TX2440 ARM开发板Uboot移植（五、yaffs2文件系统的支持）

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。

1、 在原来对Nand操作的命令集列表中添加Yaffs2对Nand的写命令，修改 common/cmd_nand.c 文件，在U_BOOT_CMD约461行处加入读写Yaffs2格式的命令：

U_BOOT_CMD(nand, 5, 1, do_nand,  "nand    - NAND sub-system\n",  "info                  - show available NAND devices\n"  "nand device [dev]     - show or set current device\n"  "nand read[.jffs2]     - addr off|partition size\n"  "nand write[.jffs2]    - addr off|partition size - read/write `size' bytes starting\n"  "    at offset `off' to/from memory address `addr'\n"   "nand read[.yaffs2] - addr off size - read the `size' byte yaffs image starting\n"   "    at offset `off' to memory address `addr'\n"   "nand write[.yaffs2] - addr off size - write the `size' byte yaffs image starting\n"   "    at offset `off' from memory address `addr'\n"  "nand erase [clean] [off size] - erase `size' bytes from\n"  "    offset `off' (entire device if not specified)\n" ... ...

2、在该文件中，在对nand操作的do_nand函数中添加yaffs2对nand的操作：

int do_nand(cmd_tbl_t * cmdtp, int flag, int argc, char *argv[])   ... ...   s = strchr(cmd, '.');   if (s != NULL && (!strcmp(s, ".jffs2") || !strcmp(s, ".e") || !strcmp(s, ".i"))) {          。。。。。。   } else if (  s != NULL && !strcmp(s, ".yaffs2")){       if (read) {         /* read */         nand_read_options_t opts;         memset(&opts, 0, sizeof(opts));         opts.buffer = (u_char*) addr;         opts.length = size;         opts.offset = off;         opts.readoob = 1;         opts.quiet   = quiet;         ret = nand_read_opts(nand, &opts);       } else {         /* write */         nand_write_options_t opts;         memset(&opts, 0, sizeof(opts));         opts.buffer = (u_char*) addr;         opts.length = size;         opts.offset = off;         /* opts.forceyaffs = 1; */         opts.noecc = 1;         opts.writeoob = 1;         opts.blockalign = 1;         opts.quiet      = quiet;         opts.skipfirstblk = 1;         ret = nand_write_opts(nand, &opts);       }     }else if (s != NULL && !strcmp(s, ".oob")) {    /* read out-of-band data */

3、修改 include/nand.h 文件，在nand_write_options增加skipfirstblk成员：

struct nand_write_options {  u_char *buffer;  /* memory block containing image to write */  ulong length;  /* number of bytes to write */  ulong offset;  /* start address in NAND */  int quiet;  /* don't display progress messages */  int autoplace;  /* if true use auto oob layout */  int forcejffs2;  /* force jffs2 oob layout */  int forceyaffs;  /* force yaffs oob layout */  int noecc;  /* write without ecc */  int writeoob;  /* image contains oob data */  int pad;  /* pad to page size */  int blockalign;  /* 1|2|4 set multiple of eraseblocks to align to */  int skipfirstblk; };

4、修改drivers/mtd/nand/nand_util.c文件的nand_write_opts函数，增加对skipfirstblk成员的支持：

size_t written; int result; int skipfirstblk = opts->skipfirstblk;  ... ...  while (blockstart != (mtdoffset & (~erasesize_blockalign+1))) {    ... ...  }  /* skip the first good block when wirte yaffs image*/  if(skipfirstblk){   mtdoffset += erasesize_blockalign;   skipfirstblk = 0;   continue;  }    readlen = meminfo->oobblock;  ... ...

5、修改drivers/mtd/nand/nand_base.c文件的nand_write_page函数，注释掉因前面设置opts.noecc=1导致烧写Nand Flash过程中出现的提示信息：

case NAND_ECC_NONE:   //printk (KERN_WARNING "Writing data without ECC to NAND-FLASH is not recommended\n");   this->write_buf(mtd, this->data_poi, mtd->oobblock);   break;