snippets: add a snippet for RAM boot on RP2350 SoC

Should be also possible on RP2040 but has less practical applications due to lack of UART boot.

Usage: `west build -b rpi_pico2/rp2350a/m33 -S rp2350-ram-boot samples/subsys/usb/console`

Signed-off-by: Dmitrii Sharshakov <d3dx12.xx@gmail.com>

Author: dsseng

snippets/rp2350-ram-boot/rp2350-ram-boot.overlay

@@ -0,0 +1,61 @@
+/*
+ * Copyright (c) 2025 Dmitrii Sharshakov
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/* We should partition SRAM between executable and data */
+/delete-node/ &sram0;
+
+&flash0 {
+	/* remove image definition and code partition in Flash */
+	/delete-node/ partitions;
+};
+
+#define RP2350_RAM_TOTAL_SIZE DT_SIZE_K(520)
+#define RP2350_RAM_CODE_SIZE  DT_SIZE_K(256)
+// Has to be adjusted as 0x20000000 + RP2350_RAM_CODE_SIZE if code partition is resized
+#define RP2350_RAM_OFFSET     20040000
+#define RP2350_IMAGE_DEF_SIZE 0x100
+
+/ {
+	chosen {
+		zephyr,sram = &sram0_ram;
+		zephyr,flash = &sram0_code;
+	};
+
+	sram0_code: memory@20000000 {
+		compatible = "mmio-sram";
+		reg = <0x20000000 RP2350_RAM_CODE_SIZE>;
+
+		partitions {
+			compatible = "fixed-partitions";
+			#address-cells = <1>;
+			#size-cells = <1>;
+
+			/* Reserved memory for an image definition block added by linker.
+			 * The block is much smaller than 256 bytes, but in practice the
+			 * linker places the vector table at a much larger alignment offset.
+			 */
+			image_def: partition@0 {
+				label = "image_def";
+				reg = <0x00000000 RP2350_IMAGE_DEF_SIZE>;
+				read-only;
+			};
+
+			/* Actual code, whole code RAM - 0x100 for header */
+			code_partition: partition@100 {
+				label = "code-partition";
+				reg = <RP2350_IMAGE_DEF_SIZE
+					(RP2350_RAM_CODE_SIZE - RP2350_IMAGE_DEF_SIZE)>;
+				read-only;
+			};
+		};
+	};
+
+	sram0_ram: memory@RP2350_RAM_OFFSET {
+		compatible = "mmio-sram";
+		reg = <(0x20000000 + RP2350_RAM_CODE_SIZE)
+			(RP2350_RAM_TOTAL_SIZE - RP2350_RAM_CODE_SIZE - RP2350_IMAGE_DEF_SIZE)>;
+	};
+};

snippets/rp2350-ram-boot/snippet.yml

@@ -0,0 +1,6 @@
+# Copyright (c) 2025 Dmitrii Sharshakov
+# SPDX-License-Identifier: Apache-2.0
+
+name: rp2350-ram-boot
+append:
+  EXTRA_DTC_OVERLAY_FILE: rp2350-ram-boot.overlay

soc/raspberrypi/rpi_pico/rp2350/linker.ld

@@ -7,9 +7,12 @@
  */
 
 #if CONFIG_RP2_REQUIRES_IMAGE_DEFINITION_BLOCK
+#include <zephyr/devicetree.h>
+
 MEMORY
 {
-	IMAGE_DEF_FLASH (r) : ORIGIN = 0x10000000, LENGTH = 128
+	/* place image definition before the image start as per DT */
+	IMAGE_DEF_FLASH (r) : ORIGIN = DT_REG_ADDR(DT_CHOSEN(zephyr_flash)), LENGTH = 128
 }
 
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