Add ability to add output marker via external signal

For example, a script to flash the chip can use this to mark the
output so that it's clear when the target was actually reset.

itm-decode.py

@@ -13,6 +13,20 @@ color_lookup = { "red": 31, "green": 32, "cyan": 36, "yellow": 33 }
 def color(name, text):
     return "\033[%dm%s\033[0m" % (color_lookup[name], text);
 
+try:
+    # On Unix systems, print an additional marker in the output stream
+    # when SIGUSR1 or SIGUSR2 is received.  This is just to help clarify
+    # output when the chip is externally reset, etc.
+    import signal
+    def sigusr1_handler(signum, frame):
+        print(color("yellow", "--- mark ---"))
+    def sigusr2_handler(signum, frame):
+        print(color("yellow", "--- reset ---"))
+    signal.signal(signal.SIGUSR1, sigusr1_handler)
+    signal.signal(signal.SIGUSR2, sigusr2_handler)
+except AttributeError as e:
+    pass
+
 class ResyncException(Exception):
     pass
 
@@ -69,6 +83,7 @@ class ITMParser:
                     except TimeoutException as e:
                         # Timeout inside a parser should be reported.
                         print(color("red", "Timeout"))
+                        break
             except ResyncException as e:
                 print(color("red", "Resync"))
 
@@ -153,15 +168,32 @@ def main(argv):
     args = parser.parse_args()
 
     ser = serial.Serial(args.device, args.baudrate)
-    ser.timeout = 1
+
+    print(color('green', 'ready'))
 
     def input_stream():
         while True:
+            # Read one byte with a 1s timeout.
+            ser.timeout = 1
             data = ser.read(1)
             if len(data) == 0:
+                # Timeout
                 yield None
-            else:
+                continue
-                yield data[0]
+            yield data[0]
+
+            # Then read as many more as there are immediately
+            # available, and send them.  This is more efficient than
+            # reading each individual byte, when they're coming in
+            # fast.  Once they stop, we'll go back to the normal
+            # 1 byte read with timeout.
+            ser.timeout = 0
+            while True:
+                data = ser.read(65536)
+                if len(data) == 0:
+                    break
+                for c in data:
+                    yield c
 
     try:
         ITMParser(input_stream()).process()