let's use the same general names across projects so I don't have to think about multiple paths

firmware/app/CMakeLists.txt

@@ -0,0 +1,5 @@
+cmake_minimum_required(VERSION 3.20.0)
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(blinky)
+
+target_sources(app PRIVATE src/main.c)

firmware/app/prj.conf

@@ -0,0 +1 @@
+CONFIG_GPIO=y

firmware/app/src/main.c

@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2016 Intel Corporation
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <stdio.h>
+#include <zephyr/kernel.h>
+#include <zephyr/drivers/gpio.h>
+
+/* 1000 msec = 1 sec */
+#define SLEEP_TIME_MS 100
+
+/* The devicetree node identifier for the "led0" alias. */
+#define LED0_NODE DT_ALIAS(led0)
+
+/*
+ * A build error on this line means your board is unsupported.
+ * See the sample documentation for information on how to fix this.
+ */
+static const struct gpio_dt_spec led = GPIO_DT_SPEC_GET(LED0_NODE, gpios);
+
+int main(void)
+{
+    int ret;
+    bool led_state = true;
+
+    if (!gpio_is_ready_dt(&led))
+    {
+        return 0;
+    }
+
+    ret = gpio_pin_configure_dt(&led, GPIO_OUTPUT_ACTIVE);
+    if (ret < 0)
+    {
+        return 0;
+    }
+
+    while (1)
+    {
+        ret = gpio_pin_toggle_dt(&led);
+        if (ret < 0)
+        {
+            return 0;
+        }
+
+        led_state = !led_state;
+        printf("LED state: %s\n", led_state ? "ON" : "OFF");
+        k_msleep(SLEEP_TIME_MS);
+    }
+    return 0;
+}

firmware/west.yml

@@ -0,0 +1,26 @@
+manifest:
+  # self:
+  #   west-commands: scripts/west-commands.yml
+
+  remotes:
+    - name: zephyrproject-rtos
+      url-base: https://github.com/zephyrproject-rtos
+    # - name: mcu-tools
+    #   url-base: https://github.com/mcu-tools
+
+  projects:
+    - name: zephyr
+      remote: zephyrproject-rtos
+      revision: main
+      import: true
+      #   # By using name-allowlist we can clone only the modules that are
+      #   # strictly needed by the application.
+      #   name-allowlist:
+      #     - cmsis      # required by the ARM port
+      #     - hal_nordic # required by the custom_plank board (Nordic based)
+      #     - hal_stm32  # required by the nucleo_f302r8 board (STM32 based)
+      #     - zcbor      # required by mcuboot serial
+      #     - tinycrypt
+    # - name: mcuboot
+    #   remote: mcu-tools
+    #   revision: main