2.5 KiB
File System Interfaces
LVGL has a File system module to provide an abstraction layer for various file system drivers. You still need to provide the drivers and libraries, this extension provides only the bridge between FATFS, LittleFS, STDIO, POSIX, WIN32 and LVGL.
Built in wrappers
FATFS
Bridge for FatFS. FatFS itself is not part of LVGL, but can be added and initialized externally.
LittleFS
Though lv_fs_littlefs uses LittleFS API, the LittleFS library needs other external libraries that handle the mounting of partitions and low-level accesses, according to the given architecture. The functions for the latter are given to the lfs_t structure as pointers by an external low-level library.
There's a convenience function called lv_fs_littlefs_set_driver(LV_FS_LITTLEFS_LETTER, my_lfs), specific to lv_fs_littlefs, to attach a lfs_t object's pointer to a registered driver-letter. See its comments for more info.
esp_littlefs is a wrapper for LittleFS to be used in Espressif ESP-devices. It handles the mounting and has the low-level littlefs_api functions to read/write/erase blocks that LittleFS library needs. On mounting by esp_littlefs the lfs_t structures are created. You need to get a handle to these to use ESP with lv_fs_littlefs, as all functions use that lfs_t in LittleFS to identify the mounted partition.
In case you don't find a special function in the lv_fs_littlefs wrapper, you can look for it in the esp_littlefs API and use it directly, as lv_fs_littlefs and the esp_littlefs APIs can be used side-by-side.
STDIO
Bride to C standard functions on Linux and Windows. For example fopen, fread, etc.
POSIX
Bride to POSIX functions on Linux and Windows. For example open, read, etc.
WIN32
Bride to Win32 API function. For example CreateFileA, ReadFile, etc.
Usage
In lv_conf.h enable LV_USE_FS_... and assign an upper cased letter to LV_FS_..._LETTER (e.g. 'S').
After that you can access files using that driver letter. E.g. "S:path/to/file.txt".
The work directory can be set with LV_FS_..._PATH. E.g. "/home/joe/projects/" The actual file/directory paths will be appended to it.
Cached reading is also supported if LV_FS_..._CACHE_SIZE is set to not 0 value. lv_fs_read caches this size of data to lower the number of actual reads from the storage.