从头开始移植u-boot和linux kernel 到imx6ul之u-boot

soc的启动一般都有下面这几个阶段：
1.soc上电，执行IROM中的厂商固话的boot_strap 代码
2.IROM中的boot_strap 代码初始化IRAM
3.并把IROM中的boot_strap 代码拷贝到IRAM中
4.跳到IRAM中继续执行boot_strap 代码
5.在IRAM中的boot_strap 代码初始化外部RAM，也就是主memory，一般是某种DDR器件。
6.在IRAM中的boot_strap 代码根据硬件的启动模式配置从对应的启动介质中拷贝用户的启动代码到RAM中
7.执行RAM中的用户的启动代码
总之，就像滚雪球一样，从最初的IROM中往外开疆拓土，最后完成用户程序（比如操作系统）的运行。
正好手中有一块NXP 的imx6ul开发板，想做个u-boot的移植实验，看看能够跑起u-boot的最小配置是怎么样的。
首先，找一个u-boot版本入手
http://www.denx.de/wiki/U-Boot/SourceCode

ftp://ftp.denx.de/pub/u-boot/

心想既然要移植，那就找个最新的版本吧。但下载下来后提示我的交叉编译工具版本太老了，高版本的u-boot中已经需要v4.6版本以上的gcc交叉编译工具了，已经不支持我手上的v4.5版本交叉工具链了。
最终，找来找去，发现u-boot-2017.11这个版本是最后一个能支持我手上的交叉编译工具版本的，所以只能下这个版本的进行试验了。
2.source 一下交叉编译工具环境变量
1.解压u-boot源码压缩包到工作目录
2. make board_xxx_default_config
3.make menuconfig
make
然后发现生成了uboot-spl
而我的imx6ul一般使用uboot.imx格式的文件，这个是在u-boot.bin基础上做了些修改，能够被IROM中的boot_strap解析的uboot镜像格式，使用这种格式，就可以借助boot_strap代码帮助我们初始化DDR，有了DDR，其他什么都好办了。
1.添加一个board配置

配置文件my_imx6ul_defconfig 中为空
清理一下工作目录，确保旧的配置什么的都被清理干净

make 一下我们的配置

root@ubuntu:~/my-imx6/02_source/u-boot-2017.11# ls configs/
mx6ul_14x14_evk_defconfig  my_imx6ul_defconfig
root@ubuntu:~/my-imx6/02_source/u-boot-2017.11# cat configs/my_imx6ul_defconfig 
root@ubuntu:~/my-imx6/02_source/u-boot-2017.11# make distclean
  CLEAN   scripts/basic
  CLEAN   scripts/kconfig
  CLEAN   .config
root@ubuntu:~/my-imx6/02_source/u-boot-2017.11# make my_imx6ul_defconfig
  HOSTCC  scripts/basic/fixdep
  HOSTCC  scripts/kconfig/conf.o
  SHIPPED scripts/kconfig/zconf.tab.c
  SHIPPED scripts/kconfig/zconf.lex.c
  SHIPPED scripts/kconfig/zconf.hash.c
  HOSTCC  scripts/kconfig/zconf.tab.o
  HOSTLD  scripts/kconfig/conf
#
# configuration written to .config
#

提示配置已经被写到了.config中，让我们看一下现在.config中是什么样的：

#
# Automatically generated file; DO NOT EDIT.
# U-Boot 2017.11 Configuration
#
# CONFIG_ARC is not set
# CONFIG_ARM is not set
# CONFIG_M68K is not set
# CONFIG_MICROBLAZE is not set
# CONFIG_MIPS is not set
# CONFIG_NDS32 is not set
# CONFIG_NIOS2 is not set
# CONFIG_PPC is not set
CONFIG_SANDBOX=y
# CONFIG_SH is not set
# CONFIG_X86 is not set
# CONFIG_XTENSA is not set

#
# General setup
#
CONFIG_LOCALVERSION=""
CONFIG_LOCALVERSION_AUTO=y
CONFIG_CC_OPTIMIZE_FOR_SIZE=y
# CONFIG_DISTRO_DEFAULTS is not set
CONFIG_SYS_MALLOC_F=y
CONFIG_SYS_MALLOC_F_LEN=0x400
CONFIG_SPL_SYS_MALLOC_F_LEN=0x400
CONFIG_TPL_SYS_MALLOC_F_LEN=0x400
CONFIG_EXPERT=y
CONFIG_SYS_MALLOC_CLEAR_ON_INIT=y
# CONFIG_TOOLS_DEBUG is not set
# CONFIG_PHYS_64BIT is not set

#
# Boot images
#
# CONFIG_ANDROID_BOOT_IMAGE is not set
# CONFIG_FIT is not set
CONFIG_SYS_EXTRA_OPTIONS=""
CONFIG_ARCH_FIXUP_FDT_MEMORY=y

#
# API
#
# CONFIG_API is not set

#
# Boot timing
#
# CONFIG_BOOTSTAGE is not set
CONFIG_BOOTSTAGE_RECORD_COUNT=30
CONFIG_SPL_BOOTSTAGE_RECORD_COUNT=5
CONFIG_BOOTSTAGE_STASH_ADDR=0
CONFIG_BOOTSTAGE_STASH_SIZE=0x1000

#
# Boot media
#
# CONFIG_NAND_BOOT is not set
# CONFIG_ONENAND_BOOT is not set
# CONFIG_QSPI_BOOT is not set
# CONFIG_SATA_BOOT is not set
# CONFIG_SD_BOOT is not set
# CONFIG_SPI_BOOT is not set
CONFIG_BOOTDELAY=2
# CONFIG_USE_BOOTARGS is not set

#
# Console
#
# CONFIG_CONSOLE_RECORD is not set
CONFIG_IDENT_STRING=""
CONFIG_LOGLEVEL=4
CONFIG_SPL_LOGLEVEL=4
# CONFIG_SILENT_CONSOLE is not set
# CONFIG_PRE_CONSOLE_BUFFER is not set
# CONFIG_CONSOLE_MUX is not set
# CONFIG_SYS_CONSOLE_IS_IN_ENV is not set
# CONFIG_SYS_CONSOLE_OVERWRITE_ROUTINE is not set
# CONFIG_SYS_CONSOLE_ENV_OVERWRITE is not set
# CONFIG_SYS_CONSOLE_INFO_QUIET is not set
# CONFIG_SYS_STDIO_DEREGISTER is not set
CONFIG_DEFAULT_FDT_FILE=""
# CONFIG_VERSION_VARIABLE is not set
CONFIG_BOARD_LATE_INIT=y
# CONFIG_DISPLAY_CPUINFO is not set
CONFIG_DISPLAY_BOARDINFO=y

#
# Start-up hooks
#
# CONFIG_ARCH_EARLY_INIT_R is not set
# CONFIG_ARCH_MISC_INIT is not set
# CONFIG_BOARD_EARLY_INIT_F is not set

#
# Security support
#
CONFIG_HASH=y

#
# SPL / TPL
#

#
# Command line interface
#
CONFIG_CMDLINE=y
# CONFIG_HUSH_PARSER is not set
CONFIG_SYS_PROMPT="=> "

#
# Autoboot options
#
CONFIG_AUTOBOOT=y
# CONFIG_AUTOBOOT_KEYED is not set

#
# FASTBOOT
#
CONFIG_BUILD_BIN2C=y

#
# Commands
#

#
# Info commands
#
CONFIG_CMD_BDI=y
CONFIG_CMD_CONFIG=y
CONFIG_CMD_CONSOLE=y
# CONFIG_CMD_CPU is not set
# CONFIG_CMD_LICENSE is not set

#
# Boot commands
#
CONFIG_CMD_BOOTD=y
CONFIG_CMD_BOOTM=y
# CONFIG_CMD_BOOTZ is not set
# CONFIG_CMD_BOOTMENU is not set
CONFIG_CMD_ELF=y
CONFIG_CMD_GO=y
CONFIG_CMD_RUN=y
CONFIG_CMD_IMI=y
# CONFIG_CMD_IMLS is not set
CONFIG_CMD_XIMG=y
# CONFIG_CMD_POWEROFF is not set
# CONFIG_CMD_THOR_DOWNLOAD is not set
# CONFIG_CMD_ZBOOT is not set

#
# Environment commands
#
# CONFIG_CMD_ASKENV is not set
CONFIG_CMD_EXPORTENV=y
CONFIG_CMD_IMPORTENV=y
CONFIG_CMD_EDITENV=y
# CONFIG_CMD_GREPENV is not set
CONFIG_CMD_SAVEENV=y
CONFIG_CMD_ENV_EXISTS=y
# CONFIG_CMD_ENV_CALLBACK is not set
# CONFIG_CMD_ENV_FLAGS is not set

#
# Memory commands
#
CONFIG_CMD_CRC32=y
CONFIG_CRC32_VERIFY=y
# CONFIG_CMD_EEPROM is not set
# CONFIG_LOOPW is not set
# CONFIG_CMD_MD5SUM is not set
# CONFIG_CMD_MEMINFO is not set
CONFIG_CMD_MEMORY=y
# CONFIG_CMD_MEMTEST is not set
# CONFIG_CMD_MX_CYCLIC is not set
# CONFIG_CMD_SHA1SUM is not set
# CONFIG_CMD_STRINGS is not set

#
# Compression commands
#
CONFIG_CMD_LZMADEC=y
# CONFIG_CMD_UNZIP is not set
# CONFIG_CMD_ZIP is not set

#
# Device access commands
#
# CONFIG_CMD_ARMFLASH is not set
# CONFIG_CMD_CLK is not set
# CONFIG_CMD_DEMO is not set
# CONFIG_CMD_DFU is not set
CONFIG_CMD_DM=y
# CONFIG_CMD_FDC is not set
CONFIG_CMD_FLASH=y
CONFIG_CMD_FPGA=y
# CONFIG_CMD_FPGA_LOADBP is not set
# CONFIG_CMD_FPGA_LOADFS is not set
# CONFIG_CMD_FPGA_LOADMK is not set
# CONFIG_CMD_FPGA_LOADP is not set
# CONFIG_CMD_FPGAD is not set
# CONFIG_CMD_FUSE is not set
# CONFIG_CMD_GPIO is not set
# CONFIG_CMD_GPT is not set
# CONFIG_RANDOM_UUID is not set
# CONFIG_CMD_IDE is not set
CONFIG_CMD_IO=y
CONFIG_CMD_IOTRACE=y
# CONFIG_CMD_I2C is not set
CONFIG_CMD_LOADB=y
CONFIG_CMD_LOADS=y
# CONFIG_CMD_MMC is not set
# CONFIG_CMD_NAND is not set
# CONFIG_CMD_MMC_SPI is not set
# CONFIG_CMD_ONENAND is not set
# CONFIG_CMD_PART is not set
# CONFIG_CMD_PCI is not set
# CONFIG_CMD_PCMCIA is not set
# CONFIG_CMD_READ is not set
CONFIG_CMD_SATA=y
# CONFIG_CMD_SAVES is not set
# CONFIG_CMD_SDRAM is not set
# CONFIG_CMD_SF is not set
CONFIG_CMD_SF_TEST=y
# CONFIG_CMD_SPI is not set
# CONFIG_CMD_TSI148 is not set
# CONFIG_CMD_UNIVERSE is not set
# CONFIG_CMD_USB is not set
# CONFIG_CMD_USB_SDP is not set
# CONFIG_CMD_USB_MASS_STORAGE is not set

#
# Shell scripting commands
#
CONFIG_CMD_ECHO=y
CONFIG_CMD_ITEST=y
CONFIG_CMD_SOURCE=y
CONFIG_CMD_SETEXPR=y

#
# Network commands
#
CONFIG_CMD_NET=y
# CONFIG_CMD_TFTPPUT is not set
# CONFIG_CMD_TFTPSRV is not set
# CONFIG_CMD_RARP is not set
# CONFIG_CMD_DHCP is not set
# CONFIG_CMD_PXE is not set
CONFIG_CMD_NFS=y
# CONFIG_CMD_MII is not set
# CONFIG_CMD_PING is not set
# CONFIG_CMD_CDP is not set
# CONFIG_CMD_SNTP is not set
# CONFIG_CMD_DNS is not set
# CONFIG_CMD_LINK_LOCAL is not set
# CONFIG_CMD_ETHSW is not set

#
# Misc commands
#
# CONFIG_CMD_BSP is not set
# CONFIG_CMD_CACHE is not set
# CONFIG_CMD_DISPLAY is not set
# CONFIG_CMD_LED is not set
# CONFIG_CMD_DATE is not set
# CONFIG_CMD_TIME is not set
CONFIG_CMD_GETTIME=y
CONFIG_CMD_MISC=y
# CONFIG_CMD_TIMER is not set
# CONFIG_CMD_QFW is not set
# CONFIG_CMD_TERMINAL is not set
# CONFIG_CMD_UUID is not set

#
# Power commands
#

#
# Security commands
#
# CONFIG_CMD_AES is not set
# CONFIG_CMD_BLOB is not set
CONFIG_CMD_HASH=y
CONFIG_HASH_VERIFY=y

#
# Firmware commands
#

#
# Filesystem commands
#
# CONFIG_CMD_BTRFS is not set
# CONFIG_CMD_EXT2 is not set
# CONFIG_CMD_EXT4 is not set
# CONFIG_CMD_FAT is not set
# CONFIG_CMD_FS_GENERIC is not set
# CONFIG_CMD_FS_UUID is not set
# CONFIG_CMD_JFFS2 is not set
# CONFIG_CMD_MTDPARTS is not set
CONFIG_MTDIDS_DEFAULT=""
CONFIG_MTDPARTS_DEFAULT=""
# CONFIG_CMD_REISER is not set
CONFIG_CMD_SCSI=y
# CONFIG_CMD_ZFS is not set

#
# Debug commands
#
# CONFIG_CMD_BEDBUG is not set
# CONFIG_CMD_DIAG is not set
# CONFIG_CMD_IRQ is not set
# CONFIG_CMD_KGDB is not set
# CONFIG_CMD_TRACE is not set
# CONFIG_CMD_UBI is not set

#
# Partition Types
#
CONFIG_PARTITIONS=y
# CONFIG_MAC_PARTITION is not set
# CONFIG_DOS_PARTITION is not set
# CONFIG_ISO_PARTITION is not set
# CONFIG_AMIGA_PARTITION is not set
# CONFIG_EFI_PARTITION is not set
# CONFIG_PARTITION_UUIDS is not set
CONFIG_SUPPORT_OF_CONTROL=y

#
# Device Tree Control
#
# CONFIG_OF_CONTROL is not set
# CONFIG_OF_BOARD_FIXUP is not set
# CONFIG_MULTI_DTB_FIT is not set
CONFIG_MKIMAGE_DTC_PATH="dtc"

#
# Environment
#
CONFIG_ENV_IS_NOWHERE=y
# CONFIG_ENV_IS_IN_EEPROM is not set
# CONFIG_ENV_IS_IN_FAT is not set
# CONFIG_ENV_IS_IN_FLASH is not set
# CONFIG_ENV_IS_IN_MMC is not set
# CONFIG_ENV_IS_IN_NAND is not set
# CONFIG_ENV_IS_IN_NVRAM is not set
# CONFIG_ENV_IS_IN_ONENAND is not set
# CONFIG_ENV_IS_IN_REMOTE is not set
# CONFIG_ENV_IS_IN_SPI_FLASH is not set
# CONFIG_ENV_IS_IN_UBI is not set
# CONFIG_ENV_AES is not set
CONFIG_NET=y
# CONFIG_NET_RANDOM_ETHADDR is not set
# CONFIG_NETCONSOLE is not set
CONFIG_NET_TFTP_VARS=y
CONFIG_BOOTP_VCI_STRING="U-Boot"

#
# Device Drivers
#

#
# Generic Driver Options
#
CONFIG_DM=y
CONFIG_DM_WARN=y
# CONFIG_DM_DEBUG is not set
CONFIG_DM_DEVICE_REMOVE=y
CONFIG_DM_STDIO=y
CONFIG_DM_SEQ_ALIAS=y
# CONFIG_SPL_DM_SEQ_ALIAS is not set
# CONFIG_REGMAP is not set
# CONFIG_DEVRES is not set
CONFIG_DM_DEV_READ_INLINE=y
# CONFIG_ADC is not set
# CONFIG_ADC_EXYNOS is not set
# CONFIG_ADC_SANDBOX is not set
# CONFIG_SARADC_ROCKCHIP is not set
# CONFIG_AHCI is not set
CONFIG_SATA=y

#
# SATA/SCSI device support
#
CONFIG_BLK=y
# CONFIG_BLOCK_CACHE is not set
# CONFIG_IDE is not set

#
# Clock
#
# CONFIG_CLK is not set
# CONFIG_CPU is not set

#
# Hardware crypto devices
#
# CONFIG_FSL_CAAM is not set
# CONFIG_SYS_FSL_SEC_BE is not set
# CONFIG_SYS_FSL_SEC_LE is not set

#
# Demo for driver model
#
# CONFIG_DM_DEMO is not set

#
# DFU support
#

#
# DMA Support
#
# CONFIG_DMA is not set
# CONFIG_TI_EDMA3 is not set

#
# FPGA support
#
# CONFIG_FPGA_ALTERA is not set
# CONFIG_FPGA_SOCFPGA is not set
# CONFIG_FPGA_XILINX is not set

#
# GPIO Support
#
CONFIG_DM_GPIO=y
# CONFIG_ALTERA_PIO is not set
# CONFIG_DWAPB_GPIO is not set
# CONFIG_AT91_GPIO is not set
# CONFIG_ATMEL_PIO4 is not set
# CONFIG_INTEL_BROADWELL_GPIO is not set
# CONFIG_INTEL_ICH6_GPIO is not set
# CONFIG_IMX_RGPIO2P is not set
# CONFIG_LPC32XX_GPIO is not set
# CONFIG_MSM_GPIO is not set
# CONFIG_CMD_PCA953X is not set
# CONFIG_PCF8575_GPIO is not set
# CONFIG_ROCKCHIP_GPIO is not set
# CONFIG_SANDBOX_GPIO is not set
# CONFIG_CMD_TCA642X is not set
# CONFIG_TEGRA_GPIO is not set
# CONFIG_TEGRA186_GPIO is not set
# CONFIG_VYBRID_GPIO is not set
# CONFIG_DM_74X164 is not set
# CONFIG_DM_PCA953X is not set
# CONFIG_MPC85XX_GPIO is not set

#
# I2C support
#
CONFIG_DM_I2C=y
# CONFIG_DM_I2C_