Add basic README and more help

README.md

@@ -0,0 +1,22 @@
+rdatool
+=======
+RDA8851 & family host interface tool (CoolSand)
+
+Requirements
+------------
+
+ * Python 2.7 / Python 3.5
+ * pyserial (python-serial / python3-serial package on Ubuntu/Debian, pyserial
+   on pypi)
+
+Usage
+-----
+
+See `rdatool.py --help`.
+
+Notes
+-----
+
+CH341 USB-UART IC used on some AIR200(T) devkits does not seem to manage to
+keep up with CoolSand host interface baudrate on Linux (921600 baud). Use
+something more reliable, like CP2102 or FT232.

rdatool.py

@@ -286,9 +286,14 @@ def cli_at(client, args):
 def cli_chipid(client, args):
     logging.info('Chip ID: %08x', client.chipid())
 
+DEFAULT_SERIAL = '/dev/serial/by-id/usb-Silicon_Labs_CP2102_USB_to_UART_' \
+    + 'Bridge_Controller_0001-if00-port0'
+
 parser = argparse.ArgumentParser()
-parser.add_argument('--verbose', '-v', action='count', default=0)
-parser.add_argument('--port', '-p', default='/dev/serial/by-id/usb-Silicon_Labs_CP2102_USB_to_UART_Bridge_Controller_0001-if00-port0')
+parser.add_argument('--verbose', '-v', action='count', default=0,
+                    help='show debug information')
+parser.add_argument('--port', '-p', default=DEFAULT_SERIAL,
+                    help='serial port')
 subparsers = parser.add_subparsers()
 
 trace_parser = subparsers.add_parser('trace', help='show trace')