定位到\s3c-u-boot-1.1.6\cpu\s3c64xx\start.s，打开该文件
/*
* armboot - Startup Code for S3C6400/ARM1176 CPU-core
*
* Copyright (c) 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., Temple Place, Suite , Boston,
* MA - USA
*
* -- - Restructured codes by jsgood (jsgood.yang@samsung.com)
* -- - 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
以上代码主要检查CONFIG_ENABLE_MMU，已在/include/configs/smdk6410.h中定义
/*
*************************************************************************
*
* Jump vector table as in table . in []
*
*************************************************************************
*/ .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
//以上代码中的.globl相当于c语言中的extenal，而_start相对于C语言中使用goto语句时的调转标签，b是arm汇编中的不带返回的调转指令。最后的ldr命令，是Load Register的缩写，主要用于从存储器将一个32位的字数据送到目的寄存器中，最常用的用法是：
ldr pc,标号1
...
标号1：
.word 标号2
...
标号2：
... (具体执行的代码）
即，将地址为标号1的内容放入到pc，而地址为标号1中的内容正好又是标号2，所以去执行标号后的代码。
_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 *= */
.global _end_vect
_end_vect: .balignl ,0xdeadbeef
以上代码是接上面的代码，其中.word代码为其分别一个word=32bit=4Byte的地址空间；balignl表示字节对齐，即在此表示，接下来的代码，都要16字节对齐，不足之处，用0xdeadbeef填充。
/*
*************************************************************************
*
* 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:
.word TEXT_BASE
该值的具体地址在s3c-u-boot-1.1.6/board/samsung/smdk6410/config.mk中
/*
* 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 .globl _armboot_start
_armboot_start:
.word _start
宏CFG_PHY_UBOOT_BASE定义内存地址
/*
* These are defined in the board-specific linker script.
*/
.globl _bss_start
_bss_start:
.word __bss_start .globl _bss_end
_bss_end:
.word _end
如注释所示，该地址的值在s3c-u-boot/board/samsung/smdk6410/u-boot.lds中定义
#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
如注释所示，该地址的值中运行时计算得到
/*
* the actual reset code
*/ reset:
/*
* set the cpu to SVC32 mode
*/
mrs r0,cpsr
bic r0,r0,#0x1f
orr r0,r0,#0xd3
msr cpsr,r0
cpsr是Current Program Status Register的缩写，表示当前程序状态寄存器，与此对应的是SPSR.程序状态寄存器的格式为： 31 30 29 28 27-- 8 7 6 5 4 3 2 1 0
N Z C V Reserved I F T M4 M3 M2 M1 M0
其中：
mrs是Move From Status Register的缩写，用于将程序状态寄存器的内容传送到通用寄存器中；
bic是Bit Clear的缩写，用于清除操作数1的某些位，并把结果放置到目的寄存器中；
orr是Logical OR的缩写，用于将两个操作数进行逻辑与，并把结果放到目的寄存器中；
msr是Move To Status Register的缩写，将操作数的内容传送到程序状态寄存器中。
另外：
0x1f=00011111
0xdf=11011111
/*
*************************************************************************
*
* CPU_init_critical registers
*
* setup important registers
* setup memory timing
*
*************************************************************************
*/
/*
* we do sys-critical inits only at reboot,
* not when booting from ram!
*/
cpu_init_crit:
/*
* flush v4 I/D caches
*/
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
*/
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 */
ldr r0, =0x70000000
orr r0, r0, #0x13
mcr p15,0,r0,c15,c2,4 @ 256M(0x70000000-0x7fffffff)
以上代码，通过寄存器P15来设置，主要参考arm1176数据手册（它是6410），
#ifdef CONFIG_BOOT_ONENAND
ldr r0, =0x70000000 @ onenand controller setup
orr r0, r0, #0x100000
ldr r1, =0x4000
orr r1, r1, #0xe0
str r1, [r0] #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
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
以上是通过onenand启动方式代码
/*
* Go setup Memory and board specific bits prior to relocation.
*/
bl lowlevel_init /* go setup pll,mux,memory */
以上通过调用的函数，进行板纺初始化
/* 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 */
以上是
#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
以上是使用nor nand方式启动代码
#ifdef CONFIG_BOOT_NAND
mov r0, #0x1000
bl copy_from_nand
#endif
以上是通过调用，使用nand 方式启动代码
#ifdef CONFIG_BOOT_MOVINAND
ldr sp, _TEXT_PHY_BASE
bl movi_bl2_copy
b after_copy
#endif
以上是通过sd卡方式启动代码
#ifdef CONFIG_BOOT_ONENAND
ldr sp, =0x50000000 @ temporary stack #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 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 ( = / ) stmia sp, {r0-r7} @ backup 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
以上是启动代码
after_copy:
#ifdef CONFIG_ENABLE_MMU
enable_mmu:
/* enable domain access */
ldr r5, =0x0000ffff
mcr p15, , r5, c3, c0, @ 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, , r1, c2, c0, /* Enable the MMU */
mmu_on:
mrc p15, , r0, c1, c0,
orr r0, r0, # /* Set CR_M to enable MMU */
mcr p15, , r0, c1, c0,
nop
nop
nop
nop
#endif skip_hw_init:
/* Set up the stack */
stack_setup:
#ifdef CONFIG_MEMORY_UPPER_CODE
ldr sp, =(CFG_UBOOT_BASE + CFG_UBOOT_SIZE - 0xc)
#else
ldr r0, _TEXT_BASE /* upper 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, # /* leave words for abort-stack */ #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... */
add r0, r0, #
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 'st 2blocks to RAM because U-boot's size is larger than 1block(128k) size
*/
.globl copy_from_nand
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, #
mov fp, # /* no previous frame, so fp= */
mov r9, #0x1000
bl copy_uboot_to_ram : tst r0, #0x0
bne copy_failed ldr r0, =0x0c000000
ldr r1, _TEXT_PHY_BASE
: ldr r3, [r0], #
ldr r4, [r1], #
teq r3, r4
bne compare_failed /* not matched */
subs r9, r9, #
bne 1b : 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
*
*************************************************************************
*/
@
@ 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+) @ move past gbl and a couple spots for abort stack
str lr, [r0] @ save caller lr in position of saved stack
mrs r0, spsr @ get the spsr
str lr, [r0, #] @ save spsr in position of saved stack
ldr r0, [r13] @ restore r0
add r13, r13, # @ 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
*/
.align
undefined_instruction:
get_bad_stack
bad_save_user_regs
bl do_undefined_instruction .align
software_interrupt:
get_bad_stack_swi
bad_save_user_regs
bl do_software_interrupt .align
prefetch_abort:
get_bad_stack
bad_save_user_regs
bl do_prefetch_abort .align
data_abort:
get_bad_stack
bad_save_user_regs
bl do_data_abort .align
not_used:
get_bad_stack
bad_save_user_regs
bl do_not_used #ifdef CONFIG_USE_IRQ .align
irq:
get_irq_stack
irq_save_user_regs
bl do_irq
irq_restore_user_regs .align
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
irq:
get_bad_stack
bad_save_user_regs
bl do_irq .align
fiq:
get_bad_stack
bad_save_user_regs
bl do_fiq #endif
.align
.global arm1136_cache_flush
arm1136_cache_flush:
mcr p15, , r1, c7, c5, @ 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
.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