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Document HID keyboard events

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This commit is contained in:
Romain Vimont 2021-12-28 12:16:20 +01:00
parent 6261bb0b5a
commit 826ddf1a6e
1 changed files with 75 additions and 1 deletions
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76
app/src/hid_keyboard.c
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@ -126,6 +126,80 @@ static const unsigned char keyboard_report_desc[] = {
0xC0
};
/**
* A keyboard HID event is 8 bytes long:
*
* - byte 0: modifiers (1 flag per modifier key, 8 possible modifier keys)
* - byte 1: reserved (always 0)
* - bytes 2 to 7: pressed keys (6 at most)
*
* 7 6 5 4 3 2 1 0
* +---------------+
* byte 0: |. . . . . . . .| modifiers
* +---------------+
* ^ ^ ^ ^ ^ ^ ^ ^
* | | | | | | | `- left Ctrl
* | | | | | | `--- left Shift
* | | | | | `----- left Alt
* | | | | `------- left Gui
* | | | `--------- right Ctrl
* | | `----------- right Shift
* | `------------- right Alt
* `--------------- right Gui
*
* +---------------+
* byte 1: |0 0 0 0 0 0 0 0| reserved
* +---------------+
*
* +---------------+
* bytes 2 to 7: |. . . . . . . .| scancode of 1st key pressed
* +---------------+
* |. . . . . . . .| scancode of 2nd key pressed
* +---------------+
* |. . . . . . . .| scancode of 3rd key pressed
* +---------------+
* |. . . . . . . .| scancode of 4th key pressed
* +---------------+
* |. . . . . . . .| scancode of 5th key pressed
* +---------------+
* |. . . . . . . .| scancode of 6th key pressed
* +---------------+
*
* If there are less than 6 keys pressed, the last items are set to 0.
* For example, if A and W are pressed:
*
* +---------------+
* bytes 2 to 7: |0 0 0 0 0 1 0 0| A is pressed (scancode = 4)
* +---------------+
* |0 0 0 1 1 0 1 0| W is pressed (scancode = 26)
* +---------------+
* |0 0 0 0 0 0 0 0| ^
* +---------------+ | only 2 keys are pressed, the
* |0 0 0 0 0 0 0 0| | remaining items are set to 0
* +---------------+ |
* |0 0 0 0 0 0 0 0| |
* +---------------+ |
* |0 0 0 0 0 0 0 0| v
* +---------------+
*
* Pressing more than 6 keys is not supported. If this happens (typically,
* never in practice), report a "phantom state":
*
* +---------------+
* bytes 2 to 7: |0 0 0 0 0 0 0 1| ^
* +---------------+ |
* |0 0 0 0 0 0 0 1| | more than 6 keys pressed:
* +---------------+ | the list is filled with a special
* |0 0 0 0 0 0 0 1| | rollover error code (0x01)
* +---------------+ |
* |0 0 0 0 0 0 0 1| |
* +---------------+ |
* |0 0 0 0 0 0 0 1| |
* +---------------+ |
* |0 0 0 0 0 0 0 1| v
* +---------------+
*/
static unsigned char
sdl_keymod_to_hid_modifiers(SDL_Keymod mod) {
unsigned char modifiers = HID_MODIFIER_NONE;
@ -217,7 +291,7 @@ convert_hid_keyboard_event(struct sc_hid_keyboard *kb,
// USB HID protocol says that if keys exceeds report count, a
// phantom state should be reported
if (keys_pressed_count >= HID_KEYBOARD_MAX_KEYS) {
// Pantom state:
// Phantom state:
// - Modifiers
// - Reserved
// - ErrorRollOver * HID_MAX_KEYS