diff --git a/artiq/gateware/test/rtio/test_sed_lane_distributor.py b/artiq/gateware/test/rtio/test_sed_lane_distributor.py
new file mode 100644
index 000000000..76c719fb9
--- /dev/null
+++ b/artiq/gateware/test/rtio/test_sed_lane_distributor.py
@@ -0,0 +1,114 @@
+import unittest
+
+from migen import *
+
+from artiq.gateware.rtio import cri
+from artiq.gateware.rtio.sed import lane_distributor
+
+
+LANE_COUNT = 8
+
+
+def simulate(input_events):
+    dut = lane_distributor.LaneDistributor(LANE_COUNT, 16, [("channel", 8), ("timestamp", 32)], 3)
+
+    output = []
+    access_results = []
+
+    def gen():
+        for channel, timestamp in input_events:
+            yield dut.cri.chan_sel.eq(channel)
+            yield dut.cri.timestamp.eq(timestamp)
+            yield
+
+            yield dut.cri.cmd.eq(cri.commands["write"])
+            yield
+            yield dut.cri.cmd.eq(cri.commands["nop"])
+
+            access_time = 0
+            yield
+            while (yield dut.cri.o_status) & 0x01:
+                yield
+                access_time += 1
+
+            status = (yield dut.cri.o_status)
+            access_status = "ok"
+            if status & 0x02:
+                access_status = "underflow"
+            if status & 0x04:
+                access_status = "sequence_error"
+
+            access_results.append((access_status, access_time))
+
+    @passive
+    def monitor_lane(n, lio, wait_time):
+        yield lio.writable.eq(1)
+        while True:
+            while not (yield lio.we):
+                yield
+            seqn = (yield lio.seqn)
+            channel = (yield lio.payload.channel)
+            timestamp = (yield lio.payload.timestamp)
+            output.append((n, seqn, channel, timestamp))
+
+            yield lio.writable.eq(0)
+            for i in range(wait_time):
+                yield
+            yield lio.writable.eq(1)
+            yield
+
+    generators = [gen()]
+    for n, lio in enumerate(dut.lane_io):
+        if n == 6:
+            wait_time = 1
+        elif n == 7:
+            wait_time = 4
+        else:
+            wait_time = 0
+        generators.append(monitor_lane(n, lio, wait_time))
+    run_simulation(dut, generators)
+
+    return output, access_results
+
+
+class TestLaneDistributor(unittest.TestCase):
+    def test_regular(self):
+        # Assumes lane 0 does not have wait time.
+        N = 16
+        output, access_results = simulate([(42+n, (n+1)*8) for n in range(N)])
+        self.assertEqual(output, [(0, n, 42+n, (n+1)*8) for n in range(N)])
+        self.assertEqual(access_results, [("ok", 0)]*N)
+
+    def test_wait_time(self):
+        output, access_results = simulate([(42+n, 8) for n in range(LANE_COUNT)])
+        self.assertEqual(output, [(n, n, 42+n, 8) for n in range(LANE_COUNT)])
+        expected_access_results = [("ok", 0)]*LANE_COUNT
+        expected_access_results[6] = ("ok", 1)
+        expected_access_results[7] = ("ok", 4)
+        self.assertEqual(access_results, expected_access_results)
+
+    def test_lane_switch(self):
+        N = 32
+        output, access_results = simulate([(42+n, n+8) for n in range(N)])
+        self.assertEqual(output, [((n-n//8) % LANE_COUNT, n, 42+n, n+8) for n in range(N)])
+        self.assertEqual([ar[0] for ar in access_results], ["ok"]*N)
+
+    def test_sequence_error(self):
+        input_events = [(42+n, 8) for n in range(LANE_COUNT+1)]
+        input_events.append((42+LANE_COUNT+1, 16))
+        output, access_results = simulate(input_events)
+        self.assertEqual(len(output), len(input_events)-1)  # event with sequence error must get discarded
+        self.assertEqual([ar[0] for ar in access_results[:LANE_COUNT]], ["ok"]*LANE_COUNT)
+        self.assertEqual(access_results[LANE_COUNT][0], "sequence_error")
+
+    def test_underflow(self):
+        N = 16
+        input_events = [(42+n, (n+1)*8) for n in range(N-2)]
+        input_events.append((0, 0))  # timestamp < 8 underflows
+        input_events.append((42+N-2, N*8))
+        output, access_results = simulate(input_events)
+        self.assertEqual(len(output), len(input_events)-1)  # event with underflow must get discarded
+        self.assertEqual([ar[0] for ar in access_results[:N-2]], ["ok"]*(N-2))
+        self.assertEqual(access_results[N-2][0], "underflow")
+        self.assertEqual(output[N-2], (0, N-2, 42+N-2, N*8))
+        self.assertEqual(access_results[N-1][0], "ok")