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