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, 0);    /* Mount a logical drive */

FS_VOLUME_NAND 代表 “路径”

第二　　进入函数 f_mount()内

 1 /*-----------------------------------------------------------------------*/
 2 /* Mount/Unmount a Logical Drive                                         */
 3 /*-----------------------------------------------------------------------*/
 4 
 5 FRESULT f_mount (
 6     FATFS* fs,            /* Pointer to the file system object (NULL:unmount)*/
 7     const TCHAR* path,    /* Logical drive number to be mounted/unmounted */
 8     BYTE opt              /* 0:Do not mount (delayed mount), 1:Mount immediately */
 9 )
10 {
11     FATFS *cfs;
12     int vol;
13     FRESULT res;
14     const TCHAR *rp = path;
15 
16 
17     vol = get_ldnumber(&rp);
18     if (vol < 0) return FR_INVALID_DRIVE;
19     cfs = FatFs[vol];                    /* Pointer to fs object */
20 
21     if (cfs) {
22 #if _FS_LOCK
23         clear_lock(cfs);
24 #endif
25 #if _FS_REENTRANT                        /* Discard sync object of the current volume */
26         if (!ff_del_syncobj(cfs->sobj)) return FR_INT_ERR;
27 #endif
28         cfs->fs_type = 0;                /* Clear old fs object */
29     }
30 
31     if (fs) {
32         fs->fs_type = 0;                 /* Clear new fs object */
33 #if _FS_REENTRANT                        /* Create sync object for the new volume */
34         if (!ff_cre_syncobj((BYTE)vol, &fs->sobj)) return FR_INT_ERR;
35 #endif
36     }
37     FatFs[vol] = fs;                     /* Register new fs object */
38 
39     if (!fs || opt != 1) return FR_OK;   /* Do not mount now, it will be mounted later */
40 
41     res = find_volume(&fs, &path, 0);    /* Force mounted the volume */
42     LEAVE_FF(fs, res);
43 }

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()

 1 /*-----------------------------------------------------------------------*/
 2 /* Get logical drive number from path name                               */
 3 /*-----------------------------------------------------------------------*/
 4 
 5 static
 6 int get_ldnumber (        /* Returns logical drive number (-1:invalid drive) */
 7     const TCHAR** path    /* Pointer to pointer to the path name */
 8 )
 9 {
10     const TCHAR *tp, *tt;
11     UINT i;
12     int vol = -1;
13 
14 
15     if (*path) {    /* If the pointer is not a null */
16         for (tt = *path; (UINT)*tt >= (_USE_LFN ? ' ' : '!') && *tt != ':'; tt++) ;    /* Find ':' in the path */
17         if (*tt == ':') {    /* If a ':' is exist in the path name */
18             tp = *path;
19             i = *tp++ - '0'; 
20             if (i < 10 && tp == tt) {    /* Is there a numeric drive id? */
21                 if (i < _VOLUMES) {      /* If a drive id is found, get the value and strip it */
22                     vol = (int)i;
23                     *path = ++tt;
24                 }
25             } else {      /* No numeric drive number */
26 #if _STR_VOLUME_ID        /* Find string drive id */
27                 static const char* const str[] = {_VOLUME_STRS};
28                 const char *sp;
29                 char c;
30                 TCHAR tc;
31 
32                 i = 0; tt++;
33                 do {
34                     sp = str[i]; tp = *path;
35                     do {    /* Compare a string drive id with path name */
36                         c = *sp++; tc = *tp++;
37                         if (IsLower(tc)) tc -= 0x20;
38                     } while (c && (TCHAR)c == tc);
39                 } while ((c || tp != tt) && ++i < _VOLUMES);    /* Repeat for each id until pattern match */
40                 if (i < _VOLUMES) {    /* If a drive id is found, get the value and strip it */
41                     vol = (int)i;
42                     *path = tt;
43                 }
44 #endif
45             }
46             return vol;
47         }
48 #if _FS_RPATH && _VOLUMES >= 2
49         vol = CurrVol;    /* Current drive */
50 #else
51         vol = 0;          /* Drive 0 */
52 #endif
53     }
54     return vol;
55 }

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

 1 #include "stdio.h"
 2 
 3 void ptf(char **p);
 4 
 5 int main(void)
 6 {
 7     char *pstr = "0:wojiushiyixia";
 8     
 9     ptf(&pstr);
10     
11     return 0;
12 }
13 
14 void ptf(char **p)
15 {
16     if(*p)
17     {
18         printf("*p = %d\n", *p);
19         printf("*p = %s\n", *p);
20     }
21     else
22     {
23         printf("*p = NULL\n");
24     }
25     
26 }

运行环境 C-Free5.0

运行结果

示例二 多参数宏定义

 1 #include "stdio.h"
 2 
 3 #define _VOLUME_STRS    "RAM","NAND","CF","SD1","SD2","USB1","USB2","USB3"
 4 
 5 
 6 int main(void)
 7 {
 8     int i;    
 9     static const char* const str[] = {_VOLUME_STRS};
10     
11     for(i = 0; i < 8; i++)
12     {
13         printf("str[%d] = %s\n", i, str[i]);
14     }
15     
16     return 0;
17 }

运行环境 C-Free5.0

运行结果

学习1__STM32--FatFS之逻辑盘符与物理盘符

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