Fatfs

fatfs - FAT16 or FAT32 Support

This is a special implementation of FAT16/32 file system support. While it
can be tested in a non-AVR environment, it is designed to be RAM frugal
enough to run on systems with 1K RAM, or larger. Because it is designed
to operate with a maximum of one disk sector buffer, it is not efficient
by design.

The user supplies his own disk I/O routines so that the library is
completely independent of the physical disk implementation. The fatfs
package was however, designed with SD/MMC card support in mind.

Additionally, the user may call File System date/time routines to update
the file system's concept of date and time. In this manner, fatfs is
decoupled from the host's concept of date and time.

Unsupported Features

• FAT 12
• Sector sizes other than 512 bytes
• Long file names

FAT Support

The fatfs package supports the maintenance of up to 4 FAT tables. Only the first
FAT is ever searched, though all parallel FAT tables are updated if there are
changes. However, for SD/MMC card use, you may wish to format for just one FAT table,
for greater efficiency.

Facilities

• Directory read/search/create and delete operations
• Sector Read/Write operations
• Text Line Read/Write operations
• Binary String Read/Write operations
• Directory path operations

Data Types

Most of the underlying data types come from Interfaces:

• Unsigned_8
• Unsigned_16
• Unsigned_32

Arrays of these types are defined in fatfs as:

type U8_Array is array(Unsigned_16 range <>) of Unsigned_8;
type U16_Array is array(Unsigned_16 range <>) of Unsigned_16;
type U32_Array is array(Unsigned_16 range <>) of Unsigned_32;

Type Block_512

For Convenience, there is also a Sector Buffer type defined as follows:

type Block_Type is array(Unsigned_16 range <>) of Unsigned_8;
for Block_Type'Component_Size use 8;
for Block_Type'Alignment use 4;

subtype Block_512 is Block_Type(0..511);

It is recommended that you use type Block_512 wherever a sector buffer is required.

Type FS_Type

The enumerated type FS_Type indicates the type of FAT file system support is involved:

type FS_Type is (
   FS_FAT12,                       -- FAT12 (unsupported)
   FS_FAT16,                       -- FAT16
   FS_FAT32,                       -- FAT32
   FS_Unknown                      -- Unknown or bad media
);

Only FAT16 and FAT32 are currently supported. FAT12 involves FAT entries that span sector boundaries, which would have bloated the suppport code. Since FAT12 is intended for small file systems, the decision was made not to support it.

Misc. Types

type FAT_Copies_Type is new Unsigned_8;      -- # of FAT tables
type Sector_Type is new Unsigned_32;         -- Disk sector #
type Cluster_Type is new Sector_Type;        -- Cluster #

type Year_Type is mod 2**7;         -- Year in directory entry (minus 1980)
type Month_Type is mod 2**4;        -- Month in directory entry
type Day_Type is mod 2**5;          -- Day in directory entry
type Hour_Type is mod 2**5;         -- Hour in directory entry
type Minute_Type is mod 2**6;       -- Minute in directory entry
type Seconds2_Type is mod 2**5;     -- Seconds / 2 in directory entry

Boot Sector

type Boot_Sector_Type is record
Jump :                  Bytes(0..2);        -- 0-2 :    Jump to bootstrap
OEM_Name :              String(3..10);      -- 3-10 :   OEM name/version (E.g. "IBM  3.3", "IBM 20.0", "MSDOS5.0")
Bytes_Per_Sector :      Unsigned_16;        -- 11-12 :  Bytes per sector (512 for FAT12)
Sectors_Per_Cluster :   Unsigned_8;         -- 13 :     1, 2, 3, 8, 16, 32, 64, 128
Reserved_Sectors :      Unsigned_16;        -- 14-15 :  For FAT 12/16 = 1, FAT32 = 32
FAT_Copies :            FAT_Copies_Type;    -- 16 :     2
Root_Dir_Entries :      Unsigned_16;        -- 17-18 :  FAT12=224, FAT32=0, 512 recommended for FAT16
Total_Sectors_in_FS :   Unsigned_16;        -- 19-20 :  2880 when not FAT32 and < 32MB
Media_Descriptor :      Unsigned_8;         -- 21 :     F0 = 1.44MB floppy, F8 = HD
Sectors_Per_FAT :       Unsigned_16;        -- 22-23 :  9, FAT32 = 0
Sectors_Per_Track :     Unsigned_16;        -- 24-25 :  12
No_Of_Heads :           Unsigned_16;        -- 26-27 :  2 for double sided diskette
Hidden_Sectors_32 :     Unsigned_32;        -- 28-31 :  FAT32
Total_Sectors_32 :      Unsigned_32;        -- 32-35 :  FAT32
Sectors_Per_FAT_32 :    Unsigned_32;        -- 36-39 :  FAT32
Mirror_Flags :          Unsigned_16;        -- 40-41 :  FAT32
FS_Version_Major :      Unsigned_8;         -- 42-42 :  FAT32
FS_Version_Minor :      Unsigned_8;         -- 43-43 :  FAT32
Root_Dir_First_Cluster: Unsigned_32;        -- 44-47 :  FAT32
FS_Info_Sector :        Unsigned_16;        -- 48-49 :  FAT32
Backup_Boot_Sector :    Unsigned_16;        -- 50-51 :  FAT32
Reserved :              Bytes(52..63);      -- 52-63 :  FAT32
Bootstrap_Code :        Bytes(64..509);
Signature :             Bytes(0..1);        -- 510-511: 55 AA
end record;

for Boot_Sector_Type'Alignment use 4;

Directory Entry Type

type Dir_Entry_Type is record
Filename :      String(1..8);
Extension :     String(1..3);
Reserved_7 :    Boolean;
Reserved_6 :    Boolean;
Archive :       Boolean;
Subdirectory :  Boolean;
Volume_Name :   Boolean;
System_File :   Boolean;
Hidden_File :   Boolean;
Read_Only :     Boolean;
Reserved :      String(1..8);
Cluster_High :  Unsigned_16;        -- FAT32 only
Hour :          Hour_Type;
Minute :        Minute_Type;
Second2 :       Seconds2_Type;
Year :          Year_Type;
Month :         Month_Type;
Day :           Day_Type;
First_Cluster : Unsigned_16;
File_Size :     Unsigned_32;
end record;

File System API

• [FATFS_File_System ]
• [FATFS_Directory ]
• [FATFS_Sector_IO ]
• [FATFS_Text_IO ]
• [FATFS_Binary_IO ]
• [FATFS_Pathname ]