每日一貼,今天的容內關鍵字為地址代碼
???? /arch/arm920t/cpu/start.s 件文就是uboot 的第一階段，uboot的前4K容內，即nandflash中的前4K容內會被拷貝到cpu中的SRAM中運行，這一小段代碼擔任初始化硬件環境，并將殘余的Uboot代碼加載到內存中去。從而跳到轉第二階段，在第二階段運行之前要需建立棧堆。
???? IRQ_STACK_START??? .word 0x0badc0de
???? FRQ_STACK_START??? .word 0x0badc0de
????/*
?*? armboot - Startup Code for ARM920 CPU-core
?*
??*/
?
?
????#include <config.h>
????#include <version.h>
?
?
????/*
?*************************************************************************
?*
?* Jump vector table as in table 3.1 in [1]
?*
?*************************************************************************
?*/
?
?
????.globl _start
????_start:? b?????? reset????? ?? //b 是跳轉指令，即跳到轉reset 標簽處。接著返回到此處。
???? ldr? pc, _undefined_instruction 置設斷中向量表 0x0 0x4.....0x8 0xc
???? ldr? pc, _software_interrupt
???? ldr? pc, _prefetch_abort
???? ldr? pc, _data_abort
???? ldr? pc, _not_used
???? ldr? pc, _irq
???? ldr? pc, _fiq
?
????_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
????
利用.word
來在以后位置放置一個值，這個值實際上就用對應的斷中理處函數的地址
;.word的義意為在以后地址處放入一個16bits值
???? .balignl 16,0xdeadbeef
?
?
????/*
?*************************************************************************
?*
?* Startup Code (reset vector)
?*
?* do important init only if we don't start from memory!
?* relocate armboot to ram
?* setup stack
?* jump to second stage //從英文注釋中可以看出starts.o的作用。
?*
?*************************************************************************
?*/
?
????_TEXT_BASE:
???? .word??? TEXT_BASE
?
????.globl _armboot_start
????_armboot_start:
???? .word _start
?
????/*
?* These are defined in the board-specific linker script. 針對不同板類型的鏈接腳本中經已義定過了，體具的腳本？？
?*/
????.globl _bss_start?? //未初始化的數據段開始地址
????_bss_start:
???? .word __bss_start
?
????.globl _bss_end? //結束地址
????_bss_end:
???? .word _end
?
????#ifdef CONFIG_USE_IRQ?? //斷中是不是經已置配。
????/* IRQ stack memory (calculated at run-time) */
????.globl IRQ_STACK_START
????IRQ_STACK_START:
???? .word??? 0x0badc0de? //棧堆的始起地址。
?
????/* IRQ stack memory (calculated at run-time) */
????.globl FIQ_STACK_START
????FIQ_STACK_START:
???? .word 0x0badc0de
????#endif
?
?
????/*
?* the actual reset code
?*/
???? _start: 入口處，馬上跳到轉reset 處，在SVC狀態下要關閉有所斷中。
????reset:
???? /*
???? ?* set the cpu to SVC32 mode // 超等用戶態, 操縱統系用使的保護模式。統系復位和軟件斷中時進入該模式。
???? ?*/
???? mrs? r0,cpsr? ? // 將以后cpsr 的狀態為保存到r0中。
???? bic? r0,r0,#0x1f ? //bic ，位清零指令。0x1f=00011111 ，相當于清除低5位。剛好是模式位。
???? orr? r0,r0,#0xd3? // 或指令。很明顯是置模式位。0xd3=11010011 以及置設5，6，7位的狀態位。制止FIQ,IRQ，處于arm狀態。低5位為10011，則對應超等用戶態。
???? msr? cpsr,r0? // 在將r0 中的值賦給狀態寄存器cpsr
?
????/* turn off the watchdog */ 關閉看門狗
????#if defined(CONFIG_S3C2400)
????# define pWTCON??????? 0x15300000
????# define INTMSK??????? 0x14400008??? /* Interupt-Controller base addresses */
????# define CLKDIVN?? 0x14800014??? /* clock divisor register */
????#elif defined(CONFIG_S3C2410) 我們的是2410 ，如果移植其它的，則可以添加關相的基地址
????# define pWTCON??????? 0x53000000? //pWTCON 看門狗寄存器的基地址，手冊上就是WTCON ，這里多一個p
????# define INTMSK??????? 0x4A000008??? /* Interupt-Controller base addresses */
????# define INTSUBMSK 0x4A00001C 斷中子掩碼寄存器
????# define CLKDIVN?? 0x4C000014??? /* clock divisor register */
????#endif
?
???? 將看門狗寄存器清空，其各位含意為，第0 位為1則當看門狗定時器溢出時重啟，為0則不重啟，初始值為1
???? 第2 位為斷中使能位，初值為0
???? 第3 ，4位為時鐘頻分銀子，初值為00
???? 第5 位為看門狗的使能位，初值為1
???? 第8~15 位為比例因子，初值為0x80
????#if defined(CONFIG_S3C2400) || defined(CONFIG_S3C2410)
???? ldr???? r0, =pWTCON //將pWTCON寄存器的地址賦給r0
???? mov??? ?r1, #0x0
???? str???? r1, [r0]? // 將pWTCON 有所位置為0，就關閉看門狗了，實際上只要將第5位置0可即。
?
???? /*
???? ?* mask all IRQs by setting all bits in the INTMR - default
???? ?*/
???? mov? r1, #0xffffffff
???? ldr? r0, =INTMSK? //蔽屏有所的斷中
???? str? r1, [r0]
????# if defined(CONFIG_S3C2410)
???? ldr? r1, =0x7ff?? 011111111111 ，很多料資上是0x3ff 。手冊上定規有13位可用
???? ldr? r0, =INTSUBMSK 如果是2410, 這個寄存器也要蔽屏
???? str? r1, [r0] // 將低13 位全都置1 13位可用 而不是12位
????# endif
?
???? /* FCLK:HCLK:PCLK = 1:2:4 */
???? /* default FCLK is 120 MHz ! */ 時鐘置設
???? ldr? r0, =CLKDIVN
???? mov? r1, #3
???? str? r1, [r0]
????#endif?? /* CONFIG_S3C2400 || CONFIG_S3C2410 */
?
???? /*
???? ?* we do sys-critical inits only at reboot,
???? ?* not when booting from ram!
???? ?*/
????#ifndef CONFIG_SKIP_LOWLEVEL_INIT 避免重復用引cpu_init_crit 函數。
???? bl?? cpu_init_crit
????#endif
???? ?
???? 橙色的分部代碼，是針對從nor flash 中啟動的設備。對于不是從nandflash中啟動的設備，沒什么用。這一段似乎也能行執代碼制復.
???? #ifndef CONFIG_SKIP_RELOCATE_UBOOT?
???? relocate:????????????? /* relocate U-Boot to RAM?? ??? */
???? ???? adr? r0, _start???????? /* r0 <- current position of code?? */
???? 查看以后代碼的地址信息，若從ram 中運行，則_start=_TEXT_BASE,否則_start = 0x00000000
???? ???? ldr? r1, _TEXT_BASE???????? /* test if we run from flash or RAM */
???? ???? cmp???? r0, r1????????????????? /* don't reloc during debug???????? */
???? ???? beq???? stack_setup 若相稱，則建立棧堆
???? ?
???? ???? ldr? r2, _armboot_start? ?? 若不等，則表現從flash 中運行，重定向代碼
???? ???? ldr? r3, _bss_start ??????? 獲得未初始化數據段地址
???? ???? sub? r2, r3, r2???????? /* r2 <- size of armboot??????????? */ 代碼段的度長
???? ???? add? r2, r0, r2???????? /* r2 <- source end address???????? */ 代碼的度長
???? ?
???? copy_loop:
???? 制復代碼，r0 為代碼的始起地址，r1為ram中地址，r2為代碼的終止地址，每次copy后將r0的值遞增同r2較比來判斷是不是制復成完。
???? ???? 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 */
???? ???? /* Set up the stack??????????????????????????? ??? */
???? stack_setup:
???? ???? ldr? r0, _TEXT_BASE???????? /* upper 128 KiB: relocated uboot?? */
???? ???? sub? r0, r0, #CFG_MALLOC_LEN /* malloc area? 192K??????????????????? */
???? ???? sub? r0, r0, #CFG_GBL_DATA_SIZE /* bdinfo 配分128 節字來存儲開發板信息??????? */
???? #ifdef CONFIG_USE_IRQ
???? ???? sub? r0, r0, #(CONFIG_STACKSIZE_IRQ+CONFIG_STACKSIZE_FIQ)
???? #endif 再減去12 節字用于棧點起
???? ???? sub? sp, r0, #12??????? /* leave 3 words for abort-stack??? */
???? ?
???? 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
?
???? #if 0
???? ???? /* try doing this stuff after the relocation */
???? ???? ldr???? r0, =pWTCON
???? ???? mov???? r1, #0x0
???? ???? str???? r1, [r0]
???? ?
???? ???? /*
???? ???? ?* mask all IRQs by setting all bits in the INTMR - default
???? ???? ?*/
???? ???? mov? r1, #0xffffffff
???? ???? ldr? r0, =INTMR
???? ???? str? r1, [r0]
???? ?
???? ???? /* FCLK:HCLK:PCLK = 1:2:4 */
???? ???? /* default FCLK is 120 MHz ! */
???? ???? ldr? r0, =CLKDIVN
???? ???? mov? r1, #3
???? ???? str? r1, [r0]
???? ???? /* END stuff after relocation */
???? #endif
???? 當初的設別，大都是利用SDRAM 與NANDFLASH獨特作用，因此為了支撐能從nand_flash中啟動，要需添加面下的紅色代碼。
???? ?
???? #ifdef CONFIG_S3C2410_NAND_BOOT
???? bl copy_myself
???? ?
???? @jump to ram
???? ldr r1,=on_the_ram
???? add pc,r1,#0
???? nop
???? nop
???? 1:
???? b 1b
???? on_the_ram
???? #endif
?
???? ldr? pc, _start_armboot
?
????_start_armboot:??? .word start_armboot
?
???? #ifdef CONFIG_S3C2410_NAND_BOOT
???? copy_myself:
???? mov r10.lr? 將以后的lr 保存到r10中，保存斷點地址
???? @reset nand
???? mov r1,#NAND_CTL_BASE nandflash 基地址
???? ldr r2,0xf830 r2 = 1111 ，1000 ，0011，0000 第15位為nandflash控制器使能位，第12位初始化ECC，第11位nFCE使能？？？？？有問題
???? str r2,[r1,#oNFCONF]
???? ldr r2,[r1,#oNFCONF]
???? ?
???? bic r2,r2,#0x800?? 將第11 位清零指令，使能片芯
???? str r2,[r1,#oNFCONF]
???? 寫入令命
???? mov r2,#0xff?? @reset command
???? strb r2,[r1,#oNFCMD]
????
?
????
mov r3,#0?
????
1:
??add r3, r3, #0x1????
//
循環等待
??
????
cmp r3, #0xa
??blt 1b
2:
利用狀態寄存器試測flash
部內操縱是不是成完，如果成完則狀態寄存器將返回1.NFSTAT最后位一為0時，表現正在忙，為1表現閑暇
??ldr r2, [r1, #oNFSTAT]
@ wait ready
??tst r2, #0x1
//tst
位試測指令
??beq 2b
??ldr r2, [r1, #oNFCONF]
制止片芯
??orr r2, r2, #0x800
@ disable chip
??str r2, [r1, #oNFCONF]
@ get read to call C functions (for nand_read())
建立棧堆，棧點起0x33f00000
，巨細為0x8000
??ldr sp, DW_STACK_START ???????
@ setup stack pointer
??mov fp, #0 ???????????????????
@ no previous frame, so fp=0
???? ?
???? ?
????
@ copy U-Boot to RAM
。r0 r1 r2
為傳入到Nand_read_ll中的三個參數，
nand_read_ll(
unsigned
char
*buf,
unsigned
long
start_addr,
int
size)
????可知，
??ldr r0, =UBOOT_RAM_BASE?
??mov r1, #0x0
?
?//mov r2, #0x20000?
//UBOOT
巨細為128K
這三個參數傳入到nand_read_ll中
????
mov r2. #0x30000
//
置設為192k
。
??bl nand_read_ll
??tst r0, #0x0 ???
r0
為返回值nand_read_ll
的返回值
??beq ok_nand_read
bad_nand_read:
loop2: b loop2 @ infinite loop
ok_nand_read:
nand_flash
通過ecc
驗校來保障拷貝到SDRAM中的容內是確正的
@ verify
??mov r0, #0
??ldr r1, =TEXT_BASE
??mov r2, #0x400
@ 4 bytes * 1024 = 4K-bytes
，每條指令占4
個節字，共挪動0x400即1024次,加起來就挪動了4*1024即4K的巨細
go_next:
??ldr r3, [r0], #4
??ldr r4, [r1], #4
??teq r3, r4
??bne notmatch
??subs r2, r2, #4
??beq stack_setup
??bne go_next
notmatch:
loop3: b loop3 @ infinite loop
#endif @ CONFIG_S3C2410_NAND_BOOT
?
?
????/*
?*************************************************************************
?*
?* CPU_init_critical registers
?*
?* setup important registers
?* setup memory timing
?*
?*************************************************************************
?*/
?
?
????#ifndef CONFIG_SKIP_LOWLEVEL_INIT? cpu 的置設，楚清I/D cache, 清除TLB
????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
?
???? /*
???? ?* before relocating, we have to setup RAM timing 在重定位之前，要需設初始化內存時序，因為內存時鐘是開發板獨立的。
???? ?* because memory timing is board-dependend, you will
???? ?* find a lowlevel_init.S in your board directory.
???? ?*/
???? mov? ip, lr??????? // 返回到reset
???? bl?? lowlevel_init
???? mov? lr, ip
???? mov? pc, lr??????? // 從lowlevel_init 中，返回到reset
????#endif /* CONFIG_SKIP_LOWLEVEL_INIT */
?
????/*
?*************************************************************************
?*
?* Interrupt handling 斷中函數的理處。義定各種常異指令。
?*
?*************************************************************************
?*/
?
????@
????@ 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
???? stmia??? sp, {r0 - r12}????????????? @ Calling r0-r12
???? ldr? r2, _armboot_start
???? sub? r2, r2, #(CONFIG_STACKSIZE+CFG_MALLOC_LEN)
???? sub? r2, r2, #(CFG_GBL_DATA_SIZE+8)? @ set base 2 words into abort stack
???? ldmia??? r2, {r2 - r3}????????? @ get pc, cpsr
???? add? r0, sp, #S_FRAME_SIZE?????? @ restore sp_SVC
?
???? add? r5, sp, #S_SP
???? mov? r1, lr
???? stmia??? r5, {r0 - r3}????????? @ save sp_SVC, lr_SVC, pc, cpsr
???? mov? r0, sp
???? .endm
?
???? .macro?? irq_save_user_regs
???? sub? sp, sp, #S_FRAME_SIZE
???? stmia??? sp, {r0 - r12}????????????? @ Calling r0-r12
???? add ????r8, sp, #S_PC
???? 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
???? sub? r13, r13, #(CONFIG_STACKSIZE+CFG_MALLOC_LEN)
???? sub? r13, r13, #(CFG_GBL_DATA_SIZE+8) @ reserved a couple spots in abort stack
?
???? str? lr, [r13]????????? @ save caller lr / spsr
???? mrs? lr, spsr
???? str???? lr, [r13, #4]
?????????????????
???? mov? r13, #MODE_SVC????????????? @ prepare SVC-Mode
???? @ msr??? spsr_c, r13
???? msr? spsr, r13
???? mov? lr, pc
???? movs pc, lr
???? .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? 5
????undefined_instruction:
???? get_bad_stack
???? bad_save_user_regs
???? bl ? do_undefined_instruction
?
???? .align?? 5
????software_interrupt:
???? get_bad_stack
???? 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
文章結束給大家分享下程序員的一些笑話語錄： 騰訊總舵主馬化騰，有人曾經戲稱如果在Z國選舉總統，馬化騰一定當選，因為只要QQ來一個彈窗”投馬總，送Q幣”即可。
更多文章、技術交流、商務合作、聯系博主
微信掃碼或搜索：z360901061
微信掃一掃加我為好友
QQ號聯系： 360901061
您的支持是博主寫作最大的動力，如果您喜歡我的文章，感覺我的文章對您有幫助，請用微信掃描下面二維碼支持博主2元、5元、10元、20元等您想捐的金額吧，狠狠點擊下面給點支持吧，站長非常感激您！手機微信長按不能支付解決辦法：請將微信支付二維碼保存到相冊，切換到微信，然后點擊微信右上角掃一掃功能，選擇支付二維碼完成支付。
【本文對您有幫助就好】元
