Add --hold-tx to test PTT

Signed-off-by: Chris Fiege <chris@tinyhost.de>

sa868/__init__.py

 import argparse
 import serial
 import logging
+import time
 
 class SA868(object):
 
@@ -89,6 +90,14 @@ class SA868(object):
             0 if highpass else 1),
         "+DMOSETFILTER:")
 
+    def set_tx(self, state):
+        if state:
+            self._serial.rts = True
+            self._logger.info("Activating TX")
+        else:
+            self._logger.info("Deactivatig TX")
+            self._serial.rts = False
+
 
 def main():
     parser = argparse.ArgumentParser()
@@ -98,6 +107,7 @@ def main():
     parser.add_argument("--set-filter", help="Sets the pre-/de-emphasis, highpass- and lowpass-filter. Use {off, on}", nargs=3, metavar=("pre_de_emphasis", "lowpass", "highpass"))
     parser.add_argument("--get-rssi", help="Prints the current RSSI to STDOUT", action="store_true")
     parser.add_argument("--no-ping", help="Disables the initial ping of the device", action="store_true")
+    parser.add_argument("--hold-tx", help="Asserts tx for N seconds", nargs=1, type=float)
     parser.add_argument("-v", help="Be more verbose", action="store_true")
     args = parser.parse_args()
 
@@ -123,5 +133,10 @@ def main():
     if args.get_rssi:
         print(s.get_rssi())
 
+    if args.hold_tx:
+        s.set_tx(True)
+        time.sleep(args.hold_tx[0])
+        s.set_tx(False)
+
 if __name__ == "__main__":
     main()