diff --git a/src/eth/tb/basex.py b/src/eth/tb/basex.py
index ab4566d..9225998 100644
--- a/src/eth/tb/basex.py
+++ b/src/eth/tb/basex.py
@@ -139,6 +139,7 @@ class BaseXSerdesSource():
 
         self.enable_dic = True
         self.ifg = 12
+        self.truncate_preamble = False
 
         self.bit_offset = 0
 
@@ -434,6 +435,11 @@ class BaseXSerdesSource():
                         # /S/
                         d_val = XgmiiCtrl.START # /K27.7/
                         k_val = True
+                        if self.truncate_preamble:
+                            if self.gmii_rep_count:
+                                rep_cnt = self.gmii_rep_count
+                            else:
+                                frame_offset += 1
                     elif frame_offset >= len(frame.data):
                         # /T/
                         d_val = XgmiiCtrl.TERM # /K29.7/
@@ -483,7 +489,7 @@ class BaseXSerdesSource():
 
                 if rep_cnt > 0:
                     rep_cnt -= 1
-                elif self.gmii_rep_count and odd:
+                elif self.gmii_rep_count and (odd or frame is not None):
                     rep_cnt = self.gmii_rep_count
 
             # if self.slip is not None and self.slip.value:
diff --git a/src/eth/tb/taxi_axis_basex_rx_16/test_taxi_axis_basex_rx_16.py b/src/eth/tb/taxi_axis_basex_rx_16/test_taxi_axis_basex_rx_16.py
index d76a250..c7763f2 100644
--- a/src/eth/tb/taxi_axis_basex_rx_16/test_taxi_axis_basex_rx_16.py
+++ b/src/eth/tb/taxi_axis_basex_rx_16/test_taxi_axis_basex_rx_16.py
@@ -109,11 +109,12 @@ class TB:
                 self.stats[stat] += int(getattr(self.dut, stat).value)
 
 
-async def run_test(dut, gbx_cfg=None, payload_lengths=None, payload_data=None, ifg=12, pre_len=8):
+async def run_test(dut, gbx_cfg=None, payload_lengths=None, payload_data=None, ifg=12, pre_trunc=False):
 
     tb = TB(dut, gbx_cfg)
 
     tb.source.ifg = ifg
+    tb.source.truncate_preamble = pre_trunc
     tb.dut.cfg_rx_max_pkt_len.value = 9218-1
     tb.dut.cfg_rx_enable.value = 1
 
@@ -127,7 +128,6 @@ async def run_test(dut, gbx_cfg=None, payload_lengths=None, payload_data=None, i
 
     for test_data in test_frames:
         test_frame = GmiiFrame.from_payload(test_data, tx_complete=tx_frames.append)
-        test_frame.data = test_frame.data[8-pre_len:]
         await tb.source.send(test_frame)
         total_bytes += len(test_data)+4
         total_pkts += 1
@@ -320,7 +320,7 @@ if getattr(cocotb, 'top', None) is not None:
     factory.add_option("payload_lengths", [size_list])
     factory.add_option("payload_data", [incrementing_payload])
     # factory.add_option("ifg", list(range(0, 13)))
-    factory.add_option("pre_len", [8, 7])
+    factory.add_option("pre_trunc", [False, True])
     factory.add_option("gbx_cfg", gbx_cfgs)
     factory.generate_tests()
 
diff --git a/src/eth/tb/taxi_axis_basex_rx_8/test_taxi_axis_basex_rx_8.py b/src/eth/tb/taxi_axis_basex_rx_8/test_taxi_axis_basex_rx_8.py
index 6ac17ce..64edf4e 100644
--- a/src/eth/tb/taxi_axis_basex_rx_8/test_taxi_axis_basex_rx_8.py
+++ b/src/eth/tb/taxi_axis_basex_rx_8/test_taxi_axis_basex_rx_8.py
@@ -124,11 +124,12 @@ class TB:
                 self.stats[stat] += int(getattr(self.dut, stat).value)
 
 
-async def run_test(dut, gbx_cfg=None, sgmii_speed=None, payload_lengths=None, payload_data=None, ifg=12, pre_len=8):
+async def run_test(dut, gbx_cfg=None, sgmii_speed=None, payload_lengths=None, payload_data=None, ifg=12, pre_trunc=False):
 
     tb = TB(dut, gbx_cfg, sgmii_speed)
 
     tb.source.ifg = ifg
+    tb.source.truncate_preamble = pre_trunc
     tb.dut.cfg_rx_max_pkt_len.value = 9218-1
     tb.dut.cfg_rx_enable.value = 1
 
@@ -142,7 +143,6 @@ async def run_test(dut, gbx_cfg=None, sgmii_speed=None, payload_lengths=None, pa
 
     for test_data in test_frames:
         test_frame = GmiiFrame.from_payload(test_data, tx_complete=tx_frames.append)
-        test_frame.data = test_frame.data[8-pre_len:]
         await tb.source.send(test_frame)
         total_bytes += max(len(test_data), 60)+4
         total_pkts += 1
@@ -335,7 +335,7 @@ if getattr(cocotb, 'top', None) is not None:
     factory.add_option("payload_lengths", [size_list])
     factory.add_option("payload_data", [incrementing_payload])
     factory.add_option("ifg", [0, 1, 11, 12])
-    factory.add_option("pre_len", [8, 7])
+    factory.add_option("pre_trunc", [False, True])
     factory.add_option("sgmii_speed", [None, 1, 2])
     factory.add_option("gbx_cfg", gbx_cfgs)
     factory.generate_tests()
diff --git a/src/eth/tb/taxi_gmii_basex_dec/test_taxi_gmii_basex_dec.py b/src/eth/tb/taxi_gmii_basex_dec/test_taxi_gmii_basex_dec.py
index 8fec9a2..70219eb 100644
--- a/src/eth/tb/taxi_gmii_basex_dec/test_taxi_gmii_basex_dec.py
+++ b/src/eth/tb/taxi_gmii_basex_dec/test_taxi_gmii_basex_dec.py
@@ -73,11 +73,12 @@ class TB:
         await RisingEdge(self.dut.clk)
 
 
-async def run_test(dut, gbx_cfg=None, payload_lengths=None, payload_data=None, ifg=12, pre_len=8):
+async def run_test(dut, gbx_cfg=None, payload_lengths=None, payload_data=None, ifg=12, pre_trunc=8):
 
     tb = TB(dut, gbx_cfg)
 
     tb.source.ifg = ifg
+    tb.source.truncate_preamble = pre_trunc
 
     await tb.reset()
 
@@ -85,7 +86,6 @@ async def run_test(dut, gbx_cfg=None, payload_lengths=None, payload_data=None, i
 
     for test_data in test_frames:
         test_frame = GmiiFrame.from_payload(test_data)
-        test_frame.data = test_frame.data[8-pre_len:]
         await tb.source.send(test_frame)
 
     for test_data in test_frames:
@@ -147,7 +147,7 @@ if getattr(cocotb, 'top', None) is not None:
     factory.add_option("payload_lengths", [size_list])
     factory.add_option("payload_data", [incrementing_payload])
     factory.add_option("ifg", list(range(0, 13)))
-    factory.add_option("pre_len", [8, 7])
+    factory.add_option("pre_trunc", [False, True])
     factory.generate_tests()
 
     factory = TestFactory(run_test_an)