uboot流程分析--修改android启动模式按键
本人用的android平台用的bootloader用的是uboot，貌似大多数手持设备平台都不用这个，因为功能过于强大用不上，反而显得太复杂了。不知道这个平台开发者是怎么想的。既然用了那就来分析一下，顺便修改一下其中的几个小问题，以符合我们的要求。
uboot等同于其他所有的bootloader程序，从根本上讲是一个稍复杂的裸机程序，是最底层的东西，要分析裸机程序我们要从它的连接文件开始。连接文件（.lds文件）定义了程序编译之后整个连接过程，这样我们就可以找到这个程序的第一句汇编代码，进而来下一步分析。uboot的链接文件代码在android\bootable\bootloader\uboot-imx\u-boot.lds
OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm") //文件输出格式
OUTPUT_ARCH(arm)
ENTRY(_start) //首地址标示符
SECTIONS
{
. = 0x00000000; //其实地址0
. = ALIGN(4); //4字节对齐
.text : //代码段
{
board/freescale/mx6q_sabresd/flash_header.o (.text.flasheader) //第一个文件是board/freescale/mx6q_sabresd/flash_header.o
cpu/arm_cortexa8/start.o //第二个cpu/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) //剩余的所有代码
}
. = ALIGN(4);
.rodata : { *(SORT_BY_ALIGNMENT(SORT_BY_NAME(.rodata*))) } //readonly data 段
. = ALIGN(4);
.data : { *(.data) } //所有的readonly data
. = ALIGN(4);
.got : { *(.got) }
. = .;
__u_boot_cmd_start = .; //u_boot_cmd段，里面是所有uboot命令的一个列表
.u_boot_cmd : { *(.u_boot_cmd) }
__u_boot_cmd_end = .;
. = ALIGN(4);
_end_of_copy = .;
__bss_start = .; //bss段 就是内存数据段
.bss : { *(.bss) }
_end = .;
}
从上面的代码可以看出我们编译生成的二进制应用程序组成是：代码段->rodata段->uboot命令列表->bss段。我们启动这个应用程序时候是从，0地址开始的，因此我们来看
board/freescale/mx6q_sabresd/flash_header.s这个文件。
这个文件中除了分配内存和宏定义的伪汇编指令以外，真正执行的命令有一条
.section ".text.flasheader", "x"
b _start
.org CONFIG_FLASH_HEADER_OFFSET.globl _start
_start: b reset reset:
/*
* set the cpu to SVC32 mode cpu设置成32位管理模式
*/
mrs r0, cpsr
bic r0, r0, #0x1f
orr r0, r0, #0xd3
msr cpsr,r0
#if (CONFIG_OMAP34XX) //因为我们的cpu不是ompa的 所以这段不会编译
.............................
#endif
/* the mask ROM code should have PLL and others stable */
#ifndef CONFIG_SKIP_LOWLEVEL_INIT
bl cpu_init_crit
#endif这里接下来执行cpu_init_crit
/*************************************************************************
*
* 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 //关闭mmu
*/
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//执行lowlevel_init这个函数代码在
@\bootloader\uboot-imx\board\freescale\mx6q_sabresd\lowlevel_init.S中
@主要对时钟,外部ram，rom等进行了初始化代码不贴了。
mov lr, ip @ restore link
mov pc, lr @ back to my caller初始化完成后，接下来执行
#ifndef CONFIG_SKIP_RELOCATE_UBOOT
relocate: @ relocate U-Boot to RAM 将uboot重新定位到内存中
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 debug测试当前代码是否已经在内存中
beq stack_setup @如果在的话就直接跳转到stack_setup
ldr r2, _armboot_start @如果不在的话，加载_armboot_start地址到r2中。_armboot_start是uboot执行的主体c函数。
ldr r3, _bss_start
sub r2, r3, r2 @ r2 <- size of armboot计算bss_start-armboot_start 保存到R2中，也就是uboot的总大小
add r2, r0, r2 @ r2 <- source end address 计算出uboot代码和rodata地址
copy_loop: @ copy 32 bytes at a time //开始拷贝
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 */
/* Set up the stack */
stack_setup:
ldr r0, _TEXT_BASE @ upper 128 KiB: relocated uboot
sub r0, r0, #CONFIG_SYS_MALLOC_LEN @ malloc area//为c语言malloc函数分配内存
sub r0, r0, #CONFIG_SYS_GBL_DATA_SIZE @ bdinfo
#ifdef CONFIG_USE_IRQ
sub r0, r0, #(CONFIG_STACKSIZE_IRQ + CONFIG_STACKSIZE_FIQ)
#endif
sub sp, r0, #12 @ leave 3 words for abort-stack//分配c语言堆栈
and sp, sp, #~7 @ 8 byte alinged for (ldr/str)d
/* Clear BSS (if any). Is below tx (watch load addr - need space) */
clear_bss:
ldr r0, _bss_start @ find start of bss segment //清除bss段
ldr r1, _bss_end @ stop here
mov r2, #0x00000000 @ clear value
clbss_l:
str r2, [r0] @ clear BSS location
cmp r0, r1 @ are we at the end yet
add r0, r0, #4 @ increment clear index pointer
bne clbss_l @ keep clearing till at end
#ifdef CONFIG_ARCH_MMU
bl board_mmu_init //初始化mmu
#endif
ldr pc, _start_armboot @ jump to C code以上所有的初始化就已经完成了，接下类正式执行c语言代码了。这才是我们的重点
_start_armboot: .word start_armboot接下来正式看C代码，也就是start_armboot这个函数代码在android\bootable\bootloader\uboot-imx\lib_arm\board.c中
void start_armboot (void)
{
init_fnc_t **init_fnc_ptr;
char *s;
#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 - CONFIG_SYS_MALLOC_LEN - sizeof(gd_t));
//分配一段内存.在cpu存储控制器初始化之前，是不能访问外部ram的，因此需要一小段
//内存来运行最初的初始化函数，这段内存一般是cpu内部ram
/* 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));
gd->flags |= GD_FLG_RELOC;
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 ();
}
}注意看这里init_sequence的定义
init_fnc_t *init_sequence[] = {
#if defined(CONFIG_ARCH_CPU_INIT)
arch_cpu_init, /* basic arch cpu dependent setup */
#endif
board_init, /* basic board dependent setup */
#if defined(CONFIG_USE_IRQ)
interrupt_init, /* set up exceptions */
#endif
timer_init, /* initialize timer */
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
#if defined(CONFIG_HARD_I2C) || defined(CONFIG_SOFT_I2C)
init_func_i2c,
#endif
dram_init, /* configure available RAM banks */
#if defined(CONFIG_CMD_PCI) || defined (CONFIG_PCI)
arm_pci_init,
#endif
display_dram_config,
NULL,
};
我们继续看板子的其他配置
#ifdef CONFIG_LCD //lcd缓存设置
/* board init may have inited fb_base */
if (!gd->fb_base) {
# 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);
lcd_setmem (addr);
gd->fb_base = addr;
}
#endif /* CONFIG_LCD */
env_relocate ();//设置环境变量 也就是printenv 打印出来的那些
#ifdef CONFIG_VFD
/* must do this after the framebuffer is allocated */
drv_vfd_init(); //空函数
#endif /* CONFIG_VFD */
#ifdef CONFIG_SERIAL_MULTI
serial_initialize();//串口初始化
#endif
/* IP Address */
gd->bd->bi_ip_addr = getenv_IPaddr ("ipaddr");
#if defined CONFIG_SPLASH_SCREEN && defined CONFIG_VIDEO_MX5
setup_splash_image();//lcd显示log
#endif
//重新定义stdio的位置，在本环境中被定义到了串口上
stdio_init (); /* get the devices list going. */
jumptable_init ();//把一些初始化函数的指针放到gd中，为以后调用
#if defined(CONFIG_API)
/* Initialize API */
api_init ();
#endif
console_init_r (); /* fully init console as a device 控制台初始化*/
#if defined(CONFIG_ARCH_MISC_INIT)
/* miscellaneous arch dependent initialisations */
arch_misc_init ();//空函数
#endif
#if defined(CONFIG_MISC_INIT_R)
/* miscellaneous platform dependent initialisations */
misc_init_r ();//空函数
#endif
/* enable exceptions */
enable_interrupts ();//使能中断
/* Perform network card initialisation if necessary */
#ifdef CONFIG_DRIVER_TI_EMAC
/* XXX: this needs to be moved to board init */
extern void davinci_eth_set_mac_addr (const u_int8_t *addr);//不编译
if (getenv ("ethaddr")) {
uchar enetaddr[6];
eth_getenv_enetaddr("ethaddr", enetaddr);
davinci_eth_set_mac_addr(enetaddr);
}
#endif
#ifdef CONFIG_DRIVER_CS8900
/* XXX: this needs to be moved to board init */
cs8900_get_enetaddr ();//不编译
#endif
#if defined(CONFIG_DRIVER_SMC91111) || defined (CONFIG_DRIVER_LAN91C96)
/* XXX: this needs to be moved to board init */
if (getenv ("ethaddr")) {
uchar enetaddr[6];
eth_getenv_enetaddr("ethaddr", enetaddr);//不编译
smc_set_mac_addr(enetaddr);
}
#endif /* CONFIG_DRIVER_SMC91111 || CONFIG_DRIVER_LAN91C96 */
#if defined(CONFIG_ENC28J60_ETH) && !defined(CONFIG_ETHADDR)
extern void enc_set_mac_addr (void);//不编译
enc_set_mac_addr ();
#endif /* CONFIG_ENC28J60_ETH && !CONFIG_ETHADDR*/
/* Initialize from environment */
if ((s = getenv ("loadaddr")) != NULL) {
load_addr = simple_strtoul (s, NULL, 16);
}
#if defined(CONFIG_CMD_NET)
if ((s = getenv ("bootfile")) != NULL) {
copy_filename (BootFile, s, sizeof (BootFile));
}
#endif
#ifdef BOARD_LATE_INIT
board_late_init (); //初始化i2c，pmic等
#endif#ifdef CONFIG_ANDROID_RECOVERY
check_recovery_mode(); //检测是否进入recovery
#endif
#if defined(CONFIG_CMD_NET)
#if defined(CONFIG_NET_MULTI)
puts ("Net: ");
#endif
eth_initialize(gd->bd); //根据gd的配置初始化以太网
#if defined(CONFIG_RESET_PHY_R)
debug ("Reset Ethernet PHY\n");
reset_phy();
#endif
#endif
#ifdef CONFIG_FASTBOOT
check_fastboot_mode(); //检测是否进入fastboot
#endif从代码里可以看出我们是首先检测recovery，然后才检测fastboot模式。
我们先来看原版是怎么做的，首先是recovery
void check_recovery_mode(void)
{
if (check_key_pressing())
setup_recovery_env();
else if (check_recovery_cmd_file()) {
puts("Recovery command file founded!\n");
setup_recovery_env();
}
}
没有按键就检测uboot命令文件，看是不是主系统要求进入recovery
因此我们这里的重点是check_key_pressing()这个函数，仔细研究发现这个函数用的是uboot
标准的gpio驱动，官方给我们移植的uboot里面并没有初始化这个驱动，而是自己另外写的。也就是说
我们调用check_key_pressing()这个函数永远都返回0值而执行else if (check_recovery_cmd_file())这一句
我们来看 check_recovery_cmd_file()
int check_recovery_cmd_file(void)
{
int button_pressed = 0;
int recovery_mode = 0;
recovery_mode = check_and_clean_recovery_flag();//读取kernel的recovery标志位，如果有的话就要进入recovery
/* Check Recovery Combo Button press or not. */
mxc_iomux_v3_setup_pad(MX6X_IOMUX(PAD_GPIO_5__GPIO_1_5)); //初始化vol down的gpio
gpio_direction_input(GPIO_VOL_DN_KEY);
if (gpio_get_value(GPIO_VOL_DN_KEY) == 0) { /* VOL_DN key is low assert *///如果vol down已经按下
button_pressed = 1;
printf("Recovery key pressed\n");
}
return recovery_mode || button_pressed; //返回进入recovery
}也就是说官方修改的uboot走了偷懒的方法，直接在check_recovery_cmd_file()增加了一个按键的盘定。很不正规
因此我们下一步要修改它,从官方的基础上走，我们也不走标准uboot 按键驱动，而是自己写。
修改之前先来看原版fastboot怎么进入的
/* export to lib_arm/board.c */
void check_fastboot_mode(void)
{
if (fastboot_check_and_clean_flag())
do_fastboot(NULL, 0, 0, 0);
}
/* check if the recovery bit is set by kernel, it can be set by kernel
* issue a command '# reboot fastboot' */
int fastboot_check_and_clean_flag(void)
{
int flag_set = 0;
u32 reg;
reg = readl(SRC_BASE_ADDR + SRC_GPR10);
flag_set = !!(reg & ANDROID_FASTBOOT_BOOT);
/* clean it in case looping infinite here.... */
if (flag_set) {
reg &= ~ANDROID_FASTBOOT_BOOT;
writel(reg, SRC_BASE_ADDR + SRC_GPR10);
}
return flag_set;
}
ANDROID_FASTBOOT_BOOT位是否被kernel置位，并没有按键，因此我们的板子不可能靠
按键进入fastboot的实际情况也确实这样。因此我们要修改这一块，由于我们的cpu在power键按住5s
以后会强制关机。因此开机后我们必须松开power键，我们板子检测的按键只能是1个。开机时vol up键进入
recovery，按住vol down进入fastboot模式。我们修改代码如下
新建个按键检测函数check_key()
int check_key(void)
{
#define PRESSED_VOLUP 1
#define PRESSED_VOLDOWN 2
#define KEY_MASK (PRESSED_VOLUP|PRESSED_VOLDOWN)
#define RECOVERY_KEY_MASK (PRESSED_VOLUP)
#define FASTBOOT_KEY_MASK (PRESSED_VOLDOWN)
int state = 0;
mxc_iomux_v3_setup_pad(MX6X_IOMUX(PAD_GPIO_5__GPIO_1_5));//vol down
mxc_iomux_v3_setup_pad(MX6X_IOMUX(PAD_GPIO_5__GPIO_1_4));//vol up
gpio_direction_input(GPIO_VOL_DN_KEY);
gpio_direction_input(GPIO_VOL_UP_KEY);
if (gpio_get_value(GPIO_VOL_UP_KEY) == 0)
state |= PRESSED_VOLUP;
if (gpio_get_value(GPIO_VOL_DN_KEY) == 0)
state |= PRESSED_VOLDOWN;
//如果摁下power+voldown就进入fastboot 这个的优先级要比recovery高。
//就算同时按下power+volup+voldown三个键也要进入fastboot模式
if ((state & KEY_MASK) == FASTBOOT_KEY_MASK)
return 1;
if(((state & KEY_MASK) == FASTBOOT_KEY_MASK))
return 2;
return 0;
}主函数判定的代码段修改为
if (check_key()==1)
do_fastboot(NULL, 0, 0, 0);
if (check_key()==2)
setup_recovery_env();
if (check_and_clean_recovery_flag()) {
setup_recovery_env();
}
if (fastboot_check_and_clean_flag())
do_fastboot(NULL, 0, 0, 0);这样我们的启动模式按键就修改完成了，编译后测试成功。
下面我们还有代码没有分析完：uboot的主循环：main_loop()
代码在：\bootable\bootloader\uboot-imx\common\main.c
void main_loop (void)
{
#ifndef CONFIG_SYS_HUSH_PARSER
static char lastcommand[CONFIG_SYS_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 */
#if defined(CONFIG_UPDATE_TFTP)
update_tftp ();
#endif /* CONFIG_UPDATE_TFTP */
#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 CONFIG_SYS_HUSH_PARSER
u_boot_hush_start ();
#endif
#if defined(CONFIG_HUSH_INIT_VAR)
hush_init_var ();
#endif
#ifdef CONFIG_AUTO_COMPLETE
install_auto_complete();
#endif
#ifdef CONFIG_PREBOOT
if ((p = getenv ("preboot")) != NULL) {
# ifdef CONFIG_AUTOBOOT_KEYED
int prev = disable_ctrlc(1); /* disable Control C checking */
# endif
# ifndef CONFIG_SYS_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;//计算bootdelay
debug ("### main_loop entered: bootdelay=%d\n\n", bootdelay);
# ifdef CONFIG_BOOT_RETRY_TIME
init_cmd_timeout ();
# endif /* CONFIG_BOOT_RETRY_TIME */
#ifdef CONFIG_POST
if (gd->flags & GD_FLG_POSTFAIL) {
s = getenv("failbootcmd");
}
else
#endif /* CONFIG_POST */
#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");//得到bootcmd命令
debug ("### main_loop: bootcmd=\"%s\"\n", s ? s : "");
//每10ms从控制台读取一个字符,并且显示倒计时。如果读取成功的话就继续执行main_loop代码，
//如果失败的话就执行下面的run_command(s,0)
if (bootdelay >= 0 && s && !abortboot (bootdelay)) {
# ifdef CONFIG_AUTOBOOT_KEYED
int prev = disable_ctrlc(1); /* disable Control C checking */
# endif
# ifndef CONFIG_SYS_HUSH_PARSER
run_command (s, 0);//执行 bootcmd命令
# 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 CONFIG_SYS_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
/*
* Main Loop for Monitor Command Processing
*/
#ifdef CONFIG_SYS_HUSH_PARSER
parse_file_outer();
/* This point is never reached */
for (;;);
#else
for (;;) { //如果bootdelay时候有按键 就进入命令处理模式
#ifdef CONFIG_BOOT_RETRY_TIME
if (rc >= 0) {
/* Saw enough of a valid command to
* restart the timeout.
*/
reset_cmd_timeout();
}
#endif
len = readline (CONFIG_SYS_PROMPT);//从控制台读取一行数据，以回车为标志
flag = 0; /* assume no special flags for now */
if (len > 0)
z (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 ("\n");
else
rc = run_command (lastcommand, flag);//处理这条命令
if (rc <= 0) {
/* invalid command or not repeatable, forget it */
lastcommand[0] = 0;
}
}
#endif /*CONFIG_SYS_HUSH_PARSER*/
} 到了这里整个的uboot流程已经走完了。从这里可以知道，uboot正式运行以后，实现的所有功能都是通过命令实现的，要继续分析的话，就要分析uboot的命令的实现了。
我们在下一篇文章里面讲述uboot命令是怎么实现的，kernel是怎么启动的。