Mistake on this page?
Report an issue in GitHub or email us

FATFileSystem

FATFileSystem class hierarchy

The FAT file system is an established disk-oriented file system that you can find on Mbed OS, Windows, Linux and Mac OS X. Due to its age and popularity, the FAT file system has become the standard for portable storage, such as flash drivers and SD cards.

  • Portable - Due to its nearly universal support across operating systems, the FAT file system provides access to storage from both the embedded system and your PC.

  • Embedded - Built on the ChanFS project, the FAT file system is optimized for embedded systems.

For additional information, please see the storage overview page.

Use cases

The main reason to use the FAT file system is its usefulness on portable storage. Because of this, most applications using FAT in conjunction with an SD card.

The first step to using the FAT file system is formatting storage with FAT. You can do this on a PC with the native format command or on Mbed OS with the format function.

Note: The FAT file system requires at minimum 256 erase blocks. You can find the number of blocks on a block device by dividing the block device's size by its erase size.

The FAT file system supports external flash; however, it must allocate a full erase block for internal operations, which can become large for some forms of flash. If RAM consumption becomes a problem, we suggest switching to LittleFileSystem. The Mbed OS file system APIs make switching file systems a straightforward task. One common strategy is to use the FAT file system for debugging and switch to LittleFileSystem when the application becomes stable.

Usage

Instantiate the FATFileSystem class with a block device and file path.

The API that this presents is the standard Mbed OS file system API. Once declared, Mbed OS provides the retargeting layer for the standard C library.

You can swap the FAT file system in place with other Mbed OS file systems, which is a good method for prototyping applications.

FATFileSystem class reference

Public Member Functions
 FATFileSystem (const char *name=NULL, BlockDevice *bd=NULL)
virtual int mount (BlockDevice *bd)
virtual int unmount ()
virtual int reformat (BlockDevice *bd, int allocation_unit)
virtual int reformat (BlockDevice *bd=NULL)
virtual int remove (const char *path)
virtual int rename (const char *path, const char *newpath)
virtual int stat (const char *path, struct stat *st)
virtual int mkdir (const char *path, mode_t mode)
virtual int statvfs (const char *path, struct statvfs *buf)
 Public Member Functions inherited from mbed::FileSystem
 FileSystem (const char *name=NULL)
 Public Member Functions inherited from mbed::FileSystemLike
 FileSystemLike (const char *name=NULL)
FileHandleopen (const char *path, int flags)
DirHandleopendir (const char *path)
 Public Member Functions inherited from mbed::FileSystemHandle
virtual ~FileSystemHandle ()
 Public Member Functions inherited from mbed::FileBase
 FileBase (const char *name, PathType t)
const char * getName (void)
PathType getPathType (void)
Static Public Member Functions
static int format (BlockDevice *bd, bd_size_t cluster_size=0)
 Static Public Member Functions inherited from mbed::FileBase
static FileBaselookup (const char *name, unsigned int len)
static FileBaseget (int n)
Protected Member Functions
virtual int file_open (mbed::fs_file_t *file, const char *path, int flags)
virtual int file_close (mbed::fs_file_t file)
virtual ssize_t file_read (mbed::fs_file_t file, void *buffer, size_t len)
virtual ssize_t file_write (mbed::fs_file_t file, const void *buffer, size_t len)
virtual int file_sync (mbed::fs_file_t file)
virtual off_t file_seek (mbed::fs_file_t file, off_t offset, int whence)
virtual off_t file_tell (mbed::fs_file_t file)
virtual off_t file_size (mbed::fs_file_t file)
virtual int dir_open (mbed::fs_dir_t *dir, const char *path)
virtual int dir_close (mbed::fs_dir_t dir)
virtual ssize_t dir_read (mbed::fs_dir_t dir, struct dirent *ent)
virtual void dir_seek (mbed::fs_dir_t dir, off_t offset)
virtual off_t dir_tell (mbed::fs_dir_t dir)
virtual void dir_rewind (mbed::fs_dir_t dir)
virtual void lock ()
virtual void unlock ()
virtual int mount (BlockDevice *bd, bool mount)
 Protected Member Functions inherited from mbed::FileSystem
virtual int file_isatty (fs_file_t file)
virtual void file_rewind (fs_file_t file)
virtual size_t dir_size (fs_dir_t dir)
virtual int open (FileHandle **file, const char *path, int flags)
virtual int open (DirHandle **dir, const char *path)

FATFileSystem example

/* mbed Microcontroller Library
 * Copyright (c) 2006-2013 ARM Limited
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#include "mbed.h"
#include <stdio.h>
#include <errno.h>

// Block devices
#include "SPIFBlockDevice.h"
#include "DataFlashBlockDevice.h"
#include "SDBlockDevice.h"
#include "HeapBlockDevice.h"

// File systems
#include "LittleFileSystem.h"
#include "FATFileSystem.h"


// Physical block device, can be any device that supports the BlockDevice API
SPIFBlockDevice bd(
        MBED_CONF_SPIF_DRIVER_SPI_MOSI,
        MBED_CONF_SPIF_DRIVER_SPI_MISO,
        MBED_CONF_SPIF_DRIVER_SPI_CLK,
        MBED_CONF_SPIF_DRIVER_SPI_CS);

// File system declaration
LittleFileSystem fs("fs");


// Set up the button to trigger an erase
InterruptIn irq(BUTTON1);
void erase() {
    printf("Initializing the block device... ");
    fflush(stdout);
    int err = bd.init();
    printf("%s\n", (err ? "Fail :(" : "OK"));
    if (err) {
        error("error: %s (%d)\n", strerror(-err), err);
    }

    printf("Erasing the block device... ");
    fflush(stdout);
    err = bd.erase(0, bd.size());
    printf("%s\n", (err ? "Fail :(" : "OK"));
    if (err) {
        error("error: %s (%d)\n", strerror(-err), err);
    }

    printf("Deinitializing the block device... ");
    fflush(stdout);
    err = bd.deinit();
    printf("%s\n", (err ? "Fail :(" : "OK"));
    if (err) {
        error("error: %s (%d)\n", strerror(-err), err);
    }
}


// Entry point for the example
int main() {
    printf("--- Mbed OS filesystem example ---\n");

    // Setup the erase event on button press, use the event queue
    // to avoid running in interrupt context
    irq.fall(mbed_event_queue()->event(erase));

    // Try to mount the filesystem
    printf("Mounting the filesystem... ");
    fflush(stdout);
    int err = fs.mount(&bd);
    printf("%s\n", (err ? "Fail :(" : "OK"));
    if (err) {
        // Reformat if we can't mount the filesystem
        // this should only happen on the first boot
        printf("No filesystem found, formatting... ");
        fflush(stdout);
        err = fs.reformat(&bd);
        printf("%s\n", (err ? "Fail :(" : "OK"));
        if (err) {
            error("error: %s (%d)\n", strerror(-err), err);
        }
    }

    // Open the numbers file
    printf("Opening \"/fs/numbers.txt\"... ");
    fflush(stdout);
    FILE *f = fopen("/fs/numbers.txt", "r+");
    printf("%s\n", (!f ? "Fail :(" : "OK"));
    if (!f) {
        // Create the numbers file if it doesn't exist
        printf("No file found, creating a new file... ");
        fflush(stdout);
        f = fopen("/fs/numbers.txt", "w+");
        printf("%s\n", (!f ? "Fail :(" : "OK"));
        if (!f) {
            error("error: %s (%d)\n", strerror(errno), -errno);
        }

        for (int i = 0; i < 10; i++) {
            printf("\rWriting numbers (%d/%d)... ", i, 10);
            fflush(stdout);
            err = fprintf(f, "    %d\n", i);
            if (err < 0) {
                printf("Fail :(\n");
                error("error: %s (%d)\n", strerror(errno), -errno);
            }
        }
        printf("\rWriting numbers (%d/%d)... OK\n", 10, 10);

        printf("Seeking file... ");
        fflush(stdout);
        err = fseek(f, 0, SEEK_SET);
        printf("%s\n", (err < 0 ? "Fail :(" : "OK"));
        if (err < 0) {
            error("error: %s (%d)\n", strerror(errno), -errno);
        }
    }

    // Go through and increment the numbers
    for (int i = 0; i < 10; i++) {
        printf("\rIncrementing numbers (%d/%d)... ", i, 10);
        fflush(stdout);

        // Get current stream position
        long pos = ftell(f);

        // Parse out the number and increment
        int32_t number;
        fscanf(f, "%d", &number);
        number += 1;

        // Seek to beginning of number
        fseek(f, pos, SEEK_SET);
    
        // Store number
        fprintf(f, "    %d\n", number);

        // Flush between write and read on same file
        fflush(f);
    }
    printf("\rIncrementing numbers (%d/%d)... OK\n", 10, 10);

    // Close the file which also flushes any cached writes
    printf("Closing \"/fs/numbers.txt\"... ");
    fflush(stdout);
    err = fclose(f);
    printf("%s\n", (err < 0 ? "Fail :(" : "OK"));
    if (err < 0) {
        error("error: %s (%d)\n", strerror(errno), -errno);
    }
    
    // Display the root directory
    printf("Opening the root directory... ");
    fflush(stdout);
    DIR *d = opendir("/fs/");
    printf("%s\n", (!d ? "Fail :(" : "OK"));
    if (!d) {
        error("error: %s (%d)\n", strerror(errno), -errno);
    }

    printf("root directory:\n");
    while (true) {
        struct dirent *e = readdir(d);
        if (!e) {
            break;
        }

        printf("    %s\n", e->d_name);
    }

    printf("Closing the root directory... ");
    fflush(stdout);
    err = closedir(d);
    printf("%s\n", (err < 0 ? "Fail :(" : "OK"));
    if (err < 0) {
        error("error: %s (%d)\n", strerror(errno), -errno);
    }

    // Display the numbers file
    printf("Opening \"/fs/numbers.txt\"... ");
    fflush(stdout);
    f = fopen("/fs/numbers.txt", "r");
    printf("%s\n", (!f ? "Fail :(" : "OK"));
    if (!f) {
        error("error: %s (%d)\n", strerror(errno), -errno);
    }

    printf("numbers:\n");
    while (!feof(f)) {
        int c = fgetc(f);
        printf("%c", c);
    }

    printf("\rClosing \"/fs/numbers.txt\"... ");
    fflush(stdout);
    err = fclose(f);
    printf("%s\n", (err < 0 ? "Fail :(" : "OK"));
    if (err < 0) {
        error("error: %s (%d)\n", strerror(errno), -errno);
    }

    // Tidy up
    printf("Unmounting... ");
    fflush(stdout);
    err = fs.unmount();
    printf("%s\n", (err < 0 ? "Fail :(" : "OK"));
    if (err < 0) {
        error("error: %s (%d)\n", strerror(-err), err);
    }
        
    printf("Mbed OS filesystem example done!\n");
}


Important Information for this Arm website

This site uses cookies to store information on your computer. By continuing to use our site, you consent to our cookies. If you are not happy with the use of these cookies, please review our Cookie Policy to learn how they can be disabled. By disabling cookies, some features of the site will not work.