我们之前讲到的UBOOT的第一阶段初始化,都是一些硬件的操作,之后的操作便在比较复杂的函数中去实现了,也是我们上节课讲到的:
这里把_start_armboot的地址赋值给pc,而_start_armboot的地址为:
也就是跳到start_armboot这个地址里。这应该是一个函数,我们看看这个函数的定义:
void start_armboot (void) { init_fnc_t **init_fnc_ptr; char *s; #ifndef CFG_NO_FLASH ulong size; #endif #if defined(CONFIG_VFD) || defined(CONFIG_LCD) unsigned long addr; #endif /* Pointer is writable since we allocated a register for it */ gd = (gd_t*)(_armboot_start - CFG_MALLOC_LEN - sizeof(gd_t)); /* compiler optimization barrier needed for GCC >= 3.4 */ __asm__ __volatile__("": : :"memory"); memset ((void*)gd, 0, sizeof (gd_t)); gd->bd = (bd_t*)((char*)gd - sizeof(bd_t)); memset (gd->bd, 0, sizeof (bd_t)); monitor_flash_len = _bss_start - _armboot_start; for (init_fnc_ptr = init_sequence; *init_fnc_ptr; ++init_fnc_ptr) { if ((*init_fnc_ptr)() != 0) { hang (); } } #ifndef CFG_NO_FLASH /* configure available FLASH banks */ size = flash_init (); display_flash_config (size); #endif /* CFG_NO_FLASH */ #ifdef CONFIG_VFD # ifndef PAGE_SIZE # define PAGE_SIZE 4096 # endif /* * reserve memory for VFD display (always full pages) */ /* bss_end is defined in the board-specific linker script */ addr = (_bss_end + (PAGE_SIZE - 1)) & ~(PAGE_SIZE - 1); size = vfd_setmem (addr); gd->fb_base = addr; #endif /* CONFIG_VFD */ #ifdef CONFIG_LCD # ifndef PAGE_SIZE # define PAGE_SIZE 4096 # endif /* * reserve memory for LCD display (always full pages) */ /* bss_end is defined in the board-specific linker script */ addr = (_bss_end + (PAGE_SIZE - 1)) & ~(PAGE_SIZE - 1); size = lcd_setmem (addr); gd->fb_base = addr; #endif /* CONFIG_LCD */ /* armboot_start is defined in the board-specific linker script */ mem_malloc_init (_armboot_start - CFG_MALLOC_LEN); #if (CONFIG_COMMANDS & CFG_CMD_NAND) puts ("NAND: "); nand_init(); /* go init the NAND */ #endif #ifdef CONFIG_HAS_DATAFLASH AT91F_DataflashInit(); dataflash_print_info(); #endif /* initialize environment */ env_relocate (); #ifdef CONFIG_VFD /* must do this after the framebuffer is allocated */ drv_vfd_init(); #endif /* CONFIG_VFD */ /* IP Address */ gd->bd->bi_ip_addr = getenv_IPaddr ("ipaddr"); /* MAC Address */ { int i; ulong reg; char *s, *e; char tmp[64]; i = getenv_r ("ethaddr", tmp, sizeof (tmp)); s = (i > 0) ? tmp : NULL; for (reg = 0; reg < 6; ++reg) { gd->bd->bi_enetaddr[reg] = s ? simple_strtoul (s, &e, 16) : 0; if (s) s = (*e) ? e + 1 : e; } #ifdef CONFIG_HAS_ETH1 i = getenv_r ("eth1addr", tmp, sizeof (tmp)); s = (i > 0) ? tmp : NULL; for (reg = 0; reg < 6; ++reg) { gd->bd->bi_enet1addr[reg] = s ? simple_strtoul (s, &e, 16) : 0; if (s) s = (*e) ? e + 1 : e; } #endif } devices_init (); /* get the devices list going. */ #ifdef CONFIG_CMC_PU2 load_sernum_ethaddr (); #endif /* CONFIG_CMC_PU2 */ jumptable_init (); console_init_r (); /* fully init console as a device */ #if defined(CONFIG_MISC_INIT_R) /* miscellaneous platform dependent initialisations */ misc_init_r (); #endif Port_Init(); if (!PreLoadedONRAM) { /* enable exceptions */ enable_interrupts (); /* add by www.100ask.net */ usb_init(); } /* Perform network card initialisation if necessary */ #ifdef CONFIG_DRIVER_CS8900 cs8900_get_enetaddr (gd->bd->bi_enetaddr); #endif #if defined(CONFIG_DRIVER_SMC91111) || defined (CONFIG_DRIVER_LAN91C96) if (getenv ("ethaddr")) { smc_set_mac_addr(gd->bd->bi_enetaddr); } #endif /* CONFIG_DRIVER_SMC91111 || CONFIG_DRIVER_LAN91C96 */ /* Initialize from environment */ if ((s = getenv ("loadaddr")) != NULL) { load_addr = simple_strtoul (s, NULL, 16); } #if (CONFIG_COMMANDS & CFG_CMD_NET) if ((s = getenv ("bootfile")) != NULL) { copy_filename (BootFile, s, sizeof (BootFile)); } #endif /* CFG_CMD_NET */ #ifdef BOARD_LATE_INIT board_late_init (); #endif #if (CONFIG_COMMANDS & CFG_CMD_NET) #if defined(CONFIG_NET_MULTI) puts ("Net: "); #endif eth_initialize(gd->bd); #endif /* main_loop() can return to retry autoboot, if so just run it again. */ for (;;) { main_loop (); } /* NOTREACHED - no way out of command loop except booting */ }
首先看到这里:
这里的话给gd_t这个结构体分配了空间,其实这就是给我们分配一些全局数据的内存。我们继续往下看:
这个init_sequence是什么?我们搜索一下,发现在本文件中有相关的定义:
init_fnc_t *init_sequence[] = { cpu_init, /* basic cpu dependent setup */ board_init, /* basic board dependent setup */ interrupt_init, /* set up exceptions */ env_init, /* initialize environment */ init_baudrate, /* initialze baudrate settings */ serial_init, /* serial communications setup */ console_init_f, /* stage 1 init of console */ display_banner, /* say that we are here */ #if defined(CONFIG_DISPLAY_CPUINFO) print_cpuinfo, /* display cpu info (and speed) */ #endif #if defined(CONFIG_DISPLAY_BOARDINFO) checkboard, /* display board info */ #endif dram_init, /* configure available RAM banks */ display_dram_config, NULL, };
我们发现,其里面都是一些函数指针,装有各种初始化函数:cpu的,开发版的,中断的,环境变量的,串口的等等。而这个init_sequence便是一个指针数组来的。所以,这个循环的意思就是分别执行各个初始化函数,如果返回值不为零的话,就会卡死在那里。这里我们研究一下其中的部分初始化函数,首先看到board_init:
int board_init (void) { S3C24X0_CLOCK_POWER * const clk_power = S3C24X0_GetBase_CLOCK_POWER(); S3C24X0_GPIO * const gpio = S3C24X0_GetBase_GPIO(); /* set up the I/O ports */ gpio->GPACON = 0x007FFFFF; gpio->GPBCON = 0x00044555; gpio->GPBUP = 0x000007FF; gpio->GPCCON = 0xAAAAAAAA; gpio->GPCUP = 0x0000FFFF; gpio->GPDCON = 0xAAAAAAAA; gpio->GPDUP = 0x0000FFFF; gpio->GPECON = 0xAAAAAAAA; gpio->GPEUP = 0x0000FFFF; gpio->GPFCON = 0x000055AA; gpio->GPFUP = 0x000000FF; gpio->GPGCON = 0xFF95FFBA; gpio->GPGUP = 0x0000FFFF; gpio->GPHCON = 0x002AFAAA; gpio->GPHUP = 0x000007FF; /* support both of S3C2410 and S3C2440, by www.100ask.net */ if (isS3C2410) { /* arch number of SMDK2410-Board */ gd->bd->bi_arch_number = MACH_TYPE_SMDK2410; } else { /* arch number of SMDK2440-Board */ gd->bd->bi_arch_number = MACH_TYPE_S3C2440; } /* adress of boot parameters */ gd->bd->bi_boot_params = 0x30000100; #if 0 icache_enable(); dcache_enable(); #endif return 0; }我们看到,函数的前面都是做一些初始化管脚的工作,初始化完管脚后,就开始设置机器ID:
/* support both of S3C2410 and S3C2440, by www.100ask.net */ if (isS3C2410) { /* arch number of SMDK2410-Board */ gd->bd->bi_arch_number = MACH_TYPE_SMDK2410; } else { /* arch number of SMDK2440-Board */ gd->bd->bi_arch_number = MACH_TYPE_S3C2440; }
检查开发板式2410还是2440,然后分别相应的值。最后则是设置内核需要的参数的地址:
/* adress of boot parameters */ gd->bd->bi_boot_params = 0x30000100;
这个值后面再讲,后面会用得到的。接下来,我们回到之前的start_armboot。我们知道,u-boot最终的目的是启动内核,所以我们现在更希望找到与启动内核比较有关的代码。我们看到接下来的代码:
这一步是初始化flash,它会识别出你当前所使用的norflash。我们继续往下看:
这一步是初始化nandflash,它会扫出单板。以上步骤,都是对flash初始化,执行了上面的步骤后,才有能力对flash进行读写,是我们从flash中读出内核并执行的基础。我们继续看:
这一步是初始化环境变量。我们继续往下看:
我们看到,到这里, 就是一个死循环了,那么这个函数是什么呢?我们进去看一下:
void main_loop (void) { #ifndef CFG_HUSH_PARSER static char lastcommand[CFG_CBSIZE] = { 0, }; int len; int rc = 1; int flag; #endif #if defined(CONFIG_BOOTDELAY) && (CONFIG_BOOTDELAY >= 0) char *s; int bootdelay; #endif #ifdef CONFIG_PREBOOT char *p; #endif #ifdef CONFIG_BOOTCOUNT_LIMIT unsigned long bootcount = 0; unsigned long bootlimit = 0; char *bcs; char bcs_set[16]; #endif /* CONFIG_BOOTCOUNT_LIMIT */ #if defined(CONFIG_VFD) && defined(VFD_TEST_LOGO) ulong bmp = 0; /* default bitmap */ extern int trab_vfd (ulong bitmap); #ifdef CONFIG_MODEM_SUPPORT if (do_mdm_init) bmp = 1; /* alternate bitmap */ #endif trab_vfd (bmp); #endif /* CONFIG_VFD && VFD_TEST_LOGO */ #ifdef CONFIG_BOOTCOUNT_LIMIT bootcount = bootcount_load(); bootcount++; bootcount_store (bootcount); sprintf (bcs_set, "%lu", bootcount); setenv ("bootcount", bcs_set); bcs = getenv ("bootlimit"); bootlimit = bcs ? simple_strtoul (bcs, NULL, 10) : 0; #endif /* CONFIG_BOOTCOUNT_LIMIT */ #ifdef CONFIG_MODEM_SUPPORT debug ("DEBUG: main_loop: do_mdm_init=%d\n", do_mdm_init); if (do_mdm_init) { char *str = strdup(getenv("mdm_cmd")); setenv ("preboot", str); /* set or delete definition */ if (str != NULL) free (str); mdm_init(); /* wait for modem connection */ } #endif /* CONFIG_MODEM_SUPPORT */ #ifdef CONFIG_VERSION_VARIABLE { extern char version_string[]; setenv ("ver", version_string); /* set version variable */ } #endif /* CONFIG_VERSION_VARIABLE */ #ifdef CFG_HUSH_PARSER u_boot_hush_start (); #endif #ifdef CONFIG_AUTO_COMPLETE install_auto_complete(); #endif #ifdef CONFIG_JFFS2_CMDLINE extern int mtdparts_init(void); if (!getenv("mtdparts")) { run_command("mtdparts default", 0); } else { mtdparts_init(); } #endif #ifdef CONFIG_PREBOOT if ((p = getenv ("preboot")) != NULL) { # ifdef CONFIG_AUTOBOOT_KEYED int prev = disable_ctrlc(1); /* disable Control C checking */ # endif # ifndef CFG_HUSH_PARSER run_command (p, 0); # else parse_string_outer(p, FLAG_PARSE_SEMICOLON | FLAG_EXIT_FROM_LOOP); # endif # ifdef CONFIG_AUTOBOOT_KEYED disable_ctrlc(prev); /* restore Control C checking */ # endif } #endif /* CONFIG_PREBOOT */ #if defined(CONFIG_BOOTDELAY) && (CONFIG_BOOTDELAY >= 0) s = getenv ("bootdelay"); bootdelay = s ? (int)simple_strtol(s, NULL, 10) : CONFIG_BOOTDELAY; debug ("### main_loop entered: bootdelay=%d\n\n", bootdelay); # ifdef CONFIG_BOOT_RETRY_TIME init_cmd_timeout (); # endif /* CONFIG_BOOT_RETRY_TIME */ if (PreLoadedONRAM) { printf("Use these steps to program the image to flash:\n"); printf("1. In OpenOCD\n"); printf(" Run the 'halt' command to halt u-boot\n"); printf(" Run the 'load_image <file> <address>' command to load file to SDRAM\n"); printf(" Run the 'resume' command to resume u-boot\n"); printf("2. In u-boot, use the flash commands to program the image to flash\n"); printf("Or, use the tftp or nfs command to download file, and then program the flash.\n"); goto PROMPT; } #ifdef CONFIG_BOOTCOUNT_LIMIT if (bootlimit && (bootcount > bootlimit)) { printf ("Warning: Bootlimit (%u) exceeded. Using altbootcmd.\n", (unsigned)bootlimit); s = getenv ("altbootcmd"); } else #endif /* CONFIG_BOOTCOUNT_LIMIT */ s = getenv ("bootcmd"); debug ("### main_loop: bootcmd=\"%s\"\n", s ? s : "<UNDEFINED>"); if (bootdelay >= 0 && s && !abortboot (bootdelay)) { # ifdef CONFIG_AUTOBOOT_KEYED int prev = disable_ctrlc(1); /* disable Control C checking */ # endif # ifndef CFG_HUSH_PARSER { printf("Booting Linux ...\n"); run_command (s, 0); } # else parse_string_outer(s, FLAG_PARSE_SEMICOLON | FLAG_EXIT_FROM_LOOP); # endif # ifdef CONFIG_AUTOBOOT_KEYED disable_ctrlc(prev); /* restore Control C checking */ # endif } # ifdef CONFIG_MENUKEY if (menukey == CONFIG_MENUKEY) { s = getenv("menucmd"); if (s) { # ifndef CFG_HUSH_PARSER run_command (s, 0); # else parse_string_outer(s, FLAG_PARSE_SEMICOLON | FLAG_EXIT_FROM_LOOP); # endif } } #endif /* CONFIG_MENUKEY */ #endif /* CONFIG_BOOTDELAY */ #ifdef CONFIG_AMIGAONEG3SE { extern void video_banner(void); video_banner(); } #endif eth_init(gd->bd); run_command("menu", 0); /* * Main Loop for Monitor Command Processing */ PROMPT: #ifdef CFG_HUSH_PARSER parse_file_outer(); /* This point is never reached */ for (;;); #else for (;;) { #ifdef CONFIG_BOOT_RETRY_TIME if (rc >= 0) { /* Saw enough of a valid command to * restart the timeout. */ reset_cmd_timeout(); } #endif len = readline (CFG_PROMPT); flag = 0; /* assume no special flags for now */ if (len > 0) strcpy (lastcommand, console_buffer); else if (len == 0) flag |= CMD_FLAG_REPEAT; #ifdef CONFIG_BOOT_RETRY_TIME else if (len == -2) { /* -2 means timed out, retry autoboot */ puts ("\nTimed out waiting for command\n"); # ifdef CONFIG_RESET_TO_RETRY /* Reinit board to run initialization code again */ do_reset (NULL, 0, 0, NULL); # else return; /* retry autoboot */ # endif } #endif if (len == -1) puts ("<INTERRUPT>\n"); else rc = run_command (lastcommand, flag); if (rc <= 0) { /* invalid command or not repeatable, forget it */ lastcommand[0] = 0; } } #endif /*CFG_HUSH_PARSER*/ }
我们看到这里:
这里首先获得bootcmd的环境变量值,然后打印出相关的信息:我们看一下bootcmd的环境变量值是多少:
我们大概可以推测,这是一条启动内核的两条指令。我们再看下面的代码:
这里是倒计时,。如果在这个倒数计时没到达到0 之前,没有输入空格键,就会打印下面的信息:
也就执行run_command(s,0),这个命令的具体内容下节课讲。