riotboot_dfu: Stay in DFU mode if button is pressed

Boards can override this; by default it's BTN0

bootloaders/riotboot_dfu/bootloader_selection.h

@@ -0,0 +1,78 @@
+/*
+ * Copyright (C) 2020 Christian Amsüss <chrysn@fsfe.org>
+ *
+ * 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 Configuration for the riotboot_dfu bootloader
+ *
+ * @author Christian Amsüss <chrysn@fsfe.org>
+ */
+
+/* Include guards and cplusplus are more of a formality; this header is local
+ * to the riotboot_dfu application that isn't written in C++ and not included
+ * from anywhere else either, but still here for consistency (and because
+ * otherwise the checks complain) */
+#ifndef BOOTLOADER_SELECTION_H
+#define BOOTLOADER_SELECTION_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Not including GPIO headers: we're not actually *doing* anything on GPIO, and
+ * if no BTN0_PIN is defined we don't define anything either */
+#include <board.h>
+
+
+/** @brief Button pin for bootloader selection
+ *
+ * This pin (typically connected to a button) is checked by the riotboot_dfu
+ * bootloader to decide whether to enter DFU mode even if a valid image is
+ * present.
+ *
+ * The default value for all boards is BTN0, if one is defined.
+ *
+ * Boards that insist on not using any button even though they have some can
+ * define BTN_BOOTLOADER_NONE in their `board.h`.
+ *
+ * */
+#if (!defined(BTN_BOOTLOADER_PIN) && defined(BTN0_PIN) && !defined(BTN_BOOTLOADER_NONE)) || DOXYGEN
+#define BTN_BOOTLOADER_PIN BTN0_PIN
+#endif
+
+/** @brief Pin mode for @ref BTN_BOOTLOADER_PIN
+ *
+ * Mode into which the riotboot_dfu bootloader will configure @ref
+ * BTN_BOOTLOADER_PIN before reading it.
+ *
+ * */
+#ifndef BTN_BOOTLOADER_MODE
+#define BTN_BOOTLOADER_MODE BTN0_MODE
+#endif
+
+/** @brief Interpretation of @ref BTN_BOOTLOADER_PIN.
+ *
+ * Set to true for active-low buttons (go to DFU if the pin is low), otherwise
+ * to false (go to DFU if the pin is high).
+ *
+ * The default value for all boards is inverted (active-low).
+ *
+ * */
+#ifndef BTN_BOOTLOADER_INVERTED
+#define BTN_BOOTLOADER_INVERTED true
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* BOOTLOADER_SELECTION_H */
+
+/** @} */

bootloaders/riotboot_dfu/main.c

@@ -27,6 +27,22 @@
 #include "riotboot/slot.h"
 #include "riotboot/usb_dfu.h"
 
+#include "bootloader_selection.h"
+
+#ifdef BTN_BOOTLOADER_PIN
+#include "periph/gpio.h"
+#endif
+
+static bool _bootloader_alternative_mode(void)
+{
+#ifdef BTN_BOOTLOADER_PIN
+    gpio_init(BTN_BOOTLOADER_PIN, BTN_BOOTLOADER_MODE);
+    return (bool)gpio_read(BTN_BOOTLOADER_PIN) != BTN_BOOTLOADER_INVERTED;
+#else
+    return false;
+#endif
+}
+
 void kernel_init(void)
 {
     uint32_t version = 0;
@@ -50,7 +66,7 @@ void kernel_init(void)
     /* Flash the unused slot if magic word is set */
     riotboot_usb_dfu_init(0);
 
-    if (slot != -1) {
+    if (slot != -1 && !_bootloader_alternative_mode()) {
         riotboot_slot_jump(slot);
     }