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一：

1◑ 从链接脚本文件u-boot.lds（'/opt/4418-source/android/u-boot' ）中可以找到代码的起始：

OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")OUTPUT_ARCH(arm)ENTRY(_stext)SECTIONS{ . = 0x00000000; . = ALIGN(4); .text : {  *(.__image_copy_start)  arch/arm/cpu/slsiap/s5p4418/start.o (.text*)  *(.text*) }

 

从中知道程序的入口点是_start，定位于arch/arm/cpu/slsiap/s5p4418/start.o （即u-boot启动的第一阶段）。

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2◑ 下面我们来仔细分析一下 start.S。（请对照数据手册阅读源码）:

 

/* * armboot - Startup Code for NXPxxxx/ARM Cortex CPU-core */#include 
     
      #include 
      
       #include 
       
        #include 
        
         #include 
         
          /* ************************************************************************* * * Exception vectors as described in ARM reference manuals * * replace arm/lib/vectors.S * ************************************************************************* */    .globl    _stext_stext:    b     reset                //u-boot的主入口，跳入了后面的reset                    ldr    pc, _undefined_instruction    ldr    pc, _software_interrupt        //这些是跳转向量表，和芯片的体系结构有关    ldr    pc, _prefetch_abort    ldr    pc, _data_abort    ldr    pc, _not_used            // ldr语句的意思是将第二个操作数（如：_undefined_instruction）指向的地址数据传给PC    ldr    pc, _irq    ldr    pc, _fiq/* ldr语句的意思是将第二个操作数（如：_undefined_instruction）指向的地址数据传给PC，undefined_instruction 为地址， 即后面标号所对的偏移地址数据  */_undefined_instruction:    .word undefined_instruction    _software_interrupt:    .word software_interrupt_prefetch_abort:    .word prefetch_abort_data_abort:        .word data_abort_not_used:        .word not_used_irq:            .word irq_fiq:            .word fiq    .balignl 16,0xdeadbeef        //16字节对齐，并以0xdeadbeef填充，它是个Magic number。/* ************************************************************************* * * Text and section base * ************************************************************************* */.globl TEXT_BASETEXT_BASE:    .word    CONFIG_SYS_TEXT_BASE        //这些和上面的一样，定义一个4字节的空间存放地址/* * These are defined in the board-specific linker script. */.globl _bss_start_ofs_bss_start_ofs:    .word __bss_start - _stext.globl _bss_end_ofs_bss_end_ofs:    .word __bss_end - _stext.globl _end_ofs_end_ofs:    .word _end - _stext/* ************************************************************************* * * Reset handling    代码从这里开始执行 * ************************************************************************* */    .globl resetreset:    bl    save_boot_params    /*     * set the cpu to SVC32 mode        让系统进入SVC（管理）员     */    mrs    r0, cpsr    bic    r0, r0, #0x1f    orr    r0, r0, #0xd3    msr    cpsr,r0    /* the mask ROM code should have PLL and others stable */#ifndef CONFIG_SKIP_LOWLEVEL_INIT    bl    cpu_init_cp15    bl    cpu_init_crit#endif#ifdef CONFIG_RELOC_TO_TEXT_BASErelocate_to_text:    /*     * relocate u-boot code on memory to text base     * for nexell arm core (add by jhkim)     */    adr    r0, _stext                /* r0 <- current position of code   */    ldr    r1, TEXT_BASE            /* test if we run from flash or RAM */    cmp r0, r1                  /* don't reloc during debug         */    beq clear_bss    ldr    r2, _bss_start_ofs    add    r2, r0, r2                /* r2 <- source end address         */copy_loop_text:    ldmia    r0!, {r3-r10}        /* copy from source address [r0]    */    stmia    r1!, {r3-r10}        /* copy to   target address [r1]    */    cmp    r0, r2                    /* until source end addreee [r2]    */    ble    copy_loop_text    ldr    r1, TEXT_BASE            /* restart at text base */    mov pc, r1clear_bss:    ldr    r0, _bss_start_ofs    ldr    r1, _bss_end_ofs    ldr    r4, TEXT_BASE            /* text addr */    add    r0, r0, r4    add    r1, r1, r4    mov    r2, #0x00000000            /* clear */clbss_l:str    r2, [r0]            /* clear loop... */    add    r0, r0, #4    cmp    r0, r1    bne    clbss_l#ifdef CONFIG_MMU_ENABLE    bl    mmu_turn_on#endif    ldr    sp, =(CONFIG_SYS_INIT_SP_ADDR)    bic    sp, sp, #7                    /* 8-byte alignment for ABI compliance */    sub    sp, #GD_SIZE                /* allocate one GD above SP */    bic    sp, sp, #7                    /* 8-byte alignment for ABI compliance */    mov    r9, sp                        /* GD is above SP */    mov    r0, #0    bl    board_init_f    mov    sp, r9                        /* SP is GD's base address */    bic    sp, sp, #7                    /* 8-byte alignment for ABI compliance */    sub    sp, #GENERATED_BD_INFO_SIZE    /* allocate one BD above SP */    bic    sp, sp, #7                    /* 8-byte alignment for ABI compliance */    mov    r0, r9                        /* gd_t *gd */    ldr r1, TEXT_BASE                /* ulong text */    mov r2, sp                        /* ulong sp */    bl    gdt_reset    /* call board_init_r(gd_t *id, ulong dest_addr) */    mov    r0, r9                            /* gd_t */    ldr    r1,  =(CONFIG_SYS_MALLOC_END)    /* dest_addr for malloc heap end */    /* call board_init_r */    ldr    pc, =board_init_r                /* this is auto-relocated! */#else    /* CONFIG_RELOC_TO_TEXT_BASE */    bl    _main#endif/*------------------------------------------------------------------------------*/ENTRY(c_runtime_cpu_setup)/* * If I-cache is enabled invalidate it */#ifndef CONFIG_SYS_ICACHE_OFF    mcr    p15, 0, r0, c7, c5, 0    @ invalidate icache    mcr     p15, 0, r0, c7, c10, 4    @ DSB    mcr     p15, 0, r0, c7, c5, 4    @ ISB#endif/* * Move vector table */    /* Set vector address in CP15 VBAR register */    ldr     r0, =_stext    mcr     p15, 0, r0, c12, c0, 0  @Set VBAR    bx    lrENDPROC(c_runtime_cpu_setup)/************************************************************************* * * void save_boot_params(u32 r0, u32 r1, u32 r2, u32 r3) *    __attribute__((weak)); * * Stack pointer is not yet initialized at this moment * Don't save anything to stack even if compiled with -O0 * *************************************************************************/ENTRY(save_boot_params)    bx    lr            @ back to my callerENDPROC(save_boot_params)    .weak    save_boot_params/************************************************************************* * * cpu_init_cp15 * * Setup CP15 registers (cache, MMU, TLBs). The I-cache is turned on unless * CONFIG_SYS_ICACHE_OFF is defined. * 操作CP15协处理器 * *************************************************************************/ENTRY(cpu_init_cp15)    /*     * Invalidate L1 I/D     */    mov    r0, #0            @ set up for MCR    mcr    p15, 0, r0, c8, c7, 0    @ invalidate TLBs    mcr    p15, 0, r0, c7, c5, 0    @ invalidate icache    mcr    p15, 0, r0, c7, c5, 6    @ invalidate BP array    dsb    isb    /*     * disable MMU stuff and caches     *下面主要是中断相关代码，但是U-boot基本不使用中断所以暂且略过。     */    mrc    p15, 0, r0, c1, c0, 0    bic    r0, r0, #0x00002000    @ clear bits 13 (--V-)    bic    r0, r0, #0x00000007    @ clear bits 2:0 (-CAM)    orr    r0, r0, #0x00000002    @ set bit 1 (--A-) Align    orr    r0, r0, #0x00000800    @ set bit 11 (Z---) BTB#ifdef CONFIG_SYS_ICACHE_OFF    bic    r0, r0, #0x00001000    @ clear bit 12 (I) I-cache#else    orr    r0, r0, #0x00001000    @ set bit 12 (I) I-cache#endif    mcr    p15, 0, r0, c1, c0, 0    mov    pc, lr            @ back to my callerENDPROC(cpu_init_cp15)#ifndef CONFIG_SKIP_LOWLEVEL_INIT/************************************************************************* * * CPU_init_critical registers * * setup important registers * setup memory timing * *************************************************************************/ENTRY(cpu_init_crit)    /*     * Jump to board specific initialization...     * The Mask ROM will have already initialized     * basic memory. Go here to bump up clock rate and handle     * wake up conditions.     *//* 调用board/lowlevel_init.S中的lowlevel_init函数，对系统总线的初始化，初始化了连接存储器的位宽、速度、刷新率等重要参数。经过这个函数的正确初始化，Nor Flash、SDRAM才可以被系统使用。 */    b    lowlevel_init        @ go setup pll,mux,memoryENDPROC(cpu_init_crit)#endif
         
        
       
      
     

 

 

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3◑现在我们再来看看lib/arm/board.c中的第二阶段入口函数board_init_r:

/* * (C) Copyright 2002-2006 * Wolfgang Denk, DENX Software Engineering, wd@denx.de. * * (C) Copyright 2002 * Sysgo Real-Time Solutions, GmbH 
     
       * Marius Groeger 
      
        * * SPDX-License-Identifier:    GPL-2.0+ *//* * To match the U-Boot user interface on ARM platforms to the U-Boot * standard (as on PPC platforms), some messages with debug character * are removed from the default U-Boot build. * * Define DEBUG here if you want additional info as shown below * printed upon startup: * * U-Boot code: 00F00000 -> 00F3C774  BSS: -> 00FC3274 * IRQ Stack: 00ebff7c * FIQ Stack: 00ebef7c */#include 
       
        #include 
        
         #include 
         
          #include 
          
           #include 
           
            #include 
            
             #include 
             
              #include 
              
               #include 
               
                #include 
                
                 #include 
                 
                  #include 
                  
                   #include 
                   
                    #include 
                    
                     #include 
                     
                      #include 
                      
                       #include 
                       
                        #ifdef CONFIG_BITBANGMII#include 
                        
                         #endifDECLARE_GLOBAL_DATA_PTR;ulong monitor_flash_len;#ifdef CONFIG_HAS_DATAFLASHextern int AT91F_DataflashInit(void);extern void dataflash_print_info(void);#endif#if defined(CONFIG_HARD_I2C) || \ defined(CONFIG_SYS_I2C)#include 
                         
                          #endif/************************************************************************ * Coloured LED functionality ************************************************************************ * May be supplied by boards if desired */inline void __coloured_LED_init(void) {}void coloured_LED_init(void) __attribute__((weak, alias("__coloured_LED_init")));inline void __red_led_on(void) {}void red_led_on(void) __attribute__((weak, alias("__red_led_on")));inline void __red_led_off(void) {}void red_led_off(void) __attribute__((weak, alias("__red_led_off")));inline void __green_led_on(void) {}void green_led_on(void) __attribute__((weak, alias("__green_led_on")));inline void __green_led_off(void) {}void green_led_off(void) __attribute__((weak, alias("__green_led_off")));inline void __yellow_led_on(void) {}void yellow_led_on(void) __attribute__((weak, alias("__yellow_led_on")));inline void __yellow_led_off(void) {}void yellow_led_off(void) __attribute__((weak, alias("__yellow_led_off")));inline void __blue_led_on(void) {}void blue_led_on(void) __attribute__((weak, alias("__blue_led_on")));inline void __blue_led_off(void) {}void blue_led_off(void) __attribute__((weak, alias("__blue_led_off")));/* ************************************************************************ * Init Utilities * ************************************************************************ * Some of this code should be moved into the core functions, * or dropped completely, * but let's get it working (again) first... */#if defined(CONFIG_ARM_DCC) && !defined(CONFIG_BAUDRATE)#define CONFIG_BAUDRATE 115200#endifstatic int init_baudrate(void){ gd->baudrate = getenv_ulong("baudrate", 10, CONFIG_BAUDRATE); return 0;}static int display_banner(void){ printf("\n\n%s\n\n", version_string); debug("U-Boot code: %08lX -> %08lX BSS: -> %08lX\n", (ulong)&_start, (ulong)&__bss_start, (ulong)&__bss_end);#ifdef CONFIG_MODEM_SUPPORT debug("Modem Support enabled\n");#endif#ifdef CONFIG_USE_IRQ debug("IRQ Stack: %08lx\n", IRQ_STACK_START); debug("FIQ Stack: %08lx\n", FIQ_STACK_START);#endif return (0);}/* * WARNING: this code looks "cleaner" than the PowerPC version, but * has the disadvantage that you either get nothing, or everything. * On PowerPC, you might see "DRAM: " before the system hangs - which * gives a simple yet clear indication which part of the * initialization if failing. */static int display_dram_config(void){ int i;#ifdef DEBUG puts("RAM Configuration:\n"); for (i = 0; i < CONFIG_NR_DRAM_BANKS; i++) { printf("Bank #%d: %08lx ", i, gd->bd->bi_dram[i].start); print_size(gd->bd->bi_dram[i].size, "\n"); }#else ulong size = 0; for (i = 0; i < CONFIG_NR_DRAM_BANKS; i++) size += gd->bd->bi_dram[i].size; puts("DRAM: "); print_size(size, "\n");#endif return (0);}#if defined(CONFIG_HARD_I2C) || defined(CONFIG_SYS_I2C)static int init_func_i2c(void){ puts("I2C: ");#ifdef CONFIG_SYS_I2C i2c_init_all();#else i2c_init(CONFIG_SYS_I2C_SPEED, CONFIG_SYS_I2C_SLAVE);#endif puts("ready\n"); return (0);}#endif#if defined(CONFIG_CMD_PCI) || defined (CONFIG_PCI)#include 
                          
                           static int arm_pci_init(void){ pci_init(); return 0;}#endif /* CONFIG_CMD_PCI || CONFIG_PCI *//* * Breathe some life into the board... * * Initialize a serial port as console, and carry out some hardware * tests. * * The first part of initialization is running from Flash memory; * its main purpose is to initialize the RAM so that we * can relocate the monitor code to RAM. *//* * All attempts to come up with a "common" initialization sequence * that works for all boards and architectures failed: some of the * requirements are just _too_ different. To get rid of the resulting * mess of board dependent #ifdef'ed code we now make the whole * initialization sequence configurable to the user. * * The requirements for any new initalization function is simple: it * receives a pointer to the "global data" structure as it's only * argument, and returns an integer return code, where 0 means * "continue" and != 0 means "fatal error, hang the system". */typedef int (init_fnc_t) (void);void __dram_init_banksize(void){ gd->bd->bi_dram[0].start = CONFIG_SYS_SDRAM_BASE; gd->bd->bi_dram[0].size = gd->ram_size;}void dram_init_banksize(void) __attribute__((weak, alias("__dram_init_banksize")));int __arch_cpu_init(void){ return 0;}int arch_cpu_init(void) __attribute__((weak, alias("__arch_cpu_init")));int __power_init_board(void){ return 0;}int power_init_board(void) __attribute__((weak, alias("__power_init_board"))); /* Record the board_init_f() bootstage (after arch_cpu_init()) */static int mark_bootstage(void){ bootstage_mark_name(BOOTSTAGE_ID_START_UBOOT_F, "board_init_f"); return 0;}init_fnc_t *init_sequence[] = { arch_cpu_init, /* basic arch cpu dependent setup */ mark_bootstage,#ifdef CONFIG_OF_CONTROL fdtdec_check_fdt,#endif#if defined(CONFIG_BOARD_EARLY_INIT_F) board_early_init_f,#endif timer_init, /* initialize timer */#ifdef CONFIG_BOARD_POSTCLK_INIT board_postclk_init,#endif#ifdef CONFIG_FSL_ESDHC get_clocks,#endif env_init, /* initialize environment */ init_baudrate, /* initialze baudrate settings */ serial_init, /* serial communications setup */ console_init_f, /* stage 1 init of console */ display_banner, /* say that we are here */ print_cpuinfo, /* display cpu info (and speed) */#if defined(CONFIG_DISPLAY_BOARDINFO) checkboard, /* display board info */#endif#if defined(CONFIG_HARD_I2C) || defined(CONFIG_SYS_I2C) init_func_i2c,#endif dram_init, /* configure available RAM banks */ NULL,};void board_init_f(ulong bootflag){ bd_t *bd; init_fnc_t **init_fnc_ptr; gd_t *id; ulong addr, addr_sp;#ifdef CONFIG_PRAM ulong reg;#endif void *new_fdt = NULL; size_t fdt_size = 0; memset((void *)gd, 0, sizeof(gd_t)); gd->mon_len = (ulong)&__bss_end - (ulong)_start;#ifdef CONFIG_OF_EMBED /* Get a pointer to the FDT */ gd->fdt_blob = __dtb_dt_begin;#elif defined CONFIG_OF_SEPARATE /* FDT is at end of image */ gd->fdt_blob = &_end;#endif /* Allow the early environment to override the fdt address */ gd->fdt_blob = (void *)getenv_ulong("fdtcontroladdr", 16, (uintptr_t)gd->fdt_blob); for (init_fnc_ptr = init_sequence; *init_fnc_ptr; ++init_fnc_ptr) { if ((*init_fnc_ptr)() != 0) { hang (); } }#ifdef CONFIG_OF_CONTROL /* For now, put this check after the console is ready */ if (fdtdec_prepare_fdt()) { panic("** CONFIG_OF_CONTROL defined but no FDT - please see " "doc/README.fdt-control"); }#endif debug("monitor len: %08lX\n", gd->mon_len); /* * Ram is setup, size stored in gd !! */ debug("ramsize: %08lX\n", gd->ram_size);#if defined(CONFIG_SYS_MEM_TOP_HIDE) /* * Subtract specified amount of memory to hide so that it won't * get "touched" at all by U-Boot. By fixing up gd->ram_size * the Linux kernel should now get passed the now "corrected" * memory size and won't touch it either. This should work * for arch/ppc and arch/powerpc. Only Linux board ports in * arch/powerpc with bootwrapper support, that recalculate the * memory size from the SDRAM controller setup will have to * get fixed. */ gd->ram_size -= CONFIG_SYS_MEM_TOP_HIDE;#endif addr = CONFIG_SYS_SDRAM_BASE + get_effective_memsize();#ifdef CONFIG_LOGBUFFER#ifndef CONFIG_ALT_LB_ADDR /* reserve kernel log buffer */ addr -= (LOGBUFF_RESERVE); debug("Reserving %dk for kernel logbuffer at %08lx\n", LOGBUFF_LEN, addr);#endif#endif#ifdef CONFIG_PRAM /* * reserve protected RAM */ reg = getenv_ulong("pram", 10, CONFIG_PRAM); addr -= (reg << 10); /* size is in kB */ debug("Reserving %ldk for protected RAM at %08lx\n", reg, addr);#endif /* CONFIG_PRAM */#if !(defined(CONFIG_SYS_ICACHE_OFF) && defined(CONFIG_SYS_DCACHE_OFF)) /* reserve TLB table */ gd->arch.tlb_size = PGTABLE_SIZE; addr -= gd->arch.tlb_size; /* round down to next 64 kB limit */ addr &= ~(0x10000 - 1); gd->arch.tlb_addr = addr; debug("TLB table from %08lx to %08lx\n", addr, addr + gd->arch.tlb_size);#endif /* round down to next 4 kB limit */ addr &= ~(4096 - 1); debug("Top of RAM usable for U-Boot at: %08lx\n", addr);#ifdef CONFIG_LCD#ifdef CONFIG_FB_ADDR gd->fb_base = CONFIG_FB_ADDR;#else /* reserve memory for LCD display (always full pages) */ addr = lcd_setmem(addr); gd->fb_base = addr;#endif /* CONFIG_FB_ADDR */#endif /* CONFIG_LCD */ /* * reserve memory for U-Boot code, data & bss * round down to next 4 kB limit */ addr -= gd->mon_len; addr &= ~(4096 - 1); debug("Reserving %ldk for U-Boot at: %08lx\n", gd->mon_len >> 10, addr);#ifndef CONFIG_SPL_BUILD /* * reserve memory for malloc() arena */ addr_sp = addr - TOTAL_MALLOC_LEN; debug("Reserving %dk for malloc() at: %08lx\n", TOTAL_MALLOC_LEN >> 10, addr_sp); /* * (permanently) allocate a Board Info struct * and a permanent copy of the "global" data */ addr_sp -= sizeof (bd_t); bd = (bd_t *) addr_sp; gd->bd = bd; debug("Reserving %zu Bytes for Board Info at: %08lx\n", sizeof (bd_t), addr_sp);#ifdef CONFIG_MACH_TYPE gd->bd->bi_arch_number = CONFIG_MACH_TYPE; /* board id for Linux */#endif addr_sp -= sizeof (gd_t); id = (gd_t *) addr_sp; debug("Reserving %zu Bytes for Global Data at: %08lx\n", sizeof (gd_t), addr_sp);#if defined(CONFIG_OF_SEPARATE) && defined(CONFIG_OF_CONTROL) /* * If the device tree is sitting immediate above our image then we * must relocate it. If it is embedded in the data section, then it * will be relocated with other data. */ if (gd->fdt_blob) { fdt_size = ALIGN(fdt_totalsize(gd->fdt_blob) + 0x1000, 32); addr_sp -= fdt_size; new_fdt = (void *)addr_sp; debug("Reserving %zu Bytes for FDT at: %08lx\n", fdt_size, addr_sp); }#endif#ifndef CONFIG_ARM64 /* setup stackpointer for exeptions */ gd->irq_sp = addr_sp;#ifdef CONFIG_USE_IRQ addr_sp -= (CONFIG_STACKSIZE_IRQ+CONFIG_STACKSIZE_FIQ); debug("Reserving %zu Bytes for IRQ stack at: %08lx\n", CONFIG_STACKSIZE_IRQ+CONFIG_STACKSIZE_FIQ, addr_sp);#endif /* leave 3 words for abort-stack */ addr_sp -= 12; /* 8-byte alignment for ABI compliance */ addr_sp &= ~0x07;#else /* CONFIG_ARM64 */ /* 16-byte alignment for ABI compliance */ addr_sp &= ~0x0f;#endif /* CONFIG_ARM64 */#else addr_sp += 128; /* leave 32 words for abort-stack */ gd->irq_sp = addr_sp;#endif debug("New Stack Pointer is: %08lx\n", addr_sp);#ifdef CONFIG_POST post_bootmode_init(); post_run(NULL, POST_ROM | post_bootmode_get(0));#endif /* Ram ist board specific, so move it to board code ... */ dram_init_banksize(); display_dram_config(); /* and display it */ gd->relocaddr = addr; gd->start_addr_sp = addr_sp; gd->reloc_off = addr - (ulong)&_start; debug("relocation Offset is: %08lx\n", gd->reloc_off); if (new_fdt) { memcpy(new_fdt, gd->fdt_blob, fdt_size); gd->fdt_blob = new_fdt; } memcpy(id, (void *)gd, sizeof(gd_t));}#if !defined(CONFIG_SYS_NO_FLASH)static char *failed = "*** failed ***\n";#endif/* * Tell if it's OK to load the environment early in boot. * * If CONFIG_OF_CONFIG is defined, we'll check with the FDT to see * if this is OK (defaulting to saying it's not OK). * * NOTE: Loading the environment early can be a bad idea if security is * important, since no verification is done on the environment. * * @return 0 if environment should not be loaded, !=0 if it is ok to load */static int should_load_env(void){#ifdef CONFIG_OF_CONTROL return fdtdec_get_config_int(gd->fdt_blob, "load-environment", 1);#elif defined CONFIG_DELAY_ENVIRONMENT return 0;#else return 1;#endif}#if defined(CONFIG_DISPLAY_BOARDINFO_LATE) && defined(CONFIG_OF_CONTROL)static void display_fdt_model(const void *blob){ const char *model; model = (char *)fdt_getprop(blob, 0, "model", NULL); printf("Model: %s\n", model ? model : "
                           
                            ");}#endif/************************************************************************ * * This is the next part if the initialization sequence: we are now * running from RAM and have a "normal" C environment, i. e. global * data can be written, BSS has been cleared, the stack size in not * that critical any more, etc. * ************************************************************************ */void board_init_r(gd_t *id, ulong dest_addr){ ulong malloc_start;#if !defined(CONFIG_SYS_NO_FLASH) ulong flash_size;#endif gd->flags |= GD_FLG_RELOC; /* tell others: relocation done */ bootstage_mark_name(BOOTSTAGE_ID_START_UBOOT_R, "board_init_r"); monitor_flash_len = (ulong)&__rel_dyn_end - (ulong)_start; /* Enable caches */ enable_caches(); debug("monitor flash len: %08lX\n", monitor_flash_len); board_init(); /* Setup chipselects */ /* * TODO: printing of the clock inforamtion of the board is now * implemented as part of bdinfo command. Currently only support for * davinci SOC's is added. Remove this check once all the board * implement this. */#ifdef CONFIG_CLOCKS set_cpu_clk_info(); /* Setup clock information */#endif serial_initialize(); debug("Now running in RAM - U-Boot at: %08lx\n", dest_addr);#ifdef CONFIG_LOGBUFFER logbuff_init_ptrs();#endif#ifdef CONFIG_POST post_output_backlog();#endif /* The Malloc area is immediately below the monitor copy in DRAM */ malloc_start = dest_addr - TOTAL_MALLOC_LEN; mem_malloc_init (malloc_start, TOTAL_MALLOC_LEN);#ifdef CONFIG_ARCH_EARLY_INIT_R arch_early_init_r();#endif#ifndef CONFIG_PMIC_REG_DUMP power_init_board();#endif#if !defined(CONFIG_SYS_NO_FLASH) puts("Flash: "); flash_size = flash_init(); if (flash_size > 0) {# ifdef CONFIG_SYS_FLASH_CHECKSUM print_size(flash_size, ""); /* * Compute and print flash CRC if flashchecksum is set to 'y' * * NOTE: Maybe we should add some WATCHDOG_RESET()? XXX */ if (getenv_yesno("flashchecksum") == 1) { printf(" CRC: %08X", crc32(0, (const unsigned char *) CONFIG_SYS_FLASH_BASE, flash_size)); } putc('\n');# else /* !CONFIG_SYS_FLASH_CHECKSUM */ print_size(flash_size, "\n");# endif /* CONFIG_SYS_FLASH_CHECKSUM */ } else { puts(failed); hang(); }#endif#if defined(CONFIG_CMD_NAND)#if defined(CONFIG_NAND_MTD) puts("NAND: "); nand_init(); /* go init the NAND */#elif defined(CONFIG_NAND_FTL)#include 
                            
                              puts("NAND FTL: "); nand_ftl_init(); /* go init the NAND */#endif#endif /* CONFIG_CMD_NAND */#if defined(CONFIG_CMD_ONENAND) onenand_init();#endif#ifdef CONFIG_GENERIC_MMC puts("MMC: "); mmc_initialize(gd->bd);#endif#ifdef CONFIG_CMD_SCSI puts("SCSI: "); scsi_init();#endif#ifdef CONFIG_HAS_DATAFLASH AT91F_DataflashInit(); dataflash_print_info();#endif /* initialize environment */ if (should_load_env()) env_relocate(); else set_default_env(NULL);#if defined(CONFIG_CMD_PCI) || defined(CONFIG_PCI) arm_pci_init();#endif stdio_init(); /* get the devices list going. */ jumptable_init();#if defined(CONFIG_API) /* Initialize API */ api_init();#endif console_init_r(); /* fully init console as a device */#ifdef CONFIG_PMIC_REG_DUMP power_init_board();#endif#ifdef CONFIG_DISPLAY_BOARDINFO_LATE# ifdef CONFIG_OF_CONTROL /* Put this here so it appears on the LCD, now it is ready */ display_fdt_model(gd->fdt_blob);# else checkboard();# endif#endif#if defined(CONFIG_ARCH_MISC_INIT) /* miscellaneous arch dependent initialisations */ arch_misc_init();#endif#if defined(CONFIG_MISC_INIT_R) /* miscellaneous platform dependent initialisations */ misc_init_r();#endif /* set up exceptions */ interrupt_init(); /* enable exceptions */ enable_interrupts(); /* Initialize from environment */ load_addr = getenv_ulong("loadaddr", 16, load_addr);#ifdef CONFIG_BOARD_LATE_INIT board_late_init();#endif#ifdef CONFIG_BITBANGMII bb_miiphy_init();#endif#if defined(CONFIG_CMD_NET) puts("Net: "); eth_initialize(gd->bd);#if defined(CONFIG_RESET_PHY_R) debug("Reset Ethernet PHY\n"); reset_phy();#endif#endif#ifdef CONFIG_POST post_run(NULL, POST_RAM | post_bootmode_get(0));#endif#if defined(CONFIG_PRAM) || defined(CONFIG_LOGBUFFER) /* * Export available size of memory for Linux, * taking into account the protected RAM at top of memory */ { ulong pram = 0; uchar memsz[32];#ifdef CONFIG_PRAM pram = getenv_ulong("pram", 10, CONFIG_PRAM);#endif#ifdef CONFIG_LOGBUFFER#ifndef CONFIG_ALT_LB_ADDR /* Also take the logbuffer into account (pram is in kB) */ pram += (LOGBUFF_LEN + LOGBUFF_OVERHEAD) / 1024;#endif#endif sprintf((char *)memsz, "%ldk", (gd->ram_size / 1024) - pram); setenv("mem", (char *)memsz); }#endif /* main_loop() can return to retry autoboot, if so just run it again. */ for (;;) { main_loop(); } /* 进入主循环，其中会读取bootdelay和bootcmd 在bootdelay时间内按下键进入命令行，否则执行bootcmd的命令。 */ /* NOTREACHED - no way out of command loop except booting */}
                            
                           
                          
                         
                        
                       
                      
                     
                    
                   
                  
                 
                
               
              
             
            
           
          
         
        
       
      
     

 

 

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