The library bootloaders will now correctly start the user application after a watchdog-based application start, even if the /HWB line is held low externally during the reset phase.

2 files changed, 29 insertions, 0 deletions

diff --git a/Bootloaders/CDC/BootloaderCDC.c b/Bootloaders/CDC/BootloaderCDC.c
index a7fc883cf..d057349c7 100644
--- a/Bootloaders/CDC/BootloaderCDC.c
+++ b/Bootloaders/CDC/BootloaderCDC.c
@@ -56,6 +56,27 @@ static uint32_t CurrAddress;
  */
 static bool RunBootloader = true;
 
+/** Magic lock for forced application start. If the HWBE fuse is programmed and BOOTRST is unprogrammed, the bootloader
+ *  will start if the /HWB line of the AVR is held low and the system is reset. However, if the /HWB line is still held
+ *  low when the application attempts to start via a watchdog reset, the bootloader will re-start. If set to the value
+ *  \ref MAGIC_BOOT_KEY the special init function \ref Application_Jump_Check() will force the application to start.
+ */
+uint32_t MagicBootKey ATTR_NO_INIT;
+
+
+/** Special startup routine to check if the bootloader was started via a watchdog reset, and if the magic application
+ *  start key has been loaded into \ref MagicBootKey. If the bootloader started via the watchdog and the key is valid,
+ *  this will force the user application to start via a software jump.
+ */
+void Application_Jump_Check(void)
+{
+	// If the reset source was the bootloader and the key is correct, clear it and jump to the application
+	if ((MCUSR & (1 << WDRF)) && (MagicBootKey == MAGIC_BOOT_KEY))
+	{
+		MagicBootKey = 0;
+		((void (*)(void))0x0000)();
+	}
+}
 
 /** Main program entry point. This routine configures the hardware required by the bootloader, then continuously
  *  runs the bootloader processing routine until instructed to soft-exit, or hard-reset via the watchdog to start
@@ -80,6 +101,9 @@ int main(void)
 
 	/* Disconnect from the host - USB interface will be reset later along with the AVR */
 	USB_Detach();
+	
+	/* Unlock the forced application start mode of the bootloader if it is restarted */
+	MagicBootKey = MAGIC_BOOT_KEY;
 
 	/* Enable the watchdog and force a timeout to reset the AVR */
 	wdt_enable(WDTO_250MS);
diff --git a/Bootloaders/CDC/BootloaderCDC.h b/Bootloaders/CDC/BootloaderCDC.h
index 4b9e7d6d8..257e884e6 100644
--- a/Bootloaders/CDC/BootloaderCDC.h
+++ b/Bootloaders/CDC/BootloaderCDC.h
@@ -67,6 +67,9 @@
 		/** Eight character bootloader firmware identifier reported to the host when requested */
 		#define SOFTWARE_IDENTIFIER          "LUFACDC"
 
+		/** Magic bootloader key to unlock forced application start mode. */
+		#define MAGIC_BOOT_KEY            0xDC42CACA
+		
 	/* Type Defines: */
 		/** Type define for a non-returning pointer to the start of the loaded application in flash memory. */
 		typedef void (*AppPtr_t)(void) ATTR_NO_RETURN;
@@ -75,6 +78,8 @@
 		static void CDC_Task(void);
 		static void SetupHardware(void);
 
+		void Application_Jump_Check(void) ATTR_INIT_SECTION(3);
+
 		void EVENT_USB_Device_ConfigurationChanged(void);
 
 		#if defined(INCLUDE_FROM_BOOTLOADERCDC_C) || defined(__DOXYGEN__)