File system¶

LVGL has a 'File system' abstraction module that enables you to attach any type of file system. A file system is identified by an assigned drive letter. For example, if an SD card is associated with the letter 'S', a file can be reached using "S:path/to/file.txt".

Ready to use drivers¶

The lv_fs_if repository contains prepared drivers using POSIX, standard C and the FATFS API. See its README for the details.

Adding a driver¶

Registering a driver¶

To add a driver, a lv_fs_drv_t needs to be initialized like below. The lv_fs_drv_t needs to be static, global or dynamically allocated and not a local variable.

static lv_fs_drv_t drv;                   /*Needs to be static or global*/
lv_fs_drv_init(&drv);                     /*Basic initialization*/

drv.letter = 'S';                         /*An uppercase letter to identify the drive */
drv.cache_size = my_cahce_size;           /*Cache size for reading in bytes. 0 to not cache.*/

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.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.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 operation is not supported.

Implementing the callbacks¶

Open callback¶

The prototype of open_cb looks like this:

void * (*open_cb)(lv_fs_drv_t * drv, const char * path, lv_fs_mode_t mode);

path is the path after the drive letter (e.g. "S:path/to/file.txt" -> "path/to/file.txt"). mode can be LV_FS_MODE_WR or LV_FS_MODE_RD to open for writes or reads.

The return value is a pointer to a file object that describes the opened file or NULL if there were any issues (e.g. the file wasn't found). The returned file object will be passed to other file system related callbacks. (see below)

Other callbacks¶

The other callbacks are quite similar. For example write_cb looks like this:

lv_fs_res_t (*write_cb)(lv_fs_drv_t * drv, void * file_p, const void * buf, uint32_t btw, uint32_t * bw);

For file_p, LVGL passes the return value of open_cb, buf is the data to write, btw is the Bytes To Write, bw is the actually written bytes.

For a template of these callbacks see lv_fs_template.c.

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 writes only 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 directories in the result but it can be a good practice to insert a '/' in front of each 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 drives for images¶

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

To use files in image widgets 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 file system module.

Values:

enumerator LV_FS_RES_OK¶

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]¶

File open mode.

Values:

enumerator LV_FS_MODE_WR¶

enumerator LV_FS_MODE_RD¶

enum lv_fs_whence_t¶

Seek modes.

Values:

enumerator LV_FS_SEEK_SET¶: Set the position from absolutely (from the start of file)

enumerator LV_FS_SEEK_CUR¶: Set the position from the current position

enumerator LV_FS_SEEK_END¶: Set the position from the end of the file

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)¶

Add a new drive

Parameters: drv -- pointer to an lv_fs_drv_t structure which is inited with the corresponding function pointers. Only pointer is saved, so the driver should be static or dynamically allocated.

lv_fs_drv_t *lv_fs_get_drv(char letter)¶

Give a pointer to a driver from its letter

Parameters: letter -- the driver letter
Returns: pointer to a driver or NULL if not found

bool lv_fs_is_ready(char letter)¶

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

Parameters: letter -- letter of the drive
Returns: true: drive is ready; false: drive is not ready

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

Open a file

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

Returns

LV_FS_RES_OK or any error from lv_fs_res_t enum

lv_fs_res_t lv_fs_close(lv_fs_file_t *file_p)¶

Close an already opened file

Parameters: file_p -- pointer to a lv_fs_file_t variable
Returns: LV_FS_RES_OK or any error from lv_fs_res_t enum

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

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.

Returns

LV_FS_RES_OK or any error from lv_fs_res_t enum

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

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.

Returns

LV_FS_RES_OK or any error from lv_fs_res_t enum

lv_fs_res_t lv_fs_seek(lv_fs_file_t *file_p, uint32_t pos, lv_fs_whence_t whence)¶

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

Parameters

file_p -- pointer to a lv_fs_file_t variable
pos -- the new position expressed in bytes index (0: start of file)
whence -- tells from where set the position. See @lv_fs_whence_t

Returns

LV_FS_RES_OK or any error from lv_fs_res_t enum

lv_fs_res_t lv_fs_tell(lv_fs_file_t *file_p, uint32_t *pos)¶

Give the position of the read write pointer

Parameters

file_p -- pointer to a lv_fs_file_t variable
pos_p -- pointer to store the position of the read write pointer

Returns

LV_FS_RES_OK or any error from 'fs_res_t'

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

Parameters

rddir_p -- pointer to a 'lv_fs_dir_t' variable
path -- path to a directory

Returns

LV_FS_RES_OK or any error from lv_fs_res_t enum

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 '/'

Parameters

rddir_p -- pointer to an initialized 'fs_dir_t' variable
fn -- pointer to a buffer to store the filename

Returns

LV_FS_RES_OK or any error from lv_fs_res_t enum

lv_fs_res_t lv_fs_dir_close(lv_fs_dir_t *rddir_p)¶

Close the directory reading

Parameters: rddir_p -- pointer to an initialized 'fs_dir_t' variable
Returns: LV_FS_RES_OK or any error from lv_fs_res_t enum

char *lv_fs_get_letters(char *buf)¶

Fill a buffer with the letters of existing drivers

Parameters: buf -- buffer to store the letters ('\0' added after the last letter)
Returns: the buffer

const char *lv_fs_get_ext(const char *fn)¶

Return with the extension of the filename

Parameters: fn -- string with a filename
Returns: pointer to the beginning extension or empty string if no extension

char *lv_fs_up(char *path)¶

Step up one level

Parameters: path -- pointer to a file name
Returns: the truncated file name

const char *lv_fs_get_last(const char *path)¶

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

Parameters: path -- pointer to a file name
Returns: pointer to the beginning of the last element in the path

struct _lv_fs_drv_t¶

Public Members

char letter¶

uint16_t cache_size¶

bool (*ready_cb)(struct _lv_fs_drv_t *drv)¶

void *(*open_cb)(struct _lv_fs_drv_t *drv, 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 (*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_whence_t whence)¶

lv_fs_res_t (*tell_cb)(struct _lv_fs_drv_t *drv, void *file_p, uint32_t *pos_p)¶

void *(*dir_open_cb)(struct _lv_fs_drv_t *drv, 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)¶

void *user_data¶: Custom file user data

struct lv_fs_file_cache_t¶

Public Members

uint32_t start¶

uint32_t end¶

uint32_t file_position¶

void *buffer¶

struct lv_fs_file_t¶

Public Members

void *file_d¶

lv_fs_drv_t *drv¶

lv_fs_file_cache_t *cache¶

struct lv_fs_dir_t¶

Public Members

void *dir_d¶

lv_fs_drv_t *drv¶