Adding AIS mode/service, implemented via Direwolf.

bands.json

@@ -367,5 +367,21 @@
     "lower_bound": 446000000,
     "upper_bound": 446200000,
     "tags": ["public"]
+  },
+  {
+    "name": "VHF Air",
+    "lower_bound": 108000000,
+    "upper_bound": 137000000,
+    "tags": ["service"]
+  },
+  {
+    "name": "VHF Marine",
+    "lower_bound": 156000000,
+    "upper_bound": 174000000,
+    "frequencies": {
+      "ais": 161975000,
+      "ais": 162025000
+    },
+    "tags": ["service"]
   }
 ]

csdr/chain/digimodes.py

@@ -43,6 +43,29 @@ class PacketDemodulator(ServiceDemodulator, DialFrequencyReceiver):
         self.parser.setDialFrequency(frequency)
 
 
+class AisDemodulator(ServiceDemodulator, DialFrequencyReceiver):
+    def __init__(self, service: bool = False):
+        self.parser = AprsParser()
+        workers = [
+            FmDemod(),
+            Convert(Format.FLOAT, Format.SHORT),
+            DirewolfModule(service=service, ais=True),
+            KissDeframer(),
+            Ax25Parser(),
+            self.parser,
+        ]
+        super().__init__(workers)
+
+    def supportsSquelch(self) -> bool:
+        return False
+
+    def getFixedAudioRate(self) -> int:
+        return 48000
+
+    def setDialFrequency(self, frequency: int) -> None:
+        self.parser.setDialFrequency(frequency)
+
+
 class PskDemodulator(SecondaryDemodulator, SecondarySelectorChain):
     def __init__(self, baudRate: float):
         self.baudRate = baudRate

owrx/aprs/module.py

@@ -14,10 +14,11 @@ logger = logging.getLogger(__name__)
 
 
 class DirewolfModule(AutoStartModule, DirewolfConfigSubscriber):
-    def __init__(self, service: bool = False):
+    def __init__(self, service: bool = False, ais: bool = False):
         self.process = None
         self.tcpSource = None
         self.service = service
+        self.ais = ais
         self.direwolfConfigPath = "{tmp_dir}/openwebrx_direwolf_{myid}.conf".format(
             tmp_dir=CoreConfig().get_temporary_directory(), myid=id(self)
         )
@@ -43,11 +44,14 @@ class DirewolfModule(AutoStartModule, DirewolfConfigSubscriber):
         file.close()
 
         # direwolf -c {direwolf_config} -r {audio_rate} -t 0 -q d -q h 1>&2
-        self.process = Popen(
-            ["direwolf", "-c", self.direwolfConfigPath, "-r", "48000", "-t", "0", "-q", "d", "-q", "h"],
-            start_new_session=True,
-            stdin=PIPE,
-        )
+        cmdLine = ["direwolf", "-c", self.direwolfConfigPath, "-r", "48000", "-t", "0", "-q", "d", "-q", "h"]
+
+        # for AIS mode, add -B AIS -A
+        if self.ais:
+            cmdLine += ["-B", "AIS", "-A"]
+
+        # launch Direwolf
+        self.process = Popen(cmdLine, start_new_session=True, stdin=PIPE)
 
         # resume in case the reader has been stop()ed before
         self.reader.resume()

owrx/dsp.py

@@ -604,6 +604,9 @@ class DspManager(SdrSourceEventClient, ClientDemodulatorSecondaryDspEventClient)
         elif mod == "packet":
             from csdr.chain.digimodes import PacketDemodulator
             return PacketDemodulator()
+        elif mod == "ais":
+            from csdr.chain.digimodes import AisDemodulator
+            return AisDemodulator()
         elif mod == "pocsag":
             from csdr.chain.digiham import PocsagDemodulator
             return PocsagDemodulator()

owrx/modes.py

@@ -130,6 +130,15 @@ class Modes(object):
             service=True,
             squelch=False,
         ),
+        DigitalMode(
+            "ais",
+            "AIS",
+            underlying=["nfm"],
+            bandpass=Bandpass(-6250, 6250),
+            requirements=["packet"],
+            service=True,
+            squelch=False,
+        ),
         DigitalMode(
             "pocsag",
             "Pocsag",

owrx/service/__init__.py

@@ -291,6 +291,9 @@ class ServiceHandler(SdrSourceEventClient):
         elif mod == "packet":
             from csdr.chain.digimodes import PacketDemodulator
             return PacketDemodulator(service=True)
+        elif mod == "ais":
+            from csdr.chain.digimodes import AisDemodulator
+            return AisDemodulator(service=True)
         elif mod == "sstv":
             from csdr.chain.digimodes import SstvDemodulator
             return SstvDemodulator(service=True)