| What: /sys/.../message | |
| Date: October 2021 | |
| KernelVersion: 5.16 | |
| Description: | |
| Controls the text message displayed on character line displays. | |
| Reading returns the current message with a trailing newline. | |
| Writing updates the displayed message. Messages longer than the | |
| display width will automatically scroll. Trailing newlines in | |
| input are automatically trimmed. | |
| Writing an empty string clears the display. | |
| Example: | |
| echo "Hello World" > message | |
| cat message # Returns "Hello World\n" | |
| What: /sys/.../num_chars | |
| Date: November 2025 | |
| KernelVersion: 6.18 | |
| Contact: Jean-Franรงois Lessard <jefflessard3@gmail.com> | |
| Description: | |
| Read-only attribute showing the character width capacity of | |
| the line display device. Messages longer than this will scroll. | |
| Example: | |
| cat num_chars # Returns "16\n" for 16-char display | |
| What: /sys/.../scroll_step_ms | |
| Date: October 2021 | |
| KernelVersion: 5.16 | |
| Description: | |
| Controls the scrolling speed for messages longer than the display | |
| width, specified in milliseconds per scroll step. | |
| Setting to 0 disables scrolling. Default is 500ms. | |
| Example: | |
| echo "250" > scroll_step_ms # 4Hz scrolling | |
| cat scroll_step_ms # Returns "250\n" | |
| What: /sys/.../map_seg7 | |
| Date: January 2024 | |
| KernelVersion: 6.9 | |
| Description: | |
| Read/write binary blob representing the ASCII-to-7-segment | |
| display conversion table used by the linedisp driver, as defined | |
| by struct seg7_conversion_map in <linux/map_to_7segment.h>. | |
| Only visible on displays with 7-segment capability. | |
| This attribute is not human-readable. Writes must match the | |
| struct size exactly, else -EINVAL is returned; reads return the | |
| entire mapping as a binary blob. | |
| This interface and its implementation match existing conventions | |
| used in segment-mapped display drivers since 2005. | |
| ABI note: This style of binary sysfs attribute *is an exception* | |
| to current "one value per file, text only" sysfs rules, for | |
| historical compatibility and driver uniformity. New drivers are | |
| discouraged from introducing additional binary sysfs ABIs. | |
| Reference interface guidance: | |
| - include/uapi/linux/map_to_7segment.h | |
| What: /sys/.../map_seg14 | |
| Date: January 2024 | |
| KernelVersion: 6.9 | |
| Description: | |
| Read/write binary blob representing the ASCII-to-14-segment | |
| display conversion table used by the linedisp driver, as defined | |
| by struct seg14_conversion_map in <linux/map_to_14segment.h>. | |
| Only visible on displays with 14-segment capability. | |
| This attribute is not human-readable. Writes must match the | |
| struct size exactly, else -EINVAL is returned; reads return the | |
| entire mapping as a binary blob. | |
| This interface and its implementation match existing conventions | |
| used by segment-mapped display drivers since 2005. | |
| ABI note: This style of binary sysfs attribute *is an exception* | |
| to current "one value per file, text only" sysfs rules, for | |
| historical compatibility and driver uniformity. New drivers are | |
| discouraged from introducing additional binary sysfs ABIs. | |
| Reference interface guidance: | |
| - include/uapi/linux/map_to_14segment.h |