Add ability to RF scan a specific frequency

This adds an optional parameter to find_rf_packet(), along with a
corresponding --rflearn parameter (defaulting to 433.92) to
broadlink_cli that specifies the frequency to tune to, rather than
requiring the frequency be found via sweeping. This is almost mandatory
for certain types of remotes that do not repeat their signals while the
button is held, and saves significant time when the frequency is known
in advance or when many buttons are to be captured in a row.

Additionally:

- A get_frequency() API is added to return the current frequency the
  device is tuned to.

- A check_frequency_ex() API is added to perform functions of both
  check_frequency() and get_frequency() in a single call.

- broadlink_cli --rfscanlearn will now report the current frequency at 1
  second intervals during sweeping, and will report the frequency it
  finally locks on to.

broadlink/remote.py

@@ -51,9 +51,25 @@ def check_frequency(self) -> bool:
         resp = self._send(0x1A)
         return resp[0] == 1
 
-    def find_rf_packet(self) -> None:
-        """Enter radiofrequency learning mode."""
-        self._send(0x1B)
+    def check_frequency_ex(self) -> (bool, float):
+        """Return (True if the frequency was identified successfully, Current frequency)"""
+        resp = self._send(0x1A)
+        return resp[0] == 1, struct.unpack('<I', resp[1:5])[0] / 1000.0
+
+    def get_frequency(self) -> float:
+        """Return frequency device is tuned to in MHz"""
+        resp = self._send(0x1A)
+        return struct.unpack('<I', resp[1:5])[0] / 1000.0
+
+    def find_rf_packet(self, frequency=None) -> None:
+        """Enter radiofrequency learning mode, optionally tuning the device to a specific frequency"""
+        payload = b''
+        if frequency is not None:
+            payload = struct.pack('<I', int(frequency * 1000.0))
+            # Without this get_frequency() may suggest it is tuned to the
+            # specified frequency, but it fails to capture any signals:
+            self.cancel_sweep_frequency()
+        self._send(0x1B, payload)
 
     def cancel_sweep_frequency(self) -> None:
         """Cancel sweep frequency."""

cli/broadlink_cli

@@ -84,6 +84,7 @@ parser.add_argument("--send", action="store_true", help="send command")
 parser.add_argument("--sensors", action="store_true", help="check all sensors")
 parser.add_argument("--learn", action="store_true", help="learn command")
 parser.add_argument("--rfscanlearn", action="store_true", help="rf scan learning")
+parser.add_argument("--rflearn", nargs="?", type=float, const=433.92, metavar="FREQUENCY", help="rf learning on specified FREQUENCY, default: 433.92")
 parser.add_argument("--learnfile", help="save learned command to a specified file")
 parser.add_argument("--durations", action="store_true",
                     help="use durations in micro seconds instead of the Broadlink format")
@@ -127,7 +128,7 @@ if args.send:
     data = durations_to_broadlink(parse_durations(' '.join(args.data))) \
         if args.durations else bytearray.fromhex(''.join(args.data))
     dev.send_data(data)
-if args.learn or (args.learnfile and not args.rfscanlearn):
+if args.learn or (args.learnfile and not args.rfscanlearn and not args.rflearn):
     dev.enter_learning()
     print("Learning...")
     start = time.time()
@@ -195,29 +196,36 @@ if args.switch:
     else:
         dev.set_power(True)
         print('* Switch to ON *')
-if args.rfscanlearn:
+if args.rfscanlearn or args.rflearn:
     dev.sweep_frequency()
-    print("Learning RF Frequency, press and hold the button to learn...")
+    if args.rfscanlearn:
+        print("Learning RF Frequency, press and hold the button to learn...")
+
+        start = time.time()
+        while time.time() - start < TIMEOUT:
+            time.sleep(1)
+            locked, frequency = dev.check_frequency_ex()
+            if locked:
+                break
+            print("Sweeping {}MHz...".format(frequency))
+        else:
+            print("RF Frequency not found")
+            dev.cancel_sweep_frequency()
+            exit(1)
+        frequency = dev.get_frequency()
 
-    start = time.time()
-    while time.time() - start < TIMEOUT:
-        time.sleep(1)
-        if dev.check_frequency():
-            break
-    else:
-        print("RF Frequency not found")
-        dev.cancel_sweep_frequency()
-        exit(1)
+        print("Found RF Frequency {}MHz - 1 of 2!".format(frequency))
+        print("You can now let go of the button")
 
-    print("Found RF Frequency - 1 of 2!")
-    print("You can now let go of the button")
+        input("Press enter to continue...")
 
-    input("Press enter to continue...")
+        dev.find_rf_packet()
+    else:
+        dev.find_rf_packet(args.rflearn)
+        print("Device tuned to {}MHz".format(dev.get_frequency()))
 
     print("To complete learning, single press the button you want to learn")
 
-    dev.find_rf_packet()
-
     start = time.time()
     while time.time() - start < TIMEOUT:
         time.sleep(1)
@@ -231,7 +239,8 @@ if args.rfscanlearn:
         print("No data received...")
         exit(1)
 
-    print("Found RF Frequency - 2 of 2!")
+    if args.rfscanlearn:
+        print("Found RF Frequency - 2 of 2!")
     learned = format_durations(to_microseconds(bytearray(data))) \
         if args.durations \
         else ''.join(format(x, '02x') for x in bytearray(data))