u-boot的启动流程分析（一）

这周翻了翻u-boot-Xilinx的源码，结合着网上看的对cortexA8、A9的u-boot的源码分析，再结合自己在Xilinx上下的u-boot源码，试着对u-boot的启动流程进行一下分析，也给自己理一下思路。

u-boot源码的目录结构：

第一阶段：

（1）start.S(arch/arm/cpu/armv7/start.S)
在flash中执行的引导代码,也就是bootloader中的stage1,负责初始化硬件环境，把u-boot从flash加载到RAM中去，对CPU的一个初始化，然后跳到board/xilinx/zynq/board.c中去执行。

第二阶段：

（2）board.c(board/xilinx/zynq/board.c)

选择板卡芯片的型号，启动fpga，选择启动方式（QSPI、SD、JTAG、NAND、NOR）、读取rom、ram。

（3）cmd/bootm.c和bootmenu.c

（4）然后在include/config/zynq_common.h中定义了Z7系列的一些硬件参数配置，比较重要的一个默认启动环境配置：

/* Default environment */
#ifndef CONFIG_EXTRA_ENV_SETTINGS
#define CONFIG_EXTRA_ENV_SETTINGS	\
	"ethaddr=00:0a:35:00:01:22\0"	\
	"kernel_image=uImage\0"	\
	"kernel_load_address=0x2080000\0" \
	"ramdisk_image=uramdisk.image.gz\0"	\
	"ramdisk_load_address=0x4000000\0"	\
	"devicetree_image=devicetree.dtb\0"	\
	"devicetree_load_address=0x2000000\0"	\
	"bitstream_image=system.bit.bin\0"	\
	"boot_image=BOOT.bin\0"	\
	"loadbit_addr=0x100000\0"	\
	"loadbootenv_addr=0x2000000\0" \
	"kernel_size=0x500000\0"	\
	"devicetree_size=0x20000\0"	\
	"ramdisk_size=0x5E0000\0"	\
	"boot_size=0xF00000\0"	\
	"fdt_high=0x20000000\0"	\
	"initrd_high=0x20000000\0"	\
	"bootenv=uEnv.txt\0" \
	"loadbootenv=load mmc 0 ${loadbootenv_addr} ${bootenv}\0" \
	"importbootenv=echo Importing environment from SD ...; " \
		"env import -t ${loadbootenv_addr} $filesize\0" \
	"sd_uEnvtxt_existence_test=test -e mmc 0 /uEnv.txt\0" \
	"preboot=if test $modeboot = sdboot && env run sd_uEnvtxt_existence_test; " \
			"then if env run loadbootenv; " \
				"then env run importbootenv; " \
			"fi; " \
		"fi; \0" \
	"mmc_loadbit=echo Loading bitstream from SD/MMC/eMMC to RAM.. && " \
		"mmcinfo && " \
		"load mmc 0 ${loadbit_addr} ${bitstream_image} && " \
		"fpga load 0 ${loadbit_addr} ${filesize}\0" \
	"norboot=echo Copying Linux from NOR flash to RAM... && " \
		"cp.b 0xE2100000 ${kernel_load_address} ${kernel_size} && " \
		"cp.b 0xE2600000 ${devicetree_load_address} ${devicetree_size} && " \
		"echo Copying ramdisk... && " \
		"cp.b 0xE2620000 ${ramdisk_load_address} ${ramdisk_size} && " \
		"bootm ${kernel_load_address} ${ramdisk_load_address} ${devicetree_load_address}\0" \
	"qspiboot=echo Copying Linux from QSPI flash to RAM... && " \
		"sf probe 0 0 0 && " \
		"sf read ${kernel_load_address} 0x100000 ${kernel_size} && " \
		"sf read ${devicetree_load_address} 0x600000 ${devicetree_size} && " \
		"echo Copying ramdisk... && " \
		"sf read ${ramdisk_load_address} 0x620000 ${ramdisk_size} && " \
		"bootm ${kernel_load_address} ${ramdisk_load_address} ${devicetree_load_address}\0" \
	"uenvboot=" \
		"if run loadbootenv; then " \
			"echo Loaded environment from ${bootenv}; " \
			"run importbootenv; " \
		"fi; " \
		"if test -n $uenvcmd; then " \
			"echo Running uenvcmd ...; " \
			"run uenvcmd; " \
		"fi\0" \
	"sdboot=if mmcinfo; then " \
			"run uenvboot; " \
			"echo Copying Linux from SD to RAM... && " \
			"load mmc 0 ${kernel_load_address} ${kernel_image} && " \
			"load mmc 0 ${devicetree_load_address} ${devicetree_image} && " \
			"load mmc 0 ${ramdisk_load_address} ${ramdisk_image} && " \
			"bootm ${kernel_load_address} ${ramdisk_load_address} ${devicetree_load_address}; " \
		"fi\0" \
	"usbboot=if usb start; then " \
			"run uenvboot; " \
			"echo Copying Linux from USB to RAM... && " \
			"load usb 0 ${kernel_load_address} ${kernel_image} && " \
			"load usb 0 ${devicetree_load_address} ${devicetree_image} && " \
			"load usb 0 ${ramdisk_load_address} ${ramdisk_image} && " \
			"bootm ${kernel_load_address} ${ramdisk_load_address} ${devicetree_load_address}; " \
		"fi\0" \
	"nandboot=echo Copying Linux from NAND flash to RAM... && " \
		"nand read ${kernel_load_address} 0x100000 ${kernel_size} && " \
		"nand read ${devicetree_load_address} 0x600000 ${devicetree_size} && " \
		"echo Copying ramdisk... && " \
		"nand read ${ramdisk_load_address} 0x620000 ${ramdisk_size} && " \
		"bootm ${kernel_load_address} ${ramdisk_load_address} ${devicetree_load_address}\0" \
	"jtagboot=echo TFTPing Linux to RAM... && " \
		"tftpboot ${kernel_load_address} ${kernel_image} && " \
		"tftpboot ${devicetree_load_address} ${devicetree_image} && " \
		"tftpboot ${ramdisk_load_address} ${ramdisk_image} && " \
		"bootm ${kernel_load_address} ${ramdisk_load_address} ${devicetree_load_address}\0" \
	"rsa_norboot=echo Copying Image from NOR flash to RAM... && " \
		"cp.b 0xE2100000 0x100000 ${boot_size} && " \
		"zynqrsa 0x100000 && " \
		"bootm ${kernel_load_address} ${ramdisk_load_address} ${devicetree_load_address}\0" \
	"rsa_nandboot=echo Copying Image from NAND flash to RAM... && " \
		"nand read 0x100000 0x0 ${boot_size} && " \
		"zynqrsa 0x100000 && " \
		"bootm ${kernel_load_address} ${ramdisk_load_address} ${devicetree_load_address}\0" \
	"rsa_qspiboot=echo Copying Image from QSPI flash to RAM... && " \
		"sf probe 0 0 0 && " \
		"sf read 0x100000 0x0 ${boot_size} && " \
		"zynqrsa 0x100000 && " \
		"bootm ${kernel_load_address} ${ramdisk_load_address} ${devicetree_load_address}\0" \
	"rsa_sdboot=echo Copying Image from SD to RAM... && " \
		"load mmc 0 0x100000 ${boot_image} && " \
		"zynqrsa 0x100000 && " \
		"bootm ${kernel_load_address} ${ramdisk_load_address} ${devicetree_load_address}\0" \
	"rsa_jtagboot=echo TFTPing Image to RAM... && " \
		"tftpboot 0x100000 ${boot_image} && " \
		"zynqrsa 0x100000 && " \
		"bootm ${kernel_load_address} ${ramdisk_load_address} ${devicetree_load_address}\0" \
		DFU_ALT_INFO \
		BOOTENV
#endif

（5）u-boot引导kernel关键地方：

U-boot 给kernel 传参数和kernel 读取参数，.u-boot 给kernel 传RAM 参数bootm.c 文件中， bootm 命令对应的 do_bootm 函数，当分析 uImage 中信息发现 OS 是 Linux 时 ， 调用 ./arch/arc/include/lib/bootm.c 文件中的 do_bootm_linux 函数来启动 Linux kernel 。