snippets: thingy91x-uart0-exp-board: new snippet

This snippet can be used to expose console and shell on Expansion Board for
thingy91x. This is useful for having nrf9151 logs on this UART interface
and nrf5340 logs on RTT interface.

Signed-off-by: Marcin Niestroj <marcin.niestroj@canonical.com>

Author: mniestroj

ncs-serial-modem/boards/nrf9160dk_nrf9160_ns.overlay

@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2026 Golioth, Inc.
+ *
+ * SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
+ */
+
+#include <nrf9160/nrf9160dk_uart1_on_if0_3.dtsi>
+
+/ {
+	chosen {
+		ncs,sm-uart = &dtr_uart1;
+	};
+};
+
+&uart1 {
+	compatible = "nordic,nrf-uarte";
+        current-speed = <115200>;
+        hw-flow-control;
+	status = "okay";
+
+	dtr_uart1: dtr-uart {
+		compatible = "nordic,dtr-uart";
+		dtr-gpios = <&interface_to_nrf52840 4 (GPIO_PULL_DOWN | GPIO_ACTIVE_LOW)>;
+		ri-gpios = <&interface_to_nrf52840 5 (GPIO_ACTIVE_LOW)>;
+		status = "okay";
+	};
+};
+
+&gpio0 {
+	status = "okay";
+	/* Use PORT event for DTR (22) pin to save power */
+	sense-edge-mask = <0x00400000>;
+};

zephyr/module.yml

@@ -3,6 +3,7 @@ build:
   kconfig: Kconfig
   settings:
     board_root: .
+    snippet_root: zephyr
 samples:
   - samples
 runners:

zephyr/snippets/thingy91x-uart0-exp-board/snippet.yml

@@ -0,0 +1,5 @@
+name: thingy91x-uart0-exp-board
+boards:
+  /thingy91x/nrf9151/ns/:
+    append:
+      EXTRA_DTC_OVERLAY_FILE: thingy91x-uart0-exp-board.overlay

zephyr/snippets/thingy91x-uart0-exp-board/thingy91x-uart0-exp-board.overlay

@@ -0,0 +1,24 @@
+&uart0 {
+	pinctrl-0 = <&uart_exp_board_default>;
+	pinctrl-1 = <&uart_exp_board_sleep>;
+};
+
+&pinctrl {
+	uart_exp_board_default: uart_exp_board_default {
+		group1 {
+			psels = <NRF_PSEL(UART_TX, 0, 18)>;
+		};
+		group2 {
+			psels = <NRF_PSEL(UART_RX, 0, 19)>;
+			bias-pull-up;
+		};
+	};
+
+	uart_exp_board_sleep: uart_exp_board_sleep {
+		group1 {
+			psels = <NRF_PSEL(UART_TX, 0, 18)>,
+				<NRF_PSEL(UART_RX, 0, 19)>;
+			low-power-enable;
+		};
+	};
+};