qmk/qmk_firmware

[Bug] When holding multiple mod-tap keys, only one gets registered as a modifier

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#13,346 opened on Jun 26, 2021

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Description

Describe the Bug

I have home-row modifiers set up with mod-tap like so:

#define HM_A LALT_T(KC_A)
#define HM_R LGUI_T(KC_R)
#define HM_S LSFT_T(KC_S)
#define HM_T LCTL_T(KC_T)

My relevant configuration is as follows:

#define TAPPING_TERM 250
#define IGNORE_MOD_TAP_INTERRUPT
#define TAPPING_FORCE_HOLD
#define PERMISSIVE_HOLD

When I input this key sequence:

HM_R down, HM_S down, KC_SPACE down, KC_SPACE up, HM_S up, HM_R up

My computer sees the following:

gui down, s down, space down, space up, s up, gui up

But I would expect to see this:

gui down, shift down, space down, space up, shift up, gui up

Basically, I would expect the second mod-tap key to also be treated as a modifier since space was pressed and released between when it was pressed and released.

System Information

  • Keyboard: Keyboardio Atreus
    • Revision (if applicable):
  • Operating system: Arch Linux
  • AVR GCC version: 11.1.0
  • ARM GCC version: 11.1.0
  • QMK Firmware version: 0.13.2
  • Any keyboard related software installed?
    • AutoHotKey
    • Karabinerk
    • Other:

Contributor guide

Research direction
Inspect the mod tap functionality in QMK firmware, specifically the `process mod tap` function and key state logic. Focus on handling multiple held mod tap keys with an intermediate key press to understand why the second mod tap key does not register as a modifier.
Tech stack
c
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
CGit
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
55