bootloader: Add support for cleaning up RAM before application boot

Adds a new Kconfig which, when enabled, will clear all RAM to 0
before loading into the application to chain load, this can be
enabled with CONFIG_SB_CLEANUP_RAM

Signed-off-by: Jamie McCrae <[email protected]>

Author: nordicjm

subsys/bootloader/Kconfig

@@ -210,6 +210,13 @@ config SB_BPROT_IN_DEBUG
 	default y
 	depends on (HAS_HW_NRF_BPROT || HAS_HW_NRF_MPU)
 
+config SB_CLEANUP_RAM
+	bool "Perform RAM cleanup"
+	depends on !FW_INFO_PROVIDE_ENABLE
+	depends on CPU_CORTEX_M4 || CPU_CORTEX_M33
+	help
+	  Sets contents of memory to 0 before jumping to application.
+
 endif # IS_SECURE_BOOTLOADER
 
 config IS_BOOTLOADER_IMG

subsys/bootloader/bl_boot/bl_boot.c

@@ -156,7 +156,34 @@ void bl_boot(const struct fw_info *fw_info)
 	__set_MSP(vector_table[0]);
 	__set_PSP(0);
 
+#if CONFIG_SB_CLEANUP_RAM
+	__asm__ volatile (
+		/* vector_table[1] -> r0 */
+		"   mov r0, %0\n"
+		/* Base to write -> r1 */
+		"   mov r1, %1\n"
+		/* Size to write -> r2 */
+		"   mov r2, %2\n"
+		/* Value to write -> r3 */
+		"   mov r3, %3\n"
+		"clear:\n"
+		"   str r3, [r1]\n"
+		"   add r1, r1, #4\n"
+		"   sub r2, r2, #4\n"
+		"   cbz r2, out\n"
+		"   b   clear\n"
+		"out:\n"
+		"   dsb\n"
+		/* Jump to reset vector of an app */
+		"   bx r0\n"
+		:
+		: "r" (vector_table[1]), "i" (CONFIG_SRAM_BASE_ADDRESS),
+		  "i" (CONFIG_SRAM_SIZE * 1024), "i" (0)
+		: "r0", "r1", "r2", "r3", "memory"
+	);
+#else
 	/* Call reset handler. */
 	((void (*)(void))vector_table[1])();
+#endif
 	CODE_UNREACHABLE;
 }

subsys/fw_info/Kconfig

@@ -118,6 +118,11 @@ config FW_INFO_VALID_VAL
 	help
 	  The value fw_info::valid will have when valid.
 
+config FW_INFO_PROVIDE_ENABLE
+	bool
+	help
+	  Hidden option, set if at least one *_EXT_API_ENABLED option is enabled.
+
 EXT_API = EXT_API_PROVIDE
 id = 0x1200
 flags = 0

subsys/fw_info/Kconfig.template.fw_info_ext_api

@@ -41,6 +41,7 @@ config $(EXT_API)_EXT_API_ATLEAST_REQUIRED
 
 config $(EXT_API)_EXT_API_ENABLED
 	bool "Provide the $(EXT_API) EXT_API to other images"
+	select FW_INFO_PROVIDE_ENABLE
 	help
 	  Provide this EXT_API to other images.