嵌入式必备知识-uboot工作过程

U-Boot 闭看门狗，关闭中断，关MMU，cache，关闭RAM时钟，内存，加载U-Boot第二阶段代码到RAM空间//norflashnand设置好 //清空bss将内核从Flash到RAMU-Boot2.1U-Boot{.=;.=.text{cpu/arm920t/start.o(.text)board/samsung/mini2440/lowlevel_init.o(.text)board/samsung/mini2440/nand_read.o}…}}第一个的是cpu/arm920t/start.o，因此u-boot.bin的代码在cpu/arm920t/start.ocpu/arm920t/start.Scpu/arm920t/start.S .globl.globl_start: /*复位ldrpc, /*ldrpc, ldrpc,/*ldrpc, ldrpc,/*未使 ldrpc,/*irqldrpc,/*fiq/*中断向量 地址_undefined_instruction:.word_software_interrupt:.word_prefetch_abort:.word.word.word.word.word.balignl2.1ARM CPSRI0IRQ 其中复位异常向量的指令“bstart_code”决定了U-BootCPUSVC*setthecputoSVC32mrsr0,bicr0,r0,/*orrorrr0,r0, 位置1msrcpsr,以上代码将CPU的工作模式位设置为管理模式，并将中断位和快中断位置一，从而了IRQ和FIQ中断。#if#if#definepWTCON0x#defineINTMSK#define /*s3c2410s3c24404#definepWTCON/*WATCHDOG控制寄存器地 #defineINTMSK/*INTMSK#defineINTSUBMSK /*INTSUBMSK#define /*CLKDIVN#s3c2440WATCHDOG，INTMSK，INTSUBMSK，CLKDIVN器的地址的设置。各个寄存器地址参见参考文献[4]。ldrldrr0,=pWTCONmovr1,#0x0strr1,[r0]/*00，关闭看门狗。否则在U-Boot，CPU*maskallIRQsbysettingallbitsintheINTMR-movr1,#0xffffffff/*1ldrr0,strstrr1,SRCPN（##ifdefined(CONFIG_S3C2440)ldrr1,=0x7fffldrr0,strr1,[r0]#endifCPU4，INTSUBMSK3215写入0x7fff就是将INTSUBMSK寄存器全部有效位（低15位）置一，从而对应的中断。MPLLCON,UPLLCON,##ifdefined(CONFIG_S3C2440)#defineMPLLCON0x4C000004#defineUPLLCONldrr0,movr1,#5strr1,[r0]ldrr0,ldrr1,=0x7F021strr1,[r0]ldrr0,ldrr1,=0x38022strr1,[r0]#/*/*FCLK:HCLK:PCLK=1:2:4/*defaultFCLKis120MHz!*/ldrr0,=CLKDIVNmovr1,#3strr1,[r0]FinCLDIVNMPLCON，UPLLCON32.2S3C2440CLKDIVN位00:HCLK=01:HCLK=HCLKFCLK/4（CAMDIVN[9]0时HCLK=FCLK/8（CAMDIVN[9]1HCLKFCLK/3（CAMDIVN[8]0时HCLKFCLK/6（CAMDIVN[8]10:PCLK= 1:PCLK=0CLKDIVN5HDIVN10CAMDIVN[9]没有被改变过，取默=1:4:8MPLLCONFCLKFinMPLLCON[19:12]MDIV，位[9:4]称PDIV，位[1:0]SDIV。MPLL(FCLK)MPLL(FCLK)= 其中：MPLLCONUPLLCON4“PLLVALUESELECTIONTABLE表2.3PLL48.0022405.0021MPLLCON=(0x7f<<12)|(0x02<<4)|(0x01)=MPLLCON=(0x7f<<12)|(0x02<<4)|(0x01)=UPLLCON=(0x38<<12)|(0x02<<4)|(0x02)=关闭#ifndef#ifndefblcpu_init_critcpu_init_critU-BootU-BootRAM#ifndef#ifndef*cachecachemovr0,mcrp15,0,r0,c7,c7,/*c70ICacheDCachemcrp15,0,r0,c8,c7,/*c80TLB*disableMMUstuffandr0,r0,@setbit12(I)I-p15,0,c0,/*保存r0*beforerelocating,wehavetosetupRAM*becausememorytimingisboard-dependend,you*findalowlevel_init.Sinyourboardmovip,lr blmovlr,movpc,#endif/*CONFIG_SKIP_LOWLEVEL_INITmrcp15,0,r0,c1,c0,/*r0mrcp15,0,r0,c1,c0,/*r0bicr0,r0,@clearbits13,9:8(--Vbicr0,r0,@clearbits7,2:0 orrr0,r0,@setbit2(A)332~337MMUCP15c1CP152.3CP15c1（部分..VI..RSBCAMVV表示异常向量表所在的位置，0；1：I0ICaches；1：开启R、S:用来与页表中的描述符一起确定内存 权B:0：CPU；1CPUC:0DCaches；1A:0：数 M:0MMU；1：332~337c1MMMURAM45#define /*13 控制器的开始地址…129 .globl/*memorycontrolconfiguration45#define /*13 控制器的开始地址…129 .globl/*memorycontrolconfiguration/*maker0relativethecurrentlocationsothatit/*readsSMRDATAoutofFLASHratherthanmemory!r0,ldrr1,subr0,r0,/*SMRDATA_TEXT_BASE13ldrr1,=BWSCON/*BusWidthStatusControllerr2,r0,142 r3,r0],#4/*13r3,[r1],r2,/*everythingisfinenowmovpc,152/*theliteralpoolsorigin154/*13.word….word……U-BootNANDFlashNORFlash.text.text{cpu/arm920t/start.o(.text)board/samsung/mini2440/lowlevel_init.o(.text)board/samsung/mini2440/nand_read.o…}board/samsung/mini2440/lowlevel_init.oU-Boot4KB对于U-BootNORFlashU-BootU-Boot的地址，而此时U-Boot还在NORFlash中，因此还需要在NORFlash中数据到RAM中。FlashSMRDATA－TEXT_BASE综上所述，lowlevel_init的作用就是将SMRDATA开始的13个值给开始地址[BWSCON]的13个寄存器，从而完成了控制器的设置。（9）U-Boot第二阶段代码到cpu/arm920t/start.SNORFlashU-BootNORFlashNANDFlashblblbBootFrmNORFlash/*判断U-BootNANDFlashNORFlashcmpr0,/*r0bBootFrmNORFlash0NAND启动，否则表示在NORFlashbeq/*跳转到NANDFlash/*NORFlash /*NANDFlash/*NANDFlash/*int{volatileunsignedint*pdw=(volatileunsignedint*)0;unsignedintdwVal;bBootFrmNORFlashU-BootNANDFlashNORFlashNORFlash10ATPCSr0int{volatileunsignedint*pdw=(volatileunsignedint*)0;unsignedintdwVal;dwValdwVal=/**pdw=;if(*pdw!=)/*写入失败，说明是在NORFlash启 {return}{*pdw=/*return}}NORFlashNANDFlash0U-Boot对于从NANDFlash启动的情况，其开始4KB的代码会被自动到CPU内部4K内存中，Flash对于从NORFlash启动的情况，NORFlash的开始地址即为0，必须通过一定令序列才Flash下面来分析NORFlashadrr0,/*r0<-currentpositionof ldrr1,/*testifwerunfromflashorRAM/*判断U-Boot是否 到RAM中运行，若是，则不用 调试U-Bootcmpr0,r1/*_start等于_TEXT_BASE说明 到RAM中运行beq212/*以下直到nand_bootNORFlashldrr2,r3,/*r2<-sizeofr0,/*r2<-sourceend/*搬运U-BootRAM r0!,{r3-/*[r0NORFlash8 r1!,{r3-/*将r3至r10寄存器的数据给地址为[r1]的内untilsourceendaddreeebNANDFlashNANDFlashmovr1,ldrr2,=((7<<12)|(7<<8)|(7<<4)|(0<<0)strr2,r1, /*NFCONF/*设置NFCONT，初始化ECC编 NANDFlashldrr2,=((1<<4)|(0<<1)|(1<<0)strr2,[r1,ldrr2,/*NFSTATstrr2,[r1,/*NANDFlashmovr2,strbr2,[r1,#oNFCMD]movr3,#0ldrsp,DW_STACK_STARTmovfp,#0ldrr0, movr1,movr2,bltstr0,/*beqloop2:b //infinite.alignDW_STACK_START:.wordSTACK_BASE+STACK_SIZE-#define#defineNAND_CTL_BASE0x4E000000NANDFlash#defineSTACK_BASE//baseaddressof#defineSTACK_SIZE//sizeof#defineoNFCONF/*NFCONFNAND_CTL_BASE#defineoNFCONT/*NFCONTNAND_CTL_BASE#defineoNFADDR/*NFADDRNAND_CTL_BASE#defineoNFDATA/*NFDATANAND_CTL_BASE#define /*NFCMDNAND_CTL_BASE#defineoNFSTAT/*NFSTATNAND_CTL_BASE#define /*NFECCNAND_CTL_BASE代码中nand_read_ll函数的作用是在NANDFlash中搬运U-Boot到RAM，该函数在board/samsung/mini2440/nand_read.cNANDFlash根据page大小可分为2种：512B/page2048B/page的。这两种NANDFlash的读操作是不同的。因此就需要U-Boot识别到NANDFlash的类型，然后采用相应的读操作，也nand_read_llNANDFlash。参考S3C2440的可以知道：根据NFCONF寄存器的Bit3（AdvFlash(Readonly)）Bit2（PageSize(Readonly)）NANDFlashBit2、Bit3NANDFlashblock2.4NFCONFBit3、Bit2NANDFlashB010256512110242048NANDFlashintnand_read_ll(unsignedchar*buf,intnand_read_ll(unsignedchar*buf,unsignedlongstart_addr,int{NFCONFBit32NANDif(NFCONF&0x8/*Bit1，2KB/pageNANDFlash{2KblockNAND}{512BblockNAND}return}/*/*设置堆栈ldrr0,/*upper128KiB:relocated subr0,r0, /*mallocsubr0,r0,#CONFIG_SYS_GBL_DATA_SIZE/*跳过全局数据区#ifdefsubr0,r0,subsp,r0,/*leave3wordsforabort- 2.2U-BootBSSldrr0,/*BSSu-boot.ldsldrr1,/*BSSu-boot.ldsmovr2,clbss_l:strr2,/*bssaddr0,r0,cmpr0,r1bleldrldrpc,_start_armboot:.word start_armboot函数在lib_arm/board.c中定义，是U-Boot第二阶段代码的。U-Boot2.3U-Bootgd_ttypedeftypedefstructglobal_dataunsigned unsigned unsignedlong /*serial_init()wascalled*/unsignedlong /*AddressofEnvironmentstruct*/unsignedlong /*ChecksumofEnvironmentvalid?*/unsignedlong fb_base;/*baseaddressofframebuffer*//*jumptable}#define#define registervolatilegd_t*gdasmDECLARE_GLOBAL_DATA_PTRgd_t存器r8中。这个也避免编译器把r8分配给其它的变量。任何想要全局数据区的代码，只要代码开头加入“DECLARE_GLOBAL_DATA_PTR”一行代码然后就可以使用gd指针来全局根据U-Bootgdgdgd=TEXT_BASE－CONFIG_SYS_MALLOC_LEN－bd_ttypedeftypedefstructbd_info/*unsigned /*IPstruct/*bi_arch_number;/*bi_boot_params;/*/*RAM{ulongulongstart;ulongsize;}init_sequencetypedefint(init_fnc_t)init_fnc_t*init_sequence[]=/*typedefint(init_fnc_t)init_fnc_t*init_sequence[]=/*cpu/arm920t/s3c24x0/timer.cmon/env_flash.c或 /*lib_arm/board.c/*drivers/serial/serial_s3c24x0.cconsole_init_f,/*1common/console.cdisplay_banner,/*U-Bootgeditlib_arm/board.c/*RAMboard/samsung/mini2440/mini2440.c/*RAMlib_arm/board.c/*/*MINI2440gd->bd->bi_arch_number=/*gd->bd->bi_boot_paramsgd->bd->bi_boot_params= dram_initboard/samsung/mini2440/mini2440.cintintdram_init{/*由于mini2440gd->bd->bi_dram[0].start=gd->bd->bi_dram[0].size=return}mini2440使用2片32MB的SDRAM组成了64MB的内存，接在控制器的BANK6，地址空间是0x 在include/configs/mini2440.h中PHYS_SDRAM_1和PHYS_SDRAM_1_SIZE 和 voidvoidstart_armboot{init_fnc_t**init_fnc_ptr;char*s;…/*gdgd=(gd_t*)(_armboot_start-CONFIG_SYS_MALLOC_LEN-…memset((void*)gd,0,sizeofgd->bd=(bd_t*)((char*)gd-sizeof(bd_t));memset(gd->bd,0,sizeof(bd_t));gd->flags|= monitor_flash_len=_bss_start-/*init_sequencefor(init_fnc_ptr=init_sequence;*init_fnc_ptr;++init_fnc_ptr)if((*init_fnc_ptr)()!=0)hang}}/*armboot_start在cpu/arm920t/start.S中被初始化为u-boot.lds连 mem_malloc_init(_armboot_start-/*NORFlash#ifndef/*configureavailableFLASHbanksdisplay_flash_config(flash_init#endif/*CONFIG_SYS_NO_FLASH…/*NANDFlash#ifputs("NAND: /*goinittheNAND…/*env_relocate…/*IPgd->bd->bi_ip_addr=getenv_IPaddrstdio_init /*getthedeviceslistgoing.jumptable_init…console_init_r /*fullyinitconsoleasadevice…/*enableexceptionsenable_interrupts#ifdef/*Initializefromenvironmentif((s=getenv("loadaddr"))!=NULL)load_addr=simple_strtoul(s,NULL,}#ifif((s=getenv("bootfile"))!=NULL)copy_filename(BootFile,s,sizeof}…/*#if#ifputs ……/*main_loop()canreturntoretryautoboot,ifsojustrunitagain.*/for(;;){main_loop}/*NOTREACHED-nowayoutofcommandloopexceptbooting}structtag_headeru32 /*taguu32/*structtagstructtag_headerhdr;union{structstructtag_headeru32 /*taguu32/*structtagstructtag_headerhdr;union{struct structtag_mem32structstruct structtag_initrd structtag_serialnrserialnr;structtag_revisionstructstructstruct Acornstructtag_acornDC21285struct }intdo_bootm_linux(intflag,intargc,char*argv[],bootm_headers_t{intdo_bootm_linux(intflag,intargc,char*argv[],bootm_headers_t{bd_t*bd=gd-charintmachid=bd-void(*theKernel)(intzero,intarch,uint #ifdefchar*commandlinegetenv("bootargs");/*U-Bootbootargs …theKernel=(void(*)(int,int,uint))images->ep;/*获取内 地址… #ifdefined(CONFIG_SETUP_MEMORY_TAGS)||defined(CONFIG_CMDLINE_TAG)||defined(CONFIG_INITRD_TAG)||defined(CONFIG_SERIAL_TAG)||defined(CONFIG_REVISION_TAG)||defined(CONFIG_LCD)||definedsetup_start_tag…100#ifdefsetup_memory_tags/*#ifdefmandline_tag(bd,commandline);/*105…setup_end_tag/*weassumethatkernelisinplace printf("\nStartingkernel… cleanup_before_linux /*CPUtheKernel(0,machid,bd-/*/*doesnotreturnreturn}staticstaticvoidsetup_start_tag(bd_t{params(structtag*)bd->bi_boot_params;/*params->hdr.tag=params->hdr.size=tag_sizeparams->u.core.flags=params->u.core.pagesize=params->u.core.rootdev=params=tag_next}ATAG_COREstaticstaticvoidsetup_memory_tags(bd_t{int/*for(i=0;i<CONFIG_NR_DRAM_BANKS;i++)params->hdr.tag=params->hdr.size=tag_sizeparams->u.mem.start=bd->bi_dram[i].start;params->u.mem.size=bd->bi_dram[i].size;paramsparams=tag_next}}setup_memory_tagsATAG_MEMstaticstaticvoidsetup_end_tag(bd_t{params->hdr.tag=ATAG_NONE;params->hdr.size=0;}CPUr1=r2=内核参数标记列表在RAMCPUIRQ与FIQ中CPU为SVC使数据Cache与指令Cacheintcleanup_before_linux{thisfunctioniscalledjustbeforeintcleanup_before_linux{thisfunctioniscalledjustbeforewecallitpreparestheprocessorfor***weturnoffcachesetcdisable_interrupts/*turnoffI/D-cache/*flushI/D-cache/*Cachereturn}由于U-BootSVCCPUvoid(*theKernel)(intzero,intarch,uint… theKernel=(void(*)(int,int,uint))images-…theKernel(0,machid,bd-4r0~r341280r0machidr1bd->bi_boot_paramsr2，从而完U-Boot添加命令的方法及U-Boot下面以添加命令（启动菜单）为例讲解U-Boot添加命令的方法建立 定义“”命 3,0, "-display ,toselecttheitemstodo"-display,toselecttheitemstodo在内存中保存命令的help字段会占用一定的配置U-Boot可以选择是否保存help字段。若在include/configs/mini2440.h中定义了CONFIG_SYS_LONGHELP宏，则在U-Boot中使用help命令查看某个命令的帮助信息时将显示usagehelp字段的内容，否则就只显示usage #define#defineU_BOOT_CMD(na