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| 1 | +What: /sys/.../message |
| 2 | +Date: October 2021 |
| 3 | +KernelVersion: 5.16 |
| 4 | +Description: |
| 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 | + |
| 18 | +What: /sys/.../num_chars |
| 19 | +Date: November 2025 |
| 20 | +KernelVersion: 6.18 |
| 21 | +Contact: Jean-François Lessard < [email protected]> |
| 22 | +Description: |
| 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 | + |
| 29 | +What: /sys/.../scroll_step_ms |
| 30 | +Date: October 2021 |
| 31 | +KernelVersion: 5.16 |
| 32 | +Description: |
| 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 | + |
| 42 | +What: /sys/.../map_seg7 |
| 43 | +Date: January 2024 |
| 44 | +KernelVersion: 6.9 |
| 45 | +Description: |
| 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 | + |
| 67 | +What: /sys/.../map_seg14 |
| 68 | +Date: January 2024 |
| 69 | +KernelVersion: 6.9 |
| 70 | +Description: |
| 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 |
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