Central side does not wake from sleep when ZMK Studio is enabled (Zephyr 4.1)

[p0ns]

Description

After upgrading to Zephyr 4.1 (commit c06fa48c), the central half of a split keyboard does not wake from deep sleep (CONFIG_ZMK_SLEEP=y) when CONFIG_ZMK_STUDIO=y is enabled. The peripheral side wakes normally.

Disabling ZMK Studio resolves the issue - the central wakes from sleep as expected.

Environment

• ZMK Version: main branch (post-Zephyr 4.1 upgrade)
• Board: nice_nano (nRF52840)
• Shield: Corne with nice_view display
• Relevant Config:

  CONFIG_ZMK_SLEEP=y
  CONFIG_ZMK_DISPLAY=y
  CONFIG_ZMK_STUDIO=y
  

Steps to Reproduce

1. Build firmware for a split keyboard central with CONFIG_ZMK_SLEEP=y and CONFIG_ZMK_STUDIO=y
2. Flash to the central half (e.g., left side)
3. Wait for the keyboard to enter deep sleep (default 15 min idle timeout)
4. Press a key on the central side
5. Expected: Keyboard wakes up
6. Actual: Keyboard does not wake; requires reset or power cycle

Workaround

Disable ZMK Studio:

# CONFIG_ZMK_STUDIO=y

Analysis

The issue appeared with the Zephyr 4.1 upgrade. Key changes in that commit:

1. PM API change in app/src/pm.c - Removed pm_device_state_is_locked() check (function was removed in Zephyr 3.7):

   // Before:
   if (!device_is_ready(dev) || pm_device_is_busy(dev) || pm_device_state_is_locked(dev) ||
       pm_device_wakeup_is_enabled(dev) || pm_device_runtime_is_enabled(dev)) {
   
   // After:
   if (!device_is_ready(dev) || pm_device_is_busy(dev) || pm_device_wakeup_is_enabled(dev) ||
       pm_device_runtime_is_enabled(dev)) {

2. Conditional compilation change - #if !defined(CONFIG_PM_DEVICE_RUNTIME_EXCLUSIVE) changed to #if defined(CONFIG_PM_DEVICE_SYSTEM_MANAGED)

ZMK Studio enables USB CDC ACM, UART RPC transport, and additional threads. One of these components may be:

• Not properly suspending before sys_poweroff()
• Holding GPIO pins in a state that blocks SENSE-based wake detection
• Missing wakeup-source configuration

The peripheral (without Studio features) wakes correctly, confirming the issue is specific to Studio-enabled central builds.

[froyomuffin]

Having the same issue in dongle mode where the keyboards would not wake properly. Was also able to get around the issue by disabling studio.