boards: shields: Add mchp_rnbd451_bt

Add board support for the Microchip RNBD451 shield.
This shield is compatible with a development board that includes a
mikroBUS socket.

Signed-off-by: James Liu <James.Liu2@microchip.com>

Author: JamesLiu-Microchip

��boards/shields/mchp_rnbd451_bt/Kconfig.defconfig

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+# Copyright (c) 2025-2026 Microchip Technology Inc.
+# SPDX-License-Identifier: Apache-2.0
+
+if SHIELD_MCHP_RNBD451_BT || \
+	SHIELD_MCHP_RNBD451_BT_MIKROBUS || \
+	SHIELD_MCHP_RNBD451_BT_XPLAINED_PRO
+
+if BT
+
+config MAIN_STACK_SIZE
+	default 2048 if BT_HOST_CRYPTO
+
+config BT_BUF_ACL_TX_COUNT
+	default 12
+
+config BT_BUF_EVT_RX_COUNT
+	default 13
+
+config BT_BUF_EVT_DISCARDABLE_COUNT
+	default 12
+
+config BT_HCI_ACL_FLOW_CONTROL
+	default n
+
+endif # BT
+
+endif   # SHIELD_MCHP_RNBD451_BT

boards/shields/mchp_rnbd451_bt/Kconfig.shield

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+# Copyright (c) 2025-2026 Microchip Technology Inc.
+# SPDX-License-Identifier: Apache-2.0
+
+config SHIELD_MCHP_RNBD451_BT
+	def_bool $(shields_list_contains,mchp_rnbd451_bt)
+
+config SHIELD_MCHP_RNBD451_BT_MIKROBUS
+	def_bool $(shields_list_contains,mchp_rnbd451_bt_mikrobus)
+
+config SHIELD_MCHP_RNBD451_BT_XPLAINED_PRO
+	def_bool $(shields_list_contains,mchp_rnbd451_bt_xplained_pro)

boards/shields/mchp_rnbd451_bt/doc/img/2080-atmbusadapter-xpro.webp

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+.. _rnbd451_add_on_shield:
+
+RNBD451 Add-on Board
+###############################
+
+Overview
+********
+
+The RNBD451 Add-on Board is an efficient low-cost development platform to evaluate and demonstrate
+the features, capabilities and interfaces of Microchip's Bluetooth® Low Energy module, RNBD451PE.
+The add-on board is compliant to the mikroBUS™ standard and includes an on-board MCP2200 USB-to-UART
+converter enabling out-of-box evaluation with no other hardware requirements.
+
+More information about the shield can be found at `RNBD451 Add-on Board Primary User Guide`_.
+
+.. figure:: img/mchp_rnbd451_bt_mikrobus.webp
+   :height: 350px
+   :align: center
+   :alt: RNBD451 Add-on Board
+
+Requirements
+************
+
+This shield is compatible with a development board that includes a mikroBUS™ socket.
+If a mikroBUS socket is not available, a mikroBUS adapter can be used to provide both an
+extension header and a mikroBUS interface. The mikroBUS™ Xplained Pro is an extension Board
+for the Xplained Pro evaluation platform,  designed to support mikroBUS™ Click boards™ with
+Xplained Pro MCU boards.
+
+
+.. figure:: img/2080-atmbusadapter-xpro.webp
+   :height: 300px
+   :align: center
+   :alt: ATMBUSADAPTER-XPRO - mikroBUS Adapter
+
+Configurations
+**************
+
+When bringing up the RNBD451 Bluetooth Low Energy (BLE) controller after a Power-On Reset (POR),
+the Zephyr Bluetooth subsystem sends the **HCI reset command** (the first HCI command) to the BLE
+controller. However, in the original design, this command is sent too early for the RNBD451, as
+it takes more than 400 ms from POR to be ready to accept the first HCI command.
+
+To address this timing issue, introduce a delay in the Zephyr application to enable Bluetooth.
+This delay ensures that the **HCI reset command** is sent at the appropriate time. Add the following
+code snippet to the application to introduce a 500 ms delay before calling ``bt_enable()``:
+
+``k_sleep(K_MSEC(500));``
+
+Programming
+***********
+
+Activate the presence of the shield for the project build by adding the
+``--shield mchp_rnbd451_bt_mikrobus`` or ``--shield mchp_rnbd451_bt_xplained_pro`` when you invoke
+``west build`` based on Mikrobus or Xplained Pro interface:
+
+.. zephyr-app-commands::
+   :app: samples/bluetooth/peripheral
+   :board: your_board_name
+   :shield: shield mchp_rnbd451_bt_mikrobus
+   :goals: build
+
+Or
+
+.. zephyr-app-commands::
+   :app: samples/bluetooth/peripheral
+   :board: your_board_name
+   :shield: mchp_rnbd451_bt_xplained_pro
+   :goals: build
+
+References
+**********
+
+.. target-notes::
+
+.. _RNBD451 Add-on Board Primary User Guide:
+   https://ww1.microchip.com/downloads/aemDocuments/documents/WSG/ProductDocuments/UserGuides/RNBD451-Add-On-Board-User-Guide-DS50003476.pdf

boards/shields/mchp_rnbd451_bt/doc/img/mchp_rnbd451_bt_mikrobus.webp

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+/*
+ * Copyright (c) 2025-2026 Microchip Technology Inc.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/*
+ * This file is intentionally empty. Please refer to shield documentation
+ * for instructions to use this shield.
+ */

boards/shields/mchp_rnbd451_bt/doc/index.rst

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+/*
+ * Copyright (c) 2025-2026 Microchip Technology Inc.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/ {
+	chosen {
+		zephyr,bt-hci = &bt_hci_uart;
+	};
+};
+
+&mikrobus_serial {
+	status = "okay";
+
+	bt_hci_uart: bluetooth {
+		compatible = "zephyr,bt-hci-uart";
+		status = "okay";
+	};
+};

boards/shields/mchp_rnbd451_bt/mchp_rnbd451_bt.overlay

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+/*
+ * Copyright (c) 2025-2026 Microchip Technology Inc.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/ {
+	chosen {
+		zephyr,bt-hci = &bt_hci_uart;
+	};
+};
+
+&ext1_serial {
+	status = "okay";
+
+	bt_hci_uart: bluetooth {
+		compatible = "zephyr,bt-hci-uart";
+		status = "okay";
+	};
+};
+
+&nvmctrl {
+	status = "okay";
+};

boards/shields/mchp_rnbd451_bt/mchp_rnbd451_bt_mikrobus.overlay

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+shields:
+  - name: mchp_rnbd451_bt_mikrobus
+    full_name: RNBD451 Add-on Board (Mikro BUS)
+    vendor: microchip
+    supported_features:
+      - bluetooth
+
+  - name: mchp_rnbd451_bt_xplained_pro
+    full_name: RNBD451 Add-on Board (Xplained Pro)
+    vendor: microchip
+    supported_features:
+      - bluetooth