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 91