refactor(boards): Move to ZMK specific variant for the bluemicro840 board

For consistency, adjust the bluemicro840 board definition to offer a
"vanilla" Zephyr board, and then ZMK variant, e.g. `bluemicro840//zmk`.

app/boards/jpconstantineau/bluemicro840/Kconfig.bluemicro840

@@ -1,8 +1,8 @@
-# Copyright (c) 2020 Pete Johanson, Derek Schmell
+# Copyright (c) 2026 Pete Johanson, Derek Schmell
 # SPDX-License-Identifier: Apache-2.0
 
 config BOARD_BLUEMICRO840
     select SOC_NRF52840_QIAA
-    imply RETAINED_MEM
-    imply RETENTION
-    imply RETENTION_BOOT_MODE
+    imply RETAINED_MEM if BOARD_BLUEMICRO840_NRF52840_ZMK
+    imply RETENTION if BOARD_BLUEMICRO840_NRF52840_ZMK
+    imply RETENTION_BOOT_MODE if BOARD_BLUEMICRO840_NRF52840_ZMK

app/boards/jpconstantineau/bluemicro840/bluemicro840.zmk.yml

@@ -1,5 +1,5 @@
 file_format: "1"
-id: bluemicro840
+id: bluemicro840//zmk
 name: BlueMicro840 v1
 type: board
 arch: arm

app/boards/jpconstantineau/bluemicro840/bluemicro840_nrf52840_zmk.dts

@@ -0,0 +1,29 @@
+/*
+ * Copyright (c) 2026 Pete Johanson, Derek Schmell
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <../boards/jpconstantineau/bluemicro840/bluemicro840.dts>
+#include <common/nordic/nrf52840_uf2_boot_mode.dtsi>
+
+/ {
+    chosen {
+        zmk,battery = &vbatt;
+    };
+
+    // Node name must match original "EXT_POWER" label to preserve user settings.
+    EXT_POWER {
+        compatible = "zmk,ext-power-generic";
+        init-delay-ms = <20>;
+        control-gpios = <&gpio0 12 GPIO_ACTIVE_HIGH>;
+    };
+
+    vbatt: vbatt {
+        compatible = "zmk,battery-voltage-divider";
+        io-channels = <&adc 7>;
+        output-ohms = <2000000>;
+        full-ohms = <(2000000 + 806000)>;
+    };
+
+};

app/boards/jpconstantineau/bluemicro840/board.yml

@@ -1,5 +1,5 @@
 board:
-  name: bluemicro840
-  vendor: jpconstantineau
-  socs:
-    - name: nrf52840
+  extend: bluemicro840
+  variants:
+    - name: zmk
+      qualifier: nrf52840

app/module/boards/jpconstantineau/bluemicro840/Kconfig.bluemicro840

@@ -0,0 +1,5 @@
+# Copyright (c) 2026 Pete Johanson, Derek Schmell
+# SPDX-License-Identifier: Apache-2.0
+
+config BOARD_BLUEMICRO840
+    select SOC_NRF52840_QIAA

app/module/boards/jpconstantineau/bluemicro840/bluemicro840.dts

@@ -6,7 +6,6 @@
 
 /dts-v1/;
 #include <nordic/nrf52840_qiaa.dtsi>
-#include <common/nordic/nrf52840_uf2_boot_mode.dtsi>
 
 #include "arduino_pro_micro_pins.dtsi"
 #include "bluemicro840-pinctrl.dtsi"
@@ -19,7 +18,6 @@
         zephyr,code-partition = &code_partition;
         zephyr,sram = &sram0;
         zephyr,flash = &flash0;
-        zmk,battery = &vbatt;
     };
 
     leds {
@@ -28,21 +26,6 @@
             gpios = <&gpio1 10 GPIO_ACTIVE_HIGH>;
         };
     };
-
-    // Node name must match original "EXT_POWER" label to preserve user settings.
-    EXT_POWER {
-        compatible = "zmk,ext-power-generic";
-        init-delay-ms = <20>;
-        control-gpios = <&gpio0 12 GPIO_ACTIVE_HIGH>;
-    };
-
-    vbatt: vbatt {
-        compatible = "zmk,battery-voltage-divider";
-        io-channels = <&adc 7>;
-        output-ohms = <2000000>;
-        full-ohms = <(2000000 + 806000)>;
-    };
-
 };
 
 &adc {

app/module/boards/jpconstantineau/bluemicro840/bluemicro840.yaml

@@ -0,0 +1,15 @@
+identifier: bluemicro840
+name: BlueMicro840_V1
+type: mcu
+arch: arm
+toolchain:
+  - zephyr
+  - gnuarmemb
+  - xtools
+supported:
+  - adc
+  - usb_device
+  - ble
+  - ieee802154
+  - pwm
+  - watchdog

app/module/boards/jpconstantineau/bluemicro840/bluemicro840_defconfig

@@ -0,0 +1,13 @@
+# SPDX-License-Identifier: MIT
+
+# Enable MPU
+CONFIG_ARM_MPU=y
+
+CONFIG_PINCTRL=y
+
+# enable GPIO
+CONFIG_GPIO=y
+
+CONFIG_USE_DT_CODE_PARTITION=y
+CONFIG_BUILD_OUTPUT_UF2=y
+

app/module/boards/jpconstantineau/bluemicro840/board.cmake

@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: MIT
+
+board_runner_args(nrfjprog "--nrf-family=NRF52" "--softreset")
+include(${ZEPHYR_BASE}/boards/common/uf2.board.cmake)
+include(${ZEPHYR_BASE}/boards/common/nrfjprog.board.cmake)

app/module/boards/jpconstantineau/bluemicro840/board.yml

@@ -0,0 +1,5 @@
+board:
+  name: bluemicro840
+  vendor: jpconstantineau
+  socs:
+    - name: nrf52840

app/module/boards/jpconstantineau/bluemicro840/pre_dt_board.cmake

@@ -0,0 +1,9 @@
+#
+# Copyright (c) 2026 The ZMK Contributors
+# SPDX-License-Identifier: MIT
+#
+
+# Suppresses duplicate unit-address warning at build time for power, clock, acl and flash-controller
+# https://docs.zephyrproject.org/latest/build/dts/intro-input-output.html
+
+list(APPEND EXTRA_DTC_FLAGS "-Wno-unique_unit_address_if_enabled")