rtio/sed: fix lane spreading and enable by default

artiq/gateware/rtio/sed/lane_distributor.py

@@ -21,7 +21,7 @@ def layout_lane_io(seqn_width, layout_payload):
 # 3. check status
 
 class LaneDistributor(Module):
-    def __init__(self, lane_count, fifo_size, layout_payload, fine_ts_width, enable_spread=False):
+    def __init__(self, lane_count, fifo_size, layout_payload, fine_ts_width, enable_spread=True):
         if lane_count & (lane_count - 1):
             raise NotImplementedError("lane count must be a power of 2")
 
@@ -67,6 +67,7 @@ class LaneDistributor(Module):
         timestamp_above_min = Signal()
         timestamp_above_laneA_min = Signal()
         timestamp_above_laneB_min = Signal()
+        force_laneB = Signal()
         use_laneB = Signal()
         use_lanen = Signal(max=lane_count)
         current_lane_plus_one = Signal(max=lane_count)
@@ -75,7 +76,7 @@ class LaneDistributor(Module):
             timestamp_above_min.eq(coarse_timestamp > self.minimum_coarse_timestamp),
             timestamp_above_laneA_min.eq(coarse_timestamp > last_lane_coarse_timestamps[current_lane]),
             timestamp_above_laneB_min.eq(coarse_timestamp > last_lane_coarse_timestamps[current_lane_plus_one]),
-            If(coarse_timestamp <= last_coarse_timestamp,
+            If(force_laneB | (coarse_timestamp <= last_coarse_timestamp),
                 use_lanen.eq(current_lane + 1),
                 use_laneB.eq(1)
             ).Else(
@@ -118,10 +119,13 @@ class LaneDistributor(Module):
 
         # current lane has been full, spread events by switching to the next.
         if enable_spread:
-            current_lane_writable_r = Signal()
+            current_lane_writable_r = Signal(reset=1)
             self.sync += [
                 current_lane_writable_r.eq(current_lane_writable),
                 If(~current_lane_writable_r & current_lane_writable,
-                    current_lane.eq(current_lane + 1)
+                    force_laneB.eq(1)
+                ),
+                If(do_write,
+                    force_laneB.eq(0)
                 )
             ]

artiq/gateware/test/rtio/test_sed_lane_distributor.py

@@ -9,7 +9,7 @@ from artiq.gateware.rtio.sed import lane_distributor
 LANE_COUNT = 8
 
 
-def simulate(input_events):
+def simulate(input_events, wait=True):
     dut = lane_distributor.LaneDistributor(LANE_COUNT, 16, [("channel", 8), ("timestamp", 32)], 3)
 
     output = []
@@ -59,12 +59,13 @@ def simulate(input_events):
 
     generators = [gen()]
     for n, lio in enumerate(dut.lane_io):
+        lio.writable.reset = 1
+        wait_time = 0
+        if wait:
             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)
 
@@ -89,7 +90,7 @@ class TestLaneDistributor(unittest.TestCase):
 
     def test_lane_switch(self):
         N = 32
-        output, access_results = simulate([(42+n, n+8) for n in range(N)])
+        output, access_results = simulate([(42+n, n+8) for n in range(N)], wait=False)
         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)
 
@@ -112,3 +113,12 @@ class TestLaneDistributor(unittest.TestCase):
         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")
+
+    def test_spread(self):
+        # get to lane 6
+        input_events = [(42+n, 8) for n in range(7)]
+        input_events.append((100, 16))
+        input_events.append((100, 32))
+        output, access_results = simulate(input_events)
+        self.assertEqual([o[0] for o in output], [x % LANE_COUNT for x in range(9)])
+        self.assertEqual([ar[0] for ar in access_results], ["ok"]*9)