tools: Add option to pyboard.py to wait for serial device to be ready.

Also prints a nicer error message if the serial connection could not be
established.

tools/pyboard.py

@@ -117,13 +117,32 @@ class TelnetToSerial:
             return n_waiting
 
 class Pyboard:
-    def __init__(self, device, baudrate=115200, user='micro', password='python'):
+    def __init__(self, device, baudrate=115200, user='micro', password='python', wait=0):
         if device and device[0].isdigit() and device[-1].isdigit() and device.count('.') == 3:
             # device looks like an IP address
             self.serial = TelnetToSerial(device, user, password, read_timeout=10)
         else:
             import serial
+            delayed = False
+            for attempt in range(wait + 1):
+                try:
                     self.serial = serial.Serial(device, baudrate=baudrate, interCharTimeout=1)
+                    break
+                except OSError, IOError: # Py2 and Py3 have different errors
+                    if wait == 0:
+                        continue
+                    if attempt == 0:
+                        sys.stdout.write('Waiting {} seconds for pyboard '.format(wait))
+                        delayed = True
+                time.sleep(1)
+                sys.stdout.write('.')
+                sys.stdout.flush()
+            else:
+                if delayed:
+                    print('')
+                raise PyboardError('failed to access ' + device)
+            if delayed:
+                print('')
 
     def close(self):
         self.serial.close()
@@ -261,13 +280,14 @@ def main():
     cmd_parser.add_argument('-u', '--user', default='micro', help='the telnet login username')
     cmd_parser.add_argument('-p', '--password', default='python', help='the telnet login password')
     cmd_parser.add_argument('-c', '--command', help='program passed in as string')
+    cmd_parser.add_argument('-w', '--wait', default=0, type=int, help='seconds to wait for USB connected board to become available')
     cmd_parser.add_argument('--follow', action='store_true', help='follow the output after running the scripts [default if no scripts given]')
     cmd_parser.add_argument('files', nargs='*', help='input files')
     args = cmd_parser.parse_args()
 
     def execbuffer(buf):
         try:
-            pyb = Pyboard(args.device, args.baudrate, args.user, args.password)
+            pyb = Pyboard(args.device, args.baudrate, args.user, args.password, args.wait)
             pyb.enter_raw_repl()
             ret, ret_err = pyb.exec_raw(buf, timeout=None, data_consumer=stdout_write_bytes)
             pyb.exit_raw_repl()
@@ -291,7 +311,7 @@ def main():
 
     if args.follow or (args.command is None and len(args.files) == 0):
         try:
-            pyb = Pyboard(args.device, args.baudrate, args.user, args.password)
+            pyb = Pyboard(args.device, args.baudrate, args.user, args.password, args.wait)
             ret, ret_err = pyb.follow(timeout=None, data_consumer=stdout_write_bytes)
             pyb.close()
         except PyboardError as er: