嵌入式Linux之我行，主要讲述和总结了本人在学习嵌入式linux中的每个步骤。一为总结经验，二希望能给想入门嵌入式Linux的朋友提供方便。如有错误之处，谢请指正。 一、移植环境

• 主  机：VMWare--Fedora 9
• 开发板：Mini2440--64MB Nand,Kernel:2.6.30.4
• 编译器：arm-linux-gcc-4.3.2.tgz
• u-boot：u-boot-2009.08.tar.bz2

二、移植步骤 上接：u-boot-2009.08在2440上的移植详解（四） 9）实现u-boot对yaffs/yaffs2文件系统下载的支持。       注意：此篇对Nand的操作是基于MTD架构方式，在“u-boot-2009.08在2440上的移植详解（三）”中讲到过。       通常一个Nnad Flash存储设备由若干块组成，1个块由若干页组成。一般128MB以下容量的Nand Flash芯片，一页大小为528B，被依次分为2个256B的主数据区和16B的额外空间；128MB以上容量的Nand Flash芯片，一页大小通常为2KB。由于Nand Flash出现位反转的概率较大，一般在读写时需要使用ECC进行错误检验和恢复。       Yaffs/yaffs2文件系统的设计充分考虑到Nand Flash以页为存取单位等的特点，将文件组织成固定大小的段(Chunk)。以528B的页为例，Yaffs/yaffs2文件系统使用前512B存储数据和16B的额外空间存放数据的ECC和文件系统的组织信息等(称为OOB数据)。通过OOB数据，不但能实现错误检测和坏块处理，同时还可以避免加载时对整个存储介质的扫描，加快了文件系统的加载速度。以下是Yaffs/yaffs2文件系统页的结构说明：            Yaffs页结构说明
==============================================
   字节                   用途
==============================================
 0 - 511                存储数据(分为两个半部)
512 - 515               系统信息
   516                  数据状态字
   517                  块状态字
518 - 519               系统信息
520 - 522               后半部256字节的ECC
523 - 524               系统信息
525 - 527               前半部256字节的ECC
==============================================
    好了，在了解Nand Flash组成和Yaffs/yaffs2文件系统结构后，我们再回到u-boot中。目前，在u-boot中已经有对Cramfs、Jffs2等文件系统的读写支持，但与带有数据校验等功能的OOB区的Yaffs/Yaffs2文件系统相比，他们是将所有文件数据简单的以线性表形式组织的。所以，我们只要在此基础上通过修改u-boot的Nand Flash读写命令，增加处理00B区域数据的功能，即可以实现对Yaffs/Yaffs2文件系统的读写支持。   实现对Yaffs或者Yaffs2文件系统的读写支持步骤如下： ①、在include/configs/my2440.h头文件中定义一个管理对Yaffs2支持的宏和开启u-boot中对Nand Flash默认分区的宏，如下： #gedit include/configs/my2440.h  //添加到文件末尾即可 #define CONFIG_MTD_NAND_YAFFS2   1 //定义一个管理对Yaffs2支持的宏
//开启Nand Flash默认分区，注意此处的分区要和你的内核中的分区保持一致
#define MTDIDS_DEFAULT "nand0=nandflash0"
#define MTDPARTS_DEFAULT "mtdparts=nandflash0:192k(bootloader)," /
                     "64k(params)," /
                     "2m(kernel)," /
                     "-(root)" ②、在原来对Nand操作的命令集列表中添加Yaffs2对Nand的写命令，如下： #gedit common/cmd_nand.c   //在U_BOOT_CMD中添加 U_BOOT_CMD(nand, CONFIG_SYS_MAXARGS, 1, do_nand,
    "NAND sub-system",
    "info - show available NAND devices/n"
    "nand device [dev] - show or set current device/n"
    "nand read - addr off|partition size/n"
    "nand write - addr off|partition size/n"
    " read/write 'size' bytes starting at offset 'off'/n"
    " to/from memory address 'addr', skipping bad blocks./n" //注意：这里只添加了yaffs2的写命令，因为我们只用u-boot下载(即写)功能，所以我们没有添加yaffs2读的命令
#if defined(CONFIG_MTD_NAND_YAFFS2)
    "nand write[.yaffs2] - addr off|partition size - write `size' byte yaffs image/n"
    " starting at offset off' from memory address addr' (.yaffs2 for 512+16 NAND)/n"
#endif
    "nand erase [clean] [off size] - erase 'size' bytes from/n"
    " offset 'off' (entire device if not specified)/n"
    "nand bad - show bad blocks/n"
    "nand dump[.oob] off - dump page/n"
    "nand scrub - really clean NAND erasing bad blocks (UNSAFE)/n"
    "nand markbad off [...] - mark bad block(s) at offset (UNSAFE)/n"
    "nand biterr off - make a bit error at offset (UNSAFE)"
#ifdef CONFIG_CMD_NAND_LOCK_UNLOCK
    "/n"
    "nand lock [tight] [status]/n"
    " bring nand to lock state or display locked pages/n"
    "nand unlock [offset] [size] - unlock section"
#endif
);
接着，在该文件中对nand操作的do_nand函数中添加yaffs2对nand的操作，如下：     if (strncmp(cmd, "read", 4) == 0 || strncmp(cmd, "write", 5) == 0)
    {
        int read;         if (argc < 4)
            goto usage;         addr = (ulong)simple_strtoul(argv[2], NULL, 16);         read = strncmp(cmd, "read", 4) == 0; /* 1 = read, 0 = write */
        printf("/nNAND %s: ", read ? "read" : "write");
        if (arg_off_size(argc - 3, argv + 3, nand, &off, &size) != 0)
            return 1;         s = strchr(cmd, '.');
        if (!s || !strcmp(s, ".jffs2") || !strcmp(s, ".e") || !strcmp(s, ".i"))
        {
            if (read)
                ret = nand_read_skip_bad(nand, off, &size, (u_char *)addr);
            else
                ret = nand_write_skip_bad(nand, off, &size, (u_char *)addr);
        } //添加yaffs2相关操作，注意该处又关联到nand_write_skip_bad函数 #if defined(CONFIG_MTD_NAND_YAFFS2)
        else if (s != NULL && (!strcmp(s, ".yaffs2")))
        {
            nand->rw_oob = 1;
            nand->skipfirstblk = 1;
            ret = nand_write_skip_bad(nand,off,&size,(u_char *)addr);
            nand->skipfirstblk = 0;
            nand->rw_oob = 0;
        }
#endif         else if (!strcmp(s, ".oob"))
        {
            /* out-of-band data */
            mtd_oob_ops_t ops =
            {
                .oobbuf = (u8 *)addr,
                .ooblen = size,
                .mode = MTD_OOB_RAW
            };             if (read)
                ret = nand->read_oob(nand, off, &ops);
            else
                ret = nand->write_oob(nand, off, &ops);
        }
        else
        {
            printf("Unknown nand command suffix '%s'./n", s);
            return 1;
        }         printf(" %zu bytes %s: %s/n", size, read ? "read" : "written", ret ? "ERROR" : "OK");         return ret == 0 ? 0 : 1;
    }
③、在include/linux/mtd/mtd.h头文件的mtd_info结构体中添加上面用到rw_oob和skipfirstblk数据成员，如下： #gedit include/linux/mtd/mtd.h   //在mtd_info结构体中添加 #if defined(CONFIG_MTD_NAND_YAFFS2)
    u_char rw_oob;
    u_char skipfirstblk;
#endif
④、在第二步关联的nand_write_skip_bad函数中添加对Nand OOB的相关操作，如下： #gedit drivers/mtd/nand/nand_util.c  //在nand_write_skip_bad函数中添加 int nand_write_skip_bad(nand_info_t *nand, loff_t offset, size_t *length, u_char *buffer)
{
    int rval;
    size_t left_to_write = *length;
    size_t len_incl_bad;
    u_char *p_buffer = buffer; #if defined(CONFIG_MTD_NAND_YAFFS2) //add yaffs2 file system support
    if(nand->rw_oob==1)   
    {
        size_t oobsize = nand->oobsize;
        size_t datasize = nand->writesize;
        int datapages = 0;         if (((*length)%(nand->oobsize+nand->writesize)) != 0)
        {
         printf ("Attempt to write error length data!/n");
         return -EINVAL;
     }         datapages = *length/(datasize+oobsize);
        *length = datapages*datasize;
        left_to_write = *length;
    }
#endif     /* Reject writes, which are not page aligned */
    if ((offset & (nand->writesize - 1)) != 0 ||
     (*length & (nand->writesize - 1)) != 0) {
        printf ("Attempt to write non page aligned data/n");
        return -EINVAL;
    }     len_incl_bad = get_len_incl_bad (nand, offset, *length);     if ((offset + len_incl_bad) >= nand->size) {
        printf ("Attempt to write outside the flash area/n");
        return -EINVAL;
    } #if !defined(CONFIG_MTD_NAND_YAFFS2) //add yaffs2 file system support
    if (len_incl_bad == *length) {
        rval = nand_write (nand, offset, length, buffer);
        if (rval != 0)
            printf ("NAND write to offset %llx failed %d/n",
                offset, rval);         return rval;
    }
#endif     while (left_to_write > 0) {
        size_t block_offset = offset & (nand->erasesize - 1);
        size_t write_size;         WATCHDOG_RESET ();         if (nand_block_isbad (nand, offset & ~(nand->erasesize - 1))) {
            printf ("Skip bad block 0x%08llx/n",
                offset & ~(nand->erasesize - 1));
            offset += nand->erasesize - block_offset;
            continue;
        } #if defined(CONFIG_MTD_NAND_YAFFS2) //add yaffs2 file system support
        if(nand->skipfirstblk==1)   
        {
            nand->skipfirstblk=0;
            printf ("Skip the first good block %llx/n", offset & ~(nand->erasesize - 1));
            offset += nand->erasesize - block_offset;
            continue;
        }
#endif         if (left_to_write < (nand->erasesize - block_offset))
            write_size = left_to_write;
        else
            write_size = nand->erasesize - block_offset;         printf("/rWriting at 0x%llx -- ",offset); //add yaffs2 file system support
        rval = nand_write (nand, offset, &write_size, p_buffer);
        if (rval != 0) {
            printf ("NAND write to offset %llx failed %d/n",
                offset, rval);
            *length -= left_to_write;
            return rval;
        }         left_to_write -= write_size;
        printf("%d%% is complete.",100-(left_to_write/(*length/100)));
        offset += write_size; #if defined(CONFIG_MTD_NAND_YAFFS2) //add yaffs2 file system support
        if(nand->rw_oob==1)   
        {
            p_buffer += write_size+(write_size/nand->writesize*nand->oobsize);
        }
        else   
        {
            p_buffer += write_size;
        }
#else
        p_buffer += write_size;
#endif     }     return 0;
}
⑤、在第四步nand_write_skip_bad函数中我们看到又对nand_write函数进行了访问，所以这一步是到nand_write函数中添加对yaffs2的支持，如下： #gedit drivers/mtd/nand/nand_base.c  //在nand_write函数中添加 static int nand_write(struct mtd_info *mtd, loff_t to, size_t len, size_t *retlen, const uint8_t *buf)
{
    struct nand_chip *chip = mtd->priv;
    int ret;   #if defined(CONFIG_MTD_NAND_YAFFS2) //add yaffs2 file system support     int oldopsmode = 0;     if(mtd->rw_oob==1)   
    {
        int i = 0;
        int datapages = 0;         size_t oobsize = mtd->oobsize;
        size_t datasize = mtd->writesize;         uint8_t oobtemp[oobsize];
        datapages = len / (datasize);         for(i = 0; i < (datapages); i++)   
        {
            memcpy((void *)oobtemp, (void *)(buf + datasize * (i + 1)), oobsize);
            memmove((void *)(buf + datasize * (i + 1)), (void *)(buf + datasize * (i + 1) + oobsize), (datapages - (i + 1)) * (datasize) + (datapages - 1) * oobsize);
            memcpy((void *)(buf+(datapages) * (datasize + oobsize) - oobsize), (void *)(oobtemp), oobsize);
        }
    }
#endif       /* Do not allow reads past end of device */
    if ((to + len) > mtd->size)
        return -EINVAL;
    if (!len)
        return 0;     nand_get_device(chip, mtd, FL_WRITING);     chip->ops.len = len;
    chip->ops.datbuf = (uint8_t *)buf;   #if defined(CONFIG_MTD_NAND_YAFFS2) //add yaffs2 file system support     if(mtd->rw_oob!=1)   
    {
        chip->ops.oobbuf = NULL;
    }
    else   
    {
        chip->ops.oobbuf = (uint8_t *)(buf + len);
        chip->ops.ooblen = mtd->oobsize;
        oldopsmode = chip->ops.mode;
        chip->ops.mode = MTD_OOB_RAW;
    }
#else
    chip->ops.oobbuf = NULL;
#endif       ret = nand_do_write_ops(mtd, to, &chip->ops);     *retlen = chip->ops.retlen;     nand_release_device(mtd);   #if defined(CONFIG_MTD_NAND_YAFFS2) //add yaffs2 file system support     chip->ops.mode = oldopsmode;
#endif       return ret;
}
OK，对yaffs2支持的代码已修改完毕，重新编译u-boot并下载到nand中，启动开发板，在u-boot的命令行输入:nand help查看nand的命令，可以看到多了一个nand write[.yaffs2]的命令，这个就是用来下载yaffs2文件系统到nand中的命令了。 ⑥、使用nand write[.yaffs2]命令把事前制作好的yaffs2文件系统下载到Nand Flash中(yaffs2文件系统的制作请参考：Linux-2.6.30.4在2440上的移植之文件系统)，下载操作步骤和效果图如下： tftp 0x30000000 root-2.6.30.4.bin //用tftp将yaffs2文件系统下载到内存的0x30000000位置

nand erase 0x250000 0x3dac000 //擦除Nand的文件系统分区

nand write.yaffs2 0x30000000 0x250000 0x658170 //将内存中的yaffs2文件系统写入Nand的文件系统分区，注意这里的0x658170是yaffs2文件系统的实际大小(可以在tftp传送完后可以看到)，要写正确，否则会形成假坏块

⑦、结合u-boot和内核来测试启动下载的yaffs2文件系统
设置u-boot启动参数bootargs，注意：这一长串参数要与内核配置里面的Boot options-->Default kernel command string的设置要一致。特别是mtdblock3要根据内核具体的分区来设，在上一篇中讲到了内核中Nand的分区情况，u-boot属于mtdblock0，param属于mtdblock1，kernel属于mtdblock2，root就属于mtdblock3，所以这里要设置成root=/dev/mtdblock3，否则文件系统无法启动成功，会出现一些什么I/O之类的错误
好了，最后重启开发板，内核引导成功，yaffs2文件系统也挂载成功，效果图如下：
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