æ¬äººç¨çandroidå¹³å°ç¨çbootloaderç¨çæ¯ubootï¼è²ä¼¼å¤§å¤æ°ææ设å¤å¹³å°é½ä¸ç¨è¿ä¸ªï¼å 为åè½è¿äºå¼ºå¤§ç¨ä¸ä¸ï¼åèæ¾å¾å¤ªå¤æäºãä¸ç¥éè¿ä¸ªå¹³å°å¼åè
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ubootçåäºå
¶ä»ææçbootloaderç¨åºï¼ä»æ ¹æ¬ä¸è®²æ¯ä¸ä¸ªç¨å¤æç裸æºç¨åºï¼æ¯æåºå±çä¸è¥¿ï¼è¦åæ裸æºç¨åºæ们è¦ä»å®çè¿æ¥æ件å¼å§ãè¿ æ¥æ件ï¼.ldsæ件ï¼å®ä¹äºç¨åºç¼è¯ä¹åæ´ä¸ªè¿æ¥è¿ç¨ï¼è¿æ ·æ们就å¯ä»¥æ¾å°è¿ä¸ªç¨åºç第ä¸å¥æ±ç¼ä»£ç ï¼è¿èæ¥ä¸ä¸æ¥åæãubootçé¾æ¥æ件代ç å¨ android\bootable\bootloader\uboot-imx\u-boot.lds
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OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm") //æ件è¾åºæ ¼å¼
OUTPUT_ARCH(arm)
ENTRY(_start) //é¦å°åæ 示符
SECTIONS
{
. = 0x00000000; //å
¶å®å°å0
. = ALIGN(4); //4åè对é½
.text : //代ç 段
{
board/freescale/mx6q_sabresd/flash_header.o (.text.flasheader) //第ä¸ä¸ªæ件æ¯board/freescale/mx6q_sabresd/flash_header.o
cpu/arm_cortexa8/start.o //第äºä¸ªcpu/arm_cortexa8/start.o
board/freescale/mx6q_sabresd/libmx6q_sabresd.a (.text)
lib_arm/libarm.a (.text)
net/libnet.a (.text)
drivers/mtd/libmtd.a (.text)
drivers/mmc/libmmc.a (.text)
. = DEFINED(env_offset) ? env_offset : .;
common/env_embedded.o(.text)
*(.text) //å©ä½çææ代ç
}
. = ALIGN(4);
.rodata : { *(SORT_BY_ALIGNMENT(SORT_BY_NAME(.rodata*))) } //readonly data 段
. = ALIGN(4);
.data : { *(.data) } //ææçreadonly data
. = ALIGN(4);
.got : { *(.got) }
. = .;
__u_boot_cmd_start = .; //u_boot_cmd段ï¼éé¢æ¯ææubootå½ä»¤çä¸ä¸ªå表
.u_boot_cmd : { *(.u_boot_cmd) }
__u_boot_cmd_end = .;
. = ALIGN(4);
_end_of_copy = .;
__bss_start = .; //bss段 å°±æ¯å
åæ°æ®æ®µ
.bss : { *(.bss) }
_end = .;
}
ä»ä¸é¢ç代ç å¯ä»¥çåºæ们ç¼è¯çæçäºè¿å¶åºç¨ç¨åºç»ææ¯ï¼ä»£ç 段->rodata段->ubootå½ä»¤å表->bss段ãæ们å¯å¨è¿ä¸ªåºç¨ç¨åºæ¶åæ¯ä»ï¼0å°åå¼å§çï¼å æ¤æ们æ¥ç
board/freescale/mx6q_sabresd/flash_header.sè¿ä¸ªæ件ã
è¿ä¸ªæ件ä¸é¤äºåé
å
ååå®å®ä¹ç伪æ±ç¼æ令以å¤ï¼çæ£æ§è¡çå½ä»¤æä¸æ¡
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.section ".text.flasheader", "x"
b _start
.org CONFIG_FLASH_HEADER_OFFSET
ä¹å°±æ¯è¯´ï¼è¿ä¸ªæ件ä¸æ§è¡å°±ç´æ¥è·³å°_start ä½ç½®å¤ã_start å¨android\bootable\bootloader\uboot-imx\cpu\arm_cortexa8\ start.Sä¸ï¼å æ¤æ们æ¥çè¿ä¸ªæ件代ç
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.globl _start
_start: b reset
è¿éç´æ¥è·³è½¬çresetä¸æ¥ä¸æ¥ç
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reset:
/*
* set the cpu to SVC32 mode cpu设置æ32ä½ç®¡ç模å¼
*/
mrs r0, cpsr
bic r0, r0, #0x1f
orr r0, r0, #0xd3
msr cpsr,r0
#if (CONFIG_OMAP34XX) //å 为æ们çcpuä¸æ¯ompaç æ以è¿æ®µä¸ä¼ç¼è¯
.............................
#endif
/* the mask ROM code should have PLL and others stable */
#ifndef CONFIG_SKIP_LOWLEVEL_INIT
bl cpu_init_crit
#endif
è¿éæ¥ä¸æ¥æ§è¡cpu_init_crit
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/*************************************************************************
*
* CPU_init_critical registers
*
* setup important registers
* setup memory timing
*
*************************************************************************/
cpu_init_crit:
/*
* Invalidate L1 I/D
*/
mov r0, #0 @ set up for MCR
mcr p15, 0, r0, c8, c7, 0 @ invalidate TLBs
mcr p15, 0, r0, c7, c5, 0 @ invalidate icache
/*
* disable MMU stuff and caches //å
³émmu
*/
mrc p15, 0, r0, c1, c0, 0
bic r0, r0, #0x00002000 @ clear bits 13 (--V-)
bic r0, r0, #0x00000007 @ clear bits 2:0 (-CAM)
orr r0, r0, #0x00000002 @ set bit 1 (--A-) Align
orr r0, r0, #0x00000800 @ set bit 12 (Z---) BTB
mcr p15, 0, r0, c1, c0, 0
/*
* Jump to board specific initialization...
* The Mask ROM will have already initialized
* basic memory. Go here to bump up clock rate and handle
* wake up conditions.
*/
mov ip, lr @ persevere link reg across call
bl lowlevel_init @ go setup pll,mux,memory//æ§è¡lowlevel_initè¿ä¸ªå½æ°ä»£ç å¨
@\bootloader\uboot-imx\board\freescale\mx6q_sabresd\lowlevel_init.Sä¸
@主è¦å¯¹æ¶é,å¤é¨ramï¼romçè¿è¡äºåå§å代ç ä¸è´´äºã
mov lr, ip @ restore link
mov pc, lr @ back to my caller
åå§åå®æåï¼æ¥ä¸æ¥æ§è¡
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#ifndef CONFIG_SKIP_RELOCATE_UBOOT
relocate: @ relocate U-Boot to RAM å°ubootéæ°å®ä½å°å
åä¸
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 debugæµè¯å½å代ç æ¯å¦å·²ç»å¨å
åä¸
beq stack_setup @å¦æå¨çè¯å°±ç´æ¥è·³è½¬å°stack_setup
ldr r2, _armboot_start @å¦æä¸å¨çè¯ï¼å è½½_armboot_startå°åå°r2ä¸ã_armboot_startæ¯ubootæ§è¡ç主ä½cå½æ°ã
ldr r3, _bss_start
sub r2, r3, r2 @ r2 <- size of armboot计ç®bss_start-armboot_start ä¿åå°R2ä¸ï¼ä¹å°±æ¯ubootçæ»å¤§å°
add r2, r0, r2 @ r2 <- source end address 计ç®åºuboot代ç årodataå°å
copy_loop: @ copy 32 bytes at a time //å¼å§æ·è´
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 */
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