1. Optimize the description of i2c_bus-related usage

Author: onexs-xsi

README.md

@@ -36,6 +36,10 @@ If used alongside `M5Unified`, include it **before** `M5IOE1`:
 >
 > Alternatively, enable `CONFIG_I2C_BUS_BACKWARD_CONFIG` in menuconfig to remove the restriction.
 
+### i2c_bus mode is not supported when M5GFX / M5Unified is present
+
+Use `begin(&M5.In_I2C, addr, freq)` instead — M5GFX already owns the I2C bus and the two drivers cannot share it.
+
 ## License
 
 - [M5IOE1 - MIT](LICENSE)

src/M5IOE1_i2c_compat.h

@@ -152,36 +152,17 @@ static inline void M5IOE1_I2C_ARDUINO_SEND_WAKE(TwoWire *wire, uint8_t addr)
 // Detect if i2c_bus is available
 //
 // ESP-IDF < 5.3.0
-//   未启用 BACKWARD_CONFIG
-//     → 不支持 i2c_bus，使用传统 driver/i2c.h Legacy API
-//   启用  BACKWARD_CONFIG
-//     → i2c_bus.h 内部回退到 driver/i2c.h，可安全使用
+//   Without BACKWARD_CONFIG: i2c_bus not supported; use legacy driver/i2c.h API.
+//   With    BACKWARD_CONFIG: i2c_bus.h falls back to driver/i2c.h internally, safe to use.
 //
 // ESP-IDF >= 5.3.0
-//   启用  BACKWARD_CONFIG
-//     → i2c_bus.h 内部使用 driver/i2c.h，无冲突风险
-//   未启用 BACKWARD_CONFIG
-//     driver/i2c.h 已被其他组件提前包含（_DRIVER_I2C_H_ 已定义）
-//       → i2c_bus.h 会自定义 i2c_config_t，与已定义的版本冲突 → 禁用
-//     driver/i2c.h 尚未被包含（_DRIVER_I2C_H_ 未定义）
-//       → 无冲突风险，按默认配置启用 i2c_bus
-//
-// Detection logic:
-//   ESP-IDF < 5.3.0:
-//     Without BACKWARD_CONFIG: i2c_bus not supported; use legacy driver/i2c.h API.
-//     With    BACKWARD_CONFIG: i2c_bus.h falls back to driver/i2c.h internally, safe to use.
-//   ESP-IDF >= 5.3.0:
-//     With    BACKWARD_CONFIG: i2c_bus.h uses driver/i2c.h internally, always conflict-free.
-//     Without BACKWARD_CONFIG:
-//       _DRIVER_I2C_H_ defined   (driver/i2c.h already included by another component)
-//         → i2c_bus.h would define its own i2c_config_t, conflicting with the existing one → disabled.
-//       _DRIVER_I2C_H_ not defined (driver/i2c.h not yet included)
-//         → no conflict risk, enable i2c_bus with default config.
-//
-// Note: _DRIVER_I2C_H_ is the include guard of driver/i2c.h (ESP-IDF legacy I2C header).
-//       Checking it at preprocessor time reflects whether driver/i2c.h was included
-//       BEFORE this header. Inclusion after this header cannot be detected here;
-//       in that case the user is responsible for ensuring no conflict (or enabling BACKWARD_CONFIG).
+//   [Highest priority] M5GFX or M5Unified is present:
+//     -> i2c_bus mode is NEVER safe (runtime conflict), disabled with #error if detected.
+//     Fix: use ioe1.begin(&M5.In_I2C, addr, freq) instead.
+//   With    BACKWARD_CONFIG (no M5GFX/M5Unified): i2c_bus.h uses driver/i2c.h internally, safe.
+//   Without BACKWARD_CONFIG (no M5GFX/M5Unified):
+//     _DRIVER_I2C_H_ defined: i2c_config_t typedef conflict risk, disabled.
+//     _DRIVER_I2C_H_ not defined: no conflict risk, enable i2c_bus.
 #if __has_include(<i2c_bus.h>)
 #if ESP_IDF_VERSION < ESP_IDF_VERSION_VAL(5, 3, 0)
 #if defined(CONFIG_I2C_BUS_BACKWARD_CONFIG)
@@ -191,14 +172,29 @@ static inline void M5IOE1_I2C_ARDUINO_SEND_WAKE(TwoWire *wire, uint8_t addr)
 #endif
 #else
 // IDF >= 5.3.0
-#if defined(CONFIG_I2C_BUS_BACKWARD_CONFIG)
-#define M5IOE1_HAS_I2C_BUS 1  // BACKWARD_CONFIG：i2c_bus.h 使用 driver/i2c.h，无冲突 / no conflict
-#elif defined(_DRIVER_I2C_H_) || (defined(__cplusplus) && __has_include(<utility/I2C_Class.hpp>))
-#define M5IOE1_HAS_I2C_BUS \
-    0  // driver/i2c.h 已包含或 M5Unified 可用（将包含 driver/i2c.h）→ i2c_config_t 冲突风险，禁用
-       // driver/i2c.h already included or M5Unified available (will include driver/i2c.h) → conflict risk, disabled
+//
+// Runtime conflict (highest priority):
+// M5GFX calls i2c_new_master_bus() (driver_ng) during global construction.
+// espressif__i2c_bus conflicts with it on both code paths:
+//   BACKWARD_CONFIG=y -> i2c_bus.c calls i2c_driver_install() (legacy) -> runtime abort()
+//   BACKWARD_CONFIG=n -> i2c_bus_v2.c calls i2c_new_master_bus() on the same port -> undefined behaviour
+// Therefore, i2c_bus mode MUST be disabled whenever M5GFX or M5Unified is in the project.
+#if __has_include(<M5GFX.h>) || __has_include(<M5Unified.h>)
+#if defined(_I2C_BUS_H_)
+#error \
+    "[M5IOE1] i2c_bus cannot be used together with M5GFX/M5Unified. " \
+    "M5GFX registers driver_ng via i2c_new_master_bus() during global construction. " \
+    "BACKWARD_CONFIG=y: i2c_bus.c calls i2c_driver_install() (legacy driver) -> runtime abort() in check_i2c_driver_conflict(). " \
+    "BACKWARD_CONFIG=n: i2c_bus_v2.c calls i2c_new_master_bus() on the same port -> undefined behaviour. " \
+    "Fix: use ioe1.begin(&M5.In_I2C, addr, freq) and set I2C_USE_MODE=0."
+#endif
+#define M5IOE1_HAS_I2C_BUS 0
+#elif defined(CONFIG_I2C_BUS_BACKWARD_CONFIG)
+#define M5IOE1_HAS_I2C_BUS 1  // BACKWARD_CONFIG, no M5GFX/M5Unified: compatible
+#elif defined(_DRIVER_I2C_H_)
+#define M5IOE1_HAS_I2C_BUS 0  // driver/i2c.h already included -> i2c_config_t typedef conflict risk, disabled
 #else
-#define M5IOE1_HAS_I2C_BUS 1  // driver/i2c.h 尚未包含，无冲突风险 / driver/i2c.h not yet included, no conflict
+#define M5IOE1_HAS_I2C_BUS 1  // no conflict risk
 #endif
 #endif
 #else