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.

1 files changed, 25 insertions, 0 deletions

diff --git a/Bootloaders/HID/BootloaderHID.c b/Bootloaders/HID/BootloaderHID.c
index d8f0186af..2255f0ffa 100644
--- a/Bootloaders/HID/BootloaderHID.c
+++ b/Bootloaders/HID/BootloaderHID.c
@@ -41,6 +41,28 @@
  */
 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.
  */
@@ -58,6 +80,9 @@ 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);