diff --git a/Demo.ipynb b/Demo.ipynb
index 6ba4c1f..dde96bc 100644
--- a/Demo.ipynb
+++ b/Demo.ipynb
@@ -115,6 +115,7 @@
    ]
   },
   {
+   "attachments": {},
    "cell_type": "markdown",
    "metadata": {},
    "source": [
@@ -125,7 +126,7 @@
     "\n",
     "A line in the circuit has a unique ID, a driver node and a receiver node. The connections in the dump show the direction (\">\" for output, \"<\" for input) and the line-ID. For example in `mycircuit`: Node-0 has one output connected to Line-1, and this Line-1 is connected to the input of Node-5.\n",
     "\n",
-    "The `interface` is the list of nodes forming the ports (inputs and outputs):"
+    "The `io_nodes` is the list of nodes forming the ports (inputs and outputs):"
    ]
   },
   {
@@ -149,7 +150,7 @@
     }
    ],
    "source": [
-    "mycircuit.interface"
+    "mycircuit.io_nodes"
    ]
   },
   {
@@ -1326,9 +1327,9 @@
  ],
  "metadata": {
   "kernelspec": {
-   "display_name": "worker",
+   "display_name": "Python 3",
    "language": "python",
-   "name": "worker"
+   "name": "python3"
   },
   "language_info": {
    "codemirror_mode": {
@@ -1340,7 +1341,12 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.6.13"
+   "version": "3.6.8"
+  },
+  "vscode": {
+   "interpreter": {
+    "hash": "31f2aee4e71d21fbe5cf8b01ff0e069b9275f58929596ceb00d14d90e3e16cd6"
+   }
   }
  },
  "nbformat": 4,
diff --git a/src/kyupy/bench.py b/src/kyupy/bench.py
index 21310d5..fb1ba1d 100644
--- a/src/kyupy/bench.py
+++ b/src/kyupy/bench.py
@@ -23,7 +23,7 @@ class BenchTransformer(Transformer):
 
     def parameters(self, args): return [self.c.get_or_add_fork(name) for name in args]
 
-    def interface(self, args): self.c.interface.extend(args[0])
+    def interface(self, args): self.c.io_nodes.extend(args[0])
 
     def assignment(self, args):
         name, cell_type, drivers = args
diff --git a/src/kyupy/circuit.py b/src/kyupy/circuit.py
index 925a51d..8310e4f 100644
--- a/src/kyupy/circuit.py
+++ b/src/kyupy/circuit.py
@@ -5,7 +5,7 @@ A node is an instance of class :class:`Node`,
 and a line is an instance of class :class:`Line`.
 """
 
-from collections import deque
+from collections import deque, defaultdict
 import re
 
 
@@ -203,7 +203,7 @@ class Circuit:
     to enforce consecutiveness.
 
     A subset of nodes can be designated as primary input- or output-ports of the circuit.
-    This is done by adding them to the :py:attr:`interface` list.
+    This is done by adding them to the :py:attr:`io_nodes` list.
     """
     def __init__(self, name=None):
         self.name = name
@@ -219,13 +219,13 @@ class Circuit:
 
         The position of a line in this list equals its index :code:`self.lines[42].index == 42`.
         """
-        self.interface = GrowingList()
+        self.io_nodes = GrowingList()
         """A list of nodes that are designated as primary input- or output-ports.
 
-        Port-nodes are contained in :py:attr:`nodes` as well as :py:attr:`interface`.
-        The position of a node in the interface list corresponds to positions of logic values in test vectors.
+        Port-nodes are contained in :py:attr:`nodes` as well as :py:attr:`io_nodes`.
+        The position of a node in the io_nodes list corresponds to positions of logic values in test vectors.
         The port direction is not stored explicitly.
-        Usually, nodes in the interface list without any lines in their :py:attr:`Node.ins` list are primary inputs,
+        Usually, nodes in the io_nodes list without any lines in their :py:attr:`Node.ins` list are primary inputs,
         and nodes without any lines in their :py:attr:`Node.outs` list are regarded as primary outputs.
         """
         self.cells = {}
@@ -248,50 +248,57 @@ class Circuit:
             d = c.forks[line.driver.name] if line.driver.kind == '__fork__' else c.cells[line.driver.name]
             r = c.forks[line.reader.name] if line.reader.kind == '__fork__' else c.cells[line.reader.name]
             Line(c, (d, line.driver_pin), (r, line.reader_pin))
-        for node in self.interface:
+        for node in self.io_nodes:
             if node.kind == '__fork__':
                 n = c.forks[node.name]
             else:
                 n = c.cells[node.name]
-            c.interface.append(n)
+            c.io_nodes.append(n)
         return c
 
     def __getstate__(self):
         nodes = [(node.name, node.kind) for node in self.nodes]
         lines = [(line.driver.index, line.driver_pin, line.reader.index, line.reader_pin) for line in self.lines]
-        interface = [n.index for n in self.interface]
+        io_nodes = [n.index for n in self.io_nodes]
         return {'name': self.name,
                 'nodes': nodes,
                 'lines': lines,
-                'interface': interface }
+                'io_nodes': io_nodes }
 
     def __setstate__(self, state):
         self.name = state['name']
         self.nodes = IndexList()
         self.lines = IndexList()
-        self.interface = GrowingList()
+        self.io_nodes = GrowingList()
         self.cells = {}
         self.forks = {}
         for s in state['nodes']:
             Node(self, *s)
         for driver, driver_pin, reader, reader_pin in state['lines']:
             Line(self, (self.nodes[driver], driver_pin), (self.nodes[reader], reader_pin))
-        for n in state['interface']:
-            self.interface.append(self.nodes[n])
+        for n in state['io_nodes']:
+            self.io_nodes.append(self.nodes[n])
 
     def __eq__(self, other):
-        return self.nodes == other.nodes and self.lines == other.lines and self.interface == other.interface
+        return self.nodes == other.nodes and self.lines == other.lines and self.io_nodes == other.io_nodes
 
     def dump(self):
         """Returns a string representation of the circuit and all its nodes.
         """
-        header = f'{self.name}({",".join([str(n.index) for n in self.interface])})\n'
+        header = f'{self.name}({",".join([str(n.index) for n in self.io_nodes])})\n'
         return header + '\n'.join([str(n) for n in self.nodes])
 
     def __repr__(self):
         name = f' {self.name}' if self.name else ''
         return f'<Circuit{name} cells={len(self.cells)} forks={len(self.forks)} ' + \
-               f'lines={len(self.lines)} ports={len(self.interface)}>'
+               f'lines={len(self.lines)} ports={len(self.io_nodes)}>'
+
+    @property
+    def cell_counts(self):
+        counts = defaultdict(int)
+        for n in self.cells.values():
+            counts[n.kind] += 1
+        return counts
 
     def topological_order(self):
         """Generator function to iterate over all nodes in topological order.
@@ -375,8 +382,8 @@ class Circuit:
 
     def io_loc(self, prefix):
         d_top = dict()
-        for i, n in enumerate(list(self.interface) + [n for n in self.nodes if 'dff' in n.kind.lower()]):
-            if m := re.match(fr'({prefix}.*?)((?:[_\[\]]\d+)*[_\[\]]*$)', n.name):
+        for i, n in enumerate(list(self.io_nodes) + [n for n in self.nodes if 'dff' in n.kind.lower()]):
+            if m := re.match(fr'({prefix}.*?)((?:\d+[_\[\]])*$)', n.name):
                 path = [m[1]] + [int(v) for v in re.split(r'[_\[\]]+', m[2]) if len(v) > 0]
                 d = d_top
                 for j in path[:-1]:
diff --git a/src/kyupy/logic_sim.py b/src/kyupy/logic_sim.py
index b9f7eed..e004463 100644
--- a/src/kyupy/logic_sim.py
+++ b/src/kyupy/logic_sim.py
@@ -32,7 +32,7 @@ class LogicSim:
         nbytes = (sims - 1) // 8 + 1
         dffs = [n for n in circuit.nodes if 'dff' in n.kind.lower()]
         latches = [n for n in circuit.nodes if 'latch' in n.kind.lower()]
-        self.interface = list(circuit.interface) + dffs + latches
+        self.interface = list(circuit.io_nodes) + dffs + latches
 
         self.width = len(self.interface)
         """The number of bits in the circuit state (number of ports + number of state-elements)."""
diff --git a/src/kyupy/schedule.py b/src/kyupy/schedule.py
index f505a50..57a706a 100644
--- a/src/kyupy/schedule.py
+++ b/src/kyupy/schedule.py
@@ -157,7 +157,7 @@ class Schedule:
     """
     def __init__(self, circuit, strip_forks=False, keep_signals=True, signal_caps=1):
         self.circuit = circuit
-        self.interface = list(circuit.interface) + [n for n in circuit.nodes if 'dff' in n.kind.lower()]
+        self.interface = list(circuit.io_nodes) + [n for n in circuit.nodes if 'dff' in n.kind.lower()]
         
         if isinstance(signal_caps, int):
             signal_caps = [signal_caps] * len(circuit.lines)
@@ -303,3 +303,8 @@ class Schedule:
                 self.vat[self.ppo_offset + i] = self.vat[n.ins[0]]
 
         self.state_length = h.max_size
+
+        from collections import defaultdict
+        self.prim_counts = defaultdict(int)
+        names_dict = SimPrim.names()
+        for op, _, _, _, _, _ in self.ops: self.prim_counts[names_dict[op]] += 1
diff --git a/src/kyupy/stil.py b/src/kyupy/stil.py
index 7cacc5b..3856f32 100644
--- a/src/kyupy/stil.py
+++ b/src/kyupy/stil.py
@@ -55,7 +55,7 @@ class StilFile:
                 capture = dict((k, v.replace('\n', '').replace('N', '-')) for k, v in call.parameters.items())
 
     def _maps(self, c):
-        interface = list(c.interface) + [n for n in c.nodes if 'DFF' in n.kind]
+        interface = list(c.io_nodes) + [n for n in c.nodes if 'DFF' in n.kind]
         intf_pos = dict((n.name, i) for i, n in enumerate(interface))
         pi_map = [intf_pos[n] for n in self.signal_groups['_pi']]
         po_map = [intf_pos[n] for n in self.signal_groups['_po']]
diff --git a/src/kyupy/verilog.py b/src/kyupy/verilog.py
index e8a20bd..10e5baf 100644
--- a/src/kyupy/verilog.py
+++ b/src/kyupy/verilog.py
@@ -96,7 +96,7 @@ class VerilogTransformer(Transformer):
                 for name in sd.names:
                     n = Node(c, name, kind=sd.kind)
                     if name in positions:
-                        c.interface[positions[name]] = n
+                        c.io_nodes[positions[name]] = n
                     if sd.kind == 'input':
                         Line(c, n, Node(c, name))
         for s1, s2 in assignments:  # pass 1.5: process signal assignments
diff --git a/src/kyupy/wave_sim.py b/src/kyupy/wave_sim.py
index 763e39f..fdfdd1c 100644
--- a/src/kyupy/wave_sim.py
+++ b/src/kyupy/wave_sim.py
@@ -117,7 +117,7 @@ class WaveSim:
         self.circuit = circuit
         self.sims = sims
         self.overflows = 0
-        self.interface = list(circuit.interface) + [n for n in circuit.nodes if 'dff' in n.kind.lower()]
+        self.interface = list(circuit.io_nodes) + [n for n in circuit.nodes if 'dff' in n.kind.lower()]
 
         self.lst_eat_valid = False
 
diff --git a/src/kyupy/wave_sim_4ig.py b/src/kyupy/wave_sim_4ig.py
index 056fdce..01f6a5d 100644
--- a/src/kyupy/wave_sim_4ig.py
+++ b/src/kyupy/wave_sim_4ig.py
@@ -117,7 +117,7 @@ class WaveSim:
         self.circuit = circuit
         self.sims = sims
         self.overflows = 0
-        self.interface = list(circuit.interface) + [n for n in circuit.nodes if 'dff' in n.kind.lower()]
+        self.interface = list(circuit.io_nodes) + [n for n in circuit.nodes if 'dff' in n.kind.lower()]
 
         self.lst_eat_valid = False
 
diff --git a/tests/test_bench.py b/tests/test_bench.py
index 44ddf7c..8b9a533 100644
--- a/tests/test_bench.py
+++ b/tests/test_bench.py
@@ -12,4 +12,4 @@ def test_b01(mydir):
 def test_simple():
     c = bench.parse('input(a, b) output(z) z=and(a,b)')
     assert len(c.nodes) == 4
-    assert len(c.interface) == 3
+    assert len(c.io_nodes) == 3
diff --git a/tests/test_circuit.py b/tests/test_circuit.py
index 446ba90..8eb4e01 100644
--- a/tests/test_circuit.py
+++ b/tests/test_circuit.py
@@ -57,9 +57,9 @@ def test_circuit():
     assert 'in1' in c.cells
     assert 'and1' not in c.cells
 
-    c.interface[0] = in1
-    c.interface[1] = in2
-    c.interface[2] = out1
+    c.io_nodes[0] = in1
+    c.io_nodes[1] = in2
+    c.io_nodes[2] = out1
 
     and1 = Node(c, 'and1', kind='and')
     Line(c, in1, and1)