File system

LittlevGL has a ‘File system’ abstraction module that enables you to attach any type of file systems. The file system is identified by a drive letter. For example, if the SD card is associated with the letter 'S', a file can be reached like "S:path/to/file.txt".

Add a driver

To add a driver, lv_fs_drv_t needs to be initialized like this:

lv_fs_drv_t drv;
lv_fs_drv_init(&drv);                     /*Basic initialization*/

drv.letter = 'S';                         /*An uppercase letter to identify the drive */
drv.file_size = sizeof(my_file_object);   /*Size required to store a file object*/
drv.rddir_size = sizeof(my_dir_object);   /*Size required to store a directory object (used by dir_open/close/read)*/
drv.ready_cb = my_ready_cb;               /*Callback to tell if the drive is ready to use */
drv.open_cb = my_open_cb;                 /*Callback to open a file */
drv.close_cb = my_close_cb;               /*Callback to close a file */
drv.read_cb = my_read_cb;                 /*Callback to read a file */
drv.write_cb = my_write_cb;               /*Callback to write a file */
drv.seek_cb = my_seek_cb;                 /*Callback to seek in a file (Move cursor) */
drv.tell_cb = my_tell_cb;                 /*Callback to tell the cursor position  */
drv.trunc_cb = my_trunc_cb;               /*Callback to delete a file */
drv.size_cb = my_size_cb;                 /*Callback to tell a file's size */
drv.rename_cb = my_size_cb;               /*Callback to rename a file */

drv.dir_open_cb = my_dir_open_cb;         /*Callback to open directory to read its content */
drv.dir_read_cb = my_dir_read_cb;         /*Callback to read a directory's content */
drv.dir_close_cb = my_dir_close_cb;       /*Callback to close a directory */

drv.free_space_cb = my_size_cb;           /*Callback to tell free space on the drive */

drv.user_data = my_user_data;             /*Any custom data if required*/

lv_fs_drv_register(&drv);                 /*Finally register the drive*/

Any of the callbacks can be NULL to indicate that that operation is not supported.

As an example of how the callbacks are used, if you use lv_fs_open(&file, "S:/folder/file.txt", LV_FS_MODE_WR), LittlevGL:

  1. Verifies that a registered drive exists with the letter 'S'.

  2. Checks if it’s open_cb is implemented (not NULL).

  3. Calls the set open_cb with "folder/file.txt" path.

Usage example

The example below shows how to read from a file:

lv_fs_file_t f;
lv_fs_res_t res;
res = lv_fs_open(&f, "S:folder/file.txt", LV_FS_MODE_RD);
if(res != LV_FS_RES_OK) my_error_handling();

uint32_t read_num;
uint8_t buf[8];
res = lv_fs_read(&f, buf, 8, &read_num);
if(res != LV_FS_RES_OK || read_num != 8) my_error_handling();

lv_fs_close(&f);

The mode in lv_fs_open can be LV_FS_MODE_WR to open for write or LV_FS_MODE_RD | LV_FS_MODE_WR for both

This example shows how to read a directory’s content. It’s up to the driver how to mark the directories, but it can be a good practice to insert a '/' in front of the directory name.

lv_fs_dir_t dir;
lv_fs_res_t res;
res = lv_fs_dir_open(&dir, "S:/folder");
if(res != LV_FS_RES_OK) my_error_handling();

char fn[256];
while(1) {
    res = lv_fs_dir_read(&dir, fn);
    if(res != LV_FS_RES_OK) {
        my_error_handling();
        break;
    }

    /*fn is empty, if not more files to read*/
    if(strlen(fn) == 0) {
        break;
    }

    printf("%s\n", fn);
}

lv_fs_dir_close(&dir);

Use drivers for images

Image objects can be opened from files too (besides variables stored in the flash).

To initialize the image, the following callbacks are required:

  • open

  • close

  • read

  • seek

  • tell

API

Typedefs

typedef uint8_t lv_fs_res_t
typedef uint8_t lv_fs_mode_t
typedef struct _lv_fs_drv_t lv_fs_drv_t

Enums

enum [anonymous]

Errors in the filesystem module.

Values:

enumerator LV_FS_RES_OK = 0
enumerator LV_FS_RES_HW_ERR
enumerator LV_FS_RES_FS_ERR
enumerator LV_FS_RES_NOT_EX
enumerator LV_FS_RES_FULL
enumerator LV_FS_RES_LOCKED
enumerator LV_FS_RES_DENIED
enumerator LV_FS_RES_BUSY
enumerator LV_FS_RES_TOUT
enumerator LV_FS_RES_NOT_IMP
enumerator LV_FS_RES_OUT_OF_MEM
enumerator LV_FS_RES_INV_PARAM
enumerator LV_FS_RES_UNKNOWN
enum [anonymous]

Filesystem mode.

Values:

enumerator LV_FS_MODE_WR = 0x01
enumerator LV_FS_MODE_RD = 0x02

Functions

void lv_fs_init(void)

Initialize the File system interface

void lv_fs_drv_init(lv_fs_drv_t *drv)

Initialize a file system driver with default values. It is used to surly have known values in the fields ant not memory junk. After it you can set the fields.

Parameters

  • drv: pointer to driver variable to initialize

void lv_fs_drv_register(lv_fs_drv_t *drv_p)

Add a new drive

Parameters

  • drv_p: pointer to an lv_fs_drv_t structure which is inited with the corresponding function pointers. The data will be copied so the variable can be local.

lv_fs_drv_t *lv_fs_get_drv(char letter)

Give a pointer to a driver from its letter

Return

pointer to a driver or NULL if not found

Parameters

  • letter: the driver letter

bool lv_fs_is_ready(char letter)

Test if a drive is rady or not. If the ready function was not initialized true will be returned.

Return

true: drive is ready; false: drive is not ready

Parameters

  • letter: letter of the drive

lv_fs_res_t lv_fs_open(lv_fs_file_t *file_p, const char *path, lv_fs_mode_t mode)

Open a file

Return

LV_FS_RES_OK or any error from lv_fs_res_t enum

Parameters

  • file_p: pointer to a lv_fs_file_t variable

  • path: path to the file beginning with the driver letter (e.g. S:/folder/file.txt)

  • mode: read: FS_MODE_RD, write: FS_MODE_WR, both: FS_MODE_RD | FS_MODE_WR

lv_fs_res_t lv_fs_close(lv_fs_file_t *file_p)

Close an already opened file

Return

LV_FS_RES_OK or any error from lv_fs_res_t enum

Parameters

lv_fs_res_t lv_fs_remove(const char *path)

Delete a file

Return

LV_FS_RES_OK or any error from lv_fs_res_t enum

Parameters

  • path: path of the file to delete

lv_fs_res_t lv_fs_read(lv_fs_file_t *file_p, void *buf, uint32_t btr, uint32_t *br)

Read from a file

Return

LV_FS_RES_OK or any error from lv_fs_res_t enum

Parameters

  • file_p: pointer to a lv_fs_file_t variable

  • buf: pointer to a buffer where the read bytes are stored

  • btr: Bytes To Read

  • br: the number of real read bytes (Bytes Read). NULL if unused.

lv_fs_res_t lv_fs_write(lv_fs_file_t *file_p, const void *buf, uint32_t btw, uint32_t *bw)

Write into a file

Return

LV_FS_RES_OK or any error from lv_fs_res_t enum

Parameters

  • file_p: pointer to a lv_fs_file_t variable

  • buf: pointer to a buffer with the bytes to write

  • btr: Bytes To Write

  • br: the number of real written bytes (Bytes Written). NULL if unused.

lv_fs_res_t lv_fs_seek(lv_fs_file_t *file_p, uint32_t pos)

Set the position of the ‘cursor’ (read write pointer) in a file

Return

LV_FS_RES_OK or any error from lv_fs_res_t enum

Parameters

  • file_p: pointer to a lv_fs_file_t variable

  • pos: the new position expressed in bytes index (0: start of file)

lv_fs_res_t lv_fs_tell(lv_fs_file_t *file_p, uint32_t *pos)

Give the position of the read write pointer

Return

LV_FS_RES_OK or any error from ‘fs_res_t’

Parameters

  • file_p: pointer to a lv_fs_file_t variable

  • pos_p: pointer to store the position of the read write pointer

lv_fs_res_t lv_fs_trunc(lv_fs_file_t *file_p)

Truncate the file size to the current position of the read write pointer

Return

LV_FS_RES_OK: no error, the file is read any error from lv_fs_res_t enum

Parameters

  • file_p: pointer to an ‘ufs_file_t’ variable. (opened with lv_fs_open )

lv_fs_res_t lv_fs_size(lv_fs_file_t *file_p, uint32_t *size)

Give the size of a file bytes

Return

LV_FS_RES_OK or any error from lv_fs_res_t enum

Parameters

  • file_p: pointer to a lv_fs_file_t variable

  • size: pointer to a variable to store the size

lv_fs_res_t lv_fs_rename(const char *oldname, const char *newname)

Rename a file

Return

LV_FS_RES_OK or any error from ‘fs_res_t’

Parameters

  • oldname: path to the file

  • newname: path with the new name

lv_fs_res_t lv_fs_dir_open(lv_fs_dir_t *rddir_p, const char *path)

Initialize a ‘fs_dir_t’ variable for directory reading

Return

LV_FS_RES_OK or any error from lv_fs_res_t enum

Parameters

  • rddir_p: pointer to a ‘fs_read_dir_t’ variable

  • path: path to a directory

lv_fs_res_t lv_fs_dir_read(lv_fs_dir_t *rddir_p, char *fn)

Read the next filename form a directory. The name of the directories will begin with ‘/’

Return

LV_FS_RES_OK or any error from lv_fs_res_t enum

Parameters

  • rddir_p: pointer to an initialized ‘fs_rdir_t’ variable

  • fn: pointer to a buffer to store the filename

lv_fs_res_t lv_fs_dir_close(lv_fs_dir_t *rddir_p)

Close the directory reading

Return

LV_FS_RES_OK or any error from lv_fs_res_t enum

Parameters

  • rddir_p: pointer to an initialized ‘fs_dir_t’ variable

lv_fs_res_t lv_fs_free_space(char letter, uint32_t *total_p, uint32_t *free_p)

Get the free and total size of a driver in kB

Return

LV_FS_RES_OK or any error from lv_fs_res_t enum

Parameters

  • letter: the driver letter

  • total_p: pointer to store the total size [kB]

  • free_p: pointer to store the free size [kB]

char *lv_fs_get_letters(char *buf)

Fill a buffer with the letters of existing drivers

Return

the buffer

Parameters

  • buf: buffer to store the letters (‘\0’ added after the last letter)

const char *lv_fs_get_ext(const char *fn)

Return with the extension of the filename

Return

pointer to the beginning extension or empty string if no extension

Parameters

  • fn: string with a filename

char *lv_fs_up(char *path)

Step up one level

Return

the truncated file name

Parameters

  • path: pointer to a file name

const char *lv_fs_get_last(const char *path)

Get the last element of a path (e.g. U:/folder/file -> file)

Return

pointer to the beginning of the last element in the path

Parameters

  • buf: buffer to store the letters (‘\0’ added after the last letter)

struct _lv_fs_drv_t

Public Members

char letter
uint16_t file_size
uint16_t rddir_size
bool (*ready_cb)(struct _lv_fs_drv_t *drv)
lv_fs_res_t (*open_cb)(struct _lv_fs_drv_t *drv, void *file_p, const char *path, lv_fs_mode_t mode)
lv_fs_res_t (*close_cb)(struct _lv_fs_drv_t *drv, void *file_p)
lv_fs_res_t (*remove_cb)(struct _lv_fs_drv_t *drv, const char *fn)
lv_fs_res_t (*read_cb)(struct _lv_fs_drv_t *drv, void *file_p, void *buf, uint32_t btr, uint32_t *br)
lv_fs_res_t (*write_cb)(struct _lv_fs_drv_t *drv, void *file_p, const void *buf, uint32_t btw, uint32_t *bw)
lv_fs_res_t (*seek_cb)(struct _lv_fs_drv_t *drv, void *file_p, uint32_t pos)
lv_fs_res_t (*tell_cb)(struct _lv_fs_drv_t *drv, void *file_p, uint32_t *pos_p)
lv_fs_res_t (*trunc_cb)(struct _lv_fs_drv_t *drv, void *file_p)
lv_fs_res_t (*size_cb)(struct _lv_fs_drv_t *drv, void *file_p, uint32_t *size_p)
lv_fs_res_t (*rename_cb)(struct _lv_fs_drv_t *drv, const char *oldname, const char *newname)
lv_fs_res_t (*free_space_cb)(struct _lv_fs_drv_t *drv, uint32_t *total_p, uint32_t *free_p)
lv_fs_res_t (*dir_open_cb)(struct _lv_fs_drv_t *drv, void *rddir_p, const char *path)
lv_fs_res_t (*dir_read_cb)(struct _lv_fs_drv_t *drv, void *rddir_p, char *fn)
lv_fs_res_t (*dir_close_cb)(struct _lv_fs_drv_t *drv, void *rddir_p)
lv_fs_drv_user_data_t user_data

Custom file user data

struct lv_fs_file_t

Public Members

void *file_d
lv_fs_drv_t *drv
struct lv_fs_dir_t

Public Members

void *dir_d
lv_fs_drv_t *drv