7.1 创建nand_read.c

【注意】
本程序只能用于读取2K/页的Nand。本人的Micro2440上的Nand Flash为256M，型号为K9F2G08
 

[www.linuxidc.com@linuxidc u-boot-2011.06]$ touch board/samsung/micro2440/nand_read.c
[www.linuxidc.com@linuxidc u-boot-2011.06]$ cat> board/samsung/micro2440/nand_read.c

#define rNFCONF  (*(volatile unsigned *)0x4E000000)
#define rNFCONT  (*(volatile unsigned *)0x4E000004)
#define rNFCMD  (*(volatile unsigned *)0x4E000008)
#define rNFADDR  (*(volatile unsigned *)0x4E00000C)
#define rNFDATA8 (*(volatile unsigned char*)0x4E000010)
#define rNFSTAT  (*(volatile unsigned *)0x4E000020)

#define CMD_READ1   0x00            /* 页读命令周期1 */
#define CMD_READ2   0x30            /* 页读命令周期2 */
#define CMD_RESET   0xFF          /* 复位    */

#define NF_CMD(cmd)   {rNFCMD=(cmd);}     /* 写命令   */
#define NF_ADDR(addr)  {rNFADDR=(addr);}    /* 写地址   */
#define NF_RDDATA8()  (rNFDATA8)         /* 读8位数据  */
#define NF_nFCE_L()   {rNFCONT&=~(1<<1);}    /* 片选使能   */
#define NF_nFCE_H()   {rNFCONT|=(1<<1);}    /* 片选禁用   */
#define NF_WAITRB()      {while(!(rNFSTAT&(1<<1)));}  /* 等待就绪   */
#define NF_CLEAR_RB()     {rNFSTAT |= (1<<2);}   /* 清除就绪/忙位 */
#define NF_DETECT_RB()     {while(!(rNFSTAT&(1<<2)));}  /* 等待就绪   */

#define TACLS  1
#define TWRPH0  2
#define TWRPH1  1

void delay(int i)
{
 while(i-->0);
}

void Nand_Init(void)
{
 rNFCONF = (TACLS<<12)|(TWRPH0<<8)|(TWRPH1<<4)|(0<<0); 
 rNFCONT = (1<<4)|(1<<1)|(1<<0);
}

static void Nand_Reset(void)
{
 NF_nFCE_L();      /* 片选使能   */
 NF_CLEAR_RB();      /* 清除就绪/忙位  */
 NF_CMD(CMD_RESET);     /* 写复位命令  */
 NF_DETECT_RB();      /* 等待就绪   */
 NF_nFCE_H();      /* 片选禁用   */
}

unsigned char Nand_ReadPage(const int page, unsigned char * const buffer)
{
 int i;
 
 Nand_Reset();
 
 NF_nFCE_L();
 NF_CLEAR_RB();

 NF_CMD(CMD_READ1); 
 NF_ADDR(0x0);
 NF_ADDR(0x0);
 NF_ADDR(page&0xff);
 NF_ADDR((page>>8)&0xff);
 NF_ADDR((page>>16)&0xff);
 NF_CMD(CMD_READ2); 
  
 NF_DETECT_RB();

 for (i = 0; i < 2048; i++) 
 {
  buffer[i] =  NF_RDDATA8();
 }
 
 NF_nFCE_H();
}

int nand_read(int start_page, int read_pages, unsigned char *buffer)
{
 int i;

 Nand_Init();
 for(i=0; i {
  Nand_ReadPage(start_page, buffer + 2048*i);
  start_page++;
 }
 return 0;
}

7.2 board/samsung/micro2440/Makefile

COBJS := micro2440.o flash.o nand_read.o

7.3 arch/arm/cpu/arm920t/u-boot.lds

 .text :
 {
  arch/arm/cpu/arm920t/start.o (.text)
  board/samsung/micro2440/libmicro2440.o    (.text)
  *(.text)
 }

【说明】

如果是在RAM中运行，一定要删去board/samsung/micro2440/libmicro2440.o    (.text)，否则在RAM中也不能运行。原因尚不理解，需要阅读代码。

7.4 arch/arm/cpu/arm920t/start.S

下面红色部分是添加的部分，黑色的代码用于定位。

#ifndef CONFIG_SKIP_LOWLEVEL_INIT
    bl cpu_init_crit
#endif

#ifdef CONFIG_S3C2440_NAND_BOOT
    ldr sp, =0x30008000
    ldr r0, =0x0;
    ldr r1, _end_ofs
    mov r1, r1, LSR #11
    add r1, r1, #1
    ldr r2, =(CONFIG_SYS_TEXT_BASE)
    bl nand_read
    ldr pc, =relocations
#endif
......
......
copy_loop:
ldmia r0!, {r9-r10} /* copy from source address [r0] */
stmia r1!, {r9-r10} /* copy to target address [r1] */
cmp r0, r2 /* until source end address [r2] */
blo copy_loop

#ifdef CONFIG_S3C2440_NAND_BOOT
relocations:
    ldr r6, =CONFIG_SYS_TEXT_BASE
#endif

#ifndef CONFIG_PRELOADER
/*
* fix .rel.dyn relocations
*/
......
......
clbss_l:str r2, [r0] /* clear loop... */
add r0, r0, #4
cmp r0, r1
bne clbss_l

bl coloured_LED_init
bl red_LED_on
#endif

#ifdef CONFIG_S3C2440_NAND_BOOT
    ldr sp, =(CONFIG_SYS_INIT_SP_ADDR)
    bic sp, sp, #7 /* 8-byte alignment for ABI compliance */
    ldr r0,=0x00000000
   ldr pc, =board_init_f
#endif

/*
* We are done. Do not return, instead branch to second part of board
* initialization, now running from RAM.
*/
#ifdef CONFIG_NAND_SPL

7.5 include/configs/micro2440.h

#define CONFIG_S3C2440_NAND_BOOT
/* #define CONFIG_SKIP_LOWLEVEL_INIT */

【说明】
由于要在Nand Flash中运行，所以需要注释掉#define CONFIG_SKIP_LOWLEVEL_INIT

7.6 arch/arm/lib/board.c

void board_init_f (ulong bootflag)
{
    ......

    gd->mon_len = _bss_end_ofs + 0x100000; /* why */

    ...... 

这里的修改参考了bscbem的日志：http://www.linuxidc.com/Linux/2011-02/32772p4.htm
如果有读者想了解原理请参考这个日志。
 

    /* relocate_code (addr_sp, id, addr); */
#ifdef CONFIG_S3C2440_NAND_BOOT /*add by wzc*/ 
    __asm__ __volatile__("mov sp,%0"::"r"(addr_sp):"sp");/*add by wzc*/ 
    board_init_r(id, addr); 
#else 
    relocate_code (addr_sp, id, addr); 
    /* NOTREACHED - relocate_code() does not return */ 
#endif
}
 
【说明】
 
至于gd->mon_len = _bss_end_ofs + 0x100000;我也不理解，需要阅读源代码才能解释。
 

7.7 下载到Nand Flash

 到这里应该就可以从Nand Flash启动了。