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