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.

Useful for UART boot as well as development.

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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