Make uf2conf.py flush STDOUT for real-time updates (#1194)

Without flushing STDOUT, the upload script's output aften are buffered
and not displayed until it completes.  Add in flush commands to allow
the IDE to display status as it changes.

Author: earlephilhower

tools/uf2conv.py

@@ -364,6 +364,7 @@ def error(msg):
         if str(args.serial).startswith("/dev/tty") or str(args.serial).startswith("COM") or str(args.serial).startswith("/dev/cu"):
             try:
                 print("Resetting " + str(args.serial))
+                sys.stdout.flush()
                 try:
                     ser = serial.Serial()
                     ser.port = args.serial
@@ -401,11 +402,14 @@ def error(msg):
             outbuf = convert_to_uf2(inpbuf)
         print("Converting to %s, output size: %d, start address: 0x%x" %
               (ext, len(outbuf), appstartaddr))
+        sys.stdout.flush()
         if args.convert or ext != "uf2":
             drives = []
             if args.output == None:
                 args.output = "flash." + ext
         else:
+            print("Scanning for RP2040 devices")
+            sys.stdout.flush()
             now = time.time()
             drives = []
             while (time.time() - now < 10.0) and (len(drives) == 0):
@@ -419,6 +423,7 @@ def error(msg):
                 error("No drive to deploy.")
         for d in drives:
             print("Flashing %s (%s)" % (d, board_id(d)))
+            sys.stdout.flush()
             write_file(d + "/NEW.UF2", outbuf)
 
         # Wait until serial port (if defined) re-appears, or 2s timeout unless UF2 drive direct upload