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发布时间：2019-06-19

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

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\n");      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.