recv: add timeout for carrier waiting

amodem/recv.py

@@ -24,17 +24,22 @@ class Detector(object):
     CARRIER_THRESHOLD = int(0.9 * CARRIER_DURATION)
     SEARCH_WINDOW = int(0.1 * CARRIER_DURATION)
 
+    TIMEOUT = 10.0  # [seconds]
+
     def __init__(self, config):
         self.freq = config.Fc
         self.omega = 2 * np.pi * self.freq / config.Fs
         self.Nsym = config.Nsym
         self.Tsym = config.Tsym
         self.maxlen = config.baud  # 1 second of symbols
+        self.max_offset = self.TIMEOUT * config.Fs
 
     def run(self, samples):
         counter = 0
         bufs = collections.deque([], maxlen=self.maxlen)
         for offset, buf in common.iterate(samples, self.Nsym, enumerate=True):
+            if offset > self.max_offset:
+                raise ValueError('Timeout waiting for carrier')
             bufs.append(buf)
 
             coeff = dsp.coherence(buf, self.omega)

tests/test_recv.py

@@ -1,4 +1,5 @@
 import numpy as np
+import pytest
 
 from amodem import dsp
 from amodem import recv
@@ -18,11 +19,12 @@ def test_detect():
     assert abs(1 - amp) < 1e-12
 
     x = np.cos(2 * np.pi * (2*config.Fc) * t)
-    try:
+    with pytest.raises(ValueError):
+        detector.run(x)
+
+    with pytest.raises(ValueError):
+        detector.max_offset = 0
         detector.run(x)
-        assert False
-    except ValueError:
-        pass
 
 
 def test_prefix():
@@ -37,12 +39,9 @@ def test_prefix():
     freq_err = r._prefix(symbols_stream(signal))
     assert abs(freq_err) < 1e-16
 
-    try:
+    with pytest.raises(ValueError):
         silence = 0 * signal
         r._prefix(symbols_stream(silence))
-        assert False
-    except ValueError:
-        pass
 
 
 def test_find_start():