U-BOOT裁减移植(一)----汇编启动代码start.S分析.doc

U-BOOT裁减移植（一）----汇编启动代码start.S分析 2010-07-05 23:31 stage1 阶段的启动代码，主要就在 start.s 文件里。此 start.s 也是系统上电后执行的第一个代码。它全部由汇编编写。 下面的代码已经针对我自己开发板S3C2440裁减移植好了 红色字体表示针对开发板新添加的蓝色字体表示注释灰色底表示原本u-boot有的函数然后被删除了 12 #include common.h3 #include config.h4 5 .globl _start6 _start:7???????? b?????? start_code8???????? ldr???? pc, _undefined_instruction9???????? ldr???? pc, _software_interrupt10???????? ldr???? pc, _prefetch_abort11???????? ldr???? pc, _data_abort12???????? ldr???? pc, _not_used13???????? ldr???? pc, _irq14???????? ldr???? pc, _fiq15 16 _undefined_instruction: .word undefined_instruction17 _software_interrupt:??? .word software_interrupt18 _prefetch_abort:??????? .word prefetch_abort19 _data_abort:??????????? .word data_abort20 _not_used:????????????? .word not_used21 _irq:?????????????????? .word irq22 _fiq:?????????????????? .word fiq23 24???????? .balignl 16,0xdeadbeef25 26 _TEXT_BASE:27???????? .word?? TEXT_BASE28 29 .globl _armboot_start30 _armboot_start: 31???????? .word _start3233 .globl _bss_start34 _bss_start:35???????? .word __bss_start36 37 .globl _bss_end38 _bss_end:39???????? .word _end 43 #ifdef CONFIG_USE_IRQ44 /* IRQ stack memory (calculated at run-time) */45 .globl IRQ_STACK_START46 IRQ_STACK_START:47???????? .word?? 0x0badc0de48 49 /* IRQ stack memory (calculated at run-time) */50 .globl FIQ_STACK_START51 FIQ_STACK_START:52???????? .word 0x0badc0de53 #endif54 55 56 /*57 * the actual start code58 */ 40 41???????? //复位启动子程序,设置为管理模式42 start_code:43???????? /*44????????? * set the cpu to SVC32 mode45????????? */46???????? mrs???? r0, cpsr47???????? bic???? r0, r0, #0x1f48???????? orr???? r0, r0, #0xd349???????? msr???? cpsr, r050 69???????? bl????? coloured_LED_init70???????? bl????? red_LED_on71 72 #if???? defined(CONFIG_AT91RM9200DK) || defined(CONFIG_AT91RM9200EK)73???????? /*74????????? * relocate exception table75????????? */76???????? ldr???? r0, =_start77???????? ldr???? r1, =0x