diff --git a/src/gateware/cxp_pipeline.py b/src/gateware/cxp_pipeline.py
index cabcdd6..00363c7 100644
--- a/src/gateware/cxp_pipeline.py
+++ b/src/gateware/cxp_pipeline.py
@@ -301,6 +301,25 @@ class RX_Debug_Buffer(Module,AutoCSR):
             self.dout_valid.status.eq(buf_out.source.stb),
         ]
 
+class Duplicate_Majority_Voter(Module):
+    def __init__(self, data, k):
+        assert data.nbits == 32
+        assert k.nbits == 4
+        
+        # Section 9.2.2.1 (CXP-001-2021)
+        # decoder should immune to single bit errors when handling duplicated characters
+        self.char = Signal(char_width)
+        self.k = Signal()
+
+        a, a_k = data[:8], k[0]
+        b, b_k = data[8:16], k[1]
+        c, c_k = data[16:24], k[2]
+        d, d_k = data[24:], k[3]
+        self.comb += [
+            self.char.eq(a&b&c | a&b&d | a&c&d | b&c&d),
+            self.k.eq(a_k&b_k&c_k | a_k&b_k&d_k | a_k&c_k&d_k | b_k&c_k&d_k),
+        ]
+
 @FullMemoryWE()
 class CXP_Data_Packet_Decode(Module):
     def __init__(self):
@@ -313,7 +332,6 @@ class CXP_Data_Packet_Decode(Module):
 
         # DEBUG: remove debug
         # TODO: decode all packet type here
-        # TODO: data&event -> memory
         # TODO: heartbeat
         type = {
             "data_stream": 0x01,
@@ -331,10 +349,23 @@ class CXP_Data_Packet_Decode(Module):
 
         self.submodules.fsm = fsm = FSM(reset_state="IDLE")
 
+        self.submodules.voter = voter = Duplicate_Majority_Voter(self.sink.data, self.sink.k)
+
+        # # Section 9.2.2.1 (CXP-001-2021)
+        # # decoder should immune to single bit errors when handling duplicated characters
+        # char_majority = Signal(char_width)
+        # k_majority = Signal()
+        # a, b, c, d = self.sink.data[:8], self.sink.data[8:16], self.sink.data[16:24], self.sink.data[24:]
+        # a_k, b_k, c_k, d_k = self.sink.k[0], self.sink.k[1], self.sink.k[2], self.sink.k[3]
+        # self.comb += [
+        #     char_majority.eq(a&b&c | a&b&d | a&c&d | b&c&d),
+        #     k_majority.eq(a_k&b_k&c_k | a_k&b_k&d_k | a_k&c_k&d_k | b_k&c_k&d_k),
+        # ]
+        
+
         fsm.act("IDLE",
             self.sink.ack.eq(1),
-            # TODO: add error correction?
-            If((self.sink.stb & (self.sink.data == Replicate(KCode["pak_start"], 4)) & (self.sink.k == 0b1111)),
+            If((self.sink.stb & (voter.char == KCode["pak_start"]) & (voter.k == 1)),
                 NextState("DECODE"),
             )
         )
@@ -345,9 +376,9 @@ class CXP_Data_Packet_Decode(Module):
         fsm.act("DECODE",
             self.sink.ack.eq(1),
             If(self.sink.stb,
-                NextValue(self.packet_type, self.sink.data[:8]),
+                NextValue(self.packet_type, voter.char),
 
-                Case(self.sink.data[:8],{
+                Case(voter.char, {
                     type["data_stream"]: NextState("STREAMING"),
                     type["control_ack_no_tag"]:[
                         NextValue(addr, addr.reset),
@@ -384,7 +415,7 @@ class CXP_Data_Packet_Decode(Module):
         fsm.act("VERIFY_TEST_PATTERN",
             self.sink.ack.eq(1),
             If(self.sink.stb,
-                If(((self.sink.data == Replicate(KCode["pak_end"], 4)) & (self.sink.k == 0b1111)),
+                If(((voter.char == KCode["pak_end"]) & (voter.k == 1)),
                     NextState("IDLE"),
                 ).Else(
                     If(((self.sink.data != Cat(cnt, cnt+1, cnt+2, cnt+3))),  
@@ -402,7 +433,7 @@ class CXP_Data_Packet_Decode(Module):
 
         # For stream data packet
         fsm.act("STREAMING",
-            If((self.sink.stb & (self.sink.data == Replicate(KCode["pak_end"], 4)) & (self.sink.k == 0b1111)),
+            If((self.sink.stb & (voter.char == KCode["pak_end"]) & (voter.k == 1)),
                 # discard K29,7
                 self.sink.ack.eq(1),
                 NextState("IDLE")
@@ -429,7 +460,7 @@ class CXP_Data_Packet_Decode(Module):
             mem_port.we.eq(0),
             self.sink.ack.eq(1),
             If(self.sink.stb,
-                If(((self.sink.data == Replicate(KCode["pak_end"], 4)) & (self.sink.k == 0b1111)),
+                If(((voter.char == KCode["pak_end"]) & (voter.k == 1)),
                     NextState("MOVE_BUFFER_PTR"),
                 ).Else(
                     mem_port.we.eq(1),
@@ -468,8 +499,10 @@ class CXP_Trig_Ack_Checker(Module, AutoCSR):
 
         self.submodules.fsm = fsm = FSM(reset_state="COPY")
 
+        self.submodules.voter = voter = Duplicate_Majority_Voter(self.sink.data, self.sink.k)
+
         fsm.act("COPY",
-            If((self.sink.stb & (self.sink.data == Replicate(KCode["io_ack"], 4)) & (self.sink.k == 0b1111)),
+            If((self.sink.stb & (voter.char == KCode["io_ack"]) & (voter.k == 1)),
                 # discard K28,6
                 self.sink.ack.eq(1),
                 NextState("CHECK_ACK")
@@ -483,7 +516,7 @@ class CXP_Trig_Ack_Checker(Module, AutoCSR):
                 NextState("COPY"),
                 # discard the word after K28,6
                 self.sink.ack.eq(1),
-                If(self.sink.data == Replicate(C(0x01, char_width), 4),
+                If((voter.char == 0x01) & (voter.k == 0),
                     self.ack.eq(1),
                 )
             )