diff --git a/artiq/gateware/rtio/sed/fifo.py b/artiq/gateware/rtio/sed/fifo.py
new file mode 100644
index 000000000..1f908a0c1
--- /dev/null
+++ b/artiq/gateware/rtio/sed/fifo.py
@@ -0,0 +1,37 @@
+from migen import *
+from migen.genlib.fifo import *
+
+from artiq.gateware.rtio.sed import layouts
+
+
+__all__ = ["FIFO"]
+
+
+class FIFO(Module):
+    def __init__(self, lane_count, mode, fifo_depth, layout_payload):
+        seqn_width = layouts.seqn_width(lane_count, fifo_width)
+        self.input = [layouts.fifo_ingress(seqn_width, layout_payload)
+                      for _ in range(lane_count)]
+        self.output = [layouts.fifo_egress(seqn_width, layout_payload)
+                       for _ in range(lane_count)]
+
+        if mode == "sync":
+            fifo_cls = fifo.SyncFIFOBuffered
+        elif mode == "async":
+            fifo_cls = fifo.AsyncFIFO
+        else:
+            raise ValueError
+
+        for input, output in zip(self.input, self.output):
+            fifo = fifo_cls(layout_len(layout_payload), fifo_depth)
+            self.submodules += fifo
+
+            self.comb += [
+                fifo.din.eq(input.payload.raw_bits()),
+                fifo.we.eq(input.we),
+                input.writable.eq(fifo.writable),
+
+                output.payload.raw_bits().eq(fifo.dout),
+                output.readable.eq(fifo.readable),
+                fifo.re.eq(output.re)
+            ]
diff --git a/artiq/gateware/rtio/sed/lane_distributor.py b/artiq/gateware/rtio/sed/lane_distributor.py
index d21d40484..c58dfeb6d 100644
--- a/artiq/gateware/rtio/sed/lane_distributor.py
+++ b/artiq/gateware/rtio/sed/lane_distributor.py
@@ -14,14 +14,10 @@ __all__ = ["LaneDistributor"]
 # 3. check status
 
 class LaneDistributor(Module):
-    def __init__(self, lane_count, fifo_size, layout_payload, fine_ts_width, enable_spread=True):
+    def __init__(self, lane_count, seqn_width, layout_payload, fine_ts_width, enable_spread=True):
         if lane_count & (lane_count - 1):
             raise NotImplementedError("lane count must be a power of 2")
 
-        # There must be a unique sequence number for every possible event in every FIFO.
-        # Plus 2 bits to detect and handle wraparounds.
-        seqn_width = bits_for(lane_count*fifo_size-1) + 2
-
         self.cri = cri.Interface()
         self.minimum_coarse_timestamp = Signal(64-fine_ts_width)
         self.lane_io = [Record(layouts.fifo_ingress(seqn_width, layout_payload))
diff --git a/artiq/gateware/rtio/sed/layouts.py b/artiq/gateware/rtio/sed/layouts.py
index 4408a5d00..5feac13b2 100644
--- a/artiq/gateware/rtio/sed/layouts.py
+++ b/artiq/gateware/rtio/sed/layouts.py
@@ -21,6 +21,12 @@ def fifo_payload(channels):
     return layout
 
 
+def seqn_width(lane_count, fifo_width):
+    # There must be a unique sequence number for every possible event in every FIFO.
+    # Plus 2 bits to detect and handle wraparounds.
+    return bits_for(lane_count*fifo_size-1) + 2
+
+
 def fifo_ingress(seqn_width, layout_payload):
     return [
         ("we", 1, DIR_M_TO_S),
diff --git a/artiq/gateware/test/rtio/test_sed_lane_distributor.py b/artiq/gateware/test/rtio/test_sed_lane_distributor.py
index c9f883db4..f7c4efa28 100644
--- a/artiq/gateware/test/rtio/test_sed_lane_distributor.py
+++ b/artiq/gateware/test/rtio/test_sed_lane_distributor.py
@@ -10,7 +10,7 @@ LANE_COUNT = 8
 
 
 def simulate(input_events, wait=True):
-    dut = lane_distributor.LaneDistributor(LANE_COUNT, 16, [("channel", 8), ("timestamp", 32)], 3)
+    dut = lane_distributor.LaneDistributor(LANE_COUNT, 8, [("channel", 8), ("timestamp", 32)], 3)
 
     output = []
     access_results = []