FAT: Added support for block sizes of 512-4096 bytes

This is necessary for support of block devices with >512 byte
blocks, such as most SPI flash parts.

- Enabled support of up to 4096 byte blocks
- Added support for heap-backed buffers using _FS_HEAPBUF
  - Necessary to avoid stack overflows
  - Avoids over-aggresive allocations of _MAX_SS
- Enabled _FS_TINY to further reduce memory footprint
  - Haven't found a downside for this yet except for possible
    thread contention

features/filesystem/fat/ChaN/ff.cpp

@@ -2249,6 +2249,13 @@ FRESULT find_volume (	/* FR_OK(0): successful, !=0: any error occurred */
 #if _MAX_SS != _MIN_SS						/* Get sector size (multiple sector size cfg only) */
 	if (disk_ioctl(fs->drv, GET_SECTOR_SIZE, &SS(fs)) != RES_OK
 		|| SS(fs) < _MIN_SS || SS(fs) > _MAX_SS) return FR_DISK_ERR;
+#endif
+#if _FS_HEAPBUF
+	if (!fs->win) {
+		fs->win = (BYTE*)ff_memalloc(SS(fs));	/* Allocate buffer to back window if necessary */
+		if (!fs->win)
+			return FR_NOT_ENOUGH_CORE;
+	}
 #endif
 	/* Find an FAT partition on the drive. Supports only generic partitioning, FDISK and SFD. */
 	bsect = 0;
@@ -2423,12 +2430,18 @@ FRESULT f_mount (
 		if (!ff_del_syncobj(cfs->sobj)) return FR_INT_ERR;
 #endif
 		cfs->fs_type = 0;				/* Clear old fs object */
+#if _FS_HEAPBUF
+		ff_memfree(cfs->win);			/* Clean up window buffer */
+#endif
 	}
 
 	if (fs) {
 		fs->fs_type = 0;				/* 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
+#if _FS_HEAPBUF
+		fs->win = 0;					/* NULL buffer to prevent use of uninitialized buffer */
 #endif
 	}
 	FatFs[vol] = fs;					/* Register new fs object */
@@ -2570,6 +2583,11 @@ FRESULT f_open (
 #endif
 			fp->fs = dj.fs;	 					/* Validate file object */
 			fp->id = fp->fs->id;
+#if !_FS_TINY && _FS_HEAPBUF
+			fp->buf = (BYTE*)ff_memalloc(SS(dj.fs));	/* Allocate buffer if necessary */
+			if (!fp->buf)
+				return FR_NOT_ENOUGH_CORE;
+#endif
 		}
 	}
 
@@ -2892,6 +2910,9 @@ FRESULT f_close (
 				fp->fs = 0;				/* Invalidate file object */
 #if _FS_REENTRANT
 			unlock_fs(fs, FR_OK);		/* Unlock volume */
+#endif
+#if !_FS_TINY && _FS_HEAPBUF
+			ff_memfree(fp->buf);		/* Deallocate buffer */
 #endif
 		}
 	}
@@ -4112,6 +4133,13 @@ FRESULT f_mkfs (
 #if _MAX_SS != _MIN_SS		/* Get disk sector size */
 	if (disk_ioctl(pdrv, GET_SECTOR_SIZE, &SS(fs)) != RES_OK || SS(fs) > _MAX_SS || SS(fs) < _MIN_SS)
 		return FR_DISK_ERR;
+#endif
+#if _FS_HEAPBUF
+	if (!fs->win) {
+		fs->win = (BYTE*)ff_memalloc(SS(fs));	/* Allocate buffer to back window if necessary */
+		if (!fs->win)
+			return FR_NOT_ENOUGH_CORE;
+	}
 #endif
 	if (_MULTI_PARTITION && part) {
 		/* Get partition information from partition table in the MBR */

features/filesystem/fat/ChaN/ff.h

@@ -104,7 +104,11 @@ typedef struct {
 	DWORD	dirbase;		/* Root directory start sector (FAT32:Cluster#) */
 	DWORD	database;		/* Data start sector */
 	DWORD	winsect;		/* Current sector appearing in the win[] */
+#if _FS_HEAPBUF
+	BYTE	*win;			/* Disk access window for Directory, FAT (and file data at tiny cfg) */
+#else
 	BYTE	win[_MAX_SS];	/* Disk access window for Directory, FAT (and file data at tiny cfg) */
+#endif
 } FATFS;
 
 
@@ -132,8 +136,12 @@ typedef struct {
 	UINT	lockid;			/* File lock ID origin from 1 (index of file semaphore table Files[]) */
 #endif
 #if !_FS_TINY
+#if _FS_HEAPBUF
+	BYTE	*buf;			/* File private data read/write window */
+#else
 	BYTE	buf[_MAX_SS];	/* File private data read/write window */
 #endif
+#endif
 } FIL;
 
 
@@ -264,14 +272,16 @@ TCHAR* f_gets (TCHAR* buff, int len, FIL* fp);						/* Get a string from the fil
 DWORD get_fattime (void);
 #endif
 
+/* Memory functions */
+#if _USE_LFN == 3 || _FS_HEAPBUF
+void* ff_memalloc (UINT msize);		/* Allocate memory block */
+void ff_memfree (void* mblock);		/* Free memory block */
+#endif
+
 /* Unicode support functions */
 #if _USE_LFN							/* Unicode - OEM code conversion */
 WCHAR ff_convert (WCHAR chr, UINT dir);	/* OEM-Unicode bidirectional conversion */
 WCHAR ff_wtoupper (WCHAR chr);			/* Unicode upper-case conversion */
-#if _USE_LFN == 3						/* Memory functions */
-void* ff_memalloc (UINT msize);			/* Allocate memory block */
-void ff_memfree (void* mblock);			/* Free memory block */
-#endif
 #endif
 
 /* Sync functions */

features/filesystem/fat/ChaN/ffconf.h

@@ -162,7 +162,7 @@
 
 
 #define	_MIN_SS		512
-#define	_MAX_SS		512
+#define	_MAX_SS		4096
 /* These options configure the range of sector size to be supported. (512, 1024,
 /  2048 or 4096) Always set both 512 for most systems, all type of memory cards and
 /  harddisk. But a larger value may be required for on-board flash memory and some
@@ -194,7 +194,7 @@
 / System Configurations
 /---------------------------------------------------------------------------*/
 
-#define	_FS_TINY	0
+#define	_FS_TINY	1
 /* This option switches tiny buffer configuration. (0:Normal or 1:Tiny)
 /  At the tiny configuration, size of the file object (FIL) is reduced _MAX_SS
 /  bytes. Instead of private sector buffer eliminated from the file object,
@@ -202,6 +202,14 @@
 /  data transfer. */
 
 
+#define _FS_HEAPBUF 1
+/* This option enables the use of the heap for allocating buffers. Otherwise
+/  _MAX_SS sized buffers are allocated statically in relevant structures (in
+/  FATFS if _FS_TINY, otherwise in FATFS and FIL)
+/  This option allows the filesystem to dynamically allocate the buffers based
+/  on underlying sector size. */
+
+
 #define _FS_NORTC	0
 #define _NORTC_MON	1
 #define _NORTC_MDAY	1

features/filesystem/fat/FATFileSystem.cpp

@@ -146,6 +146,16 @@ DWORD get_fattime(void)
            | (DWORD)(ptm->tm_sec/2    );
 }
 
+void *ff_memalloc(UINT size)
+{
+    return malloc(size);
+}
+
+void ff_memfree(void *p)
+{
+    free(p);
+}
+
 // Implementation of diskio functions (see ChaN/diskio.h)
 DSTATUS disk_status(BYTE pdrv)
 {