qmk/qmk_firmware

One shot mod keys locking when tapped in succession

Open

#10,872 opened on Nov 6, 2020

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bughelp wanted

Description

Problem

My one shot mod keys are locking when tapped in succession with no alphanumeric characters in between. This often happens as a typo (I hit the wrong mod key for what I want to do), or if I decide to do something different midway. It took me almost a year determine the sequence that triggers this behavior.

How to Reproduce

If I do Ctrl-Alt-Alt, Ctrl is locked until I long hold it.

Same for sequences like Alt-OS-OS where Alt is locked

Keyboard

Corne keyboard

OSM Bindings

#define OSM_CTL OSM(MOD_LCTL)
#define OSM_ALT OSM(MOD_LALT)
#define OSM_OS  OSM(MOD_LGUI)

Contributor guide

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.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C programming basicsQMK firmware structureOne shot modifier concept
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Investigate the one shot mod handling in `quantum/process key processor.c` or similar. The bug occurs when tapping two mods consecutively (e.g., Ctrl Alt Alt) without alpha keys; the first mod locks. Focus on the OSM state machine logic, particularly timer and state transitions during successive taps. Review existing comments on the issue for any additional context or attempted fixes.