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- UID
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http://www.openedv.com/posts/list/27427.htm
四、源码注释
本人在不破坏源码逻辑的前提下，对FatFs 0.01源代码进行了中文注释，个别函数重新修改了排版布局，以方便阅读。结合以上示意图即伪代码，相信大家会很快理解FatFs 0.01的核心思想及架构。
[cpp] view plaincopyprint? 
- #include <string.h>
- #include "ff.h" /* FatFs declarations */
- #include "diskio.h" /* Include file for user provided functions */
- FATFS *FatFs; /*
 ointer to the file system object */ - /*-------------------------------------------------------------------------
- Module rivate Functions
- -------------------------------------------------------------------------*/
- /*----------------------*/
- /* Change Window Offset */
- //读取新的扇区内容到临时缓冲区win[]，
- //如果sector为0，则只需要把win[]的内容写入对应的物理扇区即可
- static
- BOOL move_window (
- DWORD sector /* Sector number to make apperance in the FatFs->win */
- ) /* Move to zero only writes back dirty window */
- {
- DWORD wsect; //wsect用于检索FAT备份表的相应扇区
- FATFS *fs = FatFs;
- wsect = FatFs->winsect;
- /*首先检查目标扇区号是否与win[]对应的扇区号相同，如果相同则不进行任何操作。*/
- if (wsect != sector) { /* Changed current window */
- #ifndef _FS_READONLY
- BYTE n;
- //首先检测win[]的内容是否做过修改，如果修改过，则需要先将其写入SD卡中。
- if (FatFs->dirtyflag) { /* Write back dirty window if needed */
- if (disk_write(FatFs->win, wsect, 1) != RES_OK) return FALSE;
- //清除修改标记
- FatFs->dirtyflag = 0;
- /*如果当前操作的是FAT表，那么需要将修改后的FAT表拷贝到对应的FAT备份中*/
- if (wsect < (FatFs->fatbase + FatFs->sects_fat)) { /* In FAT area */
- for (n = FatFs->n_fats; n >= 2; n--) { /* Refrect the change to all FAT copies */
- wsect += FatFs->sects_fat;
- if (disk_write(FatFs->win, wsect, 1) != RES_OK) break;
- }
- }
- }
- #endif
- //然后再读取新的扇区内容到win[]中
- if (sector) {
- if (disk_read(FatFs->win, sector, 1) != RES_OK) return FALSE;
- FatFs->winsect = sector; //更新当前缓冲区的扇区号
- }
- }
- return TRUE;
- }
- /*--------------------------------------------------------------------------*/
- /* ublic Funciotns */
- /*--------------------------------------------------------------------------*/
- /*----------------------------------------------------------*/
- /* Load File System Information and Initialize FatFs Module */
- //本函数做三件事:
- // 1.初始化SD卡
- // 2.检查文件系统类型，FAT16还是FAT32
- // 3.填充FatFs对象，即记录物理磁盘的相关参数
- FRESULT f_mountdrv ()
- {
- BYTE fat;
- DWORD sect, fatend;
- FATFS *fs = FatFs;
- if (!fs) return FR_NOT_ENABLED;
- //首先对文件系统对象清空
- /* Initialize file system object */
- memset(fs, 0, sizeof(FATFS));
- //然后初始化SD卡
- /* Initialize disk drive */
- if (disk_initialize() & STA_NOINIT) return FR_NOT_READY;
- //接着收搜索DBR系统引导记录，先检查第0扇区是否就是DBR(无MBR的SD卡)，如果是则检查文件系统的类型；
- //如果不是则说明第0扇区是MBR，则根据MBR中的信息定位到DBR所在扇区，并检查该文件系统的类型
- /* Search FAT partition */
- fat = check_fs(sect = 0); /* Check sector 0 as an SFD format */
- if (!fat) { /* Not a FAT boot record, it will be an FDISK format */
- /* Check a pri-partition listed in top of the partition table */
- if (fs->win[0x1C2]) { /* Is the partition existing? */
- sect = LD_DWORD(&(fs->win[0x1C6])); /* artition offset in LBA */
- fat = check_fs(sect); /* Check the partition */
- }
- }
- if (!fat) return FR_NO_FILESYSTEM; /* No FAT patition */
- //初始化文件系统对象，根据DBR参数信息对Fs成员赋值
- /* Initialize file system object */
- //文件系统类型:FAT16/FAT32
- fs->fs_type = fat; /* FAT type */
- //单个FAT表所占的扇区数
- fs->sects_fat = /* Sectors per FAT */
- (fat == FS_FAT32) ? LD_DWORD(&(fs->win[0x24])): LD_WORD(&(fs->win[0x16]));
- //单个簇所占的扇区数
- fs->sects_clust = fs->win[0x0D]; /* Sectors per cluster */
- //FAT表总数
- fs->n_fats = fs->win[0x10]; /* Number of FAT copies */
- //FAT表起始扇区(物理扇区)
- fs->fatbase = sect + LD_WORD(&(fs->win[0x0E])); /* FAT start sector (physical) */
- //根目录项数
- fs->n_rootdir = LD_WORD(&(fs->win[0x11])); /* Nmuber of root directory entries */
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