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s3c6410_uboot中的代码重定位(nand->sdram)

本文仅探讨s3c6410从nand flash启动u-boot时的代码重定位过程

参考:

1)《USER‘S MANUAL-S3C6410X》第二章 MEMORY MAP 第八章 NAND FLASH CONTROLLER

2)u-boot源码:

u-boot-x.x.x/board/samsumg/smdk6410/lowlevel_init.S

u-boot-x.x.x/cpu/s3c64xx/start.S

u-boot-x.x.x/cpu/s3c64xx/nand_cp.c

代码重定位过程简述

由于在nand flash中无法运行代码,所以当开发板从nand flash启动时,我们需要将存储在外设nand flash中的u-boot代码搬运到sdram中运行,如何完成这个搬运工作呢?这需要借助一个跳板,即“stepping stone”,它是s3c6410的一块内置sram,开发板上电时,nand flash控制器自动将nand flash的前8K的内容拷贝到sram中并执行,这一小段启动代码除了初始化硬件外,最重要的一个工作就是将nand flash中的所有u-boot代码拷贝(即重定位)到sdram的指定地址上去,然后跳转到sdram中执行。

重定位代码解析:

1)nand接口初始化

u-boot启动时,首先执行相应硬件平台的start.S,start.S中调用lowlevel_init对时钟,uart,nand,mmu等底层硬件作初始化。

start.S:

...bl    lowlevel_init    /* go setup pll,mux,memory */...

lowlevel_init.S:

...
/*
* Nand Interface Init for SMDK6400 */nand_asm_init: ldr r0, =ELFIN_NAND_BASE ldr r1, [r0, #NFCONF_OFFSET] orr r1, r1, #0x70 orr r1, r1, #0x7700 str r1, [r0, #NFCONF_OFFSET] ldr r1, [r0, #NFCONT_OFFSET] orr r1, r1, #0x03 str r1, [r0, #NFCONT_OFFSET] mov pc, lr
...

2)代码重定位

从nand flash启动时,重定位代码如下:

start.S:

/* when we already run in ram, we don‘t need to relocate U-Boot.     * and actually, memory controller must be configured before U-Boot     * is running in ram.     */    ldr    r0, =0xff000fff    bic    r1, pc, r0        /* r0 <- current base addr of code */    ldr    r2, _TEXT_BASE        /* r1 <- original base addr in ram */    bic    r2, r2, r0        /* r0 <- current base addr of code */    cmp     r1, r2                  /* compare r0, r1                  */    beq     after_copy        /* r0 == r1 then skip flash copy   */#ifdef CONFIG_BOOT_NAND    mov    r0, #0x1000    bl    copy_from_nand#endif

r1存放当前代码运行的起始地址,r2存放u-boot即将在sdram中运行的地址,如果两个地址相等,说明此时u-boot已经在sdram中运行了,无需再执行从nand拷贝数据到sdram的动作;否则,此时u-boot还在它的临时住所sram中执行,此地不可久留,需要执行copy_from_nand将u-boot代码完完整整地拷贝到sdram中去,然后跳转到sdram中去执行剩下的代码。

/* * copy U-Boot to SDRAM and jump to ram (from NAND or OneNAND) * r0: size to be compared * Load 1‘st 2blocks to RAM because U-boot‘s size is larger than 1block(128k) size */    .globl copy_from_nandcopy_from_nand:    mov    r10, lr        /* save return address */    mov    r9, r0    /* get ready to call C functions */    ldr    sp, _TEXT_PHY_BASE    /* setup temp stack pointer */    sub    sp, sp, #12    mov    fp, #0            /* no previous frame, so fp=0 */    mov    r9, #0x1000    bl    copy_uboot_to_ram3:    tst     r0, #0x0    bne    copy_failed    ldr    r0, =0x0c000000    ldr    r1, _TEXT_PHY_BASE1:    ldr    r3, [r0], #4    ldr    r4, [r1], #4    teq    r3, r4    bne    compare_failed    /* not matched */    subs    r9, r9, #4    bne    1b4:    mov    lr, r10        /* all is OK */    mov    pc, lrcopy_failed:    nop            /* copy from nand failed */    b    copy_failedcompare_failed:    nop            /* compare failed */    b    compare_failed

真正执行拷贝动作的是copy_uboot_to_ram函数,它定义在u-boot-x.x.x/cpu/s3c64xx/nand_cp.c中,

int copy_uboot_to_ram (void){    int large_block = 0;    int i;    vu_char id;            NAND_ENABLE_CE();        NFCMD_REG = NAND_CMD_READID;        NFADDR_REG =  0x00;    /* wait for a while */        for (i=0; i<200; i++);    id = NFDATA8_REG;    id = NFDATA8_REG;    if (id > 0x80)        large_block = 1;    /* read NAND Block.     * 128KB ->240KB because of U-Boot size increase. by scsuh     * So, read 0x3c000 bytes not 0x20000(128KB).     */    return nandll_read_blocks(CFG_PHY_UBOOT_BASE, 0x3c000, large_block);}

nand flash支持两种页大小,512B和2KB,large_block = 0时,页大小为512字节,large_block = 1时,页大小为2K字节。nandll_read_blocks拷贝nand flash从第0页开始的0x3c00(240K)大小的数据到sdram的CFG_PHY_UBOOT_BASE地址处。

/* * Read data from NAND. */static int nandll_read_blocks (ulong dst_addr, ulong size, int large_block){        uchar *buf = (uchar *)dst_addr;        int i;    uint page_shift = 9;    if (large_block)        page_shift = 11;        /* Read pages */        for (i = 0; i < (0x3c000>>page_shift); i++, buf+=(1<<page_shift)) {                nandll_read_page(buf, i, large_block);        }        return 0;}

首先根据large_block判断nand flash一个页的大小,从而计算需要拷贝的页的数量,即需要拷贝(0x3c000>>page_shift)个页,nandll_read_page每次只拷贝一个页的数据。

/* * address format *              17 16         9 8            0 * -------------------------------------------- * | block(12bit) | page(5bit) | offset(9bit) | * -------------------------------------------- */static int nandll_read_page (uchar *buf, ulong addr, int large_block){        int i;    int page_size = 512;    if (large_block)        page_size = 2048;        NAND_ENABLE_CE();        NFCMD_REG = NAND_CMD_READ0;        /* Write Address */        NFADDR_REG = 0;    if (large_block)            NFADDR_REG = 0;    NFADDR_REG = (addr) & 0xff;    NFADDR_REG = (addr >> 8) & 0xff;    NFADDR_REG = (addr >> 16) & 0xff;    if (large_block)        NFCMD_REG = NAND_CMD_READSTART;        NF_TRANSRnB();    /* for compatibility(2460). u32 cannot be used. by scsuh */    for(i=0; i < page_size; i++) {                *buf++ = NFDATA8_REG;        }        NAND_DISABLE_CE();        return 0;}

从nand flash中读取数据的流程为片选(NAND_ENABLE_CE)->发读命令(NFCMD_REG)->发地址(NFADDR_REG)->发读命令(NFCMD_REG)->等待数据可读(NF_TRANSRnB)->读数据(NFDATA8_REG)。由于每次从NFDATA8_REG中只可读取1个字节的数据,所以拷贝一页需要读取512或2048次。

 

当执行完copy_uboot_to_ram返回到start.S时,nand flash中的代码重定位便完成了,此后程序跳转到sdram中执行,stepping stone的职责就此结束。