samples: fs: fat_fs: Add RAM disk sample for nrf52840dk

Add configuration for nrf52840dk that allows to create RAM
disk; this configuration does not reserve special region
in RAM using DTS but uses automatic buffer allocation, by RAM
Disk Drivers, according to RAM disk specification in DTS.

Signed-off-by: Dominik Ermel <[email protected]>

Author: de-nordic

samples/subsys/fs/fs_sample/boards/nrf52840dk_nrf52840_ram_disk.conf

@@ -0,0 +1,13 @@
+#
+# Copyright (c) 2024 Nordic Semiconductor ASA
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+CONFIG_DISK_DRIVERS=y
+CONFIG_DISK_DRIVER_RAM=y
+CONFIG_DISK_DRIVER_FLASH=n
+# There may be no files on internal SoC flash, so this Kconfig
+# options has ben enabled to create some if listing does not
+# find in the first place.
+CONFIG_FS_SAMPLE_CREATE_SOME_ENTRIES=y

samples/subsys/fs/fs_sample/boards/nrf52840dk_nrf52840_ram_disk.overlay

@@ -0,0 +1,21 @@
+/*
+ * Copyright (c) 2024 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/ {
+	msc_disk0 {
+		status="okay";
+		compatible = "zephyr,ram-disk";
+		/* Sample, to make things easier, mounts all FAT
+		 * systems at "SD".
+		 */
+		disk-name = "SD";
+		/* Disk size is 64kB, 128 sectors of 512B, the minimal
+		 * required by FAT FS.
+		 */
+		sector-size = <512>;
+		sector-count = <128>;
+	};
+};

samples/subsys/fs/fs_sample/sample.yaml

@@ -31,6 +31,12 @@ tests:
   sample.filesystem.fat_fs.nrf52840dk_nrf52840:
     build_only: true
     platform_allow: nrf52840dk/nrf52840
+  sample.filesystem.fat_fs.nrf52840dk_nrf52840_ram_disk:
+    build_only: true
+    platform_allow: nrf52840dk/nrf52840
+    extra_args:
+      - OVERLAY_CONFIG=boards/nrf52840dk_nrf52840_ram_disk.conf
+      - DTC_OVERLAY_FILE=boards/nrf52840dk_nrf52840_ram_disk.overlay
   sample.filesystem.fat_fs.nrf52840dk_nrf52840.qspi:
     build_only: true
     platform_allow: nrf52840dk/nrf52840