学习1__STM32--FatFS之逻辑盘符与物理盘符

FatFS源代码中的函数逻辑关系

第一　　调用函数 f_mount()

result = f_mount(&fs, FS_VOLUME_NAND, );    /* Mount a logical drive */

FS_VOLUME_NAND 代表 “路径”

第二　　进入函数 f_mount()内

 /*-----------------------------------------------------------------------*/

 /* Mount/Unmount a Logical Drive                                         */

 /*-----------------------------------------------------------------------*/

 FRESULT f_mount (

     FATFS* fs,            /* Pointer to the file system object (NULL:unmount)*/

     const TCHAR* path,    /* Logical drive number to be mounted/unmounted */

     BYTE opt              /* 0:Do not mount (delayed mount), 1:Mount immediately */

 )

 {

     FATFS *cfs;

     int vol;

     FRESULT res;

     const TCHAR *rp = path;

     vol = get_ldnumber(&rp);

     if (vol < ) return FR_INVALID_DRIVE;

     cfs = FatFs[vol];                    /* Pointer to fs object */

     if (cfs) {

 #if _FS_LOCK

         clear_lock(cfs);

 #endif

 #if _FS_REENTRANT                        /* Discard sync object of the current volume */

         if (!ff_del_syncobj(cfs->sobj)) return FR_INT_ERR;

 #endif

         cfs->fs_type = ;                /* Clear old fs object */

     }

     if (fs) {

         fs->fs_type = ;                 /* Clear new fs object */

 #if _FS_REENTRANT                        /* Create sync object for the new volume */

         if (!ff_cre_syncobj((BYTE)vol, &fs->sobj)) return FR_INT_ERR;

 #endif

     }

     FatFs[vol] = fs;                     /* Register new fs object */

     if (!fs || opt != ) return FR_OK;   /* Do not mount now, it will be mounted later */

     res = find_volume(&fs, &path, );    /* Force mounted the volume */

     LEAVE_FF(fs, res);

 }

代码中第17行 vol = get_ldnumber(&rp) 将路径转换为 logical drive number

第三　　进入函数 get_ldnumber()

 /*-----------------------------------------------------------------------*/

 /* Get logical drive number from path name                               */

 /*-----------------------------------------------------------------------*/

 static

 int get_ldnumber (        /* Returns logical drive number (-1:invalid drive) */

     const TCHAR** path    /* Pointer to pointer to the path name */

 )

 {

     const TCHAR *tp, *tt;

     UINT i;

     int vol = -;

     if (*path) {    /* If the pointer is not a null */

         for (tt = *path; (UINT)*tt >= (_USE_LFN ? ' ' : '!') && *tt != ':'; tt++) ;    /* Find ':' in the path */

         if (*tt == ':') {    /* If a ':' is exist in the path name */

             tp = *path;

             i = *tp++ - '';

             if (i <  && tp == tt) {    /* Is there a numeric drive id? */

                 if (i < _VOLUMES) {      /* If a drive id is found, get the value and strip it */

                     vol = (int)i;

                     *path = ++tt;

                 }

             } else {      /* No numeric drive number */

 #if _STR_VOLUME_ID        /* Find string drive id */

                 static const char* const str[] = {_VOLUME_STRS};

                 const char *sp;

                 char c;

                 TCHAR tc;

                 i = ; tt++;

                 do {

                     sp = str[i]; tp = *path;

                     do {    /* Compare a string drive id with path name */

                         c = *sp++; tc = *tp++;

                         if (IsLower(tc)) tc -= 0x20;

                     } while (c && (TCHAR)c == tc);

                 } while ((c || tp != tt) && ++i < _VOLUMES);    /* Repeat for each id until pattern match */

                 if (i < _VOLUMES) {    /* If a drive id is found, get the value and strip it */

                     vol = (int)i;

                     *path = tt;

                 }

 #endif

             }

             return vol;

         }

 #if _FS_RPATH && _VOLUMES >= 2

         vol = CurrVol;    /* Current drive */

 #else

         vol = ;          /* Drive 0 */

 #endif

     }

     return vol;

 }

本函数获取 path 后解析 path 得到 logical drive number

代码中

第15行判断 path 的内容是否为空字符 NULL

第16行检测冒号 ‘：’，for循环的条件为路径名中的字符 >= (_USE_LFN ? ' '： '!') 且 != ‘：’，只要_USE_LFN>0则第一个条件恒满足，找到冒号‘：’后则第二个条件失败，即跳出循环

第17行再次确认当前路径字符为冒号‘：’

第18行暂存*path

第19行得到路径中的首字符那个数字字符对应的数字

第20行判断该数字在0~9之中，且路径中的第二个字符为冒号‘：’

第21行判断该数字在定义的范围内

第22行将该数字赋值给vol

第46行最终将vol值返回

帮助理解的代码示例

示例一指针与字符串

 #include "stdio.h"

 void ptf(char **p);

 int main(void)

 {

     char *pstr = "0:wojiushiyixia";

     ptf(&pstr);

     return ;

 }

 void ptf(char **p)

 {

     if(*p)

     {

         printf("*p = %d\n", *p);

         printf("*p = %s\n", *p);

     }

     else

     {

         printf("*p = NULL\n");

     }

 }

运行环境 C-Free5.0

运行结果

示例二 多参数宏定义

 #include "stdio.h"

 #define _VOLUME_STRS    "RAM","NAND","CF","SD1","SD2","USB1","USB2","USB3"

 int main(void)

 {

     int i;

     static const char* const str[] = {_VOLUME_STRS};

     for(i = ; i < ; i++)

     {

         printf("str[%d] = %s\n", i, str[i]);

     }

     return ;

 }

运行环境 C-Free5.0

运行结果

巴特西

学习1__STM32--FatFS之逻辑盘符与物理盘符

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