rioboot: add option to reset to riotboot

sys/Makefile.dep

@@ -1000,10 +1000,15 @@ endif
 ifneq (,$(filter riotboot_serial, $(USEMODULE)))
   FEATURES_REQUIRED += periph_flashpage
   FEATURES_REQUIRED += periph_uart
-  USEMODULE += riotboot
+  USEMODULE += riotboot_reset
   USEMODULE += checksum
 endif
 
+ifneq (,$(filter riotboot_reset, $(USEMODULE)))
+  USEMODULE += riotboot
+  USEMODULE += usb_board_reset
+endif
+
 ifneq (,$(filter riotboot_hdr, $(USEMODULE)))
   USEMODULE += checksum
   USEMODULE += riotboot

sys/Makefile.include

@@ -131,7 +131,7 @@ ifneq (,$(filter prng,$(USEMODULE)))
   include $(RIOTBASE)/sys/random/Makefile.include
 endif
 
-ifneq (,$(filter usbus_dfu,$(USEMODULE)))
+ifneq (,$(filter usbus_dfu riotboot_reset,$(USEMODULE)))
   CFLAGS += -DCPU_RAM_BASE=$(RAM_START_ADDR)
   CFLAGS += -DCPU_RAM_SIZE=$(RAM_LEN)
 endif

sys/riotboot/reset.c

@@ -0,0 +1,32 @@
+/*
+ * Copyright (C) 2020 Benjamin Valentin
+ *
+ * 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     sys_riotboot_serial
+ * @{
+ *
+ * @file
+ * @brief       Trigger reset to riotboot.
+ *
+ * @author      Benjamin Valentin <[email protected]>
+ * @}
+ */
+
+#include <string.h>
+#include "periph/pm.h"
+#include "riotboot/magic.h"
+
+__attribute__((weak))
+void usb_board_reset_in_bootloader(void)
+{
+    uint32_t *magic = (void*)RIOTBOOT_MAGIC_ADDR;
+
+    irq_disable();
+    *magic = RIOTBOOT_MAGIC;
+    pm_reboot();
+}

sys/riotboot/serial.c

@@ -27,6 +27,7 @@
 #include "unaligned.h"
 #include "checksum/crc8.h"
 #include "riotboot/serial.h"
+#include "riotboot/magic.h"
 
 #include "board.h"
 
@@ -55,6 +56,13 @@ static inline void uart_write_byte(uart_t uart, uint8_t data)
 /* send 'hello' byte until we get enter bootloader byte or timeout */
 static bool _bootdelay(unsigned tries, volatile bool *boot_default)
 {
+    uint32_t *magic = (void*)RIOTBOOT_MAGIC_ADDR;
+
+    if (*magic == RIOTBOOT_MAGIC) {
+        *magic = 0;
+        return false;
+    }
+
     if (tries == 0) {
         return true;
     }