从nand启动的uboot

        我的开发板只有nand flash，但uboot不支持从nand flash启动，要移植uboot到自己的开发板上，需要对源码做一些修改，这里先来分析一下《ARM嵌入式linux系统开发从入门到精通》中给出的代码，虽然按照这个步骤编译出的二进制文件还有一些问题，但分析一下有助于之后对uboot的调试。由于uboot不支持从nand flash启动，所以将程序复制到DRAM里面去需要新加代码实现，一般通过copy_myself函数来实现。

      首先看一下对start.S的修改：

在ldr pc, _start_armboot前添加下面内容。

#ifdef CONFIG_S3C2410_NAND_BOOT
bl    copy_myself
    
@ jump to ram
ldr   r1, =on_the_ram
add pc, r1, #0
nop
nop
1: b     1b          @ infinite loop
on_the_ram:
#endif
在http://blog.chinaunix.net/u/29387/showart_244343.html中提到注释掉一部分relocate代码，但似乎注释的又不彻底，保留了清BSS段的代码。一个疑问是：注释掉这些内容是必须的吗？不过从出发点来说，这段代码确实是没有什么用了。

下面我们来看一下copy_myself都做了哪些事情。此处参考了vivi的copy_myself代码，一些变量的定义需要添加，后面会给出，这里直接给出
这些变量或宏所表达的意义。
#ifdef CONFIG_S3C2410_NAND_BOOT
copy_myself:
mov r10, lr                                             @r10保存返回地址
@ reset NAND                                                       @初始化nand，主要是设置相关的控制器
mov r1, #NAND_CTL_BASE                      @NAND_CTL_BASE=0x4e000000,它是和nand相关的特殊寄存器组的基地址
ldr   r2, =0xf830                                     @ initial value 0x1111,1000,0011,0000,enable nand flash controller   Initialize ECC
str   r2, [r1, #oNFCONF]                         
ldr   r2, [r1, #oNFCONF]                           
bic r2, r2, #0x800                                  @ enable chip,屏蔽[11]，0 : NAND flash nFCE = L (active),NFCE是2410的管脚，与nand
str   r2, [r1, #oNFCONF]                          @的NFCE相连
mov r2, #0xff                                         @ RESET command
strb r2, [r1, #oNFCMD]                           @ 只传送一个字节到oNFCMD
mov r3, #0                                             @ wait

1: add r3, r3, #0x1
cmp r3, #0xa
blt   1b                                                  @ 延时10个指令周期
2: ldr   r2, [r1, #oNFSTAT]                          @ wait ready，oNFSTAT的位[0]标志nand flash的状态，只读，取决于R/nB管脚。
tst    r2, #0x1                                        @1 = NAND Flash memory ready to operate
beq 2b                    
ldr   r2, [r1, #oNFCONF]
orr r2, r2, #0x800                                @ disable chip
str   r2, [r1, #oNFCONF]

@ get read to call C functions (for nand_read())
ldr   sp, DW_STACK_START                   @ setup stack pointer, DW_STACK_START： .word STACK_BASE+STACK_SIZE-4
mov fp, #0                                           @ no previous frame, so fp=0????????????????

@ copy UBOOT to RAM
ldr   r0, =UBOOT_RAM_BASE                 @UBOOT_RAM_BASE=0x33f00000
    mov     r1, #0x0                                  
mov r2, #0x30000                                @ 0x30000=192K
    bl    nand_read_ll                                  @此处nand_read_ll没有给出传递参数，这里猜想其参数依次是r0~r2种的值，这也是最合理的解释
tst    r0, #0x0                                      @此处猜想汇编调用C函数的返回值赋给r0。关于汇编调用C函数的问题，有待考证。
    beq ok_nand_read

#ifdef CONFIG_DEBUG_LL
bad_nand_read:
    ldr   r0, STR_FAIL
ldr   r1, SerBase
    bl    PrintWord
1: b     1b          @ infinite loop
#endif

ok_nand_read:
#ifdef CONFIG_DEBUG_LL
ldr   r0, STR_OK
ldr   r1, SerBase
bl    PrintWord
#endif                                                            @ 此段代码打印调试信息，前提是定义了CONFIG_DEBUG_LL，我们没有定义它，跳过！

@ verify
    mov r0, #0
ldr   r1, =UBOOT_RAM_BASE
    mov r2, #0x400                                 @ 4 bytes * 1024 = 4K-bytes，只验证前4K的内容，一点启示，这里只验证了前4k,并且根据
go_next:                                                 @要求我们应该把所有搬运代码的代码段包含在这前

                                                              @4k之 中，代码本身并没有问题，关键是所调用
ldr   r3, [r0], #4                                      @的C函数以及相关头文件是否包含在了其中
    ldr   r4, [r1], #4
teq   r3, r4
    bne notmatch
subs r2, r2, #4                               @S标志着根据结果更新N和Z，
beq done_nand_read
bne go_next

notmatch:                                      @问题会是出在这儿吗？这儿有一个死循环！
#ifdef CONFIG_DEBUG_LL
sub r0, r0, #4
ldr   r1, SerBase
    bl    PrintHexWord
ldr   r0, STR_FAIL
    ldr   r1, SerBase
bl    PrintWord
#endif
1: b     1b
done_nand_read:
#ifdef CONFIG_DEBUG_LL
ldr   r0, STR_OK
ldr   r1, SerBase
    bl    PrintWord
#endif
mov pc, r10
@ clear memory
@ r0: start address
@ r1: length
mem_clear:
mov r2, #0
    mov r3, r2
mov r4, r2
mov r5, r2
mov r6, r2
mov r7, r2
mov r8, r2
   mov r9, r2

clear_loop:
stmia      r0!, {r2-r9}
subs r1, r1, #(8 * 4)
bne clear_loop
mov pc, lr

#endif @ CONFIG_S3C2410_NAND_BOOT                         

还要在start.S中添加以下内容，用于定义栈地址变量。
#ifdef CONFIG_S3C2410_NAND_BOOT
.align 2
DW_STACK_START:
                             .word STACK_BASE+STACK_SIZE-4
#endif

在start.S中，我们调用了nand_read_ll函数，它在nand_read.c中实现，该文件是由我们在/board/mike2410目录下新建的

#include

#define __REGb(x) (*(volatile unsigned char *)(x))
#define __REGi(x) (*(volatile unsigned int *)(x))
#define NF_BASE   0x4e000000
#define NFCONF   __REGi(NF_BASE + 0x0)
#define NFCMD   __REGb(NF_BASE + 0x4)
#define NFADDR   __REGb(NF_BASE + 0x8)
#define NFDATA   __REGb(NF_BASE + 0xc)
#define NFSTAT   __REGb(NF_BASE + 0x10)
                                             @定义了NF相关寄存器
#define BUSY 1                       @这个BUSY有啥用呢？？？困惑！呵呵，屏蔽掉NFSTAT的前31位，只inline void wait_idle(void) {        @保留最后一位
    int i;

    while(!(NFSTAT & BUSY))     @如果忙，就延时一会儿
      for(i=0; i<10; i++);
}

#define NAND_SECTOR_SIZE 512
#define NAND_BLOCK_MASK   (NAND_SECTOR_SIZE - 1)

/* low level nand read function */
int
nand_read_ll(unsigned char *buf, unsigned long start_addr, int size)
{                                                  @功能：将以start_addr为起始地址，大小为size的数据段copy到以buf    int i, j;                                 @为起始地址的内存中

    if ((start_addr & NAND_BLOCK_MASK) || (size & NAND_BLOCK_MASK)) {
        return -1; /* invalid alignment */
    }

    /* chip Enable */
    NFCONF &= ~0x800;
    for(i=0; i<10; i++);

    for(i=start_addr; i < (start_addr + size);) {
      /* READ0 */
      NFCMD = 0;                           @开始读数据

      /* Write Address */
      NFADDR = i & 0xff;
      NFADDR = (i >> 9) & 0xff;
      NFADDR = (i >> 17) & 0xff;
      NFADDR = (i >> 25) & 0xff;    @对此处的理解要参考K9S1208的手册，i 对应了一个32位地址，但k9s1208只有date/addr/cmd                                                  @共用的八根地址线，要分批次发送到nand flash。

      wait_idle();

      for(j=0; j < NAND_SECTOR_SIZE; j++, i++) {
*buf = (NFDATA & 0xff);
buf++;                         @数据以字节为单位传送到buf中
      }
    }

    /* chip Disable */
    NFCONF |= 0x800; /* chip disable */

    return 0;
}

修改makefile, COBJS:=mike2410.o flash.o改为COBJS:=mike2410.o flash.o nand_read.o。

然后我们在board/mike2410目录下添加nandflash.h文件，它定义了nand flash的一些芯片配置参数。

#include

#if (CONFIG_COMMANDS & CFG_CMD_NAND)
typedef enum {
NFCE_LOW,
NFCE_HIGH
} NFCE_STATE;           /*可以用NFCE_STATE声明一个枚举类型*/

static inline void NF_Conf(u16 conf)
{
S3C2410_NAND * const nand = S3C2410_GetBase_NAND();

/*定义了一个指向S3C2410_NAND结构体(定义于s3c24x0.h)的指针nand，基地址是S3C2410_NAND_BASE(定义于S3C2410.h)*/

nand->NFCONF = conf;
}

static inline void NF_Cmd(u8 cmd)
{
S3C2410_NAND * const nand = S3C2410_GetBase_NAND();

nand->NFCMD = cmd;
}

static inline void NF_CmdW(u8 cmd)
{
NF_Cmd(cmd);
udelay(1);
}

static inline void NF_Addr(u8 addr)
{
S3C2410_NAND * const nand = S3C2410_GetBase_NAND();

nand->NFADDR = addr;
}

static inline void NF_SetCE(NFCE_STATE s) //传递参数时s只能取NFCE_LOW或NFCE_HIGH
{
S3C2410_NAND * const nand = S3C2410_GetBase_NAND();

switch (s) {
   case NFCE_LOW:
    nand->NFCONF &= ~(1<<11);     //chip enable
    break;

   case NFCE_HIGH:
    nand->NFCONF |= (1<<11);      //chip disable
    break;
}
}

static inline void NF_WaitRB(void)
{
S3C2410_NAND * const nand = S3C2410_GetBase_NAND();

while (!(nand->NFSTAT & (1<<0)));
}

static inline void NF_Write(u8 data)
{
S3C2410_NAND * const nand = S3C2410_GetBase_NAND();

nand->NFDATA = data;
}

static inline u8 NF_Read(void)
{
S3C2410_NAND * const nand = S3C2410_GetBase_NAND();

return(nand->NFDATA);
}

static inline void NF_Init_ECC(void)
{
S3C2410_NAND * const nand = S3C2410_GetBase_NAND();

nand->NFCONF |= (1<<12);
}

static inline u32 NF_Read_ECC(void)
{
S3C2410_NAND * const nand = S3C2410_GetBase_NAND();

return(nand->NFECC);
}

#endif
该头文件中定义的函数在修改的smdk2410.c中用到。

下面是对mike2410.c的修改：主要是对nand的初始化。

#include
#include

#include "nandflash.h"
/* ------------------------------------------------------------------------- */

#define FCLK_SPEED 1

#if FCLK_SPEED==0   /* Fout = 203MHz, Fin = 12MHz for Audio */
#define M_MDIV 0xC3
#define M_PDIV 0x4
#define M_SDIV 0x1
#elif FCLK_SPEED==1   /* Fout = 202.8MHz */
#define M_MDIV 0xA1
#define M_PDIV 0x3
#define M_SDIV 0x1   /*s3c2410.pdf 7-20*/
#endif

#define USB_CLOCK 1

#if USB_CLOCK==0
#define U_M_MDIV 0xA1
#define U_M_PDIV 0x3
#define U_M_SDIV 0x1
#elif USB_CLOCK==1
#define U_M_MDIV 0x48
#define U_M_PDIV 0x3
#define U_M_SDIV 0x2
#endif

static inline void delay (unsigned long loops)
{
__asm__ volatile ("1:\n"
   "subs %0, %1, #1\n"
   "bne 1b":"=r" (loops):"0" (loops));
}

/*
* Miscellaneous platform dependent initialisations
*/

int board_init (void)
{
DECLARE_GLOBAL_DATA_PTR;
S3C24X0_CLOCK_POWER * const clk_power = S3C24X0_GetBase_CLOCK_POWER();
S3C24X0_GPIO * const gpio = S3C24X0_GetBase_GPIO();

/* to reduce PLL lock time, adjust the LOCKTIME register */
clk_power->LOCKTIME = 0xFFFFFF;

/* configure MPLL */
clk_power->MPLLCON = ((M_MDIV << 12) + (M_PDIV << 4) + M_SDIV);

/* some delay between MPLL and UPLL */
delay (4000);

/* configure UPLL */
clk_power->UPLLCON = ((U_M_MDIV << 12) + (U_M_PDIV << 4) + U_M_SDIV);

/* some delay between MPLL and UPLL */
delay (8000);

/* set up the I/O ports */
gpio->GPACON = 0x007FFFFF;
gpio->GPBCON = 0x00044555;               /*针对我的板子此处应做相应的修改*，=0xBEAAF查看手册P268*/
gpio->GPBUP = 0x000007FF;                 /* 1: The pull-up function is disabled.GPB[10:0]*/
gpio->GPCCON = 0xAAAAAAAA;            /*根据开发板，改为0xAABFFEAB*/
gpio->GPCUP = 0x0000FFFF;        
gpio->GPDCON = 0xAAAAAAAA;            /*改为=0xAABFAAAB*/
gpio->GPDUP = 0x0000FFFF;        
gpio->GPECON = 0xAAAAAAAA;    
gpio->GPEUP = 0x0000FFFF;
gpio->GPFCON = 0x000055AA;              /*改为=0x7DEE*/
gpio->GPFUP = 0x000000FF;
gpio->GPGCON = 0xFF95FFBA;             /*=FFAFFFFA*/
gpio->GPGUP = 0x0000FFFF;
gpio->GPHCON = 0x002AFAAA;              /*0x3[10??]AAAA*/
gpio->GPHUP = 0x000007FF;

/* select USB port to be support for host or device */
gpio->MISCCR |= (1<<3);
gpio->MISCCR &= ~((1<<12)|(1<<13));        /*关于usb的normal和suspend???*/

/* arch number of SMDK2410-Board */
gd->bd->bi_arch_number = MACH_TYPE_SMDK2410;

/* adress of boot parameters */
gd->bd->bi_boot_params = 0x30000100;

icache_enable();
dcache_enable();

return 0;
}

/*
* NAND flash initialization.
*/
#if (CONFIG_COMMANDS & CFG_CMD_NAND)
extern ulong nand_probe(ulong physadr);
static inline void NF_Reset(void)
{
int i;
NF_SetCE(NFCE_LOW);
NF_Cmd(0xFF);   /* reset command */
for(i = 0; i < 10; i++); /* tWB = 100ns. */
NF_WaitRB();   /* wait 200~500us; */
NF_SetCE(NFCE_HIGH);
}

static inline void NF_Init(void)
{
#if 0 /* a little bit too optimistic */
#define TACLS   0
#define TWRPH0 3
#define TWRPH1 0
#else
#define TACLS   0
#define TWRPH0 4
#define TWRPH1 2
#endif

NF_Conf((1<<15)|(0<<14)|(0<<13)|(1<<12)|(1<<11)|(TACLS<<8)|(TWRPH0<<4)|(TWRPH1<<0));
}

void nand_init(void)
{
S3C2410_NAND * const nand = S3C2410_GetBase_NAND();
NF_Init();
#ifdef DEBUG
printf("NAND flash probing at 0x%.8lX\n", (ulong)nand);
#endif
printf ("%4lu KB\n", nand_probe((ulong)nand) >> 10);
}
#endif

int dram_init (void)
{
DECLARE_GLOBAL_DATA_PTR;

gd->bd->bi_dram[0].start = PHYS_SDRAM_1;      /*定义见smdk2410.h*/
gd->bd->bi_dram[0].size = PHYS_SDRAM_1_SIZE;

return 0;
}

对smdk2410.h的修改：

#ifndef __CONFIG_H
#define __CONFIG_H

/*
* High Level Configuration Options
* (easy to change)
*/
#define CONFIG_ARM920T   1 /* This is an ARM920T Core */
#define CONFIG_S3C2410   1 /* in a SAMSUNG S3C2410 SoC     */
#define CONFIG_SMDK2410   1 /* on a SAMSUNG SMDK2410 Board */

/* input clock of PLL */
#define CONFIG_SYS_CLK_FREQ 12000000/* the SMDK2410 has 12MHz input clock */

#define USE_920T_MMU   1
#undef CONFIG_USE_IRQ    /* we don't need IRQ/FIQ stuff */

#define CONFIG_CMDLINE_TAG 1 /* enable passing of ATAGS */
#define CONFIG_SETUP_MEMORY_TAGS 1
#define CONFIG_INITRD_TAG 1

/*
* Size of malloc() pool
*/
#define CFG_MALLOC_LEN   (CFG_ENV_SIZE + 128*1024)
#define CFG_GBL_DATA_SIZE 128 /* size in bytes reserved for initial data */

/*
* Hardware drivers
*/
#define CONFIG_DRIVER_CS8900 1 /* we have a CS8900 on-board */
#define CS8900_BASE   0x19000300
#define CS8900_BUS16   1 /* the Linux driver does accesses as shorts */

/*
* select serial console configuration
*/
#define CONFIG_SERIAL1          1 /* we use SERIAL 1 on SMDK2410 */

/************************************************************
* RTC
************************************************************/
#define CONFIG_RTC_S3C24X0 1

/* allow to overwrite serial and ethaddr */
#define CONFIG_ENV_OVERWRITE

#define CONFIG_BAUDRATE   115200

/***********************************************************
* Command definition
***********************************************************/
#define CONFIG_COMMANDS \
    (CONFIG_CMD_DFL | \
    CFG_CMD_CACHE | \
   CFG_CMD_ENV      | \
    CFG_CMD_PING     | \
    CFG_CMD_NAND | \
    /*CFG_CMD_EEPROM |*/ \
    /*CFG_CMD_I2C |*/ \
    CFG_CMD_REGINFO | \
    CFG_CMD_ELF)

/* this must be included AFTER the definition of CONFIG_COMMANDS (if any) */
#include

#define CONFIG_BOOTDELAY 3
/*#define CONFIG_BOOTARGS    "root=ramfs devfs=mount console=ttySA0,9600" */
/*#define CONFIG_ETHADDR 08:00:3e:26:0a:5b */
#define CONFIG_NETMASK          255.255.255.0
#define CONFIG_IPADDR   192.168.1.10
#define CONFIG_SERVERIP   192.168.1.1
/*#define CONFIG_BOOTFILE "elinos-lart" */
/*#define CONFIG_BOOTCOMMAND "tftp; bootm" */

#if (CONFIG_COMMANDS & CFG_CMD_KGDB)
#define CONFIG_KGDB_BAUDRATE 115200   /* speed to run kgdb serial port */
/* what's this ? it's not used anywhere */
#define CONFIG_KGDB_SER_INDEX 1   /* which serial port to use */
#endif

/*
* Miscellaneous configurable options
*/
#define CFG_LONGHELP     /* undef to save memory   */
#define CFG_PROMPT   "MIKE2410# " /* Monitor Command Prompt */
#define CFG_CBSIZE   256   /* Console I/O Buffer Size */
#define CFG_PBSIZE (CFG_CBSIZE+sizeof(CFG_PROMPT)+16) /* Print Buffer Size */
#define CFG_MAXARGS   16   /* max number of command args */
#define CFG_BARGSIZE   CFG_CBSIZE /* Boot Argument Buffer Size */

#define CFG_MEMTEST_START 0x30000000 /* memtest works on */
#define CFG_MEMTEST_END   0x33F00000 /* 63 MB in DRAM */

#undef CFG_CLKS_IN_HZ   /* everything, incl board info, in Hz */

#define CFG_LOAD_ADDR   0x30008000 /* default load address */

/* the PWM TImer 4 uses a counter of 15625 for 10 ms, so we need */
/* it to wrap 100 times (total 1562500) to get 1 sec. */
#define CFG_HZ    1562500

/* valid baudrates */
#define CFG_BAUDRATE_TABLE { 9600, 19200, 38400, 57600, 115200 }

/*-----------------------------------------------------------------------
* Stack sizes
*
* The stack sizes are set up in start.S using the settings below
*/
#define CONFIG_STACKSIZE (128*1024) /* regular stack */
#ifdef CONFIG_USE_IRQ
#define CONFIG_STACKSIZE_IRQ (4*1024) /* IRQ stack */
#define CONFIG_STACKSIZE_FIQ (4*1024) /* FIQ stack */
#endif

/*-----------------------------------------------------------------------
* Physical Memory Map
*/
#define CONFIG_NR_DRAM_BANKS 1    /* we have 1 bank of DRAM */
#define PHYS_SDRAM_1   0x30000000 /* SDRAM Bank #1 */
#define PHYS_SDRAM_1_SIZE 0x04000000 /* 64 MB */

#define PHYS_FLASH_1   0x00000000 /* Flash Bank #1 */

#define CFG_FLASH_BASE   PHYS_FLASH_1

/*-----------------------------------------------------------------------
* FLASH and environment organization
*/

#define CONFIG_AMD_LV400 1 /* uncomment this if you have a LV400 flash */
#if 0
#define CONFIG_AMD_LV800 1 /* uncomment this if you have a LV800 flash */
#endif

#define CFG_MAX_FLASH_BANKS 1 /* max number of memory banks */
#ifdef CONFIG_AMD_LV800
#define PHYS_FLASH_SIZE   0x00100000 /* 1MB */
#define CFG_MAX_FLASH_SECT (19) /* max number of sectors on one chip */
#define CFG_ENV_ADDR   (CFG_FLASH_BASE + 0x0F0000) /* addr of environment */
#endif
#ifdef CONFIG_AMD_LV400
#define PHYS_FLASH_SIZE   0x00080000 /* 512KB */
#define CFG_MAX_FLASH_SECT (11) /* max number of sectors on one chip */
#define CFG_ENV_ADDR   (CFG_FLASH_BASE + 0x070000) /* addr of environment */
#endif

/* timeout values are in ticks */
#define CFG_FLASH_ERASE_TOUT (5*CFG_HZ) /* Timeout for Flash Erase */
#define CFG_FLASH_WRITE_TOUT (5*CFG_HZ) /* Timeout for Flash Write */

#define CFG_ENV_IS_IN_NAND 1
#define CFG_ENV_OFFSET   0x30000
#define CFG_ENV_SIZE   0x10000 /* Total Size of Environment Sector */

/*-----------------------------------------------------------------------
* * NAND flash settings
*   */
#if (CONFIG_COMMANDS & CFG_CMD_NAND)

#define CFG_MAX_NAND_DEVICE 1 /* Max number of NAND devices   */
#define SECTORSIZE 512

#define ADDR_COLUMN 1
#define ADDR_PAGE 2
#define ADDR_COLUMN_PAGE 3

#define NAND_ChipID_UNKNOWN 0x00
#define NAND_MAX_FLOORS 1
#define NAND_MAX_CHIPS 1

#define NAND_WAIT_READY(nand) NF_WaitRB()

#define NAND_DISABLE_CE(nand) NF_SetCE(NFCE_HIGH)
#define NAND_ENABLE_CE(nand) NF_SetCE(NFCE_LOW)

#define WRITE_NAND_COMMAND(d, adr) NF_Cmd(d)
#define WRITE_NAND_COMMANDW(d, adr) NF_CmdW(d)
#define WRITE_NAND_ADDRESS(d, adr) NF_Addr(d)
#define WRITE_NAND(d, adr)   NF_Write(d)
#define READ_NAND(adr)    NF_Read()
/* the following functions are NOP's because S3C24X0 handles this in hardware */
#define NAND_CTL_CLRALE(nandptr)
#define NAND_CTL_SETALE(nandptr)
#define NAND_CTL_CLRCLE(nandptr)
#define NAND_CTL_SETCLE(nandptr)

#define CONFIG_MTD_NAND_VERIFY_WRITE 1
#define CONFIG_MTD_NAND_ECC_JFFS2 1

#endif /* CONFIG_COMMANDS & CFG_CMD_NAND */

/*
* * Nandflash Boot
*   */

#if (CONFIG_COMMANDS & CFG_CMD_NAND)
#define CONFIG_S3C2410_NAND_BOOT 1
#define STACK_BASE    0x33f00000
#define STACK_SIZE    0x8000
#define UBOOT_RAM_BASE    0x33f80000

#define NAND_CTL_BASE            0x4E000000
#define bINT_CTL(Nb)        __REG(INT_CTL_BASE + (Nb))

#define oNFCONF               0x00
#define oNFCMD                0x04
#define oNFADDR               0x08
#define oNFDATA               0x0c
#define oNFSTAT               0x10
#define oNFECC                0x14

#endif
#endif /* __CONFIG_H */

有一个问题：LV800和LV400的选择上，并不清楚自己的板子是哪种？？？？

下一步要看看uboot命令了，我们可以先从SDRAM中调试uboot，调试成功后再移植。而这需要用到一些uboot命令，趁此机会把uboot命令熟悉一下，早晚都要学的。