boards: silabs: Add support for Silabs EFR32ZG28 SoC

boards/silabs/radio_boards/xg28_rb4401c/Kconfig.defconfig

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+# Copyright (c) 2025 Shontal Biton
+# SPDX-License-Identifier: Apache-2.0
+
+if BOARD_XG28_RB4401C
+
+config LOG_BACKEND_SWO_FREQ_HZ
+	default 875000
+	depends on LOG_BACKEND_SWO
+
+if SOC_GECKO_USE_RAIL
+
+config FPU
+	default y
+
+endif # SOC_GECKO_USE_RAIL
+
+endif # BOARD_XG28_RB4401C

boards/silabs/radio_boards/xg28_rb4401c/Kconfig.xg28_rb4401c

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+# Copyright (c) 2025 Shontal Biton
+# SPDX-License-Identifier: Apache-2.0
+
+config BOARD_XG28_RB4401C
+	select SOC_PART_NUMBER_EFR32ZG28B322F1024IM68

boards/silabs/radio_boards/xg28_rb4401c/board.cmake

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+# SPDX-License-Identifier: Apache-2.0
+
+board_runner_args(jlink "--device=EFR32ZG28BxxxF1024")
+include(${ZEPHYR_BASE}/boards/common/jlink.board.cmake)
+
+board_runner_args(openocd)
+include(${ZEPHYR_BASE}/boards/common/openocd.board.cmake)
+
+board_runner_args(silabs_commander "--device=EFR32ZG28B322F1024IM68")
+include(${ZEPHYR_BASE}/boards/common/silabs_commander.board.cmake)

boards/silabs/radio_boards/xg28_rb4401c/board.yml

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+board:
+  name: xg28_rb4401c
+  full_name: EFR32xG28 868-915 MHz 20 dBm (xG28-RB4401C)
+  vendor: silabs
+  socs:
+    - name: efr32zg28b322f1024im68

boards/silabs/radio_boards/xg28_rb4401c/doc/index.rst

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+.. zephyr:board:: xg28_rb4401c
+
+Overview
+********
+
+The EFR32ZG28 Radio Board is the radio board delivered with
+`xG28-PK6024A Website`_. It contains a Wireless System-On-Chip from the
+EFR32ZG28 family built on an ARM Cortex®-M33 processor with excellent low
+power capabilities.
+
+The BRD4401C a.k.a. xG28-RB4401C radio board plugs into the Wireless Pro Kit
+Mainboard BRD4401C and is supported as one of :ref:`silabs_radio_boards`.
+
+Hardware
+********
+
+- EFR32ZG28B322F1024IM68 SoC
+- CPU core: ARM Cortex®-M33 with FPU
+- Flash memory: 1024 kB
+- RAM: 256 kB
+- Transmit power: up to +20 dBm
+- Operation frequency: 868-915 MHz
+- Crystals for LFXO (32.768 kHz) and HFXO (39 MHz).
+- Silicon Labs Si7021 relative humidity and temperature sensor
+- Low-power 128x128 pixel Memory LCD
+- Macronix ultra low power 8-Mbit SPI flash (MX25R8035F)
+
+For more information about the EFR32ZG28 SoC and BRD4401C board, refer to these
+documents:
+
+- `EFR32ZG28 Website`_
+- `EFR32ZG28 Datasheet`_
+- `EFR32xG28 Reference Manual`_
+- `XG28-PK6024A Website`_
+- `BRD4401C User Guide`_
+
+Supported Features
+==================
+
+.. zephyr:board-supported-hw::
+
+Connections and IOs
+===================
+
+In the following table, the column **Name** contains Pin names. For example, PA2
+means Pin number 2 on PORTA, as used in the board's datasheets and manuals.
+
++-------+--------------+-------------------------------------+
+| Name  | Function     | Usage                               |
++=======+==============+=====================================+
+| PA8   | UART_TX      | UART Console TX                     |
++-------+--------------+-------------------------------------+
+| PA9   | UART_RX      | UART Console RX                     |
++-------+--------------+-------------------------------------+
+| PB1   | GPIO         | Push Button 0                       |
++-------+--------------+-------------------------------------+
+| PB2   | GPIO         | LED0                                |
++-------+--------------+-------------------------------------+
+| PB3   | GPIO         | Push Button 1                       |
++-------+--------------+-------------------------------------+
+| PC1   | US1_TX       | Display/Flash SPI MOSI              |
++-------+--------------+-------------------------------------+
+| PC2   | US1_RX       | Serial Flash MISO                   |
++-------+--------------+-------------------------------------+
+| PC3   | US1_CLK      | Serial Flash/Display SPI Clock      |
++-------+--------------+-------------------------------------+
+| PC4   | US1_CS       | Serial Flash Chip Select            |
++-------+--------------+-------------------------------------+
+| PC5   | I2C0_SCL     | Si7021 I2C Clock                    |
++-------+--------------+-------------------------------------+
+| PC6   | GPIO         | External COM Inversion Signal       |
++-------+--------------+-------------------------------------+
+| PC7   | I2C0_SDA     | Si7021 I2C Data                     |
++-------+--------------+-------------------------------------+
+| PC8   | US1_CS       | Display Serial Chip Select          |
++-------+--------------+-------------------------------------+
+| PC9   | GPIO         | Display Control Access              |
++-------+--------------+-------------------------------------+
+| PC11  | GPIO         | Si7021 Enable                       |
++-------+--------------+-------------------------------------+
+| PD3   | GPIO         | LED1                                |
++-------+--------------+-------------------------------------+
+
+The default configuration can be found in
+:zephyr_file:`boards/silabs/radio_boards/xg28_rb4401c/xg28_rb4401c_defconfig`
+
+System Clock
+============
+
+The EFR32ZG28 SoC is configured to use the 39 MHz external oscillator on the
+board.
+
+Serial Port
+===========
+
+The EFR32ZG28 SoC has one USART and three EUSARTs.
+USART0 is connected to the board controller and is used for the console.
+
+Programming and Debugging
+*************************
+
+.. zephyr:board-supported-runners::
+
+Flashing
+========
+
+Connect the BRD4401C board with a mounted BRD4401C radio module to your host
+computer using the USB port.
+
+Here is an example for the :zephyr:code-sample:`hello_world` application.
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/hello_world
+   :board: xg28_rb4401c
+   :goals: flash
+
+Open a serial terminal (minicom, putty, etc.) with the following settings:
+
+- Speed: 115200
+- Data: 8 bits
+- Parity: None
+- Stop bits: 1
+
+Reset the board and you should see the following message in the terminal:
+
+.. code-block:: console
+
+   Hello World! xg28_rb4401c/efr32zg28b322f1024im68
+
+
+.. _xG28-PK6024A Website:
+   https://www.silabs.com/development-tools/wireless/efr32xg28-pro-kit-14-dbm
+
+.. _BRD4401C User Guide:
+   https://www.silabs.com/documents/public/user-guides/ug535-xg28-20dbm-user-guide.pdf
+
+.. _EFR32ZG28 Website:
+   https://www.silabs.com/wireless/z-wave/efr32zg28-z-wave-800-socs
+
+.. _EFR32ZG28 Datasheet:
+   https://www.silabs.com/documents/public/data-sheets/efr32zg28-datasheet.pdf
+
+.. _EFR32xG28 Reference Manual:
+   https://www.silabs.com/documents/public/reference-manuals/efr32xg28-rm.pdf

boards/silabs/radio_boards/xg28_rb4401c/pre_dt_board.cmake

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+# Copyright (c) 2021 Linaro Limited
+# SPDX-License-Identifier: Apache-2.0
+
+# SPI is implemented via usart so node name isn't spi@...
+list(APPEND EXTRA_DTC_FLAGS "-Wno-spi_bus_bridge")

boards/silabs/radio_boards/xg28_rb4401c/support/openocd.cfg

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+if {[info exists env(OPENOCD_INTERFACE)]} {
+	set INTERFACE $env(OPENOCD_INTERFACE)
+} else {
+	# By default connect over Debug USB port using the J-Link interface
+	set INTERFACE "jlink"
+}
+
+source [find interface/$INTERFACE.cfg]
+
+transport select swd
+
+set CHIPNAME efr32
+
+source [find target/efm32.cfg]
+
+$_TARGETNAME configure -event gdb-attach {
+	echo "Debugger attaching: halting execution"
+	reset halt
+	gdb_breakpoint_override hard
+}
+
+$_TARGETNAME configure -event gdb-detach {
+	echo "Debugger detaching: resuming execution"
+	resume
+}

boards/silabs/radio_boards/xg28_rb4401c/xg28_rb4401c-pinctrl.dtsi

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+/*
+ * Copyright (c) 2025 Shontal Biton
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <dt-bindings/pinctrl/silabs/xg28-pinctrl.h>
+
+&pinctrl {
+	eusart1_default: eusart1_default {
+		group0 {
+			pins = <EUSART1_TX_PC1>, <EUSART1_SCLK_PC3>;
+			drive-push-pull;
+			output-high;
+		};
+
+		group1 {
+			pins = <EUSART1_RX_PC2>;
+			input-enable;
+			silabs,input-filter;
+		};
+	};
+
+	i2c0_default: i2c0_default {
+		group0 {
+			pins = <I2C0_SCL_PC5>, <I2C0_SDA_PC7>;
+			drive-open-drain;
+			bias-pull-up;
+		};
+	};
+
+	timer0_default: timer0_default {
+		group0 {
+			pins = <TIMER0_CC0_PB2>, <TIMER0_CC1_PD3>;
+			drive-push-pull;
+			output-high;
+		};
+	};
+
+	usart0_default: usart0_default {
+		group0 {
+			pins = <USART0_TX_PA8>;
+			drive-push-pull;
+			output-high;
+		};
+
+		group1 {
+			pins = <USART0_RX_PA9>;
+			input-enable;
+			silabs,input-filter;
+		};
+	};
+};