qmk/qmk_firmware

Releasing a layer modifier switches back to default layer regardless of how many modifier keys are held down simultaneously.

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#10,842 opened on Nov 3, 2020

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bughelp wanted

Description

Describe the Bug

(Keymap screenshots at the bottom)

I have two MO(1) keys on my keyboard layout - one under my left thumb and one under my right thumb. On Layer 1 which is the layer that the modifier switches to, I have set the corresponding key to be KC_TRNS as I have understood from the documentation that this is the correct way to have the layer modifier work correctly on both layers.

The behaviour that I would expect from the MO(layer) modifiers is akin to the standard keyboard modifiers like Ctrl, Alt, Shift, Super etc. for example:

  1. I press and hold left Shift which allows me to write capital letters.
  2. While still holding the left Shift I can also hold down the right Shift (i.e. holding both keys down) and still type capital letters.
  3. I can let go of either of the Shift keys and still be able to write capital letters.
  4. Only once I let go of both Shift keys the modifier is finally set to an off state.

However what happens with the MO(1) modifier is the following:

  1. I press and hold the left MO(1) key which enables the corresponding Layer 1
  2. I press and hold the right MO(1) key (i.e. holding both MO(1) keys) and layer remains at Layer 1
  3. However, as soon as I release either of the MO(1) keys the layer switches back to Layer 0 even though I'm still holding one of the MO(1) keys.

It seems that releasing one of the modifier keys tells the keyboard to switch back to the default layer without taking into account the total amount of modifier keys being held down.

Could it be that I have set up the layer modifiers incorrectly or is this a bug?

System Information

  • Keyboard:
    IDOBO 75 (AVR microcontroller)
  • Revision (if applicable):
    Installed from Arch repository qmk --version says unknown but package says it's 0.0.36
  • Operating system: Linux 5.9.3-arch1-1 x86_64 GNU/Linux
  • AVR GCC version: 8.3.0
  • QMK Firmware version: 0.10.39
  • Any keyboard related software installed? A couple of custom keys defined via XKB on Linux (most likely not relevant to this issue)

Additional Context

Layer 1 and Layer 2 on my current keyboard layout (including the MO(1) keys in question):

image

image

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.
half day
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 programmingQMK basics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70
Research direction
Investigate the layer state management in QMK firmware, specifically the processing of MO(layer) keys in quantum/action layer.c. The user reports that releasing one MO key while holding another still deactivates the layer, contrary to expected behavior similar to shift keys. Look into how the layer state is updated on key release and whether it counts multiple MO keys held. Consider testing with a simple keymap to verify the behavior and if needed, propose a fix in the layer state update logic.