bootloader: create new bootloader application with DFU support

bootloaders/riotboot_dfu/Makefile

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+# Default RIOT bootloader
+APPLICATION = riotboot_dfu
+
+# Default testing board
+BOARD ?= samr21-xpro
+
+# Select the boards with riotboot feature
+FEATURES_REQUIRED += riotboot
+
+# Set RIOTBOOT_BUILD to indicate a riotboot application build
+RIOTBOOT_BUILD = 1
+# Provide a define to detect if building the bootloader
+CFLAGS += -DRIOTBOOT
+
+# Disable unused modules
+CFLAGS += -DNDEBUG -DLOG_LEVEL=LOG_NONE
+DISABLE_MODULE += core_init core_msg core_panic
+DISABLE_MODULE += auto_init auto_init_%
+
+# avoid using stdio
+USEMODULE += stdio_null
+
+# Include riotboot flash partition functionality
+USEMODULE += riotboot_slot
+
+# Add RIOTBOOT USB DFU integration
+USEMODULE=riotboot_usb_dfu
+
+# Use xtimer for scheduled reboot
+USEMODULE += xtimer
+
+# RIOT codebase
+RIOTBASE ?= $(CURDIR)/../../
+
+# USB device vendor and product ID
+# pid.codes test VID/PID, not globally unique
+
+USB_VID ?= ${USB_VID_TESTING}
+USB_PID ?= ${USB_PID_TESTING}
+
+include $(RIOTBASE)/Makefile.include
+
+# limit riotboot bootloader size
+# TODO: Manage to set this variable for boards which already embed a
+# bootloader, currently it will be overwritten
+ROM_LEN := $(RIOTBOOT_LEN)

bootloaders/riotboot_dfu/main.c

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+/*
+ * Copyright (C) 2017 Kaspar Schleiser <kaspar@schleiser.de>
+ *                    Inria
+ *               2020 Mesotic SAS
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     bootloaders
+ * @{
+ *
+ * @file
+ * @brief      RIOT-based bootloader with USB-DFU support
+ *
+ * @author     Kaspar Schleiser <kaspar@schleiser.de>
+ * @author     Francisco Acosta <francisco.acosta@inria.fr>
+ * @author     Dylan Laduranty <dylan.laduranty@mesotic.com>
+ *
+ * @}
+ */
+
+#include "cpu.h"
+#include "panic.h"
+#include "riotboot/slot.h"
+#include "riotboot/usb_dfu.h"
+
+void kernel_init(void)
+{
+    uint32_t version = 0;
+    int slot = -1;
+
+    for (unsigned i = 0; i < riotboot_slot_numof; i++) {
+        const riotboot_hdr_t *riot_hdr = riotboot_slot_get_hdr(i);
+        if (riotboot_slot_validate(i)) {
+            /* skip slot if metadata broken */
+            continue;
+        }
+        if (riot_hdr->start_addr != riotboot_slot_get_image_startaddr(i)) {
+            continue;
+        }
+        if (slot == -1 || riot_hdr->version > version) {
+            version = riot_hdr->version;
+            slot = i;
+        }
+    }
+
+    /* Flash the unused slot if magic word is set */
+    riotboot_usb_dfu_init(0);
+
+    if (slot != -1) {
+        riotboot_slot_jump(slot);
+    }
+
+    /* Nothing to boot, stay in DFU mode to flash a slot */
+    riotboot_usb_dfu_init(1);
+}
+
+NORETURN void core_panic(core_panic_t crash_code, const char *message)
+{
+    (void)crash_code;
+    (void)message;
+    while (1) {}
+}