目录

1.编译配置

2.u-boot.lds连接配置文件

3.Stage1之start.S

4.Stage2之入口start_armboot

1.编译配置

编译前先进行配置：make smdkv210single_config

其中，Makefile中make smdkv210single_config为：smdkv210single_config : unconfig

@$(MKCONFIG) $(@:_config=) arm s5pc11x smdkc110 samsung s5pc110

@echo "TEXT_BASE = 0xc3e00000" > $(obj)board/samsung/smdkc110/config.mk

这里使用了Makefile中的替换引用规则，类似常看到的例子 obj=$(srcfiles:%.c=%.o): 由.c得到对应的.o文件.这里是一样的道理: $(@:_config=) ，@代表的是target smdkv210single_config， 那么$(@:_config=)就是将smdkv210single_config中的_config替换为空，

即得到smdkv210single。

这里$(@:_config=) arm s5pc11x smdkc110 samsung s5pc110都是mkconfig(即@$(MKCONFIG))的参数，mkconfig即根目录下的脚本文件。

执行这句命令后，在include/下生成config.mk和config.h。并且Makefile包含这个config.mk。

config.mk文件：ARCH = arm

CPU = s5pc11x

BOARD = smdkc110

VENDOR = samsung

SOC = s5pc110

它指定里CPU架构，CPU型号，板子型号，CPU厂商，SOC？？(母鸡啦)

可以根据上面的这个信息找到对应的代码。比如说CPU代码在cpu/s5pc11x下，板子代码在board/samsung/smdkc110下。

2. u-boot.lds连接配置文件

对于.lds文件，它定义了整个程序编译之后的连接过程，决定了一个可执行程序的各个段的存储位置。u-boot.lds如何指定连接过程？首先它被根目录下config.mk引用，定义如下：LDSCRIPT := $(TOPDIR)/board/$(BOARDDIR)/u-boot.lds。根据这个路径，对于Android210而言，可以找到这个文件位于：board/samsung/smdkc110/u-boot.lds。其次，LDSCRIPT这个变量何时被用到？同样在config.mk中，可以找到：

LDFLAGS += -Bstatic -T $(LDSCRIPT) $(PLATFORM_LDFLAGS)

ifneq ($(TEXT_BASE),)

LDFLAGS += -Ttext $(TEXT_BASE)

endif

-T 参数指定生成可执行文件时ld连接器如何连接，TEXT_BASE是在make smdkv210single_config时写到board/samsung/smdkc110/config.mk中的，值为0xc3e00000。/*

* (C) Copyright 2002

* Gary Jennejohn, DENX Software Engineering,

*

* See file CREDITS for list of people who contributed to this

* project.

*

* This program is free software; you can redistribute it and/or

* modify it under the terms of the GNU General Public License as

* published by the Free Software Foundation; either version 2 of

* the License, or (at your option) any later version.

*

* This program is distributed in the hope that it will be useful,

* but WITHOUT ANY WARRANTY; without even the implied warranty of

* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

* GNU General Public License for more details.

*

* You should have received a copy of the GNU General Public License

* along with this program; if not, write to the Free Software

* Foundation, Inc., 59 Temple Place, Suite 330, Boston,

* MA 02111-1307 USA

*/

OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm");指定输出可执行文件是elf格式,32位ARM指令,小端

/*OUTPUT_FORMAT("elf32-arm", "elf32-arm", "elf32-arm")*/

OUTPUT_ARCH(arm);指定输出可执行文件的平台为ARM

ENTRY(_start);指定输出可执行文件的起始代码段为_start

SECTIONS

{

. = 0x00000000; ;从0x0位置开始

. = ALIGN(4); ;代码以4字节对齐

.text : ;指定代码段

{

cpu/s5pc11x/start.o (.text)

cpu/s5pc11x/s5pc110/cpu_init.o (.text)

board/samsung/smdkc110/lowlevel_init.o (.text)

cpu/s5pc11x/onenand_cp.o (.text)

cpu/s5pc11x/nand_cp.o (.text)

cpu/s5pc11x/movi.o (.text)

board/samsung/smdkc110/flash.o (.text)

common/secure.o (.text)

common/ace_sha1.o (.text)

cpu/s5pc11x/pmic.o (.text)

*(.text)

}

. = ALIGN(4);

.rodata : { *(.rodata) } ;指定只读数据段

. = ALIGN(4);

.data : { *(.data) } ;指定读/写数据段

. = ALIGN(4);

.got : { *(.got) } ;指定got段, got段式是uboot自定义的一个段, 非标准段

__u_boot_cmd_start = .; ;把__u_boot_cmd_start赋值为当前位置, 即起始位置

.u_boot_cmd : { *(.u_boot_cmd) } ;指定u_boot_cmd段, uboot把所有的uboot命令放在该段

__u_boot_cmd_end = .; ;把__u_boot_cmd_end赋值为当前位置,即结束位置

. = ALIGN(4);

.mmudata : { *(.mmudata) } ;内存管理单元数据段

. = ALIGN(4);

__bss_start = .; ;把__bss_start赋值为当前位置,即bss段的开始位置

.bss : { *(.bss) } ;指定bss段

_end = .; ;把_end赋值为当前位置,即bss段的结束位置

}

3.Stage1之start.S

uboot是典型的bootloader之一，大多数bootloader都分为stage1和stage2两部分，u-boot也不例外。依赖于CPU体系结构的代码(如设备初始化代码等)通常都放在stage1且可以用汇编语言来实现，而stage2则通常用C语言来实现，这样可以实现复杂的功能，而且有更好的可读性和移植性。u-boot的Stage1代码通常放在start.S文件中，他用汇编语言写成，其主要代码部分如下：

(1)定义入口。由于一个可执行的Image必须有一个入口点，并且只能有一个全局入口，通常这个入口放在ROM(Flash)的0x00000000地址，因此，必须通知编译器以使其知道这个入口，该工作可通过修改连接器脚本来完成。

(2)设置异常向量(Exception Vector)。

(3)设置CPU的速度、时钟频率及终端控制寄存器。

(4)初始化内存控制器。

(5)将ROM中的程序复制到RAM中。

(6)初始化堆栈。

(7)转到RAM中执行，该工作可使用指令ldr pc来完成。

根据config.mk中CPU的信息，找到对应的cpu目录为cpu/s5pc11x。首先看cpu/s5pc11x/start.S：

其中代码解释引自：http://www.cnblogs.com/Efronc/archive/2012/02/28/2371662.html/*

* armboot - Startup Code for S5PC110/ARM-Cortex CPU-core

*

* Copyright (c) 2009 Samsung Electronics

*

*

* See file CREDITS for list of people who contributed to this

* project.

*

* This program is free software; you can redistribute it and/or

* modify it under the terms of the GNU General Public License as

* published by the Free Software Foundation; either version 2 of

* the License, or (at your option) any later version.

*

* This program is distributed in the hope that it will be useful,

* but WITHOUT ANY WARRANTY; without even the implied warranty of

* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

* GNU General Public License for more details.

*

* You should have received a copy of the GNU General Public License

* along with this program; if not, write to the Free Software

* Foundation, Inc., 59 Temple Place, Suite 330, Boston,

* MA 02111-1307 USA

*

* Base codes by scsuh (sc.suh)

*/

#include

#include

#if defined(CONFIG_ENABLE_MMU)

#include

#endif

#include

#ifndef CONFIG_ENABLE_MMU

#ifndef CFG_PHY_UBOOT_BASE

#define CFG_PHY_UBOOT_BASE CFG_UBOOT_BASE

#endif

#endif

/*

*************************************************************************

*

* Jump vector table as in table 3.1 in [1]

*

*************************************************************************

*/

#if defined(CONFIG_EVT1) && !defined(CONFIG_FUSED) //阶段启动相关配置

.word 0x2000

.word 0x0

.word 0x0

.word 0x0

#endif

.globl _start

_start: b reset //复位入口，此处使用b指令为相对调整，不依赖运行地址

ldr pc, _undefined_instruction //以下进入异常处理函数

ldr pc, _software_interrupt

ldr pc, _prefetch_abort

ldr pc, _data_abort

ldr pc, _not_used

ldr pc, _irq

ldr pc, _fiq

_undefined_instruction: //定义异常处理函数地址

.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

_pad:

.word 0x12345678 /* now 16*4=64 */ //保证16字节对齐

.global _end_vect

_end_vect:

.balignl 16,0xdeadbeef //同样是保证16字节对齐，详见.align实验文章

/*

*************************************************************************

*

* Startup Code (reset vector) 启动代码(复位向量)此处仅进行重要的初始化操作，搬移代码和建立堆栈

*

* do important init only if we don't start from memory!

* setup Memory and board specific bits prior to relocation.

* relocate armboot to ram

* setup stack

*

*************************************************************************

*/

_TEXT_BASE:

.word TEXT_BASE //TEST_BASE为根目录下Makefile传递进来的参数，具体为0xc3e00000

/*

* Below variable is very important because we use MMU in U-Boot.

* Without it, we cannot run code correctly before MMU is ON.

* by scsuh. //下面的代码非常重要，因为我们使用了MMU，没有这段代码，在MMC开启前我们将不能正确的运行代码

*/

_TEXT_PHY_BASE:

.word CFG_PHY_UBOOT_BASE //由dram的物理地址0x20000000加上0x3e00000而得，即0x23e00000.这个地址为MMU开启前的物理地址

.globl _armboot_start

_armboot_start:

.word _start //复位地址，具体为0xc3e00010

/*

* These are defined in the board-specific linker script.

*/

.globl _bss_start

_bss_start:

.word __bss_start //__bss_start在链接脚本文件中的bss段开始，_end在bss段结尾，用于清零bss端，这两个值在链接时才确定

.globl _bss_end

_bss_end:

.word _end

#if defined(CONFIG_USE_IRQ) //如果使用中断，定义中断栈地址

/* IRQ stack memory (calculated at run-time) */

.globl IRQ_STACK_START

IRQ_STACK_START:

.word 0x0badc0de

/* IRQ stack memory (calculated at run-time) */

.globl FIQ_STACK_START

FIQ_STACK_START:

.word 0x0badc0de

#endif

/*

* the actual reset code

*/

reset:

/*

* set the cpu to SVC32 mode and IRQ & FIQ disable

*/

@;mrs r0,cpsr

@;bic r0,r0,#0x1f

@;orr r0,r0,#0xd3

@;msr cpsr,r0

msr cpsr_c, #0xd3 @ I & F disable, Mode: 0x13 - SVC //进入svc模式，中断禁止

/*

*************************************************************************

*

* CPU_init_critical registers

*

* setup important registers

* setup memory timing

*

*************************************************************************

*/

/*

* we do sys-critical inits only at reboot, //仅在关键初始化时执行，而不是在从ram复位时执行

* not when booting from ram!

*/

cpu_init_crit:

#ifndef CONFIG_EVT1

#if 0

bl v7_flush_dcache_all

#else

bl disable_l2cache //禁止l2cache

mov r0, #0x0 @

mov r1, #0x0 @ i

mov r3, #0x0

mov r4, #0x0

lp1:

mov r2, #0x0 @ j

lp2:

mov r3, r1, LSL #29 @ r3 = r1(i) <<29

mov r4, r2, LSL #6 @ r4 = r2(j) <<6

orr r4, r4, #0x2 @ r3 = (i<<29)|(j<<6)|(1<<1)

orr r3, r3, r4

mov r0, r3 @ r0 = r3

bl CoInvalidateDCacheIndex //清除数据缓存 8 * 1024

add r2, #0x1 @ r2(j)++

cmp r2, #1024 @ r2 < 1024

bne lp2 @ jump to lp2

add r1, #0x1 @ r1(i)++

cmp r1, #8 @ r1(i) < 8

bne lp1 @ jump to lp1

bl set_l2cache_auxctrl //锁定l2cache

bl enable_l2cache //使能l2cache地址对齐

#endif

#endif

bl disable_l2cache //禁止l2cache

bl set_l2cache_auxctrl_cycle //锁定l2cache

bl enable_l2cache //使能l2cache

/*

* Invalidate L1 I/D

*/

mov r0, #0 @ set up for MCR

mcr p15, 0, r0, c8, c7, 0 @ invalidate TLBs //禁止TLB

mcr p15, 0, r0, c7, c5, 0 @ invalidate icache //禁止指令缓存

/*

* disable MMU stuff and caches

*/

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 12 (Z---) BTB

mcr p15, 0, r0, c1, c0, 0 //禁止MMC和cache

/* Read booting information */

ldr r0, =PRO_ID_BASE

ldr r1, [r0,#OMR_OFFSET]

bic r2, r1, #0xffffffc1 //读取启动信息

#ifdef CONFIG_VOGUES

/* PS_HOLD(GPH0_0) set to output high */

ldr r0, =ELFIN_GPIO_BASE

ldr r1, =0x00000001

str r1, [r0, #GPH0CON_OFFSET]

ldr r1, =0x5500

str r1, [r0, #GPH0PUD_OFFSET]

ldr r1, =0x01

str r1, [r0, #GPH0DAT_OFFSET]

#endif

/* NAND BOOT */

cmp r2, #0x0 @ 512B 4-cycle //识别各种启动方式，并将识别到的启动识别码写入R3中

moveq r3, #BOOT_NAND

cmp r2, #0x2 @ 2KB 5-cycle

moveq r3, #BOOT_NAND

cmp r2, #0x4 @ 4KB 5-cycle 8-bit ECC

moveq r3, #BOOT_NAND

cmp r2, #0x6 @ 4KB 5-cycle 16-bit ECC

moveq r3, #BOOT_NAND

cmp r2, #0x8 @ OneNAND Mux

moveq r3, #BOOT_ONENAND

/* SD/MMC BOOT */

cmp r2, #0xc

moveq r3, #BOOT_MMCSD

/* NOR BOOT */

cmp r2, #0x14

moveq r3, #BOOT_NOR

#if 0 /* Android C110 BSP uses OneNAND booting! */

/* For second device booting */

/* OneNAND BOOTONG failed */

cmp r2, #0x8

moveq r3, #BOOT_SEC_DEV

#endif

/* Uart BOOTONG failed */

cmp r2, #(0x1<<4)

moveq r3, #BOOT_SEC_DEV

ldr r0, =INF_REG_BASE

str r3, [r0, #INF_REG3_OFFSET] //将启动标识码写入INF_REG3中

/*

* Go setup Memory and board specific bits prior to relocation. //重定位前初始化存储器和板特殊位

*/

ldr sp, =0xd0036000 /* end of sram dedicated to u-boot */ //分配给u-boot的sram的结尾 sram为0xd0020000-d003ffff 分配大小为90k

sub sp, sp, #12 /* set stack */

mov fp, #0

bl lowlevel_init /* go setup pll,mux,memory */ //调用lowlevel_init函数初始化pll memory等与板子相关的内容 函数位于board目录下

/* To hold max8698 output before releasing power on switch,

* set PS_HOLD signal to high

*/

ldr r0, =0xE010E81C /* PS_HOLD_CONTROL register */ //PS_HOLD输出高电平，PS_HOLD使能。PMIC相关

ldr r1, =0x00005301 /* PS_HOLD output high */

str r1, [r0]

/* get ready to call C functions */

ldr sp, _TEXT_PHY_BASE /* setup temp stack pointer */ //建立临时栈指针，内容为0x23e00000

sub sp, sp, #12

mov fp, #0 /* no previous frame, so fp=0 */

/* when we already run in ram, we don't need to relocate U-Boot.

* and actually, memory controller must be configured before U-Boot //如果程序已经在ram中运行，我们不需要重新定位u-boot。

* is running in ram. //实际上存储器一定在u-boot在ram中运行前被初始化了

*/

ldr r0, =0xff000fff

bic r1, pc, r0 /* r0

ldr r2, _TEXT_BASE /* r1

bic r2, r2, r0 /* r0

cmp r1, r2 /* compare r0, r1 */

beq after_copy /* r0 == r1 then skip flash copy */ //如果r1=r2，跳过复制部分

#if defined(CONFIG_EVT1)

/* If BL1 was copied from SD/MMC CH2 */

ldr r0, =0xD0037488

ldr r1, [r0] //取0xd0037488地址的值

ldr r2, =0xEB200000

cmp r1, r2

beq mmcsd_boot //如果等于0xEB200000,跳转到mmcsd_boot

#endif

ldr r0, =INF_REG_BASE //读取存储的INF_REG3中的启动类型

ldr r1, [r0, #INF_REG3_OFFSET]

cmp r1, #BOOT_NAND /* 0x0 => boot device is nand */

beq nand_boot

cmp r1, #BOOT_ONENAND /* 0x1 => boot device is onenand */

beq onenand_boot

cmp r1, #BOOT_MMCSD

beq mmcsd_boot

cmp r1, #BOOT_NOR

beq nor_boot

cmp r1, #BOOT_SEC_DEV

beq mmcsd_boot

nand_boot:

mov r0, #0x1000 //以下函数实现代码的搬移

bl copy_from_nand

b after_copy

onenand_boot:

bl onenand_bl2_copy

b after_copy

mmcsd_boot:

#if DELETE

ldr sp, _TEXT_PHY_BASE

sub sp, sp, #12

mov fp, #0

#endif

bl movi_bl2_copy

b after_copy

nor_boot:

bl read_hword

b after_copy

after_copy:

#if defined(CONFIG_ENABLE_MMU)

enable_mmu:

/* enable domain access */

ldr r5, =0x0000ffff //定义使能域的访问权限

mcr p15, 0, r5, c3, c0, 0 @load domain access register

/* Set the TTB register */

ldr r0, _mmu_table_base

ldr r1, =CFG_PHY_UBOOT_BASE

ldr r2, =0xfff00000

bic r0, r0, r2

orr r1, r0, r1

mcr p15, 0, r1, c2, c0, 0 //将MMU启用前的的mmu_table_base转成sdram中的地址，并写入cp15的c2中

/* Enable the MMU */

mmu_on:

mrc p15, 0, r0, c1, c0, 0 //启用mmu

orr r0, r0, #1

mcr p15, 0, r0, c1, c0, 0

nop

nop

nop

nop

#endif

skip_hw_init:

/* Set up the stack */

stack_setup:

#if defined(CONFIG_MEMORY_UPPER_CODE)

ldr sp, =(CFG_UBOOT_BASE + CFG_UBOOT_SIZE - 0x1000)

#else

ldr r0, _TEXT_BASE /* upper 128 KiB: relocated uboot */

sub r0, r0, #CFG_MALLOC_LEN /* malloc area */

sub r0, r0, #CFG_GBL_DATA_SIZE /* bdinfo */

#if defined(CONFIG_USE_IRQ)

sub r0, r0, #(CONFIG_STACKSIZE_IRQ+CONFIG_STACKSIZE_FIQ)

#endif

sub sp, r0, #12 /* leave 3 words for abort-stack */ //为取址终止异常预留3个字空间

#endif

clear_bss:

ldr r0, _bss_start /* find start of bss segment */

ldr r1, _bss_end /* stop here */

mov r2, #0x00000000 /* clear */

clbss_l:

str r2, [r0] /* clear loop... */ //清除bss端内存

add r0, r0, #4

cmp r0, r1

ble clbss_l

ldr pc, _start_armboot

_start_armboot: //第一阶段结束，进入c程序阶段

.word start_armboot

#if defined(CONFIG_ENABLE_MMU)

_mmu_table_base:

.word mmu_table

#endif

/*

* copy U-Boot to SDRAM and jump to ram (from NAND or OneNAND)

* r0: size to be compared

* Load 1'st 2blocks to RAM because U-boot's size is larger than 1block(128k) size

*/

.globl copy_from_nand

copy_from_nand:

push {lr} /* save return address */

mov r9, r0

mov r9, #0x100 /* Compare about 8KB */

bl copy_uboot_to_ram //从nandflash中读取512k到0x23e00000中

tst r0, #0x0

bne copy_failed

#if defined(CONFIG_EVT1)

ldr r0, =0xd0020000 //iram的起始地址

#else

ldr r0, =0xd0030000 //iram的中间地址

#endif

ldr r1, _TEXT_PHY_BASE /* 0x23e00000 */

1: ldr r3, [r0], #4 //取r0+4地址的值到r3中

ldr r4, [r1], #4 //取r1+4地址的值到r4中

teq r3, r4

bne compare_failed /* not matched */ //如果r3和r4不相等，比较失败

subs r9, r9, #4

bne 1b

pop {pc} /* all is OK */ //复制成功，返回

copy_failed:

nop /* copy from nand failed */

b copy_failed

compare_failed:

nop /* compare failed */

b compare_failed

/*

* we assume that cache operation is done before. (eg. cleanup_before_linux())

* actually, we don't need to do anything about cache if not use d-cache in U-Boot

* So, in this function we clean only MMU. by scsuh

*

* void theLastJump(void *kernel, int arch_num, uint boot_params);

*/

#if defined(CONFIG_ENABLE_MMU)

.globl theLastJump

theLastJump:

mov r9, r0 //保存内核地址

ldr r3, =0xfff00000

ldr r4, _TEXT_PHY_BASE

adr r5, phy_last_jump

bic r5, r5, r3

orr r5, r5, r4

mov pc, r5

phy_last_jump:

/*

* disable MMU stuff //关闭MMU

*/

mrc p15, 0, r0, c1, c0, 0

bic r0, r0, #0x00002300 /* clear bits 13, 9:8 (--V- --RS) */

bic r0, r0, #0x00000087 /* clear bits 7, 2:0 (B--- -CAM) */

orr r0, r0, #0x00000002 /* set bit 2 (A) Align */

orr r0, r0, #0x00001000 /* set bit 12 (I) I-Cache */

mcr p15, 0, r0, c1, c0, 0

mcr p15, 0, r0, c8, c7, 0 /* flush v4 TLB */

mov r0, #0

mov pc, r9 //跳转到内核地址

#endif

/*

*************************************************************************

*

* Interrupt handling

*

*************************************************************************

*/

@

@ IRQ stack frame.

@

#define S_FRAME_SIZE 72

#define S_OLD_R0 68

#define S_PSR 64

#define S_PC 60

#define S_LR 56

#define S_SP 52

#define S_IP 48

#define S_FP 44

#define S_R10 40

#define S_R9 36

#define S_R8 32

#define S_R7 28

#define S_R6 24

#define S_R5 20

#define S_R4 16

#define S_R3 12

#define S_R2 8

#define S_R1 4

#define S_R0 0

#define MODE_SVC 0x13

#define I_BIT 0x80

/* //定义异常时保存寄存器的宏

* use bad_save_user_regs for abort/prefetch/undef/swi ...

* use irq_save_user_regs / irq_restore_user_regs for IRQ/FIQ handling

*/

.macro bad_save_user_regs

sub sp, sp, #S_FRAME_SIZE @ carve out a frame on current user stack

stmia sp, {r0 - r12} @ Save user registers (now in svc mode) r0-r12

ldr r2, _armboot_start

sub r2, r2, #(CFG_MALLOC_LEN)

sub r2, r2, #(CFG_GBL_DATA_SIZE+8) @ set base 2 words into abort stack

ldmia r2, {r2 - r3} @ get values for "aborted" pc and cpsr (into parm regs)

add r0, sp, #S_FRAME_SIZE @ grab pointer to old stack

add r5, sp, #S_SP

mov r1, lr

stmia r5, {r0 - r3} @ save sp_SVC, lr_SVC, pc, cpsr

mov r0, sp @ save current stack into r0 (param register)

.endm

.macro irq_save_user_regs

sub sp, sp, #S_FRAME_SIZE

stmia sp, {r0 - r12} @ Calling r0-r12

add r8, sp, #S_PC @ !!!! R8 NEEDS to be saved !!!! a reserved stack spot would be good.

stmdb r8, {sp, lr}^ @ Calling SP, LR

str lr, [r8, #0] @ Save calling PC

mrs r6, spsr

str r6, [r8, #4] @ Save CPSR

str r0, [r8, #8] @ Save OLD_R0

mov r0, sp

.endm

.macro irq_restore_user_regs

ldmia sp, {r0 - lr}^ @ Calling r0 - lr

mov r0, r0

ldr lr, [sp, #S_PC] @ Get PC

add sp, sp, #S_FRAME_SIZE

subs pc, lr, #4 @ return & move spsr_svc into cpsr

.endm

.macro get_bad_stack

ldr r13, _armboot_start @ setup our mode stack (enter in banked mode)

sub r13, r13, #(CFG_MALLOC_LEN) @ move past malloc pool

sub r13, r13, #(CFG_GBL_DATA_SIZE+8) @ move to reserved a couple spots for abort stack

str lr, [r13] @ save caller lr in position 0 of saved stack

mrs lr, spsr @ get the spsr

str lr, [r13, #4] @ save spsr in position 1 of saved stack

mov r13, #MODE_SVC @ prepare SVC-Mode

@ msr spsr_c, r13

msr spsr, r13 @ switch modes, make sure moves will execute

mov lr, pc @ capture return pc

movs pc, lr @ jump to next instruction & switch modes.

.endm

.macro get_bad_stack_swi

sub r13, r13, #4 @ space on current stack for scratch reg.

str r0, [r13] @ save R0's value.

ldr r0, _armboot_start @ get data regions start

sub r0, r0, #(CFG_MALLOC_LEN) @ move past malloc pool

sub r0, r0, #(CFG_GBL_DATA_SIZE+8) @ move past gbl and a couple spots for abort stack

str lr, [r0] @ save caller lr in position 0 of saved stack

mrs r0, spsr @ get the spsr

str lr, [r0, #4] @ save spsr in position 1 of saved stack

ldr r0, [r13] @ restore r0

add r13, r13, #4 @ pop stack entry

.endm

.macro get_irq_stack @ setup IRQ stack

ldr sp, IRQ_STACK_START

.endm

.macro get_fiq_stack @ setup FIQ stack

ldr sp, FIQ_STACK_START

.endm

/*

* exception handlers //异常处理句柄

*/

.align 5

undefined_instruction:

get_bad_stack

bad_save_user_regs

bl do_undefined_instruction

.align 5

software_interrupt:

get_bad_stack_swi

bad_save_user_regs

bl do_software_interrupt

.align 5

prefetch_abort:

get_bad_stack

bad_save_user_regs

bl do_prefetch_abort

.align 5

data_abort:

get_bad_stack

bad_save_user_regs

bl do_data_abort

.align 5

not_used:

get_bad_stack

bad_save_user_regs

bl do_not_used

#if defined(CONFIG_USE_IRQ)

.align 5

irq:

get_irq_stack

irq_save_user_regs

bl do_irq

irq_restore_user_regs

.align 5

fiq:

get_fiq_stack

/* someone ought to write a more effiction fiq_save_user_regs */

irq_save_user_regs

bl do_fiq

irq_restore_user_regs

#else

.align 5

irq:

get_bad_stack

bad_save_user_regs

bl do_irq

.align 5

fiq:

get_bad_stack

bad_save_user_regs

bl do_fiq

#endif

.align 5

.global arm_cache_flush

arm_cache_flush:

mcr p15, 0, r1, c7, c5, 0 @ invalidate I cache

mov pc, lr @ back to caller

/*

* v7_flush_dcache_all()

*

* Flush the whole D-cache.

*

* Corrupted registers: r0-r5, r7, r9-r11

*

* - mm - mm_struct describing address space

*/

.align 5

.global v7_flush_dcache_all

v7_flush_dcache_all:

ldr r0, =0xffffffff

mrc p15, 1, r0, c0, c0, 1 @ Read CLIDR

ands r3, r0, #0x7000000

mov r3, r3, LSR #23 @ Cache level value (naturally aligned)

beq Finished

mov r10, #0

Loop1:

add r2, r10, r10, LSR #1 @ Work out 3xcachelevel

mov r1, r0, LSR r2 @ bottom 3 bits are the Ctype for this level

and r1, r1, #7 @ get those 3 bits alone

cmp r1, #2

blt Skip @ no cache or only instruction cache at this level

mcr p15, 2, r10, c0, c0, 0 @ write the Cache Size selection register

mov r1, #0

mcr p15, 0, r1, c7, c5, 4 @ PrefetchFlush to sync the change to the CacheSizeID reg

mrc p15, 1, r1, c0, c0, 0 @ reads current Cache Size ID register

and r2, r1, #0x7 @ extract the line length field

add r2, r2, #4 @ add 4 for the line length offset (log2 16 bytes)

ldr r4, =0x3FF

ands r4, r4, r1, LSR #3 @ R4 is the max number on the way size (right aligned)

clz r5, r4 @ R5 is the bit position of the way size increment

ldr r7, =0x00007FFF

ands r7, r7, r1, LSR #13 @ R7 is the max number of the index size (right aligned)

Loop2:

mov r9, r4 @ R9 working copy of the max way size (right aligned)

Loop3:

orr r11, r10, r9, LSL r5 @ factor in the way number and cache number into R11

orr r11, r11, r7, LSL r2 @ factor in the index number

mcr p15, 0, r11, c7, c6, 2 @ invalidate by set/way

subs r9, r9, #1 @ decrement the way number

bge Loop3

subs r7, r7, #1 @ decrement the index

bge Loop2

Skip:

add r10, r10, #2 @ increment the cache number

cmp r3, r10

bgt Loop1

Finished:

mov pc, lr

.align 5

.global disable_l2cache

disable_l2cache:

mrc p15, 0, r0, c1, c0, 1

bic r0, r0, #(1<<1)

mcr p15, 0, r0, c1, c0, 1

mov pc, lr

.align 5

.global enable_l2cache

enable_l2cache:

mrc p15, 0, r0, c1, c0, 1

orr r0, r0, #(1<<1)

mcr p15, 0, r0, c1, c0, 1

mov pc, lr

.align 5

.global set_l2cache_auxctrl

set_l2cache_auxctrl:

mov r0, #0x0

mcr p15, 1, r0, c9, c0, 2

mov pc, lr

.align 5

.global set_l2cache_auxctrl_cycle

set_l2cache_auxctrl_cycle:

mrc p15, 1, r0, c9, c0, 2

bic r0, r0, #(0x1<<29)

bic r0, r0, #(0x1<<21)

bic r0, r0, #(0x7<<6)

bic r0, r0, #(0x7<<0)

mcr p15, 1, r0, c9, c0, 2

mov pc,lr

.align 5

CoInvalidateDCacheIndex:

;/* r0 = index */

mcr p15, 0, r0, c7, c6, 2

mov pc,lr

#if defined(CONFIG_INTEGRATOR) && defined(CONFIG_ARCH_CINTEGRATOR)

/* Use the IntegratorCP function from board/integratorcp/platform.S */

#elif defined(CONFIG_S5PC11X)

/* For future usage of S3C64XX*/

#else

.align 5

.globl reset_cpu

reset_cpu:

ldr r1, rstctl /* get addr for global reset reg */

mov r3, #0x2 /* full reset pll+mpu */

str r3, [r1] /* force reset */

mov r0, r0

_loop_forever:

b _loop_forever

rstctl:

.word PM_RSTCTRL_WKUP

#endif

State 1最后，调用里start_armboot函数，这个函数是State2的入口函数。

4.Stage2之入口start_armboot

start_armboot函数是纯C写的，位于lib_arm/board.c中。此函数经过一系列的动作之后，最终进入main_loop循环。main_loop位于common/main.c中，它主要用于执行common下定义的一些cmd。在正常启动的情况下，main_loop会在abortboot处等待n秒中(n一般是设置在uboot环境变量中，可以用getenv冲env中读取，一般设置成3s)，然后从env中读取bootcmd的值，用run_command执行bootcmd命令。对于原始Android210来讲，bootcmd=nand read C0008000 600000 400000;bootm C0008000。

bootcmd中调用里两个命令，分别是nand和bootm。

nand命令，对应的源文件是common/cmd_nand.c。它的主要功能是...

bootm命令，对应的源文件是common/cmd_bootm.c。命令格式：U_BOOT_CMD(

bootm, CFG_MAXARGS, 1, do_bootm,

"bootm - boot application p_w_picpath from memory\n",

"[addr [arg ...]]\n - boot application p_w_picpath stored in memory\n"

"\tpassing arguments 'arg ...'; when booting a Linux kernel,\n"

"\t'arg' can be the address of an initrd p_w_picpath\n"

#if defined(CONFIG_OF_LIBFDT)

"\tWhen booting a Linux kernel which requires a flat device-tree\n"

"\ta third argument is required which is the address of the\n"

"\tdevice-tree blob. To boot that kernel without an initrd p_w_picpath,\n"

"\tuse a '-' for the second argument. If you do not pass a third\n"

"\ta bd_info struct will be passed instead\n"

#endif

#if defined(CONFIG_FIT)

"\t\nFor the new multi component uImage format (FIT) addresses\n"

"\tmust be extened to include component or configuration unit name:\n"

"\taddr: - direct component p_w_picpath specification\n"

"\taddr# - configuration specification\n"

"\tUse iminfo command to get the list of existing component\n"

"\tp_w_picpaths and configurations.\n"

#endif

);

可以看到命令名为bootm，对应执行函数为do_bootm:

/*******************************************************************/

/* bootm - boot application p_w_picpath from p_w_picpath in memory */

/*******************************************************************/

int do_bootm (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])

{

p_w_picpath_header_t *hdr;

ulong addr;

ulong iflag;

const char *type_name;

uint unc_len = CFG_BOOTM_LEN;

uint8_t comp, type, os;

void *os_hdr;

ulong os_data, os_len;

ulong p_w_picpath_start, p_w_picpath_end;

ulong load_start, load_end;

ulong mem_start;

phys_size_t mem_size;

struct lmb lmb;

memset ((void *)&p_w_picpaths, 0, sizeof (p_w_picpaths));

p_w_picpaths.verify = getenv_yesno ("verify");

...........

lmb_reserve(&lmb, load_start, (load_end - load_start));

#if defined(CONFIG_ZIMAGE_BOOT)

after_header_check:

os = hdr->ih_os;

#endif

switch (os) {

default: /* handled by (original) Linux case */

case IH_OS_LINUX:

#ifdef CONFIG_SILENT_CONSOLE

fixup_silent_linux();

#endif

do_bootm_linux (cmdtp, flag, argc, argv, &p_w_picpaths);

break;

case IH_OS_NETBSD:

do_bootm_netbsd (cmdtp, flag, argc, argv, &p_w_picpaths);

break;

.............

return 1;

}

其中有do_bootm_linux函数，这个函数是启动kernel的函数。对于Android210来讲，这个文件位于lib_arm/bootm.c中。do_bootm_linux:

void do_bootm_linux (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[],

bootm_headers_t *p_w_picpaths)

{

ulong initrd_start, initrd_end;

ulong ep = 0;

bd_t *bd = gd->bd;

char *s;

int machid = bd->bi_arch_number;

void (*theKernel)(int zero, int arch, uint params);

int ret;

#ifdef CONFIG_CMDLINE_TAG

char *commandline = getenv ("bootargs");

#endif

/* find kernel entry point */

if (p_w_picpaths->legacy_hdr_valid) {

ep = p_w_picpath_get_ep (&p_w_picpaths->legacy_hdr_os_copy);

#if defined(CONFIG_FIT)

} else if (p_w_picpaths->fit_uname_os) {

ret = fit_p_w_picpath_get_entry (p_w_picpaths->fit_hdr_os,

p_w_picpaths->fit_noffset_os, &ep);

if (ret) {

puts ("Can't get entry point property!\n");

goto error;

}

#endif

} else {

puts ("Could not find kernel entry point!\n");

goto error;

}

theKernel = (void (*)(int, int, uint))ep;

s = getenv ("machid");

if (s) {

machid = simple_strtoul (s, NULL, 16);

printf ("Using machid 0x%x from environment\n", machid);

}

ret = boot_get_ramdisk (argc, argv, p_w_picpaths, IH_ARCH_ARM,

&initrd_start, &initrd_end);

if (ret)

goto error;

show_boot_progress (15);

debug ("## Transferring control to Linux (at address %08lx) ...\n",

(ulong) theKernel);

#if defined (CONFIG_SETUP_MEMORY_TAGS) || \

defined (CONFIG_CMDLINE_TAG) || \

defined (CONFIG_INITRD_TAG) || \

defined (CONFIG_SERIAL_TAG) || \

defined (CONFIG_REVISION_TAG) || \

defined (CONFIG_LCD) || \

defined (CONFIG_VFD) || \

defined (CONFIG_MTDPARTITION)

setup_start_tag (bd);

#ifdef CONFIG_SERIAL_TAG

setup_serial_tag (¶ms);

#endif

#ifdef CONFIG_REVISION_TAG

setup_revision_tag (¶ms);

#endif

#ifdef CONFIG_SETUP_MEMORY_TAGS

setup_memory_tags (bd);

#endif

#ifdef CONFIG_CMDLINE_TAG

setup_commandline_tag (bd, commandline);

#endif

#ifdef CONFIG_INITRD_TAG

if (initrd_start && initrd_end)

setup_initrd_tag (bd, initrd_start, initrd_end);

#endif

#if defined (CONFIG_VFD) || defined (CONFIG_LCD)

setup_videolfb_tag ((gd_t *) gd);

#endif

#ifdef CONFIG_MTDPARTITION

setup_mtdpartition_tag();

#endif

setup_end_tag (bd);

#endif

/* we assume that the kernel is in place */

printf ("\nStarting kernel ...\n\n");

#ifdef CONFIG_USB_DEVICE

{

extern void udc_disconnect (void);

udc_disconnect ();

}

#endif

cleanup_before_linux ();

theKernel (0, machid, bd->bi_boot_params);

/* does not return */

return;

error:

do_reset (cmdtp, flag, argc, argv);

return;

}

do_bootm_linux中最后一个参数是bootm_headers_t *p_w_picpaths。