builder.py: Added comments on filtering

nengo_loihi/builder.py

@@ -278,6 +278,7 @@ def build_ensemble(model, ens):
         group.bias[:] = bias
         model.build(ens.neuron_type, ens.neurons, group)
 
+    # set default filter just in case no other filter gets set
     group.configure_filter(INTER_TAU, dt=model.dt, default=True)
 
     if ens.noise is not None:
@@ -465,7 +466,7 @@ def build_connection(model, conn):
     transform = get_samples(
         conn.transform, conn.size_out, d=conn.size_mid, rng=rng)
 
-    tau_s = 0.0
+    tau_s = 0.0  # `synapse is None` gets mapped to `tau_s = 0.0`
     if isinstance(conn.synapse, nengo.synapses.Lowpass):
         tau_s = conn.synapse.tau
     elif conn.synapse is not None:
@@ -575,6 +576,7 @@ def build_connection(model, conn):
             weights2 = 0.5 * gain * np.vstack([weights,
                                                -weights] * INTER_N).T
 
+        # use tau_s for filter into interneurons, and INTER_TAU for filter out
         dec_cx.configure_filter(tau_s, dt=model.dt)
         post_tau = INTER_TAU