132 lines
4.6 KiB
Markdown
132 lines
4.6 KiB
Markdown
# File system
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LVGL has a 'File system' abstraction module that enables you to attach any type of file system.
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A file system is identified by an assigned drive letter.
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For example, if an SD card is associated with the letter `'S'`, a file can be reached using `"S:path/to/file.txt"`.
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## Ready to use drivers
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The [lv_fs_if](https://github.com/lvgl/lv_fs_if) repository contains prepared drivers using POSIX, standard C and the [FATFS](http://elm-chan.org/fsw/ff/00index_e.html) API.
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See its [README](https://github.com/lvgl/lv_fs_if#readme) for the details.
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## Adding a driver
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### Registering a driver
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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.
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```c
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static lv_fs_drv_t drv; /*Needs to be static or global*/
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lv_fs_drv_init(&drv); /*Basic initialization*/
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drv.letter = 'S'; /*An uppercase letter to identify the drive */
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drv.cache_size = my_cache_size; /*Cache size for reading in bytes. 0 to not cache.*/
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drv.ready_cb = my_ready_cb; /*Callback to tell if the drive is ready to use */
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drv.open_cb = my_open_cb; /*Callback to open a file */
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drv.close_cb = my_close_cb; /*Callback to close a file */
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drv.read_cb = my_read_cb; /*Callback to read a file */
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drv.write_cb = my_write_cb; /*Callback to write a file */
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drv.seek_cb = my_seek_cb; /*Callback to seek in a file (Move cursor) */
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drv.tell_cb = my_tell_cb; /*Callback to tell the cursor position */
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drv.dir_open_cb = my_dir_open_cb; /*Callback to open directory to read its content */
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drv.dir_read_cb = my_dir_read_cb; /*Callback to read a directory's content */
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drv.dir_close_cb = my_dir_close_cb; /*Callback to close a directory */
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drv.user_data = my_user_data; /*Any custom data if required*/
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lv_fs_drv_register(&drv); /*Finally register the drive*/
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```
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Any of the callbacks can be `NULL` to indicate that operation is not supported.
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### Implementing the callbacks
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#### Open callback
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The prototype of `open_cb` looks like this:
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```c
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void * (*open_cb)(lv_fs_drv_t * drv, const char * path, lv_fs_mode_t mode);
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```
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`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.
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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).
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The returned file object will be passed to other file system related callbacks. (see below)
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### Other callbacks
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The other callbacks are quite similar. For example `write_cb` looks like this:
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```c
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lv_fs_res_t (*write_cb)(lv_fs_drv_t * drv, void * file_p, const void * buf, uint32_t btw, uint32_t * bw);
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```
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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.
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For a template of these callbacks see [lv_fs_template.c](https://github.com/lvgl/lvgl/blob/master/examples/porting/lv_port_fs_template.c).
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## Usage example
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The example below shows how to read from a file:
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```c
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lv_fs_file_t f;
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lv_fs_res_t res;
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res = lv_fs_open(&f, "S:folder/file.txt", LV_FS_MODE_RD);
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if(res != LV_FS_RES_OK) my_error_handling();
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uint32_t read_num;
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uint8_t buf[8];
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res = lv_fs_read(&f, buf, 8, &read_num);
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if(res != LV_FS_RES_OK || read_num != 8) my_error_handling();
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lv_fs_close(&f);
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```
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*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*
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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.
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```c
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lv_fs_dir_t dir;
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lv_fs_res_t res;
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res = lv_fs_dir_open(&dir, "S:/folder");
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if(res != LV_FS_RES_OK) my_error_handling();
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char fn[256];
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while(1) {
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res = lv_fs_dir_read(&dir, fn);
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if(res != LV_FS_RES_OK) {
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my_error_handling();
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break;
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}
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/*fn is empty, if not more files to read*/
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if(strlen(fn) == 0) {
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break;
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}
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printf("%s\n", fn);
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}
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lv_fs_dir_close(&dir);
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```
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## Use drives for images
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[Image](/widgets/core/img) objects can be opened from files too (besides variables stored in the compiled program).
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To use files in image widgets the following callbacks are required:
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- open
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- close
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- read
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- seek
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- tell
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## API
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```eval_rst
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.. doxygenfile:: lv_fs.h
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:project: lvgl
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```
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