void s_init(void)

{

/*

* The ROM will only have set up sufficient pinmux to allow for the

* first 4KiB NOR to be read, we must finish doing what we know of

* the NOR mux in this space in order to continue.

*/

#ifdef CONFIG_NOR_BOOT

enable_norboot_pin_mux();

#endif

watchdog_disable();               //arch/arm/cpu/armv7/am33xx/board.c

set_uart_mux_conf();            // xx/board/ti/am335x/board.c

setup_clocks_for_console();   // arch/arm/cpu/armv7/am335x/Clock_am33xx.c

uart_soft_reset();                 // arch/arm/cpu/armv7/am33xx/board.c

#if defined(CONFIG_SPL_AM33XX_ENABLE_RTC32K_OSC)  // include/configs/ti_am335x_common.h

/* Enable RTC32K clock */

rtc32k_enable();                  // arch/arm/cpu/armv7/am33xx/board.c

#endif

}

ENTRY(_main)

/*

* Set up initial C runtime environment and call board_init_f(0). 因为后面是C语言环境，首先是设置堆栈

*/

#if defined(CONFIG_SPL_BUILD) && defined(CONFIG_SPL_STACK)

ldr    sp, =(CONFIG_SPL_STACK)                                                   //设置堆栈为后边调用board_init_f做准备

#else

ldr    sp, =(CONFIG_SYS_INIT_SP_ADDR)

#endif

#if defined(CONFIG_CPU_V7M)    /* v7M forbids using SP as BIC destination */

mov    r3, sp

bic    r3, r3, #

mov    sp, r3

#else

bic    sp, sp, #    /* 8-byte alignment for ABI compliance */

#endif

mov    r0, sp

bl    board_init_f_alloc_reserve                                     //2. 为gd_t结构体保留空间理论上有些函数可以用了，例如：preloader_console_init()初始化串口，common/init/board_init.c

mov    sp, r0

/* set up gd here, outside any C code */

mov    r9, r0

bl    board_init_f_init_reserve                      //3. 初始化gd_t(清零)  common/init/board_init.c

                    //gd_t的地址存在r9寄存器中，结构体中存放的是全局参数

mov r0, #

bl    board_init_f

#if ! defined(CONFIG_SPL_BUILD)

/*

* Set up intermediate environment (new sp and gd) and call

* relocate_code(addr_moni). Trick here is that we'll return

* 'here' but relocated.

*/

ldr    sp, [r9, #GD_START_ADDR_SP]    /* sp = gd->start_addr_sp */

#if defined(CONFIG_CPU_V7M)    /* v7M forbids using SP as BIC destination */

mov    r3, sp

bic    r3, r3, #

mov    sp, r3

#else

bic    sp, sp, #    /* 8-byte alignment for ABI compliance */

#endif

ldr    r9, [r9, #GD_BD]    /* r9 = gd->bd */

sub    r9, r9, #GD_SIZE    /* new GD is below bd */

adr    lr, here

ldr    r0, [r9, #GD_RELOC_OFF]    /* r0 = gd->reloc_off */

add    lr, lr, r0

#if defined(CONFIG_CPU_V7M)

orr    lr, #    /* As required by Thumb-only */

#endif

ldr    r0, [r9, #GD_RELOCADDR]    /* r0 = gd->relocaddr */

b    relocate_code

here:

/*

* now relocate vectors

*/

bl    relocate_vectors

/* Set up final (full) environment */

bl    c_runtime_cpu_setup    /* we still call old routine here */

#endif

#if !defined(CONFIG_SPL_BUILD) || defined(CONFIG_SPL_FRAMEWORK)

# ifdef CONFIG_SPL_BUILD

/* Use a DRAM stack for the rest of SPL, if requested */

bl    spl_relocate_stack_gd

cmp    r0, #

movne    sp, r0

movne    r9, r0

# endif

ldr    r0, =__bss_start    /* this is auto-relocated! */

#ifdef CONFIG_USE_ARCH_MEMSET

ldr    r3, =__bss_end    /* this is auto-relocated! */

mov    r1, #0x00000000    /* prepare zero to clear BSS */

subs    r2, r3, r0    /* r2 = memset len */

bl    memset

#else

ldr    r1, =__bss_end    /* this is auto-relocated! */

mov    r2, #0x00000000    /* prepare zero to clear BSS */

clbss_l:cmp    r0, r1    /* while not at end of BSS */

#if defined(CONFIG_CPU_V7M)

itt    lo

#endif

strlo    r2, [r0]    /* clear 32-bit BSS word */

addlo    r0, r0, #    /* move to next */

blo    clbss_l

#endif

#if ! defined(CONFIG_SPL_BUILD)

bl coloured_LED_init

bl red_led_on

#endif

/* call board_init_r(gd_t *id, ulong dest_addr) */

mov r0, r9 /* gd_t */

ldr    r1, [r9, #GD_RELOCADDR]    /* dest_addr */

/* call board_init_r */

#if defined(CONFIG_SYS_THUMB_BUILD)

ldr    lr, =board_init_r    /* this is auto-relocated! */

bx    lr

#else

ldr    pc, =board_init_r    /* this is auto-relocated! */

#endif

/* we should not return here. */

#endif

ENDPROC(_main)

 void board_init_f(ulong dummy)

 {

 board_early_init_f();

 preloader_console_init();  //初始化uart，使用Puts函数

 sdram_init();

 }

 int board_early_init_f(void)

 {

     prcm_init();    //系统外设时钟初始化使能，SPI，I2C,uart,gpio.....

     set_mux_conf_regs();  //系统外设引功能配置，spi，I2C，uart,gpio.

     return ;

 }

 void prcm_init()

 {

     enable_basic_clocks();

     scale_vcores();

     setup_dplls();

 }

void set_mux_conf_regs(void)

{

    __maybe_unused struct am335x_baseboard_id header;

    if (read_eeprom(&header) < )

        puts("Could not get board ID.\n");

    enable_board_pin_mux(&header);

        puts("enable_board_pin.\n");

}

void enable_board_pin_mux(struct am335x_baseboard_id *header)

{

    /* Do board-specific muxes. */

    if (board_is_bone(header)) {

        /* Beaglebone pinmux */

        configure_module_pin_mux(mii1_pin_mux);

        configure_module_pin_mux(mmc0_pin_mux);

#if defined(CONFIG_NAND)

        configure_module_pin_mux(nand_pin_mux);

#elif defined(CONFIG_NOR)

        configure_module_pin_mux(bone_norcape_pin_mux);

#else

        configure_module_pin_mux(mmc1_pin_mux);

#endif

    } else if (board_is_gp_evm(header)) {

        /* General Purpose EVM */

        unsigned short profile = detect_daughter_board_profile();

        configure_module_pin_mux(rgmii1_pin_mux);

        configure_module_pin_mux(mmc0_pin_mux);

        /* In profile #2 i2c1 and spi0 conflict. */

        if (profile & ~PROFILE_2)

            configure_module_pin_mux(i2c1_pin_mux);

        /* Profiles 2 & 3 don't have NAND */

#ifdef CONFIG_NAND

        if (profile & ~(PROFILE_2 | PROFILE_3))

            configure_module_pin_mux(nand_pin_mux);

#endif

        else if (profile == PROFILE_2) {

            configure_module_pin_mux(mmc1_pin_mux);

            configure_module_pin_mux(spi0_pin_mux);

        }

    } else if (board_is_idk(header)) {

        /* Industrial Motor Control (IDK) */

        configure_module_pin_mux(mii1_pin_mux);

        configure_module_pin_mux(mmc0_no_cd_pin_mux);

    } else if (board_is_evm_sk(header)) {

        /* Starter Kit EVM */

        configure_module_pin_mux(i2c1_pin_mux); // 配置I2C1对应的引脚为功能引脚，u-boot-2016.03/board/ti/am335x/mux.c

        configure_module_pin_mux(gpio0_7_pin_mux);

        configure_module_pin_mux(rgmii1_pin_mux);

        configure_module_pin_mux(mmc0_pin_mux_sk_evm);

    } else if (board_is_bone_lt(header)) {

        /* Beaglebone LT pinmux */

        configure_module_pin_mux(mii1_pin_mux);

        configure_module_pin_mux(mmc0_pin_mux);

#if defined(CONFIG_NAND) && defined(CONFIG_EMMC_BOOT)

        configure_module_pin_mux(nand_pin_mux);

#elif defined(CONFIG_NOR) && defined(CONFIG_EMMC_BOOT)

        configure_module_pin_mux(bone_norcape_pin_mux);

#else

        configure_module_pin_mux(mmc1_pin_mux);

#endif

    } else {

        puts("Unknown board, cannot configure pinmux.");

        hang();

    }

}

void sdram_init(void)

{

    __maybe_unused struct am335x_baseboard_id header;

    if (read_eeprom(&header) < )

        puts("Could not get board ID.\n");

    if (board_is_evm_sk(&header)) {

        /*

         * EVM SK 1.2A and later use gpio0_7 to enable DDR3.

         * This is safe enough to do on older revs.

         */

        gpio_request(GPIO_DDR_VTT_EN, "ddr_vtt_en"); //请求GPIO0_7脚是否有效，AM335x共有GPIO=32*4.如果GPIO_DDR_VTT_EN的数值在0~127之间，返回0

        gpio_direction_output(GPIO_DDR_VTT_EN, );//使GPIO的第8脚，GPIO0_7输出1，使能SDRAM芯片的电源

    }

    if (board_is_evm_sk(&header))

        config_ddr(, &ioregs_evmsk, &ddr3_data,

               &ddr3_cmd_ctrl_data, &ddr3_emif_reg_data, );

    else if (board_is_bone_lt(&header))

        config_ddr(, &ioregs_bonelt,

               &ddr3_beagleblack_data,

               &ddr3_beagleblack_cmd_ctrl_data,

               &ddr3_beagleblack_emif_reg_data, );

    else if (board_is_evm_15_or_later(&header))

        config_ddr(, &ioregs_evm15, &ddr3_evm_data,

               &ddr3_evm_cmd_ctrl_data, &ddr3_evm_emif_reg_data, );

    else

        config_ddr(, &ioregs, &ddr2_data,

               &ddr2_cmd_ctrl_data, &ddr2_emif_reg_data, );

               debug(">>spl:SDRAM_init()\n");

               puts(">>spl:SDRAM_init()\n");

}

ulong spl_relocate_stack_gd(void)

{

#ifdef CONFIG_SPL_STACK_R

    gd_t *new_gd;

    ulong ptr = CONFIG_SPL_STACK_R_ADDR;

#ifdef CONFIG_SPL_SYS_MALLOC_SIMPLE

    if (CONFIG_SPL_STACK_R_MALLOC_SIMPLE_LEN) {

        if (!(gd->flags & GD_FLG_SPL_INIT))

            panic_str("spl_init must be called before heap reloc");

        ptr -= CONFIG_SPL_STACK_R_MALLOC_SIMPLE_LEN;

        gd->malloc_base = ptr;

        gd->malloc_limit = CONFIG_SPL_STACK_R_MALLOC_SIMPLE_LEN;

        gd->malloc_ptr = ;

    }

#endif

    /* Get stack position: use 8-byte alignment for ABI compliance */

    ptr = CONFIG_SPL_STACK_R_ADDR - roundup(sizeof(gd_t),);

    new_gd = (gd_t *)ptr;

    memcpy(new_gd, (void *)gd, sizeof(gd_t));

#if !defined(CONFIG_ARM)

    gd = new_gd;

#endif

    return ptr;

#else

    return ;

#endif

}

board_init_r

{

     、经行memory的malloc池的初始化

      、timer_init() 初始化时钟 arch/arm/cpu/armv7/omap_common

      、spl_board_init() arch/arm/cpu/armv7/omap_common/boot-common.c

      、jump_to_image_no_args(&spl_image) // 跳转u-boot入口地址 entry_point，entry_point是由u-boot.img头部信息提供的
      5、SPL结束其生命，将控制权交给u-boot/Linux

}

void spl_board_init(void)

{

    /*

     * Save the boot parameters passed from romcode.

     * We cannot delay the saving further than this,

     * to prevent overwrites.

     */

    save_omap_boot_params(); // 这里讲boot_device的参数传递给spl_boot_list（自己理解），确定以什么方式加载u-boot.img（uart or spi or mmc or nand....）

    /* Prepare console output */

   // preloader_console_init();

#if defined(CONFIG_SPL_NAND_SUPPORT) || defined(CONFIG_SPL_ONENAND_SUPPORT)

    gpmc_init();

#endif

#ifdef CONFIG_SPL_I2C_SUPPORT

    i2c_init(CONFIG_SYS_OMAP24_I2C_SPEED, CONFIG_SYS_OMAP24_I2C_SLAVE);

#endif

#if defined(CONFIG_AM33XX) && defined(CONFIG_SPL_MUSB_NEW_SUPPORT)

    arch_misc_init();

#endif

#if defined(CONFIG_HW_WATCHDOG)

    hw_watchdog_init();

#endif

#ifdef CONFIG_AM33XX

    am33xx_spl_board_init();

#endif

}