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声明：

本文转载自《U-BOOT移植过程详解: u-boot.bin》

u-boot.bin

这里的u-boot.bin指的是不包含SPL的stage2部分的代码. 它会被SPL搬移到RAM的某个地址处开始运行. 本篇下面提到的u-boot.bin时, 也是指的这个概念.

代码分析

u-boot.lds: 它的位置在上文中我们分析了
根据u-boot.lds中的规则, 与SPL阶段一样, CPUDIR/start.o被放在了最前面. 它与SPL阶段对应的是同一个文件arch/arm/cpu/armv7/start.S
start.S
与SPL中start.S的执行流程基本一致, 不同的地方是, 这里的start.S会负责处理异常中断.

ctr0.S

_main

ENTRY(_main)  

/*  
 * Set up initial C runtime environment and call board_init_f(0).  
 */  

#if defined(CONFIG_SPL_BUILD) && defined(CONFIG_SPL_STACK)  
    ldr sp, =(CONFIG_SPL_STACK)  
#else  
    ldr sp, =(CONFIG_SYS_INIT_SP_ADDR)  
#endif  
    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  

sp, gd相关, 参考SPL中的_main
bl board_init_f: 跳转到board_init_f
SPL最后也是跳转到board_init_f, 它们有什么不一样吗? 是的, 完全不一样. 由于SPL阶段与u-boot.bin阶段编译选项的不同, 会导致不同的c文件被编译. 这里的board_init_f实现函数与SPL阶段board_init_f的实现函数不是同一个.

#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 */  
    bic sp, sp, #7  /* 8-byte alignment for ABI compliance */  
    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  
    ldr r0, [r9, #GD_RELOCADDR]     /* r0 = gd->relocaddr */  
    b   relocate_code  
here:  

/* Set up final (full) environment */  

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

    ldr r0, =__bss_start    /* this is auto-relocated! */  
    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 */  
    strlo   r2, [r0]        /* clear 32-bit BSS word */  
    addlo   r0, r0, #4      /* move to next */  
    blo clbss_l  

    bl coloured_LED_init  
    bl red_led_on  

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

    /* we should not return here. */  

#endif  

#if ! defined(CONFIG_SPL_BUILD) : 说明只有在u-boot.bin阶段, 才会执行这段代码. 这里也与SPL阶段不一样
b relocate_code : 把代码relocate到编译地址处
ldr pc, =board_init_r: 调用board_init_r, 同样, 该函数实现的地方与SPL阶段的也不一样.
arch/arm/lib/board.c

board_init_f

gd的定义在board.c里面, 有一行: DECLARE_GLOBAL_DATA_PTR;
memset清零, 说明从这里开始, 重新对gd进行初始化.
那我们在前面的代码很看到很多对gd的操作啊, 有什么用呢? 主要是在一些汇编代码里面引用了gd的相关变量. 哪些变量可能被引用到呢? 在这里 lib/asm-offsets.c

#ifdef CONFIG_OF_EMBED  
    /* Get a pointer to the FDT */  
    gd->fdt_blob = _binary_dt_dtb_start;  
#elif defined CONFIG_OF_SEPARATE  
    /* FDT is at end of image */  
    gd->fdt_blob = (void *)(_end_ofs + _TEXT_BASE);  
#endif  
    /* Allow the early environment to override the fdt address */  
    gd->fdt_blob = (void *)getenv_ulong("fdtcontroladdr", 16,  
                        (uintptr_t)gd->fdt_blob); 

fdt相关, 类似于linux内核里面的dtb. 暂不分析

for (init_fnc_ptr = init_sequence; *init_fnc_ptr; ++init_fnc_ptr) {  
    if ((*init_fnc_ptr)() != 0) {  
        hang ();  
    }  
}  

依次调用init_sequence里面的函数, 如果某个函数执行失败, 即返回值不为0, 就会hang
具体有哪些函数, 见下文.

#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  

fdt相关, 暂不分析

#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  

隐藏一块MEM, uboot不会touch它. 同样也可以做到让linux kernel不touch它.
一般ppc或者powerpc体系架构才会用到这个

 addr = CONFIG_SYS_SDRAM_BASE + gd->ram_size;  

#ifdef CONFIG_LOGBUFFER  
#ifndef CONFIG_ALT_LB_ADDR  
    /* reserve kernel log buffer */  
    addr -= (LOGBUFF_RESERVE);  
    debug("Reserving %dk for kernel logbuffer at %08lx
", 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
", reg, addr);  
#endif /* CONFIG_PRAM */  

#if !(defined(CONFIG_SYS_ICACHE_OFF) && defined(CONFIG_SYS_DCACHE_OFF))  
    /* reserve TLB table */  
    gd->arch.tlb_size = 4096 * 4;  
    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
", 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
", 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
", 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
",  
            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
",  
            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
",  
            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
",  
              fdt_size, addr_sp);  
    }  
#endif  

    /* 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
",  
        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  
    addr_sp += 128; /* leave 32 words for abort-stack   */  
    gd->irq_sp = addr_sp;  
#endif  
    interrupt_init();  

    debug("New Stack Pointer is: %08lx
", addr_sp);  

#ifdef CONFIG_POST  
    post_bootmode_init();  
    post_run(NULL, POST_ROM | post_bootmode_get(0));  
#endif  

    gd->bd->bi_baudrate = gd->baudrate;  
    /* 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 - _TEXT_BASE;  
    debug("relocation Offset is: %08lx
", 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));  

这一段主要是在做内存分配动作.
addr = CONFIG_SYS_SDRAM_BASE + gd->ram_size; 从RAM的顶部地址开始
LOGBUFF_RESERVE : Reserving %dk for kernel logbuffer
pram : Reserving %ldk for protected RAM
tlb_addr: reserve TLB table(16K), 然后会把地址对齐到64K处.
addr &= ~(4096 - 1): 做完上面的内存分配动作之后, 在保留4KB的空间. 干嘛用还不清楚.
relocaddr: 在接来下的RAM就是U-boot可以用的了 : Top of RAM usable for U-Boot
LCD
如果用户定义了CONFIG_FB_ADDR, 那这里就不为LCD保留显存了
如果用户定义了CONFIG_LCD, 又没有定义CONFIG_FB_ADDR, 则为LCD保留一块显存
Code, data, bss : reserve memory for U-Boot code, data & bss
malloc : reserve memory for malloc() arena, 突然想起了堆和栈的区别, 网上查了一下, 用户自己分配和释放的属于堆区. 貌似这个地方就是堆区哦.
bd : Board Info struct
gd: Global Data
fdt
irq_sp : IRQ & FIQ 栈指针. 向下生长
start_addr_sp : 系统栈指针. 主要是在C函数调用过程中, 函数参数, 返回地址的入栈出栈操作.
reloc_off : gd->reloc_off = addr - _TEXT_BASE;
relocate offset, 这里的意思暂时没弄懂
gd->bd->bi_arch_number = CONFIG_MACH_TYPE; /* board id for Linux */ 这个赋值动作, 记得老版本的uboot是在BOARDDIR下面做的.
dram_init_banksize : 需要在BOARDDIR下面实现, 告诉系统有几块RAM, 每一块的大小是多少.

init_sequence

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 */  
#if defined(CONFIG_DISPLAY_CPUINFO)  
    print_cpuinfo,      /* display cpu info (and speed) */  
#endif  
#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,  
};  

arch_cpu_init
一般厂商会实现, 根据实际需要初始化CPU相关的一些东西
如果没有其他实现, 就会用board.c中的weak实现.
mark_bootstage
Record the board_init_f() bootstage (after arch_cpu_init())
fdtdec_check_fdt : fdt相关, 暂不分析
board_early_init_f
一般在BOARDDIR下面实现, 初始化必要的硬件
timer_init
时钟初始化
board_postclk_init
get_clocks
env_init
以nandflash为例, 此时还没有对nandflash进行初始化, 所以这个函数的实现不会从nand中去读取实际保存的变量. 只是简单标记env_valid为1
env_common.c中的env_relocate() will do the real validation
init_baudrate
初始化gd->baudrate
gd->baudrate = getenv_ulong(“baudrate”, 10, CONFIG_BAUDRATE);
serial_init
uboot的serial子系统相关
console_init_f
stage 1 init of console
Called before relocation - use serial functions
print_cpuinfo
display cpu info (and speed)
checkboard
display board info
dram_init
初始化gd->ram_size
接下来的code会做内存分配, 需要用到这个值. 注意, 如果有多块DRAM, 起始地址不一样, 那这里的ram_size应该只是其中1块的大小.
比如BANK1: 0x20000000 64M; BANK2: 0x40000000 64M; 那这个ram_size应该是64M, 而不是128M. 具体原因, 可以看上文中的内存分配动作

board_init_r

gd->flags |= GD_FLG_RELOC;   /* tell others: relocation done */  

做过relocate之后, 才调用的board_init_r

board_init();   /* Setup chipselects */  

board_init需要在BOARDDIR中实现.

serial_initialize();  

uboot的serial子系统相关. 完成实际的串口初始化工作

/* 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);  

dest_addr是_main的汇编代码传递进来的参数 GD_RELOCADDR.
GD_RELOCADDR是在board_init_f阶段被赋值的.

power_init_board();  

可以选择性的在BOARDDIR下实现.
如果没有实现, 则会使用board.c中的weak实现

nand_init(); 

nandflash初始化, 会调用mtd/nand/nand.c中的nand_init

mmc_initialize  

sd卡初始化, 会调用drivers/mmc/mmc.c中的mmc_initialize

env_relocate 

board_init_f->init_sequence中的env_init其实没有做什么实质性动作, 因为当时nand还没有初始化
所以这里的env_relocate会调用common/env_common.c中的env_relocate, 继而开始做实质性的env初始动作. 也就是从nandflash中读取我们自己设置的环境变量

stdio_init 

调用common/stdio.c中的stdio_init, 做一些IO相关的初始化
lcd, video, keyboard, nc, jtag等等

jumptable_init

调用include/_exports.h中定义的各种通用的操作函数
get_version, getc, malloc, udelay等等

console_init_r();   /* fully init console as a device */ 

控制台最终初始化

#ifdef CONFIG_BOARD_LATE_INIT  
    board_late_init();  
#endif  

可以选择性的在BOARDDIR中定义board_late_init, 做一些最后的初始化动作

#if defined(CONFIG_CMD_NET)  
    puts("Net:   ");  
    eth_initialize(gd->bd);  
#if defined(CONFIG_RESET_PHY_R)  
    debug("Reset Ethernet PHY
");  
    reset_phy();  
#endif  
#endif 

在BOARDDIR中实现eth_initialize, 初始化网络
在BOARDDIR中实现reset_phy, 复位phy.

for (;;) {  
    main_loop();  
}  

进入common/main.c中的main_loop
如果没有按下空格键, uboot会执行bootcmd中的命令
如果按下空格键, 则会进入控制台, 与用户交互, 执行命令

总结

stage1 vs stage2
stage1也就是SPL, stage2也就是本篇所指的u-boot.bin, 主要有以下不同点
u-boot.bin在start.S中会对异常中断进行响应
u-boot.bin中的board_init_f实现与SPL阶段不一样
u-boot.bin中的board_init_r实现与SPL阶段不一样
global_data
u-boot.bin会对全局数据gd先清理, 然后在重新初始化.

需要实现的函数
dram_init_banksize: BOARDDIR下实现
告诉系统有几块RAM, 每一块的大小是多少.
board_early_init_f : BOARDDIR下实现
board_init : BOARDDIR下实现
eth_initialize : BOARDDIR下实现