Override Reset_Handler to jump to bootloader

Author: matthijskooijman

cores/arduino/stm32/startup_stm32yyxx.S

@@ -3,3 +3,8 @@
 #if defined(CMSIS_STARTUP_FILE)
 #include CMSIS_STARTUP_FILE
 #endif
+
+# Expose Reset_Handler under a different name, to allow overriding it
+# with a strong symbol and then calling the original.
+.global Original_Reset_Handler
+.thumb_set Original_Reset_Handler,Reset_Handler

libraries/SrcWrapper/src/stm32/bootloader.c

@@ -13,7 +13,7 @@
 /* Private definitions to manage system memory address */
 #define SYSMEM_ADDR_COMMON 0xFFF
 
-static bool BootIntoBootloaderAfterReset __attribute__((__section__(".noinit")));
+static bool BootIntoBootloaderAfterReset;
 
 typedef struct {
   uint32_t devID;
@@ -87,6 +87,18 @@ WEAK void jumpToBootloaderRequested(void)
   NVIC_SystemReset();
 }
 
+// This overrides the Reset_Handler that is run on reset before
+// *anything* else (including memory initialization). Only the stack
+// pointer is set up by this time.
+void Reset_Handler()
+{
+  // Jump to the bootloader if needed.
+  jumpToBootloader();
+
+  // Continue with regular startup by calling the original reset handler
+  Original_Reset_Handler();
+}
+
 /* Jump to system memory boot from user application */
 WEAK void jumpToBootloader(void)
 {

libraries/SrcWrapper/src/stm32/hw_config.c

@@ -60,9 +60,6 @@ void hw_config_init(void)
   /* Initialize the HAL */
   HAL_Init();
 
-  /* Check if a jump to system memory boot requested */
-  jumpToBootloader();
-
   /* Configure the system clock */
   SystemClock_Config();