qmk/qmk_firmware

[Bug] Crash when using GP26-29 as keyboard matrix pins on RP2040

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#25930 opened on Jan 4, 2026

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bughelp wanted

Description

Describe the Bug

I built keyboards using several development boards with the RP2040 as the main controller. When I enable any one of GP26-GP29 as a matrix pin, the compilation completes successfully, but after flashing the firmware to the board, the program crashes immediately and the board reboots into the bootloader. The strangest part is that this issue does not occur on all of my boards—even with two identical RP2040-based boards, one crashes every time I flash the firmware, while the other works perfectly without any issues. Since the crash only happens when GP26 to GP29 are enabled, I suspect there is a conflict between the ADC and GPIO during the initialization phase. I have no idea how to troubleshoot or resolve this problem, so I would greatly appreciate any help or guidance you can provide.

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.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Knowledge of QMK firmwareRP2040 datasheetDebugging crashes
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
25
Research direction
The issue suggests a conflict between ADC and GPIO initialization on RP2040. Start by examining QMK's initialization code for RP2040 in `platforms/chibios/drivers/` or `drivers/arm/rp2040/`. Look for any default ADC configuration that might interfere with GP26-29 when used as matrix pins. Check the `board init` function and GPIO setup. Also review the RP2040 datasheet for pad control registers. Consider creating a minimal test configuration to reproduce the crash. No linked PRs found; this is a fresh bug.