仿照Linux下的U-Boot来DIY自己的arm11(6410)的bootloader

U-Boot是用于多种嵌入式CPU（ MIPS、x86、ARM等）的bootloader程序,U-Boot不仅支持嵌入式Linux系统的引导，还支持VxWorks, QNX等多种嵌入式操作系统。

查看S3C6410_Internal_ROM_Booting.pdf可看到系统启动的原理图如下：

linux的Uboot分析

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。

SECTIONS {
...
secname start BLOCK(align) (NOLOAD) : AT ( ldadr )
{ contents } >region :phdr =fill
...
}

secname和contents是必须的，其他的都是可选的。下面挑几个常用的看看：

1、secname：段名
2、contents：决定哪些内容放在本段，可以是整个目标文件，也可以是目标文件中的某段（代码段、数据段等）
3、start：本段连接（运行）的地址，如果没有使用AT（ldadr），本段存储的地址也是start。GNU网站上说start可以用任意一种描述地址的符号来描述。
4、AT（ldadr）：定义本段存储（加载）的地址。

结合u-boot.lds进行分析：

OUTPUT_FORMAT("elf32­littlearm", "elf32­littlearm", "elf32­littlearm")
        //指定输出可执行文件是elf格式,32位ARM指令,小端
        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/s3c64xx/start.o (.text)  //代码的第一个代码部分
              cpu/s3c64xx/s3c6410/cpu_init.o// (.text)//初始化CPU
              cpu/s3c64xx/onenand_cp.o // (.text)
              cpu/s3c64xx/nand_cp.o //(.text)//拷贝nandflash 8K至stepstone
              cpu/s3c64xx/movi.o //(.text)//把nandflash剩余部分拷贝至DRAM中运行
              *(.text)//代码剩余部分
              lib_arm/div0.o
                }
                . = 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)
        __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
        }

在链接器脚本中可以看出，程序入口时start.s，下面开始分析start.s

/*
 *  armboot - Startup Code for S3C6400/ARM1176 CPU-core
 *
 *  Copyright (c) 2007 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
 *
 * 2007-09-21 - Restructured codes by jsgood (jsgood.yang@samsung.com)
 * 2007-09-21 - Added moviNAND and OneNAND boot codes by jsgood (jsgood.yang@samsung.com)
 * Base codes by scsuh (sc.suh)
 */

#include <config.h>
#include <version.h>
#ifdef CONFIG_ENABLE_MMU
#include <asm/proc/domain.h>
#endif
#include <regs.h>

#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]
 *
 *************************************************************************
 */
//global声明一个符号可被其它文件引用，相当于声明了一个全局变量，.globl与.global相同。
//该部分为处理器的异常处理向量表。地址范围为0x0000 0000 ~ 0x0000 0020,刚好8条指令。  (1)
.globl _start     
_start: b reset
 ldr pc, _undefined_instruction
 ldr pc, _software_interrupt
 ldr pc, _prefetch_abort
 ldr pc, _data_abort
 ldr pc, _not_used
 ldr pc, _irq
 ldr pc, _fiq
// .word伪操作用于分配一段字内存单元（分配的单元都是字对齐的），并用伪操作中的expr初始化。.long与.int作用与之//相同。

_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
_pad:
 .word 0x12345678 /* now 16*4=64 */
.global _end_vect
_end_vect:

 .balignl 16,0xdeadbeef
/*
 *************************************************************************
 *
 * Startup Code (reset vector)
 *
 * 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在开发板相关的目录中的config.mk文件中定义, 它定义了
// 代码在运行时所在的地址, 那么_TEXT_BASE中保存了这个地址
_TEXT_BASE:
 .word TEXT_BASE

/*
 * 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.
 */
_TEXT_PHY_BASE:
 .word CFG_PHY_UBOOT_BASE
// 声明 _armboot_start 并用 _start 来进行初始化，在board/u-boot.lds中定义
.globl _armboot_start
_armboot_start:
 .word _start

/*
 * These are defined in the board-specific linker script.
 */
// 声明_bss_start并用__bss_start来初始化，其中__bss_start定义在与板相关的u-boot.lds中。
// _bss_start保存的是__bss_start这个标号所在的地址, 这里涉及到当前代码所在
// 的地址不是编译时的地址的情况, 这里直接取得该标号对应的地址, 不受编译时
// 地址的影响. _bss_end也是同样的道理.
.globl _bss_start
_bss_start:
 .word __bss_start

.globl _bss_end
_bss_end:
 .word _end

#ifdef CONFIG_USE_IRQ
/* 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
 */
//  MRS {<cond>} Rd,CPSR|SPSR 将CPSR｜SPSR传送到Rd
//  使用这两条指令将状态寄存器传送到一般寄存器，只修改必要的位，再将结果传送回状态寄存器，这样可以最好地完成对CRSP或者SPSR的修改
//  MSR {<cond>} CPSR_<field>|SPSR_<field>,Rm 或者是 MSR {<cond>} CPSR_f|SPSR_f,#<32-bit immediate>
//  MRS与MSR配合使用，作为更新PSR的“读取－－修改－－写回”序列的一部分
//  bic r0,r1,r2  ;r0:=r1 and not r2
//  orr ro,r1,r2  ;r0:=r1 or r2
//  这几条指令执行完毕后，进入SVC模式，该模式主要用来处理软件中断(SWI)
reset:
 /*
  * set the cpu to SVC32 mode
  */
 mrs r0,cpsr
 bic r0,r0,#0x1f
 orr r0,r0,#0xd3
 msr cpsr,r0

/*
 *************************************************************************
 *
 * CPU_init_critical registers
 *
 * setup important registers
 * setup memory timing
 *
 *************************************************************************
 */
        /*
        * we do sys-critical inits only at reboot,
        * not when booting from ram!
        */
//cpu初始化
cpu_init_crit:
 /*
  * flush v4 I/D caches
  */
  //关闭I/Dcaches
 mov r0, #0
 mcr p15, 0, r0, c7, c7, 0 /* flush v3/v4 cache */
 mcr p15, 0, r0, c8, c7, 0 /* flush v4 TLB */

 /*
  * disable MMU stuff and caches
  */
  //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

 /* Peri port setup */
 //外设基地址设置
 ldr r0, =0x70000000
 orr r0, r0, #0x13
    mcr p15,0,r0,c15,c2,4      @ 256M(0x70000000-0x7fffffff)
//因为是只定义了6410，别的都忽略
#ifdef CONFIG_BOOT_ONENAND
 ldr r0, =0x70000000  @ onenand controller setup
 orr r0, r0, #0x100000
 ldr r1, =0x4000
 orr r1, r1, #0xe0
 str r1, [r0]
//关闭6410的看门狗
#if defined(CONFIG_S3C6410) || defined(CONFIG_S3C6430)
 orr r0, r0, #300  @ disable watchdog
 mov r1, #1
 str r1, [r0]

 mov r1, #0x23000000  @ start buffer register
 orr r1, r1, #0x30000
 orr r1, r1, #0xc800
#else  //不执行
 mov r1, =0x20000000  @ start buffer register
 orr r1, r1, #0xc30000
 orr r1, r1, #0xc800
#endif

 sub r0, r1, #0x0400  @ start address1 register

 ldr r2, [r1, #0x84]  @ ecc bypass
 orr r2, r2, #0x100
 str r2, [r1, #0x84]

 mov r3, #0x0  @ DFS, FBA
 str r3, [r0, #0x00]
 str r3, [r0, #0x04]  @ select dataram for DDP as 0

 mov r4, #0x104  @ interrupt register
 mov r5, #0x0002  @ FPA, FSA
 mov r6, #0x0800  @ BSA

onenand_bl1_load:
 str r5, [r0, #0x1c]  @ save FPA, FSA
 orr r6, r6, #0x02  @ BSC
 str r6, [r1, #0x00]  @ save BSA, BSC
 str r3, [r1, r4]  @ clear interrupt
 str r3, [r1, #0x80]  @ write load command

 mov r7, #0x100  @ need small delay

onenand_wait_loop1:
 subs r7, r7, #0x1
 bne onenand_wait_loop1

 add r5, r5, #0x2  @ next FPA, FSA
 sub r6, r6, #0x2
 add r6, r6, #0x200  @ next BSA
 cmp r5, #0x8
 bne onenand_bl1_load
#endif

 /*
  * Go setup Memory and board specific bits prior to relocation.
  */
 bl lowlevel_init /* go setup pll,mux,memory */

 /* when we already run in ram, we don't need to relocate U-Boot.
  * and actually, memory controller must be configured before U-Boot
  * is running in ram.
  */
 
  ldr r0, =0xff000fff
 
 

 bic r1, pc, r0  /* r0 <- current base addr of code */
 ldr r2, _TEXT_BASE  /* r1 <- original base addr in ram */
 bic r2, r2, r0  /* r0 <- current base addr of code */
 cmp    r1, r2                  /* compare r0, r1                  */
 beq    after_copy  /* r0 == r1 then skip flash copy  */
//使用nandflash，此处忽略
#ifdef CONFIG_BOOT_NOR  /* relocate U-Boot to RAM */
 adr r0, _start  /* r0 <- current position of code  */
 ldr r1, _TEXT_PHY_BASE /* r1 <- destination                */
 ldr r2, _armboot_start
 ldr r3, _bss_start
 sub r2, r3, r2  /* r2 <- size of armboot            */
 add r2, r0, r2  /* r2 <- source end address        */

nor_copy_loop:
 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 nor_copy_loop
 b after_copy
#endif
//从Nandflash启动，执行此处代码
#ifdef CONFIG_BOOT_NAND
 mov r0, #0x1000
 bl copy_from_nand
#endif

#ifdef CONFIG_BOOT_MOVINAND
 ldr sp, _TEXT_PHY_BASE
 bl movi_bl2_copy
 b after_copy
#endif
//使用nandflash，此处忽略
#ifdef CONFIG_BOOT_ONENAND
 ldr sp, =0x50000000  @ temporary stack
//设置地址并分配空间
#ifdef CONFIG_S3C6400
 mov r1, =0x20000000  @ start buffer register
 orr r1, r1, #0xc30000
 orr r1, r1, #0xc800
#else
 mov r1, #0x23000000  @ start buffer register
 orr r1, r1, #0x30000
 orr r1, r1, #0xc800
#endif

 ldr r2, [r1, #0x84]  @ ecc bypass
 orr r2, r2, #0x100
 str r2, [r1, #0x84]

 sub r0, r1, #0x0400  @ start address1 register

 str r3, [r0, #0x00]
 str r3, [r0, #0x04]  @ select dataram for DDP as 0

 mov r4, #0x104  @ interrupt register

 mov r6, #0x0c00  @ fixed dataram1 sector number
 str r6, [r1, #0x00]

 mov r3, #0x0  @ DFS, FBA
 mov r5, #0x0000  @ FPA, FSA
 ldr r9, =CFG_PHY_UBOOT_BASE @ destination

onenand_bl2_load:
 str r3, [r0, #0x00]  @ save DFS, FBA
 str r5, [r0, #0x1c]  @ save FPA, FSA

 mov r7, #0x0  @ clear interrupt
 str r7, [r1, r4]
 str r7, [r1, #0x80]  @ write load command

 mov r8, #0x1000
onenand_wait_loop2:
 subs r8, r8, #0x1
 bne onenand_wait_loop2

onenand_wait_int:  @ wait INT and RI
 ldr r7, [r1, r4]
 mov r8, #0x8000
 orr r8, r8, #0x80
 tst r7, r8
 beq onenand_wait_int

 mov r7, #0x0  @ clear interrupt
 str r7, [r1, r4]

 mov r8, #0xc00  @ source address (dataram1)
 mov r10, #0x40  @ copy loop count (64 = 2048 / 32)

 stmia sp, {r0-r7}  @ backup
//把代码拷贝至DRAM
onenand_copy_to_ram:
 ldmia r8!, {r0-r7}
 stmia r9!, {r0-r7}
 subs r10, r10, #0x1
 bne onenand_copy_to_ram

 ldmia sp, {r0-r7}  @ restore

 add r5, r5, #0x4  @ next FPA
 cmp r5, #0x100  @ last FPA?
 bne onenand_bl2_load

 /* next block */
 mov r5, #0x0  @ reset FPA
 add r3, r3, #0x1  @ next FBA
 cmp r3, #0x2  @ last FBA?
 bne onenand_bl2_load
 b after_copy
#endif

#ifdef CONFIG_BOOT_ONENAND_IROM
 ldr sp, _TEXT_PHY_BASE
 bl onenand_bl2_copy
 b after_copy
#endif
//进入DRAM执行
after_copy:
#ifdef CONFIG_ENABLE_MMU
开MMU
enable_mmu:
 /* enable domain access */
 ldr r5, =0x0000ffff
 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

 /* Enable the MMU */
mmu_on:
 mrc p15, 0, r0, c1, c0, 0
 orr r0, r0, #1  /* Set CR_M to enable MMU */
 mcr p15, 0, r0, c1, c0, 0
 nop
 nop
 nop
 nop
#endif

skip_hw_init:
 /* Set up the stack          */
stack_setup:
//分配堆栈
#ifdef CONFIG_MEMORY_UPPER_CODE
 ldr sp, =(CFG_UBOOT_BASE + CFG_UBOOT_SIZE - 0xc)
#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                        */
#ifdef CONFIG_USE_IRQ
 sub r0, r0, #(CONFIG_STACKSIZE_IRQ+CONFIG_STACKSIZE_FIQ)
#endif
 sub sp, r0, #12  /* leave 3 words for abort-stack    */

#endif
//将未初始化数据段_bss_start----_bss_end中的数据清零
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...                    */
 add r0, r0, #4
 cmp r0, r1
 ble clbss_l

 ldr pc, _start_armboot

_start_armboot:
 .word start_armboot

#ifdef 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
 //从NANDflash中拷贝8K以后的代码值DRAM
copy_from_nand:
 mov r10, lr  /* save return address */

 mov r9, r0
 /* get ready to call C functions */
 ldr sp, _TEXT_PHY_BASE /* setup temp stack pointer */
 sub sp, sp, #12
 mov fp, #0  /* no previous frame, so fp=0 */
 mov r9, #0x1000
 bl copy_uboot_to_ram

3: tst  r0, #0x0
 bne copy_failed

 ldr r0, =0x0c000000
 ldr r1, _TEXT_PHY_BASE
1: ldr r3, [r0], #4
 ldr r4, [r1], #4
 teq r3, r4
 bne compare_failed /* not matched */
 subs r9, r9, #4
 bne 1b

4: mov lr, r10  /* all is OK */
 mov pc, lr

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);
 */
#ifdef CONFIG_ENABLE_MMU
 .globl theLastJump
theLastJump:
 mov r9, r0
 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
  */
 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
#endif
/*
 *************************************************************************
 *
 * Interrupt handling
 *
 *************************************************************************
 */
 //中断处理
@
@ 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

/*
 * 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
 */
 //几种工作模式
 .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

#ifdef 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 arm1136_cache_flush
arm1136_cache_flush:
  mcr p15, 0, r1, c7, c5, 0 @ invalidate I cache
  mov pc, lr  @ back to caller

#if defined(CONFIG_INTEGRATOR) && defined(CONFIG_ARCH_CINTEGRATOR)
/* Use the IntegratorCP function from board/integratorcp/platform.S */
#elif defined(CONFIG_S3C64XX)
/* 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

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