diff --git a/src/gateware/cxp_downconn.py b/src/gateware/cxp_downconn.py
index a414ad1..57ae8c6 100644
--- a/src/gateware/cxp_downconn.py
+++ b/src/gateware/cxp_downconn.py
@@ -56,9 +56,12 @@ class Receiver(Module):
        
         self.source = stream.Endpoint(word_layout)
 
+        data_valid = Signal()
         self.sync.cxp_gtx_rx += [
+            data_valid.eq(gtx.comma_checker.rxfsm.ongoing("READY")),
+
             self.source.stb.eq(0),
-            If(gtx.rx_ready & self.source.ack & ~((gtx.decoders[0].d == 0xBC) & (gtx.decoders[0].k == 1)),
+            If(data_valid & self.source.ack & ~((gtx.decoders[0].d == 0xBC) & (gtx.decoders[0].k == 1)),
                 self.source.stb.eq(1),
                 self.source.data.eq(Cat(gtx.decoders[i].d for i in range(4))),
                 self.source.k.eq(Cat(gtx.decoders[i].k for i in range(4))),
@@ -66,17 +69,22 @@ class Receiver(Module):
         ]
 
         # DEBUG: tx fifos for loopback
-        # fw -> fifo (sys) -> cdc fifo -> gtx tx
+        # fw -> -> cdc fifo -> buffered fifo -> gtx tx
         
-        tx_fifo = stream.AsyncFIFO(word_layout, 512)
-        self.submodules += ClockDomainsRenamer({"write": "sys", "read": "cxp_gtx_tx"})(tx_fifo)
-        self.sink = tx_fifo.sink
-    
-        self.tx_stb_sys = Signal()
-        txstb = Signal()
-        self.specials += MultiReg(self.tx_stb_sys, txstb, odomain="cxp_gtx_tx")
+        cdc_fifo = stream.AsyncFIFO(word_layout, 512)
+        self.submodules += ClockDomainsRenamer({"write": "sys", "read": "cxp_gtx_tx"})(cdc_fifo)
+        self.sink = cdc_fifo.sink
 
-        word_count = Signal(max=100)
+        # fix timing violation
+        cdr = ClockDomainsRenamer("cxp_gtx_tx")
+        self.submodules.buf = tx_fifo = cdr(stream.SyncFIFO(word_layout, 2, buffered=True))
+
+        self.comb += [
+            cdc_fifo.source.connect(tx_fifo.sink),
+        ]
+    
+        idle_period = 50 # press in word
+        word_count = Signal(max=idle_period)
 
         # JANK: fix the every 98th word got eaten
         # cnt      97    98   99       0
@@ -85,11 +93,11 @@ class Receiver(Module):
         self.sync.cxp_gtx_tx += [
             tx_fifo.source.ack.eq(0),
 
-            If(word_count == 99,
+            If(word_count == idle_period-1,
                 word_count.eq(word_count.reset),
             ).Else(
-                If(tx_fifo.source.stb & txstb,
-                    If(word_count != 98, tx_fifo.source.ack.eq(1)),
+                If(tx_fifo.source.stb,
+                    If(word_count != idle_period-2, tx_fifo.source.ack.eq(1)),
                     word_count.eq(word_count + 1),
                 )
             )
@@ -97,7 +105,7 @@ class Receiver(Module):
 
         # NOTE: prevent the first word send twice due to stream stb delay 
         self.comb += [
-            If((tx_fifo.source.stb & tx_fifo.source.ack & (word_count != 99)),
+            If((tx_fifo.source.stb & tx_fifo.source.ack & (word_count != idle_period-1)),
                 gtx.encoder.d[0].eq(tx_fifo.source.data[:8]),
                 gtx.encoder.d[1].eq(tx_fifo.source.data[8:16]),
                 gtx.encoder.d[2].eq(tx_fifo.source.data[16:24]),