1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
|
.. _overview_file_system:
===========
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
********************
LVGL contains prepared drivers for the API of POSIX, standard C,
Windows, and `FATFS <http://elm-chan.org/fsw/ff/00index_e.html>`__.
Learn more :ref:`here <libs_filesystem>`.
Adding a driver
***************
Registering a driver
--------------------
To add a driver, a :cpp:type:`lv_fs_drv_t` needs to be initialized like below.
The :cpp:type:`lv_fs_drv_t` needs to be static, global or dynamically allocated
and not a local variable.
.. code:: c
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_cache_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:
.. code:: c
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 :cpp:enumerator:`LV_FS_MODE_WR` or :cpp:enumerator:`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:
.. code:: c
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 <https://github.com/lvgl/lvgl/blob/master/examples/porting/lv_port_fs_template.c>`__.
Usage example
*************
The example below shows how to read from a file:
.. code:: c
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 :cpp:func:`lv_fs_open` can be :cpp:enumerator:`LV_FS_MODE_WR` to open for writes
only or :cpp:enumerator:`LV_FS_MODE_RD` ``|`` :cpp:enumerator:`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.
.. code:: c
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, sizeof(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
*********************
:ref:`Image <lv_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
.. _overview_file_system_api:
API
***
|
