2017.01 U-Boot启动流程源码详解：关键步骤与初始化

/***********************************************
u-boot 2017.01启动过程分析
2019-08-23
***********************************************/

/* SPL阶段 */
u-boot-spl.lds(arch/arm/cpu/armv7/sunxi/u-boot-spl.lds)
|--> vectors.S(arch/arm/lib/vectors.S)
|--> start.S(arch/arm/cpu/armv7/start.S)
|--> save_boot_params
|--> /*set SVC mode .. disable FIQ and IRQ*/
|--> cpu_init_cp15(arch/arm/cpu/armv7/start.S) /*disable MMU stuff and caches*/
|--> cpu_init_crit(arch/arm/cpu/armv7/start.S)
|--> lowlevel_init(arch/arm/cpu/armv7/lowlevel_init.S) /* 板级初始化，设置栈空间 */
|--> s_init(arch/arm/mach-ompa2/am33xx/board.c)
|--> rtc_only(arch/arm/mach-ompa2/am33xx/board.c)
|--> _main(arch/arm/lib/crt0.S )
|--> board_init_f(arch/arm/mach-ompa2/am33xx/board.c)
|--> early_system_init(arch/arm/mach-ompa2/am33xx/board.c)
|--> watchdog_disable(arch/arm/mach-ompa2/am33xx/board.c)  /* 禁止看门狗 */
|--> set_uart_mux_conf(board/ti/am335x/board.c)    /* 设置串口 */
|--> setup_early_clocks(arch/arm/mach-ompa2/am33xx/clock.c)
|--> uart_soft_reset(arch/arm/mach-ompa2/am33xx/board.c)
|--> board_early_init_f(arch/arm/mach-ompa2/am33xx/board.c)
|--> prcm_init(arch/arm/mach-ompa2/am33xx/clock.c)
|--> set_mux_conf_regs(board/ti/am335x/board.c)
|--> sdram_init(board/ti/am335x/board.c) /* 初始化DDR */
|--> board_init_r(common/spl/spl.c)
|--> gd->bd = &bdata /* gd是保存在r9寄存器的,即r9保存的是指向gdata的指针 */
|--> timer_init(arch/arm/cpu/armv7/sunxi/timer.c)  /* 初始化时钟 */

|--> spl_board_init(arch/arm/mach-omap2/boot-common.c) 
|--> save_omap_boot_params(arch/arm/mach-omap2/boot-common.c) /* 保存启动的device和mode */
|--> preloader_console_init(common/spl/spl.c)  /* 初始化gd部分数据结构 波特率 */
|--> serial_init( drivers/serial/serial.c) /* 串口初始化 */
|--> am33xx_spl_board_init() /* 设置频率 */
|--> boot_from_devices(common/spl/spl.c)
|--> spl_ll_find_loader(common/spl/spl.c)
|--> ll_entry_start(include/linker_lists.h)
|--> SPL_LOAD_IMAGE_METHOD("MMC1", 0, BOOT_DEVICE_MMC1, spl_mmc_load_image)(common/spl/spl_mmc.c)
|--> spl_mmc_load_image(common/spl/spl_mmc.c)
|--> mmc_load_image_raw_os(common/spl/spl_mmc.c)
|--> mmc_load_legacy(common/spl/spl_mmc.c)
|--> spl_parse_image_header(common/spl/spl.c) /* 解析 header */
|--> jump_to_image_no_args(common/spl/spl.c)
|--> image_entry /* 结束SPL过程,跳转到u-boot */



/* u-boot阶段 */
u-boot.lds(board/ti/am335x/u-boot.lds)
|--> vectors.S(arch/arm/lib/vectors.S)
|--> start.S(arch/arm/cpu/armv7/start.S)
... ...
|--> _main(arch/arm/lib/crt0.S )
|--> board_init_f_alloc_reserve(common/init/board_init.c) /* 为u-boot的gd结构体分配空间 */
|--> board_init_f_init_reserve(common/init/board_init.c)  /* 将gd结构体清零 */
|--> board_init_f(common/board_f.c) /* 将gd结构体清零 */
|--> initcall_run_list(init_sequence_f) (lib/initcall.c)
|--> init_sequence_f[](common/board_f.c) /* 函数指针数组 */
|--> /* 初始化各种外设，比如使能看门狗，串口打印，控制台，并保存板子信息到gd等等 */