uboot start.S文件分析
U-boot 第一个开始文件arch\arm\cpu\arm1176\start.S
start.S文件分析:
/*
* armboot - Startup Code for ARM1176 CPU-core
*
* Copyright (c) 2007 Samsung Electronics
*
* Copyright (C) 2008
* Guennadi Liakhovetki, DENX Software Engineering, <lg@denx.de>
*
* 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
#if !defined(CONFIG_ENABLE_MMU) && !defined(CONFIG_SYS_PHY_UBOOT_BASE)
#define CONFIG_SYS_PHY_UBOOT_BASE CONFIG_SYS_UBOOT_BASE
#endif
/*
*************************************************************************
*
* Jump vector table as in table 3.1 in [1]
*
*************************************************************************
*/
.globl _start
_start: b reset
/*异常向量表，为中断异常作准备*/
/* 当异常发生pc会跳到.wrod后面的地址处处理异常*/
#ifndef CONFIG_NAND_SPL
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
/*未定义指令异常,程序从地址0x4处开始执行*/
_undefined_instruction:
.word undefined_instruction
/*软件中断处理指令,,从0x8处开始执行*/
_software_interrupt:
.word software_interrupt
/*指令预取中止*/
_prefetch_abort:
.word prefetch_abort
/*数据访问中止*/
_data_abort:
.word data_abort
/**/
_not_used:
.word not_used
/*外部中断请求*/
_irq:
.word irq
/*快速中断请求*/
_fiq:
.word fiq
_pad:
.word 0x12345678 /* now 16*4=64 */
#else
. = _start + 64
#endif
.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
*
*************************************************************************
*/
/*uboot代码的运行地址*/
_TEXT_BASE:
/*uboot程序的运行地址为0xc7e00000
即代码放到我们的sdram中*/
.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.
*/
/*uboot会开启mmu, 以下是开启mmu前uboot存放的真实物理地址
_TEXT_PHY_BASE:
.word CONFIG_SYS_PHY_UBOOT_BASE
/*_start标号和编译时运行的地址有关系,
text_base参数通知编译器程序运行在0xc7e00000
那么标号也是此值
*/
.globl _armboot_start
_armboot_start:
.word _start
/*
* These are defined in the board-specific linker script.
*/
/*在u-boot.lds中指定*/
.globl _bss_start
_bss_start:
.word __bss_start
.globl _bss_end
_bss_end:
.word _end
/*
* the actual reset code
*/
reset:
/*
* set the cpu to SVC32 mode
*/
/*使cpu的模式为管理模式.即保证cpsr低五位的值为10011*/
mrs r0, cpsr /*r0=cpsr*/
bic r0, r0, #0x3f /*后后6位清零*/
orr r0, r0, #0xd3 /*11010011*/
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_init_crit:
/*
* When booting from NAND - it has definitely been a reset, so, no need
* to flush caches and disable the MMU
*/
#ifndef CONFIG_NAND_SPL
/*
* 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) /*0为小端，1为大端*/
orr r0, r0, #0x00000002 @ set bit 2 (A) Align /*打开地址对齐检察*/
orr r0, r0, #0x00001000 @ set bit 12 (I) I-Cache /*打开指令缓存*/
/* Prepare to disable the MMU */
adr r2, mmu_disable_phys
sub r2, r2, #(CONFIG_SYS_PHY_UBOOT_BASE - TEXT_BASE)
b mmu_disable
.align 5
/* Run in a single cache-line */
mmu_disable:
mcr p15, 0, r0, c1, c0, 0
nop
nop
mov pc, r2
mmu_disable_phys:
#ifdef CONFIG_DISABLE_TCM
/*
* Disable the TCMs
*/
mrc p15, 0, r0, c0, c0, 2 /* Return TCM details */
cmp r0, #0
beq skip_tcmdisable
mov r1, #0
mov r2, #1
tst r0, r2
mcrne p15, 0, r1, c9, c1, 1 /* Disable Instruction TCM if present*/
tst r0, r2, LSL #16
mcrne p15, 0, r1, c9, c1, 0 /* Disable Data TCM if present*/
skip_tcmdisable:
#endif
#endif
#ifdef CONFIG_PERIPORT_REMAP
/* Peri port setup */
ldr r0, =CONFIG_PERIPORT_BASE
orr r0, r0, #CONFIG_PERIPORT_SIZE
mcr p15,0,r0,c15,c2,4
#endif
/*
* Go setup Memory and board specific bits prior to relocation.
*/
/*初始化工作：关看门狗、关闭中断、初始化时钟、
nand flash初始化、内存控制器初始化、
*/
bl lowlevel_init /* go setup pll,mux,memory */
#ifndef CONFIG_SKIP_RELOCATE_UBOOT
relocate: /* relocate U-Boot to RAM */
adr r0, _start /* r0 <- current position of code */
ldr r1, _TEXT_BASE /* test if we run from flash or RAM */
cmp r0, r1 /* don't reloc during debug */
beq stack_setup
ldr r2, _armboot_start
ldr r3, _bss_start
sub r2, r3, r2 /* r2 <- size of armboot */
add r2, r0, r2 /* r2 <- source end address */
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 copy_loop
#endif /* CONFIG_SKIP_RELOCATE_UBOOT */
#ifdef CONFIG_ENABLE_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, =CONFIG_SYS_PHY_UBOOT_BASE
ldr r2, =0xfff00000
bic r0, r0, r2
orr r1, r0, r1
mcr p15, 0, r1, c2, c0, 0
/* Enable the MMU */
mrc p15, 0, r0, c1, c0, 0
orr r0, r0, #1 /* Set CR_M to enable MMU */
/* Prepare to enable the MMU */
adr r1, skip_hw_init
and r1, r1, #0x3fc
ldr r2, _TEXT_BASE
ldr r3, =0xfff00000
and r2, r2, r3
orr r2, r2, r1
b mmu_enable
.align 5
/* Run in a single cache-line */
mmu_enable:
mcr p15, 0, r0, c1, c0, 0
nop
nop
mov pc, r2
skip_hw_init:
#endif
/* Set up the stack */
stack_setup:
ldr r0, =CONFIG_SYS_UBOOT_BASE /* base of copy in DRAM */
sub r0, r0, #CONFIG_SYS_MALLOC_LEN /* malloc area */
sub r0, r0, #CONFIG_SYS_GBL_DATA_SIZE /* bdinfo */
sub sp, r0, #12 /* leave 3 words for abort-stack */
bic sp, sp, #7 /* 8-byte alignment for ABI compliance */
/*清bss段内容*/
clear_bss:
ldr r0, _bss_start /* find start of bss segment */
ldr r1, _bss_end /* stop here */
mov r2, #0 /* clear */
clbss_l:
str r2, [r0] /* clear loop... */
add r0, r0, #4
cmp r0, r1
ble clbss_l
#ifndef CONFIG_NAND_SPL
ldr pc, _start_armboot
_start_armboot:
.word start_armboot
#else
/*check boot status */
#define MEM_CFG_STAT 0x7E00F12C
ldr r1, =MEM_CFG_STAT /* address of reg MEM_CFG_STAT*/
ldr r0, [r1]
mov r1, #0x60
and r1, r0, r1 /*r1 = MEM_CFG_STAT & CFG_BOOT_LOC */
cmp r1, #0x60 /*Internal ROM*/
beq boot_from_irom
cmp r1, #0x00 /*Stepping Stone area in NFCON*/
beq nand_boot
b reset
/* .word nand_boot*/
boot_from_irom:
b mmc_boot_copy /*MINI6410 boot from Internal ROM-->MMC boot*/
#endif
#ifdef CONFIG_ENABLE_MMU
_mmu_table_base:
.word mmu_table
#endif
#ifndef CONFIG_NAND_SPL
/*
* 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 ...
*/
.macro bad_save_user_regs
/* carve out a frame on current user stack */
sub sp, sp, #S_FRAME_SIZE
/* Save user registers (now in svc mode) r0-r12 */
stmia sp, {r0 - r12}
ldr r2, _armboot_start
sub r2, r2, #(CONFIG_SYS_MALLOC_LEN)
/* set base 2 words into abort stack */
sub r2, r2, #(CONFIG_SYS_GBL_DATA_SIZE+8)
/* get values for "aborted" pc and cpsr (into parm regs) */
ldmia r2, {r2 - r3}
/* grab pointer to old stack */
add r0, sp, #S_FRAME_SIZE
add r5, sp, #S_SP
mov r1, lr
/* save sp_SVC, lr_SVC, pc, cpsr */
stmia r5, {r0 - r3}
/* save current stack into r0 (param register) */
mov r0, sp
.endm
.macro get_bad_stack
/* setup our mode stack (enter in banked mode) */
ldr r13, _armboot_start
/* move past malloc pool */
sub r13, r13, #(CONFIG_SYS_MALLOC_LEN)
/* move to reserved a couple spots for abort stack */
sub r13, r13, #(CONFIG_SYS_GBL_DATA_SIZE + 8)
/* save caller lr in position 0 of saved stack */
str lr, [r13]
/* get the spsr */
mrs lr, spsr
/* save spsr in position 1 of saved stack */
str lr, [r13, #4]
/* prepare SVC-Mode */
mov r13, #MODE_SVC
@ msr spsr_c, r13
/* switch modes, make sure moves will execute */
msr spsr, r13
/* capture return pc */
mov lr, pc
/* jump to next instruction & switch modes. */
movs pc, lr
.endm
.macro get_bad_stack_swi
/* space on current stack for scratch reg. */
sub r13, r13, #4
/* save R0's value. */
str r0, [r13]
/* get data regions start */
ldr r0, _armboot_start
/* move past malloc pool */
sub r0, r0, #(CONFIG_SYS_MALLOC_LEN)
/* move past gbl and a couple spots for abort stack */
sub r0, r0, #(CONFIG_SYS_GBL_DATA_SIZE + 8)
/* save caller lr in position 0 of saved stack */
str lr, [r0]
/* get the spsr */
mrs r0, spsr
/* save spsr in position 1 of saved stack */
str lr, [r0, #4]
/* restore r0 */
ldr r0, [r13]
/* pop stack entry */
add r13, r13, #4
.endm
/*
* exception handlers
*/
.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
.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 /* CONFIG_NAND_SPL */
链接地址:\board\samsung\mini6410\u-boot-nand.lds
程序的一般步骤：
1 初始化：关看门狗
初始化时钟
初始化sdram
2 把程序从nand flash拷贝到sdram
3 设置sp
