Add comment for the procedure of downloading device controller.

update.cpp

@@ -376,6 +376,38 @@ bool Update::downloadBinaryToDC(QString const &bFile) const {
     return true;
 }
 
+/*
+ Using the DC bootloader:
+ 1  :   bl_reboot()      // send to application, want DC2 to reset (in order to start
+                        // the bootloader)
+ 2  :   bl_startBL():   // send within 4s after DC poewer-on, otherwise bl is left
+ 3  :   bl_check():     // send command to verify if bl is up
+ 4  :   bl_isUp():      // returns true if bl is up and running
+
+ 5  :   bl_sendAddress(blockNumber)
+                        // send start address, nr of 64-byte block, start with 0
+                        // will be sent only for following block-numbers:
+                        // 0, 1024, 2048, 3072 and 4096, so basically every 64kByte
+                        // for other addresses nothing happens
+
+ 6  :   bl_wasSendingAddOK()
+                        // return val:  0: no response by now
+                        //              1: error
+                        //             10: OK
+
+ 7  :   bl_sendDataBlock()
+                        // send 64 byte from bin file
+
+ 8  :   bl_sendLastBlock()
+                        // send this command after all data are transferred
+
+ 9  :   bl_wasSendingDataOK()
+                        // return val:  0: no response by now
+                        //              1: error
+                        //             10: OK
+
+ 10 :   bl_stopBL()     // leave bl and start (the new) application
+ */
 bool Update::updateBinary(char const *fileToSendToDC) {
     qInfo() << "updating device controller binary" << fileToSendToDC;
     QFile fn(fileToSendToDC);