skip initial spikes

common.py

@@ -46,6 +46,12 @@ class SaturationError(ValueError):
     pass
 
 
+def check_saturation(x):
+    peak = np.max(np.abs(x))
+    if peak > SATURATION_THRESHOLD:
+        raise SaturationError(peak)
+
+
 def load(fileobj, time=False):
     return loads(fileobj.read(), time=time)
 
@@ -53,10 +59,6 @@ def load(fileobj, time=False):
 def loads(data, time=False):
     x = np.fromstring(data, dtype='int16')
     x = x / scaling
-    peak = np.max(np.abs(x))
-    if peak > SATURATION_THRESHOLD:
-        raise SaturationError(peak)
-
     if time:
         t = np.arange(len(x)) / Fs
         return t, x
@@ -121,6 +123,10 @@ def icapture(iterable, result):
         result.append(i)
         yield i
 
+
+def take(iterable, n):
+    return np.array(list(itertools.islice(iterable, n)))
+
 if __name__ == '__main__':
 
     import pylab

recv.py

@@ -85,11 +85,6 @@ def find_start(buf, length):
     return np.argmax(cumsumP[length:] - cumsumP[:-length])
 
 
-def take(symbols, n):
-    symbols = itertools.islice(symbols, n)
-    return np.array(list(symbols))
-
-
 def receive_prefix(symbols):
     S = take(symbols, len(train.prefix))[:, carrier_index]
     sliced = np.round(S)
@@ -228,14 +223,13 @@ def main(fname):
     log.info('Running MODEM @ {:.1f} kbps'.format(sigproc.modem_bps / 1e3))
 
     fd = sys.stdin if (fname == '-') else open(fname, 'rb')
-    samples = stream.iread(fd)
-    result = detect(samples, Fc)
-    if result is None:
-        log.warning('No carrier detected')
-        return
+    signal = stream.iread(fd)
+    take(signal, 100)  # skip initial 0.1 second, due to spurious spikes
+    stream.check = check_saturation
 
     size = 0
-    bits = receive(result, frequencies)
+    signal = detect(signal, Fc)
+    bits = receive(signal, frequencies)
     try:
         for chunk in decode(bits):
             sys.stdout.write(chunk)

stream.py

@@ -14,6 +14,7 @@ class Reader(object):
 
     def __init__(self, fd):
         self.fd = fd
+        self.check = None
 
     def __iter__(self):
         return self
@@ -26,8 +27,12 @@ class Reader(object):
             data = self.fd.read(left)
             if data:
                 block.extend(data)
+
             if len(block) == self.BUFSIZE:
-                return common.loads(str(block))
+                values = common.loads(str(block))
+                if self.check:
+                    self.check(values)
+                return values
 
             time.sleep(self.WAIT)