Fix for dangling ports

src/lava/magma/compiler/subcompilers/channel_map_updater.py

@@ -36,15 +36,21 @@ def add_src_ports(self, src_ports: ty.List[AbstractSrcPort]) -> None:
 
     def add_src_port(self, src_port: AbstractSrcPort) -> None:
         for dst_port in src_port.get_dst_ports():
-            self.add_port_pair(src_port, dst_port)
+            # If the dst_port is still a source port, then it is
+            # a dangling branch and need not be processed.
+            if not isinstance(dst_port, AbstractSrcPort):
+                self.add_port_pair(src_port, dst_port)
 
     def add_dst_ports(self, dst_ports: ty.List[AbstractDstPort]) -> None:
         for dst_port in dst_ports:
             self.add_dst_port(dst_port)
 
     def add_dst_port(self, dst_port: AbstractDstPort) -> None:
         for src_port in dst_port.get_src_ports():
-            self.add_port_pair(src_port, dst_port)
+            # If the src_port is still a destination port, then it is
+            # a dangling branch and need not be processed.
+            if not isinstance(src_port, AbstractDstPort):
+                self.add_port_pair(src_port, dst_port)
 
     def add_port_pair(self,
                       src_port: AbstractSrcPort,

tests/lava/magma/runtime/test_io_ports.py

@@ -23,6 +23,7 @@
 class HP1(AbstractProcess):
     def __init__(self, **kwargs):
         super().__init__(**kwargs)
+        self.h_var = Var(shape=(2,))
         self.h_out = OutPort(shape=(2,))
 
 
@@ -38,6 +39,7 @@ def __init__(self, **kwargs):
 class P1(AbstractProcess):
     def __init__(self, **kwargs):
         super().__init__(**kwargs)
+        self.var = Var(shape=(2,), init=4)
         self.out = OutPort(shape=(2,))
 
 
@@ -60,6 +62,8 @@ def __init__(self, proc):
         # the nested process
         self.p1 = P1()
         self.p1.out.connect(proc.out_ports.h_out)
+        # Reference h_var with var of the nested process
+        proc.vars.h_var.alias(self.p1.var)
 
 
 # A minimal hierarchical PyProcModel implementing HP2
@@ -82,11 +86,13 @@ def __init__(self, proc):
 @requires(CPU)
 @tag('floating_pt')
 class PyProcModel1(PyLoihiProcessModel):
+    var: np.ndarray = LavaPyType(np.ndarray, np.int32)
     out: PyOutPort = LavaPyType(PyOutPort.VEC_DENSE, int)
 
     def run_spk(self):
         # Send data
         data = np.array([1, 2])
+        self.var = data + 2
         self.out.send(data)
 
 
@@ -252,6 +258,24 @@ def test_branching_hierarchical(self):
         self.assertTrue(np.all(recv3.h_var.get() == np.array([1, 2])))
         sender.stop()
 
+    def test_dangling_input(self):
+        """Checks if the hierarchical process works with dangling input i.e.
+        input not connected at all."""
+        receiver = HP2()
+        receiver.run(condition=RunSteps(num_steps=2),
+                     run_cfg=Loihi1SimCfg(select_sub_proc_model=True))
+        self.assertTrue(np.all(receiver.h_var.get() == np.array([0, 0])))
+        receiver.stop()
+
+    def test_dangling_output(self):
+        """Checks if the hierarchical process works with dangling output i.e.
+        output not conected at all."""
+        sender = HP1()
+        sender.run(condition=RunSteps(num_steps=2),
+                   run_cfg=Loihi1SimCfg(select_sub_proc_model=True))
+        self.assertTrue(np.all(sender.h_var.get() == np.array([3, 4])))
+        sender.stop()
+
 
 if __name__ == '__main__':
     unittest.main()

tutorials/in_depth/tutorial06_hierarchical_processes.ipynb

@@ -461,13 +461,6 @@
     "layer1 = DenseLayer(shape=dim, weights=weights1, bias_mant=4, vth=10)\n",
     "# Connect the first DenseLayer to the second DenseLayer.\n",
     "layer0.s_out.connect(layer1.s_in)\n",
-    "# Instantiate 'plugs' for the dangling InPort and OutPort of the DenseLayers.\n",
-    "# (This is a work around and will be solved more elegantly later.)\n",
-    "inport_plug = source.RingBuffer(data=np.zeros((dim[0], 1)))\n",
-    "outport_plug = sink.RingBuffer(shape=(dim[0],), buffer=1)\n",
-    "# Connect the 'plugs' to their respective ports.\n",
-    "inport_plug.s_out.connect(layer0.s_in)\n",
-    "layer1.s_out.connect(outport_plug.a_in)\n",
     "\n",
     "print('Layer 1 weights: \\n', layer1.weights.get(),'\\n')\n",
     "print('\\n ----- \\n')\n",