evdev_notes.md

• event docs

codes resolved with python evdev

dict(evdev.resolve_ecodes_dict({3: [0, 1, 24, 25, 26, 27]}))

evdev Message Structure

• https://stackoverflow.com/questions/23480741/obtaining-evdev-event-code-from-raw-bytes

• 4 byte unsigned integer - seconds

• 4 byte unsigned integer - microseconds

• 2 byte unsigned integer - type

• 2 byte unsigned integer - code

• 4 byte signed integer - value

Coordinate Systems

  Stylus          Touch         TKinter
+---------+    +---------+    +---------+
| x       |    |       y |    | +---x   |
| |       |    |       | |    | |       |
| |       |    |       | |    | |       |
| +--- y  |    |   x---+ |    | y       |
+---------+    +---------+    +---------+
|o   o   o|    |o   o   o|    |o   o   o|
+---------+    +---------+    +---------+

evdev Event Files and Codes

event0 - Stylus

• type 0 - ev_sync
• type 1 - ev_key
  • code [code #] - [name] - [desc] - [range]
  • code 320 - toolpen - -
  • code 321 - toolrubber - -
  • code 330 - touch - -
  • code 331 - stylus - -
  • code 332 - stylus2 - -
• type 3 - ev_abs - absolute
  • code 0 - abs_x - xpos - (0: bottom, 20967: top)
  • code 1 - abs_y - ypos - (0: left, 15725: right)
  • code 24 - abs_pressure - (0, 4095)
  • code 25 - abs_distance - distance between pen and surface - (0: lowered, ~100: raised)
  • code 26 - abs_tilt_x - (-6300: pen flat pointing up, 6300: pen flat pointing down)
  • code 27 - abs_tilt_y - (-6300: pen flat pointing right, 6300: pen flat pointing left

event1 - Touch

• type 0 - ev_sync
• type 1 - ev_key
• type 3 - ev_abs
  • code 25 - abs_mt_distance - unused?
  • code 47 - abs_mt_slot - multitouch position number (see protocol example B in docs)
  • code 48 - abs_mt_touch_major - touch size major axis - needs further study {4: pointer touch, 24: thumb touch}
  • code 49 - abs_mt_touch_minor - touch size minor axis -
  • code 52 - abs_mt_orientation - touch orientation
  • code 53 - abs_mt_position_x - xpos - (0: right side, 767: left side)
  • code 54 - abs_mt_position_y - ypos - (0: bottom, 1023: top
  • code 57 - abs_mt_tracking_id - press/release
    • value=X - increments by +1 with each press
    • value=-1 - release
  • code 58 - abs_mt_pressure - not really pressure but contact area - {30: very light touch, 90: typical touch during swipe, 150: thumb on screen}

event2 - Buttons

• type 0 - ev_sync
• type 1 - ev_key
  • code 102 - home - middle button
    • value 1 - press
    • value 0 - release
  • code 105 - left - left button
  • code 106 - right - right button
  • code 116 - power - suspend button
  • code 143 - wakeup - unused?