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Linux kernel mirror (for testing)
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linux
1What: /sys/.../message
2Date: October 2021
3KernelVersion: 5.16
4Description:
5 Controls the text message displayed on character line displays.
6
7 Reading returns the current message with a trailing newline.
8 Writing updates the displayed message. Messages longer than the
9 display width will automatically scroll. Trailing newlines in
10 input are automatically trimmed.
11
12 Writing an empty string clears the display.
13
14 Example:
15 echo "Hello World" > message
16 cat message # Returns "Hello World\n"
17
18What: /sys/.../num_chars
19Date: November 2025
20KernelVersion: 6.18
21Contact: Jean-François Lessard <jefflessard3@gmail.com>
22Description:
23 Read-only attribute showing the character width capacity of
24 the line display device. Messages longer than this will scroll.
25
26 Example:
27 cat num_chars # Returns "16\n" for 16-char display
28
29What: /sys/.../scroll_step_ms
30Date: October 2021
31KernelVersion: 5.16
32Description:
33 Controls the scrolling speed for messages longer than the display
34 width, specified in milliseconds per scroll step.
35
36 Setting to 0 disables scrolling. Default is 500ms.
37
38 Example:
39 echo "250" > scroll_step_ms # 4Hz scrolling
40 cat scroll_step_ms # Returns "250\n"
41
42What: /sys/.../map_seg7
43Date: January 2024
44KernelVersion: 6.9
45Description:
46 Read/write binary blob representing the ASCII-to-7-segment
47 display conversion table used by the linedisp driver, as defined
48 by struct seg7_conversion_map in <linux/map_to_7segment.h>.
49
50 Only visible on displays with 7-segment capability.
51
52 This attribute is not human-readable. Writes must match the
53 struct size exactly, else -EINVAL is returned; reads return the
54 entire mapping as a binary blob.
55
56 This interface and its implementation match existing conventions
57 used in segment-mapped display drivers since 2005.
58
59 ABI note: This style of binary sysfs attribute *is an exception*
60 to current "one value per file, text only" sysfs rules, for
61 historical compatibility and driver uniformity. New drivers are
62 discouraged from introducing additional binary sysfs ABIs.
63
64 Reference interface guidance:
65 - include/uapi/linux/map_to_7segment.h
66
67What: /sys/.../map_seg14
68Date: January 2024
69KernelVersion: 6.9
70Description:
71 Read/write binary blob representing the ASCII-to-14-segment
72 display conversion table used by the linedisp driver, as defined
73 by struct seg14_conversion_map in <linux/map_to_14segment.h>.
74
75 Only visible on displays with 14-segment capability.
76
77 This attribute is not human-readable. Writes must match the
78 struct size exactly, else -EINVAL is returned; reads return the
79 entire mapping as a binary blob.
80
81 This interface and its implementation match existing conventions
82 used by segment-mapped display drivers since 2005.
83
84 ABI note: This style of binary sysfs attribute *is an exception*
85 to current "one value per file, text only" sysfs rules, for
86 historical compatibility and driver uniformity. New drivers are
87 discouraged from introducing additional binary sysfs ABIs.
88
89 Reference interface guidance:
90 - include/uapi/linux/map_to_14segment.h