diff --git a/README.md b/README.md
index 3d1b1c0..68e66a8 100644
--- a/README.md
+++ b/README.md
@@ -452,3 +452,19 @@ has another name, or `M5UNIFIED_ARDUINO_COMPONENT=OFF` to disable this.
 |Current<BR>Voltage<BR>Monitor| ---                               | ---                  | ---                | ---               | ---                 | ---               | ---                 | ---            |`INA3221`<BR>40h/41h<BR>(opt)|Current<BR>Voltage<BR>Monitor|
 
 
+
+
+### Fixed-board firmware
+
+Defining a positive `BOARD_ID` when building an application using M5Unified fixes
+its device identity to that `board_t` value. An undefined, explicitly empty, or zero value
+keeps automatic detection. Fixed startup reads only variants needed by the
+selected board and does not use NVS or probe other board families.
+An accepted fixed identity takes precedence over `config_t::fallback_board`,
+including when display startup fails. Call `M5.begin()` before initializing
+`M5.Display` for this configuration to take effect.
+
+A positive `BOARD_ID` unsupported by the chip also stops automatic detection;
+it does not fall back to probing another board. `BOARD_ID` has no effect if
+`M5.Display.init()` runs before `M5.begin()`. A valueless compiler option
+`-DBOARD_ID` defines the value as 1 (M5Stack), rather than an empty value.
diff --git a/src/M5Unified.hpp b/src/M5Unified.hpp
index 59410e9..14ca00a 100644
--- a/src/M5Unified.hpp
+++ b/src/M5Unified.hpp
@@ -348,7 +348,13 @@ namespace m5
       // Skipped when the application already ran Display.init(): GPIO46 may then carry the display
       // bus (StopWatch QSPI io2), which this output would overwrite. The hold is applied below,
       // once the pin map is known, only on boards that use GPIO46 as their power hold.
+#if defined (BOARD_ID) && ((BOARD_ID + 0) > 0)
+      // A fixed board can use GPIO46 for its display rather than power hold.
+      const bool gpio46_hold = Display.getBoard() == board_t::board_unknown
+                           && _get_power_hold_pin(static_cast<board_t>(BOARD_ID)) == GPIO_NUM_46;
+#else
       const bool gpio46_hold = (Display.getBoard() == m5gfx::board_t::board_unknown);
+#endif
       m5gfx::gpio::pin_backup_t gpio46_backup(GPIO_NUM_46);
       if (gpio46_hold)
       {
@@ -357,6 +363,13 @@ namespace m5
       }
 #endif
 
+      m5gfx::detect_config_t detect_config;
+      detect_config.fallback_board = cfg.fallback_board;
+      // A positive BOARD_ID fixes the device to its board_t value in M5Unified.
+#if defined (BOARD_ID) && ((BOARD_ID + 0) > 0)
+      detect_config.fixed_board = static_cast<board_t>(BOARD_ID);
+#endif
+      Display.setDetectConfig(detect_config);
       auto brightness = Display.getBrightness();
       Display.setBrightness(0);
       bool res = false;
@@ -365,20 +378,21 @@ namespace m5
       } else {
         res = Display.init_without_reset(false);
       }
-      auto board = Display.getBoard();
-      // printf("auto detect board:%d\n",board);
+      const auto fixed_board = Display.getFixedBoard();
+      auto board = fixed_board != board_t::board_unknown ? fixed_board : Display.getBoard();
       bool board_detected = (board != board_t::board_unknown);
-      if (!board_detected)
+      if (fixed_board != board_t::board_unknown)
+      {
+        // Accepted firmware identity survives display startup failure.
+        if (cfg.fallback_board != board_t::board_unknown && cfg.fallback_board != fixed_board)
+        {
+          Log(ESP_LOG_WARN, "fallback board:%u ignored for fixed board:%u",
+              static_cast<unsigned>(cfg.fallback_board), static_cast<unsigned>(fixed_board));
+        }
+      }
+      else if (!board_detected)
       {
         board = cfg.fallback_board;
-        // UIFlow selects board-specific firmware with BOARD_ID and M5GFX_BOARD.
-#if defined (CONFIG_IDF_TARGET_ESP32P4) && defined (BOARD_ID)
-#if BOARD_ID == 31
-        if (board == board_t::board_unknown) { board = board_t::board_M5CoreP4X; }
-#elif BOARD_ID == 35
-        if (board == board_t::board_unknown) { board = board_t::board_M5Tab5X; }
-#endif
-#endif
         if (board == board_t::board_unknown) { board = Display.getBoardCandidate(); }
         if (board == board_t::board_unknown) { board = _default_fallback_board(); }
       }
@@ -798,6 +812,7 @@ namespace m5
     bool _probe_i2c_addr(uint8_t sda, uint8_t scl, uint8_t addr);
 
     static void _setup_pinmap(board_t);
+    static int8_t _get_power_hold_pin(board_t);
     static bool _speaker_enabled_cb_core2(void* args, bool enabled);
     static bool _speaker_enabled_cb_cores3(void* args, bool enabled);
     static bool _speaker_enabled_cb_sticks3(void* args, bool enabled);
diff --git a/src/M5Unified.inl b/src/M5Unified.inl
index 0de5e30..0e8cdf3 100644
--- a/src/M5Unified.inl
+++ b/src/M5Unified.inl
@@ -86,6 +86,8 @@ namespace m5
 int8_t M5Unified::_get_pin_table[pin_name_max];
 
 #if defined (M5UNIFIED_PC_BUILD)
+  int8_t M5Unified::_get_power_hold_pin(board_t) { return -1; }
+
   void M5Unified::_setup_pinmap(board_t)
   {
     std::fill(_get_pin_table, _get_pin_table + pin_name_max, 255);
@@ -475,6 +477,13 @@ static constexpr const uint8_t _pin_table_mbus[][31] = {
 { board_t::board_unknown  , 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255 },
 };
 
+  int8_t M5Unified::_get_power_hold_pin(board_t id)
+  {
+    for (const auto& row : _pin_table_other1)
+    { if (row[0] == id) { return static_cast<int8_t>(row[1]); } }
+    return -1;
+  }
+
   void M5Unified::_setup_pinmap(board_t id)
   {
     if (id == board_t::board_M5Tab5X) {
@@ -1650,30 +1659,20 @@ static constexpr const uint8_t _pin_table_mbus[][31] = {
     const auto pkg = m5gfx::get_pkg_ver();
     if (pkg == 6) { return board_t::board_M5AtomPsram; } // PICO-V3
     if (pkg == 5) { return board_t::board_M5StampPico; } // PICO-D4
-    // The legacy detector defaulted D0WDQ6 to TimerCam after other probes failed.
-    if (pkg == EFUSE_RD_CHIP_VER_PKG_ESP32D0WDQ6) { return board_t::board_M5TimerCam; }
-    return board_t::board_M5AtomLite;
+    // StampPico and AtomPsram have no positive detector and remain defaults.
+    // All D0WDQ6 members have detectors; other packages have no M5 boards.
+    // Do not assume a rejected member. Unknown retains the generic I2C map.
+    return board_t::board_unknown;
 #elif defined (CONFIG_IDF_TARGET_ESP32S3)
-#if defined (BOARD_ID) && BOARD_ID == 147
-    return board_t::board_M5DualKey;
-#endif
     // ESP32-S3 package 0 is QFN56 and package 1 is LGA56.
     if (m5gfx::get_pkg_ver() == 1) { return board_t::board_M5StampS3Mini; }
     return board_t::board_M5StampS3;
 #elif defined (CONFIG_IDF_TARGET_ESP32C3)
     return board_t::board_M5StampC3U;
-#elif defined (CONFIG_IDF_TARGET_ESP32C6)
-    // Preserve legacy package/flash defaults when no detector confirms a board.
-    if (m5gfx::get_pkg_ver() == 1)
-    {
-      return REG_GET_FIELD(EFUSE_RD_MAC_SPI_SYS_4_REG, EFUSE_FLASH_CAP) == 2
-           ? board_t::board_M5StampC6 : board_t::board_M5NanoC6;
-    }
+#elif defined (CONFIG_IDF_TARGET_ESP32C6) || defined (CONFIG_IDF_TARGET_ESP32H2) || defined (CONFIG_IDF_TARGET_ESP32C5)
+    // Package-only Stamp suggestions arrive as detector candidates. Do not
+    // assume a Nano or Stamp after its positive detector rejects the board.
     return board_t::board_unknown;
-#elif defined (CONFIG_IDF_TARGET_ESP32H2)
-    return board_t::board_M5NanoH2;
-#elif defined (CONFIG_IDF_TARGET_ESP32C5)
-    return board_t::board_M5StampC5;
 #elif defined (CONFIG_IDF_TARGET_ESP32P4)
     // Unidentified P4 modules have no display or board-specific power contract.
     esp_chip_info_t info;