ESP32: Including Wire.h causes built-in IMU initialization to fail on Core Gray #366

Summary

On M5Stack Core Gray, including Wire.h causes the built-in BMI270 IMU to fail initialization with M5GFX 0.2.33.

The failure occurs during sequential initialization and does not require concurrent I2C access, external sensor communication, or radio operations.

Environment

• Board: M5Stack Core Gray (ESP32-D0WDQ6-V3, rev 3.1)
• Board package: M5Stack ESP32 2.1.4 (Arduino-ESP32 2.0.14)
• M5Unified: 0.2.26
• M5GFX: 0.2.33
• Built-in IMU: BMI270
• FQBN: m5stack:esp32:m5stack_core

Steps to reproduce

1. Build a sketch including Wire.h, M5Unified.h, and M5GFX.h.
2. Initialize M5Unified and the built-in IMU using the diagnostic sketch.
3. Read acceleration values repeatedly using M5.Imu.getAccel().
4. Observe the IMU initialization status and successful read count.

The diagnostic uses the built-in IMU without external I2C devices or concurrent bus access.

Expected behavior

The built-in BMI270 should initialize successfully, and acceleration readings should succeed.

I2C bus initialization and release should not leave the bus unusable for subsequent initialization.

Actual behavior

With unmodified M5GFX 0.2.33:

• The built-in BMI270 is not detected.
• All 40 acceleration readings fail in the Wire-only regression test.
• Reinitialization of M5GFX-owned I2C buses fails on both hardware ports.

Serial output

WIRE_ONLY_SUMMARY patched=0 samples=40 ok=0 auto_imu=0 auto_accel=0 pass=0
OWNED_SUMMARY port=0 cycles=10 init_ok=20/20 id_ok=10/20 closed_ok=0/10 pass=0
OWNED_SUMMARY port=1 cycles=10 init_ok=20/20 id_ok=10/20 closed_ok=0/10 pass=0

Additional observations

Instrumented execution shows the SDA/SCL output signal selectors changing from I2C signals 30/29 to GPIO 256/256.

During subsequent initialization, the bus is reported as externally owned (foreign_bus=1), despite having originally been initialized by M5GFX.

Earlier version comparisons also showed:

These results suggest a regression introduced between M5GFX 0.2.28 and 0.2.29.

Scope

The issue has been reproduced on M5Stack Core Gray with the environment specified above.

Other ESP32 variants and Arduino-ESP32 versions have not been tested.

An earlier blank-screen symptom has not been conclusively linked to this failure and is outside the scope of this report.