1 /*-----------------------------------------------------------------------*/ 2 /* Forward data to the stream directly (available on only tiny cfg)      */ 3 /*-----------------------------------------------------------------------*/ 4  5 FRESULT f_forward ( 6     FIL *fp,                         /* Pointer to the file object */ 7     UINT (*func)(const BYTE*,UINT),    /* Pointer to the streaming function */ 8     UINT btr,                        /* Number of bytes to forward */ 9     UINT *bf                        /* Pointer to number of bytes forwarded */10 )11 {12     FRESULT res;13     DWORD remain, clst, sect;14     UINT rcnt;15     BYTE csect;16 17 18     *bf = 0;    /* Initialize byte counter */19 20     res = validate(fp->fs, fp->id);                    /* Check validity of the object */21     if (res != FR_OK) LEAVE_FF(fp->fs, res);22     if (fp->flag & FA__ERROR)                        /* Check error flag */23         LEAVE_FF(fp->fs, FR_INT_ERR);24     if (!(fp->flag & FA_READ))                        /* Check access mode */25         LEAVE_FF(fp->fs, FR_DENIED);26 27     remain = fp->fsize - fp->fptr;28     if (btr > remain) btr = (UINT)remain;            /* Truncate btr by remaining bytes */29 30     for ( ;  btr && (*func)(0, 0);                    /* Repeat until all data transferred or stream becomes busy */31         fp->fptr += rcnt, *bf += rcnt, btr -= rcnt) {32         csect = (BYTE)(fp->fptr / SS(fp->fs) & (fp->fs->csize - 1));    /* Sector offset in the cluster */33         if ((fp->fptr % SS(fp->fs)) == 0) {            /* On the sector boundary? */34             if (!csect) {                            /* On the cluster boundary? */35                 clst = (fp->fptr == 0) ?            /* On the top of the file? */36                     fp->sclust : get_fat(fp->fs, fp->clust);37                 if (clst <= 1) ABORT(fp->fs, FR_INT_ERR);38                 if (clst == 0xFFFFFFFF) ABORT(fp->fs, FR_DISK_ERR);39                 fp->clust = clst;                    /* Update current cluster */40             }41         }42         sect = clust2sect(fp->fs, fp->clust);        /* Get current data sector */43         if (!sect) ABORT(fp->fs, FR_INT_ERR);44         sect += csect;45         if (move_window(fp->fs, sect))                /* Move sector window */46             ABORT(fp->fs, FR_DISK_ERR);47         fp->dsect = sect;48         rcnt = SS(fp->fs) - (WORD)(fp->fptr % SS(fp->fs));    /* Forward data from sector window */49         if (rcnt > btr) rcnt = btr;50         rcnt = (*func)(&fp->fs->win[(WORD)fp->fptr % SS(fp->fs)], rcnt);51         if (!rcnt) ABORT(fp->fs, FR_INT_ERR);52     }53 54     LEAVE_FF(fp->fs, FR_OK);55 }

 1 /*-----------------------------------------------------------------------*/ 2 /* 示例代码：数据传输函数，将被f_forward函数调用                                 */ 3 /*-----------------------------------------------------------------------*/ 4   5 UINT out_stream (   /* 返回已发送字节数或流状态 */ 6     const BYTE *p,  /* 将被发送的数据块的指针 */ 7     UINT btf        /* >0: 传输调用(将被发送的字节数)。0: 检测调用 */ 8 ) 9 {10     UINT cnt = 0;11  12     if (btf == 0) {     /* 检测调用 */13         /* 返回流状态(0: 忙，1: 就绪) */14         /* 当检测调用时，一旦它返回就绪，那么在后续的传输调用时，它必须接收至少一个字节，或者f_forward将以FR_INT_ERROR而失败。 */15         if (FIFO_READY) cnt = 1;16     }17     else {              /* 传输调用 */18         do {    /* 当有数据要发送并且流就绪时重复 */19             FIFO_PORT = *p++;20             cnt++;21         } while (cnt < btf && FIFO_READY);22     }23  24     return cnt;25 }26 27 28 /*-----------------------------------------------------------------------*/29 /* 示例代码：使用f_forward函数                                                    */30 /*-----------------------------------------------------------------------*/31  32 FRESULT play_file (33     char *fn        /* 待播放的音频文件名的指针 */34 )35 {36     FRESULT rc;37     FIL fil;38     UINT dmy;39  40     /* 以只读模式打开音频文件 */41     rc = f_open(&fil, fn, FA_READ);42  43     /* 重复，直到文件指针到达文件结束位置 */44     while (rc == FR_OK && fil.fptr < fil.fsize) {45  46         /* 任何其他处理... */47  48         /* 定期或请求式填充输出流 */49         rc = f_forward(&fil, out_stream, 1000, &dmy);50     }51  52     /* 该只读的音频文件对象不需要关闭就可以被丢弃 */53     return rc;54 }