-boot/，为了方便版本的切换，在此使用git工具下载，具体步骤如下：
1） clone 出仓库：
git clone git://git.denx.de/u-boot.git u-boot
2） 查看仓库的一些信息：
git status
3） 查看 release 版本(打的标签)：
git tag
4）切换到特定的标签版本下：
git checkout v2016.09.01
5） 查看本标签与其他的标签的不同：
git diff v2016.09
二 版本结构
1 版本命名变化，主要发生在2008年，以前按版本号命名，2008年后，以年月命名，如下图所示：
2 目录结构变化，随着版本地升级，目录的组织结构也发生了变化，当前使用的版本的目录结构如下所示
三 make <board>_defconfig过程
1 编译前，需要先清理源码树：make distclean
Cleaning targets: clean - Remove most generated files but keep the config mrproper - Remove all generated files + config + various backup files distclean - mrproper + remove editor backup and patch files
2 配置
rabbit@rabbit:~/work/samba/u-boot$ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- am335x_boneblack_defconfig V=1 make -f ./scripts/Makefile.build obj=scripts/basic cc -Wp,-MD,scripts/basic/.fixdep.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -o scripts/basic/fixdep scripts/basic/fixdep.c rm -f .tmp_quiet_recordmcount make -f ./scripts/Makefile.build obj=scripts/kconfig am335x_boneblack_defconfig cc -Wp,-MD,scripts/kconfig/.conf.o.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -D_GNU_SOURCE -DCURSES_LOC="<ncurses.h>" -DLOCALE -c -o scripts/kconfig/conf.o scripts/kconfig/conf.c cat scripts/kconfig/zconf.tab.c_shipped > scripts/kconfig/zconf.tab.c cat scripts/kconfig/zconf.lex.c_shipped > scripts/kconfig/zconf.lex.c cat scripts/kconfig/zconf.hash.c_shipped > scripts/kconfig/zconf.hash.c cc -Wp,-MD,scripts/kconfig/.zconf.tab.o.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -D_GNU_SOURCE -DCURSES_LOC="<ncurses.h>" -DLOCALE -Iscripts/kconfig -c -o scripts/kconfig/zconf.tab.o scripts/kconfig/zconf.tab.c cc -o scripts/kconfig/conf scripts/kconfig/conf.o scripts/kconfig/zconf.tab.o scripts/kconfig/conf --defconfig=arch/../configs/am335x_boneblack_defconfig Kconfig # # configuration written to .config #
二 make all过程
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf-
（1）uboot.bin过程
# Always append ALL so that arch config.mk's can add custom ones
ALL-y += u-boot.srec u-boot.bin u-boot.sym System.map u-boot.cfg binary_size_check ALL-$(CONFIG_ONENAND_U_BOOT) += u-boot-onenand.bin ifeq ($(CONFIG_SPL_FSL_PBL),y) ALL-$(CONFIG_RAMBOOT_PBL) += u-boot-with-spl-pbl.bin else ifneq ($(CONFIG_SECURE_BOOT), y) # For Secure Boot The Image needs to be signed and Header must also # be included. So The image has to be built explicitly ALL-$(CONFIG_RAMBOOT_PBL) += u-boot.pbl endif endif ALL-$(CONFIG_SPL) += spl/u-boot-spl.bin ALL-$(CONFIG_SPL_FRAMEWORK) += u-boot.img ALL-$(CONFIG_TPL) += tpl/u-boot-tpl.bin ALL-$(CONFIG_OF_SEPARATE) += u-boot.dtb ifeq ($(CONFIG_SPL_FRAMEWORK),y) ALL-$(CONFIG_OF_SEPARATE) += u-boot-dtb.img endif ALL-$(CONFIG_OF_HOSTFILE) += u-boot.dtb ifneq ($(CONFIG_SPL_TARGET),) ALL-$(CONFIG_SPL) += $(CONFIG_SPL_TARGET:"%"=%) endif ALL-$(CONFIG_REMAKE_ELF) += u-boot.elf ALL-$(CONFIG_EFI_APP) += u-boot-app.efi ALL-$(CONFIG_EFI_STUB) += u-boot-payload.efi ifneq ($(BUILD_ROM),) ALL-$(CONFIG_X86_RESET_VECTOR) += u-boot.rom endif 铎 # enable combined SPL/u-boot/dtb rules for tegra ifeq ($(CONFIG_TEGRA)$(CONFIG_SPL),yy) ALL-y += u-boot-tegra.bin u-boot-nodtb-tegra.bin ALL-$(CONFIG_OF_SEPARATE) += u-boot-dtb-tegra.bin endif # Add optional build target if defined in board/cpu/soc headers ifneq ($(CONFIG_BUILD_TARGET),) ALL-y += $(CONFIG_BUILD_TARGET:"%"=%) endif all: $(ALL-y)
ifeq ($(CONFIG_OF_SEPARATE),y) u-boot-dtb.bin: u-boot-nodtb.bin dts/dt.dtb FORCE $(call if_changed,cat) u-boot.bin: u-boot-dtb.bin FORCE $(call if_changed,copy) else u-boot.bin: u-boot-nodtb.bin FORCE $(call if_changed,copy) endif
u-boot-nodtb.bin: u-boot FORCE $(call if_changed,objcopy) $(call DO_STATIC_RELA,$<,$@,$(CONFIG_SYS_TEXT_BASE)) $(BOARD_SIZE_CHECK)
u-boot: $(u-boot-init) $(u-boot-main) u-boot.lds FORCE $(call if_changed,u-boot__) ifeq ($(CONFIG_KALLSYMS),y) $(call cmd,smap) $(call cmd,u-boot__) common/system_map.o endif
u-boot-init := $(head-y) u-boot-main := $(libs-y)
./scripts/Makefile.spl:51:libs-y += $(if $(BOARDDIR),board/$(BOARDDIR)/) ./scripts/Makefile.spl:55:libs-y += common/init/ ./scripts/Makefile.spl:58:libs-y += drivers/ ./scripts/Makefile.spl:59:libs-y += dts/ ./scripts/Makefile.spl:60:libs-y += fs/ ./scripts/Makefile.spl:66:libs-y := $(addprefix $(obj)/,$(libs-y)) ./scripts/Makefile.spl:67:u-boot-spl-dirs := $(patsubst %/,%,$(filter %/, $(libs-y))) ./scripts/Makefile.spl:69:libs-y := $(patsubst %/, %/built-in.o, $(libs-y)) ./scripts/Makefile.spl:78:u-boot-spl-main := $(libs-y) ./arch/arc/Makefile:5:libs-y += arch/arc/cpu/$(CPU)/ ./arch/arc/Makefile:6:libs-y += arch/arc/lib/ ./arch/openrisc/Makefile:7:libs-y += arch/openrisc/cpu/ ./arch/openrisc/Makefile:8:libs-y += arch/openrisc/lib/ ./arch/powerpc/Makefile:9:libs-y += arch/powerpc/cpu/$(CPU)/ ./arch/powerpc/Makefile:10:libs-y += arch/powerpc/cpu/ ./arch/powerpc/Makefile:11:libs-y += arch/powerpc/lib/ ./arch/sparc/Makefile:7:libs-y += arch/sparc/cpu/$(CPU)/ ./arch/sparc/Makefile:8:libs-y += arch/sparc/lib/ ./arch/arm/Makefile:71:libs-y += $(machdirs) ./arch/arm/Makefile:81:libs-y += arch/arm/cpu/$(CPU)/ ./arch/arm/Makefile:82:libs-y += arch/arm/cpu/ ./arch/arm/Makefile:83:libs-y += arch/arm/lib/ ./arch/arm/Makefile:87:libs-y += arch/arm/imx-common/ ./arch/arm/Makefile:91:libs-y += arch/arm/imx-common/ ./arch/arm/Makefile:96:libs-y += arch/arm/mach-mvebu/ ./arch/sandbox/Makefile:7:libs-y += arch/sandbox/cpu/ ./arch/sandbox/Makefile:8:libs-y += arch/sandbox/lib/ ./arch/nds32/Makefile:7:libs-y += arch/nds32/cpu/$(CPU)/ ./arch/nds32/Makefile:8:libs-y += arch/nds32/lib/ ./arch/blackfin/Makefile:7:libs-y += arch/blackfin/cpu/ ./arch/blackfin/Makefile:8:libs-y += arch/blackfin/lib/ ./arch/avr32/Makefile:7:libs-y += arch/avr32/cpu/ ./arch/avr32/Makefile:8:libs-y += arch/avr32/lib/ ./arch/mips/Makefile:7:libs-y += arch/mips/cpu/ ./arch/mips/Makefile:8:libs-y += arch/mips/lib/ ./arch/mips/Makefile:14:libs-y += $(machdirs) ./arch/nios2/Makefile:7:libs-y += arch/nios2/cpu/ ./arch/nios2/Makefile:8:libs-y += arch/nios2/lib/ ./arch/m68k/Makefile:7:libs-y += arch/m68k/cpu/$(CPU)/ ./arch/m68k/Makefile:8:libs-y += arch/m68k/lib/ ./arch/x86/Makefile:13:libs-y += arch/x86/cpu/ ./arch/x86/Makefile:14:libs-y += arch/x86/lib/ ./arch/sh/Makefile:7:libs-y += arch/sh/cpu/$(CPU)/ ./arch/sh/Makefile:8:libs-y += arch/sh/lib/ ./arch/microblaze/Makefile:7:libs-y += arch/microblaze/cpu/ ./arch/microblaze/Makefile:8:libs-y += arch/microblaze/lib/ ./Makefile:620:libs-y += lib/ ./Makefile:623:libs-y += fs/ ./Makefile:624:libs-y += net/ ./Makefile:625:libs-y += disk/ ./Makefile:626:libs-y += drivers/ ./Makefile:627:libs-y += drivers/dma/ ./Makefile:628:libs-y += drivers/gpio/ ./Makefile:629:libs-y += drivers/i2c/ ./Makefile:630:libs-y += drivers/mmc/ ./Makefile:631:libs-y += drivers/mtd/ ./Makefile:633:libs-y += drivers/mtd/onenand/ ./Makefile:635:libs-y += drivers/mtd/spi/ ./Makefile:636:libs-y += drivers/net/ ./Makefile:637:libs-y += drivers/net/phy/ ./Makefile:638:libs-y += drivers/pci/ ./Makefile:639:libs-y += drivers/power/ \ ./Makefile:645:libs-y += drivers/spi/ ./Makefile:649:libs-y += drivers/serial/ ./Makefile:650:libs-y += drivers/usb/dwc3/ ./Makefile:651:libs-y += drivers/usb/common/ ./Makefile:652:libs-y += drivers/usb/emul/ ./Makefile:653:libs-y += drivers/usb/eth/ ./Makefile:654:libs-y += drivers/usb/gadget/ ./Makefile:655:libs-y += drivers/usb/gadget/udc/ ./Makefile:656:libs-y += drivers/usb/host/ ./Makefile:657:libs-y += drivers/usb/musb/ ./Makefile:658:libs-y += drivers/usb/musb-new/ ./Makefile:659:libs-y += drivers/usb/phy/ ./Makefile:660:libs-y += drivers/usb/ulpi/ ./Makefile:661:libs-y += cmd/ ./Makefile:662:libs-y += common/ ./Makefile:665:libs-y += test/ ./Makefile:666:libs-y += test/dm/ ./Makefile:669:libs-y += $(if $(BOARDDIR),board/$(BOARDDIR)/) ./Makefile:671:libs-y := $(sort $(libs-y)) ./Makefile:673:u-boot-dirs := $(patsubst %/,%,$(filter %/, $(libs-y))) tools examples ./Makefile:677:libs-y := $(patsubst %/, %/built-in.o, $(libs-y)) ./Makefile:680:u-boot-main := $(libs-y)
（2）
uboot-spl.bin生成过程
ALL-$(CONFIG_SPL) += spl/u-boot-spl.bin
spl/u-boot-spl.bin: spl/u-boot-spl @: spl/u-boot-spl: tools prepare $(if $(CONFIG_OF_SEPARATE),dts/dt.dtb) $(Q)$(MAKE) obj=spl -f $(srctree)/scripts/Makefile.spl all
ALL-y += $(obj)/$(SPL_BIN).bin $(obj)/$(SPL_BIN).cfg ifdef CONFIG_SAMSUNG ALL-y += $(obj)/$(BOARD)-spl.bin endif ifdef CONFIG_ARCH_SOCFPGA ALL-y += $(obj)/$(SPL_BIN).sfp endif ifdef CONFIG_SUNXI ALL-y += $(obj)/sunxi-spl.bin endif ifeq ($(CONFIG_SYS_SOC),"at91") ALL-y += boot.bin endif ifdef CONFIG_ARCH_ZYNQ ALL-y += $(obj)/boot.bin endif all: $(ALL-y)
ifeq ($(CONFIG_TPL_BUILD),y) SPL_BIN := u-boot-tpl else SPL_BIN := u-boot-spl endif
1
ifeq ($(CONFIG_SPL_OF_CONTROL)$(CONFIG_OF_SEPARATE),yy) $(obj)/$(SPL_BIN)-dtb.bin: $(obj)/$(SPL_BIN)-nodtb.bin $(obj)/$(SPL_BIN)-pad.bin \ $(obj)/$(SPL_BIN).dtb FORCE $(call if_changed,cat) $(obj)/$(SPL_BIN).bin: $(obj)/$(SPL_BIN)-dtb.bin FORCE $(call if_changed,copy) else $(obj)/$(SPL_BIN).bin: $(obj)/$(SPL_BIN)-nodtb.bin FORCE $(call if_changed,copy) endif
$(obj)/$(SPL_BIN)-nodtb.bin: $(obj)/$(SPL_BIN) FORCE $(call if_changed,objcopy)
$(obj)/$(SPL_BIN): $(u-boot-spl-init) $(u-boot-spl-main) $(obj)/u-boot-spl.lds FORCE $(call if_changed,u-boot-spl)
include $(srctree)/config.mk include $(srctree)/arch/$(ARCH)/Makefile # Enable garbage collection of un-used sections for SPL KBUILD_CFLAGS += -ffunction-sections -fdata-sections LDFLAGS_FINAL += --gc-sections # FIX ME cpp_flags := $(KBUILD_CPPFLAGS) $(PLATFORM_CPPFLAGS) $(UBOOTINCLUDE) \ $(NOSTDINC_FLAGS) HAVE_VENDOR_COMMON_LIB = $(if $(wildcard $(srctree)/board/$(VENDOR)/common/Makefile),y,n) libs-y += $(if $(BOARDDIR),board/$(BOARDDIR)/) libs-$(HAVE_VENDOR_COMMON_LIB) += board/$(VENDOR)/common/ libs-$(CONFIG_SPL_FRAMEWORK) += common/spl/ libs-y += common/init/ libs-$(CONFIG_SPL_LIBCOMMON_SUPPORT) += common/ cmd/ libs-$(CONFIG_SPL_LIBDISK_SUPPORT) += disk/ libs-y += drivers/ libs-y += dts/ libs-y += fs/ libs-$(CONFIG_SPL_LIBGENERIC_SUPPORT) += lib/ libs-$(CONFIG_SPL_POST_MEM_SUPPORT) += post/drivers/ libs-$(CONFIG_SPL_NET_SUPPORT) += net/ head-y := $(addprefix $(obj)/,$(head-y)) libs-y := $(addprefix $(obj)/,$(libs-y)) u-boot-spl-dirs := $(patsubst %/,%,$(filter %/, $(libs-y))) libs-y := $(patsubst %/, %/built-in.o, $(libs-y)) # Add GCC lib ifeq ($(CONFIG_USE_PRIVATE_LIBGCC),y) PLATFORM_LIBGCC = arch/$(ARCH)/lib/lib.a PLATFORM_LIBS := $(filter-out %/lib.a, $(filter-out -lgcc, $(PLATFORM_LIBS))) $(PLATFORM_LIBGCC) endif u-boot-spl-init := $(head-y) u-boot-spl-main := $(libs-y)
$(obj)/u-boot-spl.lds: $(LDSCRIPT) FORCE $(call if_changed_dep,cpp_lds)
2
$(obj)/$(SPL_BIN).cfg: include/config.h FORCE $(call if_changed,cpp_cfg)
3
ifdef CONFIG_SAMSUNG ifdef CONFIG_VAR_SIZE_SPL VAR_SIZE_PARAM = --vs else VAR_SIZE_PARAM = endif $(obj)/$(BOARD)-spl.bin: $(obj)/u-boot-spl.bin $(if $(wildcard $(objtree)/spl/board/samsung/$(BOARD)/tools/mk$(BOARD)spl),\ $(objtree)/spl/board/samsung/$(BOARD)/tools/mk$(BOARD)spl,\ $(objtree)/tools/mkexynosspl) $(VAR_SIZE_PARAM) $< $@ endif