AM335x启动流程（BootRom-MLO-Uboot）超详细源码分析

AM335x启动流程（BootRom-MLO-Uboot）超详细源码分析写的⾮常好，收藏学习参考⽂件：1，AM335xARMCortex-A8Microprocessors(MPUs)TechnicalReferenceManual.pdf；2，am3359.pdf；1，am335x的cpu上电后，会跳到哪个地址去执⾏？答：芯⽚到uboot启动流程：ROM→MLO(SPL)→uboot.imgAM335x中bootloader被分成了3个部分：第⼀级bootloader：引导加载程序，板⼦上电后会⾃动执⾏这些代码，如选择哪种⽅式启动（NAND，SDcard，UART。。。），然后跳转转到第⼆级bootloader。这些代码应该是存放在176KB的ROM中。第⼆级bootloader：MLO（SPL），⽤以硬件初始化：关闭看门狗，关闭中断，设置CPU时钟频率、速度等操作。然后会跳转到第三级bootloader。MLO⽂件应该会被映射到64KB的InternalSRAM中。第三级bootloader：uboot.img，C代码的⼊⼝。其中第⼀级bootloader是板⼦固化的，第⼆级和第三级是通过编译uboot所得的。2，第⼆级bootloader：MLO（SPL）做了哪些事情？MLO(SPL)内存分布如下：SPL内存重映射：1<PATH:/arch/arm/cpu/armv7/omap-common/u-boot-spl.lds>2MEMORY{.sram:ORIGIN=CONFIG_SPL_TEXT_BASE,\3LENGTH=CONFIG_SPL_MAX_SIZE}4MEMORY{.sdram:ORIGIN=CONFIG_SPL_BSS_START_ADDR,\5LENGTH=CONFIG_SPL_BSS_MAX_SIZE}67OUTPUT_FORMAT("elf32-littlearm","elf32-littlearm","elf32-littlearm")8OUTPUT_ARCH(arm)9ENTRY(_start)10SECTIONS11{12.text :13{14start=.;15arch/arm/cpu/armv7/start.o(.text)16*(.text*)17}>.sram1819.=ALIGN(4);20.rodata:{*(SORT_BY_ALIGNMENT(.rodata*))}>.sram2122.=ALIGN(4);23.data:{*(SORT_BY_ALIGNMENT(.data*))}>.sram24.=ALIGN(4);25image_copy_end=.;26_end=.;2728.bss:29{30.=ALIGN(4);31bss_start=.;32*(.bss*)33.=ALIGN(4);34bss_end=.;35}>.sdram36}1123<PATH:/include/configs/am335x_evm.h>#defineCONFIG_SPL_TEXT_BASE 0x402F0400#defineCONFIG_SPL_MAX_SIZE (46*1024)4#define4#defineCONFIG_SPL_STACK LOW_LEVEL_SRAM_STACK56#defineCONFIG_SPL_BSS_START_ADDR0x800000007#defineCONFIG_SPL_BSS_MAX_SIZE 0x80000 512KB*/<spanstyle="font-size:16px;color:#003399;"><strong></strong>@1@保存启动参数save_boot_params1<PATH:/arch/arm/cpu/armv7/start.S>2/*3*theactualresetcode4*/56reset:7blsave_boot_params1<PATH:/arch/arm/cpu/armv7/omap-common/lowlevel_init.S>2.globalsave_boot_params3save_boot_params:4/*5*Seeiftheromcodepassedpointerisvalid:6*Itisnotvalidifitisnotinnon-secureSRAM7*Thismayhappenifyouarebootingwiththehelpof8*debugger9*/10ldr r2,=NON_SECURE_SRAM_START11cmpr2,r012bgt1f13ldrr2,=NON_SECURE_SRAM_END14cmpr2,r015blt1f1617/*18*storethebootparamspassedfromromcodeorsaved19*andpassedbySPL20*/21cmpr0,#022beq1f23ldrr1,=boot_params24strr0,[r1]/*/*《PATH:/arch/arm/include/asm/arch-ti81xx/omap.h》Non-secureSRAMAddressesNon-secureRAMat0x40300000fordevices.ButwekeepSRAM_BASEat0x40304000(EMUbase)sothatourcodeworksforbothEMUand*/#defineNON_SECURE_SRAM_START0x40304000#defineNON_SECURE_SRAM_END0x4030E000#defineLOW_LEVEL_SRAM_STACK0x4030B7FC12345678问题：这些参数是保存在哪⾥的？⼤概有哪些参数？答：这些参数保存的内存地址为64KB的OCMRAM中：注：DowloadedImage区域：是⽤来保存MLO（SPL）⽂件的，其最⼤可达到109KB@a2@设置CPU为SVC32模式<PATH:/arch/arm/cpu/armv7/start.S><PATH:/arch/arm/cpu/armv7/start.S>/**setthecputoSVC32mode*/mrsr0,cpsrbicr0,r0,#0x1forrr0,r0,msrcpsr,r012345678CPSR:程序状态寄存器(currentprogramstatusregister)(当前程序状态寄存器)，在任何处理器模式下被访问。它包含了条件标志位、中断禁⽌位、当前处理器模式标志以及其他的⼀些控制和状态位。CPSR在⽤户级编程时⽤于存储条件码。SPSR:程序状态保存寄存器（savedprogramstatusregister）,每⼀种处理器模式下都有⼀个状态寄存器SPSR,SPSR⽤于保存CPSR中断退出时，可以⽤SPSR来恢复CPSR。由于⽤户模式和系统模式不是异常中断模式，所以他没有SPSR。当⽤户在⽤户模式或系统模式访问SPSR，将产⽣不可预知的后果。CPSR格式如下所⽰。SPSR和CPSR格式相同。31302928272676543210NZCVQDNM(RAZ)IFTM4M3M2M1M0@a3@CPU的初始化《《PATH:/arch/arm/cpu/armv7/start.S》themaskROMcodeshouldhavePLLandothersstable*/#ifndefCONFIG_SKIP_LOWLEVEL_INITblcpu_init_crit#endif123451<PATH:/arch/arm/cpu/armv7/omap-common/lowlevel_init.S>2.globllowlevel_init3lowlevel_init:4/*5*Setupatemporarystack6*/7ldrsp,=LOW_LEVEL_SRAM_STACK89/*10*Savetheoldlr(passedinip)andthecurrentlrtostack11*/12push{ip,lr}13141415161718/**gosetuppll,mux,memory*/bls_initpop{ip,pc}问题：CPU的初始化有哪些内容？答：@b1@⾸先要设置堆栈区，因为将会调⽤C函数来实现CPU的初始化问题：这个堆栈在什么位置，其内存⼤⼩是多少？答1《PATH：/arch/arm/include/asm/arch-ti81xx/omap.h》2#defineLOW_LEVEL_SRAM_STACK0x4030B7FC<strong></strong>@b2@执⾏s_init()函数，实现CPU的初始化1123456789101112131415161718192021222324<PATH:/board/ti/am335x/evm.c>/**earlysysteminitofmuxingandclocks.*/voids_init(void){CanberemovedasA8comesupwithL2enabled*/l2_cache_enable();WDT1isalreadyrunningwhenthebootloadergetscontrol*Disableittoavoid"random"resets*/raw_writel(0xAAAA,WDT_WSPR);while(raw_readl(WDT_WWPS)0x0);raw_writel(0x5555,WDT_WSPR);while(raw_readl(WDT_WWPS)0x0);#ifdefCONFIG_SPL_BUILDSetupthePLLsandtheclocksfortheperipherals*/pll_init();/*EnableRTC32Kclock*/rtc32k_enable();UARTsoftreset*/u32regVal;u32uart_base=DEFAULT_UART_BASE;28enable_uart0_pin_mux();MotorControlBoardhasdefaultconsoleonUART3*/XXX:Thisisbeforewe'veprobed/setboard_id*/if(board_id==IA_BOARD){uart_base=UART3_BASE;34 }35regVal=raw_readl(uart_base+UART_SYSCFG_OFFSET);regVal|=UART_RESET;raw_writel(regVal,(uart_base+UART_SYSCFG_OFFSET));whileraw_readl(uart_base+UART_SYSSTS_OFFSET)&UART_CLK_RUNNING_MASK)UART_CLK_RUNNING_MASK);41Disablesmartidle*/regVal=raw_readl((uart_base+UART_SYSCFG_OFFSET));regVal|=UART_SMART_IDLE_EN;raw_writel(regVal,(uart_base+UART_SYSCFG_OFFSET));46InitializetheTimer*/init_timer();4950 preloader_console_init();5152 printf("\nlocation/board/ti/am335x\n"); 53 54 led();55 5657 config_am335x_ddr();5859 #endif60 }@c1@使能第⼆级缓冲区1/*CanberemovedasA8comesupwithL2enabled*/2l2_cache_enable();34<PATH:/arch/arm/cpu/armv7/ti81xx/cache.S>5l2_cache_enable:6push{r0,r1,r2,lr}7mrc15,0,r3,cr1,cr0,18orrr3,r3,#29mcr15,0,r3,cr1,cr0,110pop{r1,r2,r3,pc}@c2@关闭看门狗（WDT）1/*WDT1isalreadyrunningwhenthebootloadergetscontrol2*Disableittoavoid"random"resets3*/4raw_writel(0xAAAA,WDT_WSPR);5while(raw_readl(WDT_WWPS)!=0x0);6raw_writel(0x5555,WDT_WSPR);7while(raw_readl(WDT_WWPS)!=0x0);1<PATH:/arch/arm/include/asm/arch-ti81xx/cpu.h>2#defineWDT_WSPR(WDT_BASE+0x048)345<PATH:/arch/arm/include/asm/arch-ti81xx/hardware.h>6/*WatchdogTimer*/7#ifdefCONFIG_AM335X8#defineWDT_BASE 0x44E350009#else10#defineWDT_BASE 0x480C200011#endif@c3@给外设设置好PLL和时钟频率等1/*SetupthePLLsandtheclocksfortheperipherals*/2pll_init();345<PATH:/board/ti/am335x/pll.c>6/*7*ConfigurethePLL/PRCMfornecessaryperipherals8*/9voidpll_init()10{11mpu_pll_config(MPUPLL_M_500);12core_pll_config();13per_pll_config();14ddr_pll_config();15/*Enabletherequiredinterconnectclocks*/16interface_clocks_enable();17/*Enablepowerdomaintransition*/18power_domain_transition_enable();19/*Enabletherequiredperipherals*/20per_clocks_enable();21}@c4@使能32-KHz频率的实时时钟1123456/*EnableRTC32Kclock*/rtc32k_enable();《PATH/board/ti/am335x/evm.c》staticvoidrtc32k_enable(void)7{8/*Unlockthertc'sregisters*/9raw_writel(0x83e70b13,(AM335X_RTC_BASE+RTC_KICK0_REG));10raw_writel(0x95a4f1e0,(AM335X_RTC_BASE+RTC_KICK1_REG));1112/*EnabletheRTC32KOSC*/13raw_writel(0x48,(AM335X_RTC_BASE+RTC_OSC_REG));14}1516<PATH:/arch/arm/include/asm/arch-ti81xx/hardware.h>17/*RTCbaseaddress*/18#defineAM335X_RTC_BASE 0x44E3E0001920<PATH:/board/ti/am335x/evm.c>21#defineRTC_KICK0_REG 0x6c22#defineRTC_KICK1_REG 0x7023#defineRTC_OSC_REG 0x54@c5@使能UART01123456789101112131415161718192021222324252627282930/*UARTsoftreset*/u32regVal;u32uart_base=DEFAULT_UART_BASE;enable_uart0_pin_mux();/*IAMotorControlBoardhasdefaultconsoleonUART3*/XXX:Thisisbeforewe'veprobed/setboard_id*/if(board_id==IA_BOARD){uart_base=UART3_BASE;}regVal=raw_readl(uart_base+UART_SYSCFG_OFFSET);regVal|=UART_RESET;raw_writel(regVal,(uart_base+UART_SYSCFG_OFFSET));while((raw_readl(uart_base+UART_SYSSTS_OFFSET)&UART_CLK_RUNNING_MASK)!=UART_CLK_RUNNING_MASK);/*Disablesmartidle*/regVal=raw_readl((uart_base+UART_SYSCFG_OFFSET));regVal|=UART_SMART_IDLE_EN;raw_writel(regVal,(uart_base+UART_SYSCFG_OFFSET));<PATH:/arch/arm/include/asm/arch-ti81xx/cpu.h>#ifdefCONFIG_AM335X#defineDEFAULT_UART_BASE#endifUART0_BASE<PATH:/arch/arm/include/asm/arch-ti81xx/hardware.h>#ifdefCONFIG_AM335X31#defineUART0_BASE0x44E0900031#defineUART0_BASE0x44E0900032#else33#defineUART0_BASE0x48020000@c6@初始化定时器<PATH:/board/ti/am335x/evm.c><PATH:/board/ti/am335x/evm.c>staticvoidinit_timer(void){/*ResettheTimer*/raw_writel(0x2,(DM_TIMER2_BASE+TSICR_REG));/*Waituntiltheresetisdone*/while(raw_readl(DM_TIMER2_BASE+TIOCP_CFG_REG)&1);/*StarttheTimer*/raw_writel(0x1,(DM_TIMER2_BASE+TCLR_REG));}<PATH:/arch/arm/include/asm/arch-ti81xx/hardware.h>/*DMTimerbaseaddresses*/#defineDM_TIMER0_BASE0x4802C000#defineDM_TIMER1_BASE0x4802E000#defineDM_TIMER2_BASE0x48040000#defineDM_TIMER3_BASE0x48042000#defineDM_TIMER4_BASE0x48044000#defineDM_TIMER5_BASE0x48046000#defineDM_TIMER6_BASE0x48048000#defineDM_TIMER7_BASE0x4804A000InitializetheTimer*/init_timer();123456789101112131415161718192021222324252627@c7@初始化控制台，通过UART可以查看相关信息1preloader_console_init();23《PATH:/arch/arm/cpu/armv7/omap-common/spl.c》4/*ThisrequiresUARTclockstobeenabled*/5voidpreloader_console_init(void)6{7constchar*u_boot_rev=U_BOOT_VERSION;8charrev_string_buffer[50];910gd=&gdata;11gd->bd=&bdata;12gd->flags|=GD_FLG_RELOC;13gd->baudrate=CONFIG_BAUDRATE;1415serial_init(); serialcommunicationssetup*/1617/*Avoidasecond"U-Boot"comingfromthisstring*/18u_boot_rev=&u_boot_rev[7];1920printf("\nU-BootSPL%s(%s-%s)\n",u_boot_rev,U_BOOT_DATE,21U_BOOT_TIME);22omap_rev_string(rev_string_buffer);23printf("TexasInstruments%s\n",rev_string_buffer);24}<spanstyle="font-size:14px;color:#003399;"></span>@c8@配置DDR1123456789101112131415161718192021222324config_am335x_ddr();《PATH：》/*voidDDR2_EMIF_Config(void);*/staticvoidconfig_am335x_ddr(void){intdata_macro_0=intdata_macro_1=enable_ddr_clocks();config_vtp();Cmd_Macro_Config();Data_Macro_Config(data_macro_0);Data_Macro_Config(data_macro_1);raw_writel(PHY_RANK0_DELAY,DATA0_RANK0_DELAYS_0);raw_writel(PHY_RANK0_DELAY,DATA1_RANK0_DELAYS_0);raw_writel(DDR_IOCTRL_VALUE,DDR_CMD0_IOCTRL);raw_writel(DDR_IOCTRL_VALUE,DDR_CMD1_IOCTRL);25raw_writel(DDR_IOCTRL_VALUE,DDR_CMD2_IOCTRL);26raw_writel(DDR_IOCTRL_VALUE,DDR_DATA0_IOCTRL);27raw_writel(DDR_IOCTRL_VALUE,DDR_DATA1_IOCTRL);2829raw_writel(raw_readl(DDR_IO_CTRL)&0xefffffff,DDR_IO_CTRL);30raw_writel(raw_readl(DDR_CKE_CTRL)|0x00000001,DDR_CKE_CTRL);3132config_emif_ddr2();33}343536《PATH:/arm/include/asm/arch-ti81xx/cpu.h》37#defineDATA0_RANK0_DELAYS_0 (DDR_PHY_BASE_ADDR+0x134)38#defineDATA1_RANK0_DELAYS_0 (DDR_PHY_BASE_ADDR+0x1D8)3940/*DDRoffsets*/41#defineDDR_PHY_BASE_ADDR 0x44E1200042#defineDDR_IO_CTRL 0x44E10E0443#defineDDR_CKE_CTRL 0x44E1131C#defineCONTROL_BASE_ADDR 0x44E10000@cDONE@@bDONE@@a4@设置internalRAM内存空间的栈指针，调⽤board_init_f()函数SetstackpointerininternalRAMcallboard_init_f*/call_board_init_f:ldrsp,=(CONFIG_SYS_INIT_SP_ADDR)bicsp,sp,#78-bytealignmentforABIcompliance*/ldrr0,=0x00000000blboard_init_f1234561<PATH:include/configs/am335x_evm.h>2#defineCONFIG_SYS_INIT_SP_ADDR (CONFIG_SYS_INIT_RAM_ADDR+\3CONFIG_SYS_INIT_RAM_SIZE-\4GENERATED_GBL_DATA_SIZE)56#defineCONFIG_SYS_INIT_RAM_ADDRSRAM0_START7#defineCONFIG_SYS_INIT_RAM_SIZESRAM0_SIZE89<PATH:/arch/arm/include/asm/arch-ti81xx/hardware.h:begin>10#ifdefCONFIG_AM335X11#defineSRAM0_START 0x402F040012#else13#defineSRAM0_START 0x4030000014#endif15<PATH:/arch/arm/include/asm/arch-ti81xx/hardware.h:end>1617<PATH:/arch/arm/include/asm/arch-ti81xx/cpu.h:begin>18#ifdefined(CONFIG_AM335X)||defined(CONFIG_TI814X)19#defineSRAM0_SIZE (0x1B400)109KB*/20#defineSRAM_GPMC_STACK_SIZE (0x40)21#endif22<PATH:/arch/arm/include/asm/arch-ti81xx/cpu.h:end>2324<PATH:/am335x/include/generated/generic-asm-offsets.h:begin>25#defineGENERATED_GBL_DATA_SIZE(128)/*(sizeof(structglobal_data)+15)&~15*/26<PATH:/am335x/include/generated/generic-asm-offsets.h:end>1<PATH:/arch/arm/cpu/armv7/omap-common/spl.c'>2voidboard_init_f(ulongdummy)3{4/*5*Wecallrelocate_code()withrelocationtargetsameasthe6*CONFIG_SYS_SPL_TEXT_BASE.Thiswillresultinrelocationgetting7*skipped.Instead,only.bssinitializationwillhappen.That's8*allweneed9*/10debug(">>board_init_f()\n");11relocate_code(CONFIG_SPL_STACK,&gdata,CONFIG_SPL_TEXT_BASE);12}1314<PATH:/arch/arm/cpu/armv7/omap-common/spl.c:begin>15#defineCONFIG_SPL_TEXT_BASE 0x402F040016#defineCONFIG_SPL_MAX_SIZE (46*1024)17#defineCONFIG_SPL_STACK LOW_LEVEL_SRAM_STACK18<PATH:/arch/arm/cpu/armv7/omap-common/spl.c:end>1920<PATH:/arch/arm/include/asm/arch-ti81xx/omap.h:begin>21#defineLOW_LEVEL_SRAM_STACK0x4030B7FC22<PATH:/arch/arm/include/asm/arch-ti81xx/omap.h:end>112345678<PATH:/arch/arm/cpu/armv7/start.S>/*voidrelocate_code(addr_sp,gd,addr_moni)*This"function"doesnotreturn,insteaditcontinuesinRAMafterrelocatingthemonitorcode.**/9910111213.globlrelocate_coderelocate_code:movr4,r0/*saveaddr_sp*/movr5,r1/*saveaddrofgd*/movr6,r2saveaddrofdestination0x402F0400*/@a5@代码重定位如果是直接跳到下⾯的堆栈初始化代码clear_bss。如果不是就将⾃⼰从NorFlash中拷贝到内存中。NorFlash和NandFlash本质区别就在于是否进⾏代码拷贝，也就是下⾯代码所表述：⽆论是NorFlash还是NandFlash，核⼼思想就是将uboot代码搬运到内存中去运⾏，但是没有拷贝bss后⾯这段代码，只拷贝bss前⾯的代码，bss代码是放置全局变量的。Bss段代码是为了清零，拷贝过去再清零重复操作。1Setupthestack */2stack_setup:3movsp,r445adrr0,_start6cmpr0,r67moveqr9,#0 norelocation.relocationoffset(r9)=0*/8beqclear_bss skiprelocation*/9movr1,r6 r1<-scratchforcopy_loop*/10ldrr3,_image_copy_end_ofs11addr2,r0,r3 r2<-sourceendaddress */1213copy_loop: ⾃拷贝*/14ldmiar0!,{r9-r10} copyfromsourceaddress[r0]*/15stmiar1!,{r9-r10} copytargetaddress[r1]*/16cmpr0,r2 untilsourceendaddress[r2]*/17blocopy_loop@a6@清空bss段1clear_bss:23ldrr0,_bss_start_ofs4ldrr1,_bss_end_ofs5movr4,r6 relocaddr*/6addr0,r0,r47addr1,r1,r489movr2,#0x00000000 clear*/10101112131415161718192021clbss_l:strr2,[r0]addr0,r0,#4cmpr0,r1bneclbss_lclearloop...*//**Thesearedefinedintheboard-specificlinkerscript.*/.globl_bss_start_ofs_bss_start_ofs:.wordbss_start-_start bss_start=0x80000000*/@a7@调⽤函数board_init_r，⽤以完成MLO（SPI）阶段的所有初始化，并跳转到uboot.img阶段1/*2*Wearedone.Donotreturn,insteadbranchtosecondpartofboard3*initialization,nowrunningfromRAM.4*/5jump_2_ram:6/*7*IfI-cacheisenabledinvalidateit8*/9#ifndefCONFIG_SYS_ICACHE_OFF10mcrp15,0,r0,c7,c5,0@invalidateicache11mcr p15,0,r0,c7,c10,4@DSB12mcr p15,0,r0,c7,c5,4@ISB13#endif14ldrr0,_board_init_r_ofs15adrr1,_start16addlr,r0,r117addlr,lr,r918/*setupparametersforboard_init_r*/19movr0,r5 gd_t*/20movr1,r6 dest_addr*/21/*jumptoit...*/22movpc,lr2324_board_init_r_ofs:25.wordboard_init_r-_start11234《PATH:/arch/arm/cpu/armv7/omap-common/spl.c》voidboard_init_r(gd_t*id,ulongdummy){u32boot_device;5debug(">>spl:board_init_r()\n");67timer_init();8i2c_init(CONFIG_SYS_I2C_SPEED,CONFIG_SYS_I2C_SLAVE);910#ifdefCONFIG_SPL_BOARD_INIT11spl_board_init();12#endif1314boot_device=omap_boot_device();15debug("bootdevice-%d\n",boot_device);16switch(boot_device){17#ifdefCONFIG_SPL_MMC_SUPPORT18caseBOOT_DEVICE_MMC1:19caseBOOT_DEVICE_MMC2:20spl_mmc_load_image();21break;22#endif23#ifdefCONFIG_SPL_NAND_SUPPORT24caseBOOT_DEVICE_NAND:25spl_nand_load_image();26break;27#endif28#ifdefCONFIG_SPL_YMODEM_SUPPORT29caseBOOT_DEVICE_UART:30spl_ymodem_load_image();31break;32#endif33default:34printf("SPL:Un-supportedBootDevice-%d!!!\n",boot_device);35hang();36break;37}3839switch(spl_image.os){40caseIH_OS_U_BOOT:41debug("JumpingtoU-Boot\n");42jump_to_image_no_args();43break;44default:45puts("UnsupportedOSimage..Jumpingnevertheless..\n");46jump_to_image_no_args();47}48}@aDONE@3，第三级bootloader：uboot.img做了哪些事情？uboot.img内存分布如下：访问/arch/arm/lib/board.c中的board_init_f()函数：在uboot.img运⾏过程中，有两个⾮常重要的结构体：gd_t和bd_t。其中gd_t：global_data数据结构的定义，位于：/arch/arm/include/asm/global_data.h中。其成员主要是⼀些全局的系统初始化参数。其中bd_t：bd_info数据结构的定义，位于：/arch/arm/include/asm/u-boot.h中。其成员是开发板的相关参数。112345678910111213141516171819202122<PATH:/arch/arm/include/asm/global_data.h>/*Thefollowingdatastructureisplacedinsomememorywhichisavailableveryearlyafterboot(likeDPRAMonMPC8xx/MPC82xx,orsomelockedpartsofthedatacache)allowforaminimumsetofglobalvariablesduringsysteminitialization(untilwehavesetupthememorycontrollersothatwecanuseRAM).*Keepit*SMALL*andremembersetGENERATED_GBL_DATA_SIZE>sizeof(gd_t)*/typedefstructglobal_data{bd_t*bd;unsignedlongunsignedunsignedunsignedunsignedunsignedflags;baudrate;have_console;serial_init()wascalled*/env_addr;AddressofEnvironmentstruct*/env_valid;ChecksumofEnvironmentvalid?*/fb_base;baseaddressofbuffer*/#ifdefCONFIG_FSL_ESDHCunsignedlongsdhc_clk;#endif23#ifdefCONFIG_AT91FAMILY24/*"staticdata"neededbyat91'sclock.c*/25unsignedlongcpu_clk_rate_hz;26unsignedlongmain_clk_rate_hz;27unsignedlongmck_rate_hz;28unsignedlongplla_rate_hz;29unsignedlongpllb_rate_hz;30unsignedlongat91_pllb_usb_init;31#endif32#ifdefCONFIG_ARM33/*"staticdata"neededbymostoftimer.conARMplatforms*/34unsignedlongtimer_rate_hz;35unsignedlongtbl;36unsignedlongtbu;37unsignedlonglongtimer_reset_value;3839404142434445unsignedlonglastinc;#endif#ifdefCONFIG_IXP425unsignedlongtimestamp;#endifunsignedlongrelocaddr;/*StartaddressofU-BootinRAM*/phys_size_tram_size;/*RAMsize*/46unsignedlongmon_len;/*monitorlen*/47unsignedlongirq_sp; irqstackpointer*/48unsignedlongstart_addr_sp;/*start_addr_stackpointer*/49unsignedlongreloc_off;50#if!(defined(CONFIG_SYS_ICACHE_OFF)&&defined(CONFIG_SYS_DCACHE_OFF))51unsignedlongtlb_addr;52#endif53void **jt; jumptable*/54char env_buf[32];bufferforgetenv()beforereloc.*/55}gd_t;5657#defineDECLARE_GLOBAL_DATA_PTR registervolatilegd_t*gdasm("r8")585960<PATH:/arch/arm/include/asm/u-boot.h>61typedefstructbd_info{62int bi_baudrate;serialconsolebaudrate*/63unsignedlongbi_ip_addr;/*IPAddress*/64ulong bi_arch_number;uniqueidforthisboard*/65ulong bi_boot_params;wherethisboardexpectsparams*/66struct RAMconfiguration*/67{68ulongstart;69ulongsize;70} bi_dram[CONFIG_NR_DRAM_BANKS];}bd_t;其中DECLARE_GLOBAL_DATA_PTR宏定义在系统初始化过程中会被频繁调⽤，其的作⽤是，声明gd这么⼀个全局的指针，这个指针指向gd_t结构体类型，并且这个gd指针是保存在ARM的r8这个寄存器⾥⾯的。uboot.img第⼀个运⾏的⽂件还是start.o，其在运⾏访问的board_init_f()函数定义在/arch/arm/lib/board.c中：<PATH:/arch/arm/lib/board.c><PATH:/arch/arm/lib/boar