Do not use the RTC to track a bootloader request

Instead, use a .noinit variable, which survives across reboots.

Note: This file uses the bool type, so needs to include stdbool.h.
It seems that for the F4, this was indirectly included elsewhere,
but for e.g. F0, this did not seem to be the case, causing the build
to fail.

Author: matthijskooijman

cores/arduino/stm32/backup.h

@@ -59,15 +59,6 @@ extern "C" {
 #endif /* HID_MAGIC_NUMBER_BKP_VALUE */
 #endif /* BL_HID */
 
-#if !defined(SYSBL_MAGIC_NUMBER_BKP_INDEX) && defined(ENABLE_BACKUP_SUPPORT)
-#define SYSBL_MAGIC_NUMBER_BKP_INDEX LL_RTC_BKP_DR2
-#else
-#define SYSBL_MAGIC_NUMBER_BKP_INDEX 0
-#endif /* SYSBL_MAGIC_NUMBER_BKP_INDEX */
-#ifndef SYSBL_MAGIC_NUMBER_BKP_VALUE
-#define SYSBL_MAGIC_NUMBER_BKP_VALUE 0x515B
-#endif /* SYSBL_MAGIC_NUMBER_BKP_VALUE */
-
 /* Exported functions ------------------------------------------------------- */
 static inline void resetBackupDomain(void)
 {

libraries/SrcWrapper/src/stm32/bootloader.c

@@ -1,3 +1,5 @@
+#include <stdbool.h>
+
 #include "bootloader.h"
 
 #include "stm32_def.h"
@@ -11,6 +13,8 @@
 /* Private definitions to manage system memory address */
 #define SYSMEM_ADDR_COMMON 0xFFF
 
+static bool BootIntoBootloaderAfterReset __attribute__((__section__(".noinit")));
+
 typedef struct {
   uint32_t devID;
   uint32_t sysMemAddr;
@@ -79,18 +83,25 @@ uint32_t getSysMemAddr(void)
 /* Request to jump to system memory boot */
 WEAK void jumpToBootloaderRequested(void)
 {
-  enableBackupDomain();
-  setBackupRegister(SYSBL_MAGIC_NUMBER_BKP_INDEX, SYSBL_MAGIC_NUMBER_BKP_VALUE);
+  BootIntoBootloaderAfterReset = true;
   NVIC_SystemReset();
 }
 
 /* Jump to system memory boot from user application */
 WEAK void jumpToBootloader(void)
 {
-  enableBackupDomain();
-  if (getBackupRegister(SYSBL_MAGIC_NUMBER_BKP_INDEX) == SYSBL_MAGIC_NUMBER_BKP_VALUE) {
-    setBackupRegister(SYSBL_MAGIC_NUMBER_BKP_INDEX, 0);
+  // Boot into bootloader if BootIntoBootloaderAfterReset is set.
+  // Note that BootIntoBootloaderAfterReset is a noinit variable, so it
+  // s not automatically initialized on startup (so it can keep its
+  // value across resets). At initial poweron, its value can be
+  // *anything*, so only consider its value after a software reset. In
+  // all cases, clear its value (this both takes care of giving it an
+  // initial value after power-up, and prevents booting into the
+  // bootloader more than once for a single request).
+  bool doBootloader = __HAL_RCC_GET_FLAG(RCC_FLAG_SFTRST) && BootIntoBootloaderAfterReset;
+  BootIntoBootloaderAfterReset = false;
 
+  if (doBootloader) {
 #ifdef USBCON
     USBD_reenumerate();
 #endif