qmk/qmk_firmware

[Bug] (Debug logs at end) Problem with combo-mod (eg combo that resolves to KC_LSFT) into mod-tap (eg LCTL_T(KC_P)): does not capitalize.

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#16,391 opened on Feb 17, 2022

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Description

Describe the Bug

(see also debug info below) CTL_P: LCTL_T(KC_P) CMB_SFT: combo of "." and "o" that resolves to KC_LSFT Keymap here.

  1. Trying to type capital "P" gives me trouble. Done quickly: "CMB_SFT down, CTL_P down, CMB_SFT up, CTL_P up" gives me lowercase "p", but I want capital "P".
  2. Using my actual shift key at a similar speed doesn't have this issue; "KC_LSFT down, CTL_P down, KC_LSFT up, CTL_P up" gives me capital "P".
  3. Also, if I try to capitalize a non-mod-tap letter, say "U", with my combo, I don't have this problem. That is, "CMB_SFT down, KC_U down, CMB_SFT up, KC_U up", gives me capital "U".

Video example (might be a bit loud).

Based on what I understand from the debugging, I think a solution could be to keep a timer of how long ago my combo-shift was de-pressed, and if the tap of the mod-tap is triggered while the timer is under a certain number, send the shifted version. But I'm wondering if what I'm experiencing is due to a "bug" or if it's an implementation limitation.

System Information

  • Keyboard: Boardwalk, Technik_o
    • Revision (if applicable):
  • Operating system: Windows, MacOS
  • AVR GCC version: 8.4.0
  • ARM GCC version: 10.1.0
  • QMK Firmware version: 0.15.21
  • Any keyboard related software installed? N

Additional Context

Some debugging. I annotated some stuff with my understanding of what's happening.

The following gives lowercase "p", but I want capital "P".

  > 
    r/c 0123456789ABCDEF
    00: 0000000000000000
    01: 0000000000000000
  > 02: 0010000000000000
    03: 0000000000000000
    04: 0000000000000000
    
  > r/c 0123456789ABCDEF
    00: 0000000000000000
    01: 0001000000000000
    02: 0010000000000000
    03: 0000000000000000
    04: 0000000000000000
  > keyboard_report: 06 02 00 00 00 00 00 00 

    // matrix says: (02, 2) and (01, 3) are down
    // keyboard says: KC_LSFT 
    
    r/c 0123456789ABCDEF
  > 00: 0000000000000000
    01: 0001100000000000
    02: 0010000000000000
    03: 0000000000000000
    04: 0000000000000000
    
    r/c 0123456789ABCDEF
    00: 0000000000000000
    01: 0001100000000000
    02: 0000000000000000
    03: 0000000000000000
    04: 0000000000000000
    
    r/c 0123456789ABCDEF
    00: 0000000000000000
    01: 0000100000000000
    02: 0000000000000000
    03: 0000000000000000
    04: 0000000000000000
    keyboard_report: 06 00 00 00 00 00 00 00 

    // (01, 4), corresponding to LCTL_T(KC_P), is down according to the matrix
    // matrix says: (01, 4) is down
    // keyboard says:
    
    r/c 0123456789ABCDEF
    00: 0000000000000000
    01: 0000000000000000
    02: 0000000000000000
    03: 0000000000000000
    04: 0000000000000000
  > keyboard_report: 06 00 00 00 08 00 00 00 // matrix says:                          // keyboard says: KC_P
    keyboard_report: 06 00 00 00 00 00 00 00 

    // matrix says: 
    // keyboard says:

The following gives capital "U", as expected.

    r/c 0123456789ABCDEF
    00: 0000000000000000
    01: 0000000000000000
  > 02: 0010000000000000
    03: 0000000000000000
    04: 0000000000000000
  > 
    r/c 0123456789ABCDEF
    00: 0000000000000000
    01: 0001000000000000
  > 02: 0010000000000000
    03: 0000000000000000
    04: 0000000000000000
    keyboard_report: 06 02 00 00 00 00 00 00 

    // combo for shift 
    // matrix says: (02, 2) and (01, 3) are down
    // keyboard says: KC_LSFT
    
    r/c 0123456789ABCDEF
    00: 0000000000000000
    01: 0001000000000000
    02: 0010100000000000
    03: 0000000000000000
    04: 0000000000000000
    keyboard_report: 06 02 00 00 00 01 00 00 

    // (02, 4), corresponding to "U", which is a standard keycode, is hit
    // matrix says: (02, 2), (03, 3), (02, 4) are down
    // keyboard says: KC_LSFT + KC_U
    
    r/c 0123456789ABCDEF
    00: 0000000000000000
    01: 0001000000000000
    02: 0000100000000000
    03: 0000000000000000
    04: 0000000000000000
    
    r/c 0123456789ABCDEF
    00: 0000000000000000
    01: 0000000000000000
    02: 0000100000000000
    03: 0000000000000000
    04: 0000000000000000
  > keyboard_report: 06 00 00 00 00 01 00 00 

    // matrix says: (02, 4) is down
    // keyboard says: KC_U
  > 
    r/c 0123456789ABCDEF
    00: 0000000000000000
    01: 0000000000000000
  > 02: 0000000000000000
    03: 0000000000000000
    04: 0000000000000000
    keyboard_report: 06 00 00 00 00 00 00 00 

    // matrix says: 
    // keyboard says:

Using actual shift instead of a combo gives expected results:

Capital "P", rolling key sequence

    r/c 0123456789ABCDEF
    00: 0000000000000000
    01: 0000000000000000
  > 02: 0000000000000000
    03: 1000000000000000
    04: 0000000000000000
    keyboard_report: 06 02 00 00 00 00 00 00 
  > 
    r/c 0123456789ABCDEF
    00: 0000000000000000
    01: 0000100000000000
  > 02: 0000000000000000
    03: 1000000000000000
    04: 0000000000000000
  > 
    r/c 0123456789ABCDEF
    00: 0000000000000000
    01: 0000100000000000
  > 02: 0000000000000000
    03: 0000000000000000
    04: 0000000000000000
  > 
    r/c 0123456789ABCDEF
    00: 0000000000000000
    01: 0000000000000000
  > 02: 0000000000000000
    03: 0000000000000000
    04: 0000000000000000
    keyboard_report: 06 02 00 00 08 00 00 00 
    keyboard_report: 06 00 00 00 08 00 00 00 
    keyboard_report: 06 00 00 00 00 00 00 00

Capital "U", rolling key sequence

  > 
    r/c 0123456789ABCDEF
    00: 0000000000000000
    01: 0000000000000000
  > 02: 0000000000000000
    03: 1000000000000000
    04: 0000000000000000
    keyboard_report: 06 02 00 00 00 00 00 00 
  > 
    r/c 0123456789ABCDEF
    00: 0000000000000000
    01: 0000000000000000
  > 02: 0000100000000000
    03: 1000000000000000
    04: 0000000000000000
    keyboard_report: 06 02 00 00 00 01 00 00 
  > 
    r/c 0123456789ABCDEF
    00: 0000000000000000
    01: 0000000000000000
  > 02: 0000100000000000
    03: 0000000000000000
    04: 0000000000000000
    keyboard_report: 06 00 00 00 00 01 00 00 
    
    r/c 0123456789ABCDEF
    00: 0000000000000000
    01: 0000000000000000
    02: 0000000000000000
    03: 0000000000000000
    04: 0000000000000000
  > keyboard_report: 06 00 00 00 00 00 00 00

Contributor guide

Research direction
Examine the combo and mod tap interaction in QMK's process record function. Focus on the handling of combo events and how mod tap keys are processed. Identify where the shift state from the combo might be lost before the mod tap registers the tap.
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
GitC
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60