[AVR] Discover newer bootloader at runtime

Replaces #4280, only checks for the bootloader once

Tested with Hoodloader2, should work with every LUFA-derived bootloader released after 2014 (.apitable_signatures section must be placed at end of the flash)

BootloaderAPITable.S :

.global BootloaderAPI_Signatures
BootloaderAPI_Signatures:

    .long BOOT_START_ADDR ; Start address of the bootloader
    .word 0xDF00 ; Signature for the CDC class bootloader
    .word 0xDCFB ; Signature for a LUFA class bootloader

makefile:

BOOT_API_LD_FLAGS    += $(call BOOT_SECTION_LD_FLAG, .apitable_signatures,  BootloaderAPI_Signatures,  8)

2 files changed, 36 insertions, 14 deletions

diff --git a/cores/arduino/CDC.cpp b/cores/arduino/CDC.cpp
index f19b44c..0a743e1 100644
--- a/cores/arduino/CDC.cpp
+++ b/cores/arduino/CDC.cpp
@@ -34,6 +34,8 @@ typedef struct
 static volatile LineInfo _usbLineInfo = { 57600, 0x00, 0x00, 0x00, 0x00 };
 static volatile int32_t breakValue = -1;
 
+bool _updatedLUFAbootloader = false;
+
 #define WEAK __attribute__ ((weak))
 
 extern const CDCDescriptor _cdcInterface PROGMEM;
@@ -99,24 +101,32 @@ bool CDC_Setup(USBSetup& setup)
 			// with a relatively long period so it can finish housekeeping tasks
 			// like servicing endpoints before the sketch ends
 
-#ifndef MAGIC_KEY
-#define MAGIC_KEY 0x7777
-#endif
-#ifndef MAGIC_KEY_POS
-#define MAGIC_KEY_POS 0x0800
+			uint16_t magic_key_pos = MAGIC_KEY_POS;
+
+// If we don't use the new RAMEND directly, check manually if we have a newer bootloader.
+// This is used to keep compatible with the old leonardo bootloaders.
+// You are still able to set the magic key position manually to RAMEND-1 to save a few bytes for this check.
+#if MAGIC_KEY_POS != (RAMEND-1)
+			// For future boards save the key in the inproblematic RAMEND
+			// Which is reserved for the main() return value (which will never return)
+			if (_updatedLUFAbootloader) {
+				// horray, we got a new bootloader!
+				magic_key_pos = (RAMEND-1);
+			}
 #endif
 
 			// We check DTR state to determine if host port is open (bit 0 of lineState).
 			if (1200 == _usbLineInfo.dwDTERate && (_usbLineInfo.lineState & 0x01) == 0)
 			{
 #if MAGIC_KEY_POS != (RAMEND-1)
-				*(uint16_t *)(RAMEND-1) = *(uint16_t *)MAGIC_KEY_POS;
-				*(uint16_t *)MAGIC_KEY_POS = MAGIC_KEY;
-#else
-				// for future boards save the key in the inproblematic RAMEND
-				// which is reserved for the main() return value (which will never return)
-				*(uint16_t *)MAGIC_KEY_POS = MAGIC_KEY;
+				// Backup ram value if its not a newer bootloader.
+				// This should avoid memory corruption at least a bit, not fully
+				if (magic_key_pos != (RAMEND-1)) {
+					*(uint16_t *)(RAMEND-1) = *(uint16_t *)magic_key_pos;
+				}
 #endif
+				// Store boot key
+				*(uint16_t *)magic_key_pos = MAGIC_KEY;
 				wdt_enable(WDTO_120MS);
 			}
 			else
@@ -129,10 +139,15 @@ bool CDC_Setup(USBSetup& setup)
 				wdt_disable();
 				wdt_reset();
 #if MAGIC_KEY_POS != (RAMEND-1)
-				*(uint16_t *)MAGIC_KEY_POS = *(uint16_t *)(RAMEND-1);
-#else
-				*(uint16_t *)MAGIC_KEY_POS = 0x0000;
+				// Restore backed up (old bootloader) magic key data
+				if (magic_key_pos != (RAMEND-1)) {
+					*(uint16_t *)magic_key_pos = *(uint16_t *)(RAMEND-1);
+				} else
 #endif
+				{
+				// Clean up RAMEND key
+					*(uint16_t *)magic_key_pos = 0x0000;
+				}
 			}
 		}
 		return true;
diff --git a/cores/arduino/USBCore.cpp b/cores/arduino/USBCore.cpp
index 62b90ed..3c7da86 100644
--- a/cores/arduino/USBCore.cpp
+++ b/cores/arduino/USBCore.cpp
@@ -35,6 +35,7 @@ extern const u8 STRING_PRODUCT[] PROGMEM;
 extern const u8 STRING_MANUFACTURER[] PROGMEM;
 extern const DeviceDescriptor USB_DeviceDescriptor PROGMEM;
 extern const DeviceDescriptor USB_DeviceDescriptorB PROGMEM;
+extern bool _updatedLUFAbootloader;
 
 const u16 STRING_LANGUAGE[2] = {
 	(3<<8) | (2+2),
@@ -806,6 +807,12 @@ void USBDevice_::attach()
 	UDIEN = (1<<EORSTE) | (1<<SOFE) | (1<<SUSPE);	// Enable interrupts for EOR (End of Reset), SOF (start of frame) and SUSPEND
 	
 	TX_RX_LED_INIT;
+
+#if MAGIC_KEY_POS != (RAMEND-1)
+	if (pgm_read_word(FLASHEND - 1) == NEW_LUFA_SIGNATURE) {
+		_updatedLUFAbootloader = true;
+	}
+#endif
 }
 
 void USBDevice_::detach()