4 changed files with 85 additions and 622 deletions
--- a/sim_pipeline.py
+++ b/sim_pipeline.py
@ -1,393 +0,0 @@
 from migen import *
 from misoc.interconnect.csr import *
 from misoc.interconnect import stream
 from misoc.cores.liteeth_mini.mac.crc import LiteEthMACCRCEngine
 from src.gateware.cxp_pipeline import *
 class EOP_Marker(Module):
    def __init__(self):
        self.sink = stream.Endpoint(word_layout_dchar)
        self.source = stream.Endpoint(word_layout_dchar)
        # # #
        last_stb = Signal()
        self.sync += [
            If((~self.source.stb | self.source.ack),
                self.source.stb.eq(self.sink.stb),
                self.source.payload.eq(self.sink.payload),
            ),
            last_stb.eq(self.sink.stb),
        ]
        self.comb += [
            self.sink.ack.eq(~self.source.stb | self.source.ack),
            self.source.eop.eq(~self.sink.stb & last_stb),
        ]
 class Stream_MetaData_Extractor(Module):
    def __init__(self):
        self.sink = stream.Endpoint(word_layout_dchar)
        self.source = stream.Endpoint(word_layout_dchar)
        # # #
        # GOAL:
        # 0) accept four sinks??
        # 1) decode SPH, SPT
        # 2) decode Image header, line break
        # 3) verify the crc before phrasing image data downstream
        # HOW??
        # combine streams?
        # phrase linedata to sys CD
        # check stream data tag
        # only need to support mono16 for now
        self.stream_id = Signal(char_width)
        self.pak_tag = Signal(char_width)
        self.stream_pak_size = Signal(char_width * 2)
        self.submodules.fsm = fsm = FSM(reset_state="WAIT_HEADER")
        fsm.act(
            "WAIT_HEADER",
            NextValue(self.stream_id, self.stream_id.reset),
            NextValue(self.pak_tag, self.pak_tag.reset),
            NextValue(self.stream_pak_size, self.stream_pak_size.reset),
            self.sink.ack.eq(1),
            If(
                self.sink.stb,
                NextValue(self.stream_id, self.sink.dchar),
                NextState("GET_PAK_TAG"),
            ),
        )
        fsm.act(
            "GET_PAK_TAG",
            If(
                self.sink.stb,
                self.sink.ack.eq(1),
                NextValue(self.pak_tag, self.sink.dchar),
                NextState("GET_PAK_SIZE_0"),
            ),
        )
        fsm.act(
            "GET_PAK_SIZE_0",
            self.sink.ack.eq(1),
            If(
                self.sink.stb,
                NextValue(self.stream_pak_size[8:], self.sink.dchar),
                NextState("GET_PAK_SIZE_1"),
            ),
        )
        fsm.act(
            "GET_PAK_SIZE_1",
            self.sink.ack.eq(1),
            If(
                self.sink.stb,
                NextValue(self.stream_pak_size[:8], self.sink.dchar),
                NextState("STORE_BUFFER"),
            ),
        )
        fsm.act(
            "STORE_BUFFER",
            self.sink.connect(self.source),
            # both serve the same function but using the pak size I can remove eop injecter and save 1 cycle
            If(self.sink.stb,
                NextValue(self.stream_pak_size, self.stream_pak_size - 1),
                If(self.stream_pak_size == 1,
                    NextState("WAIT_HEADER"),
                )
            ),
            # If((self.sink.stb & self.sink.eop),
            #     NextState("WAIT_HEADER"),
            # )
        )
 class Frame_Decoder(Module):
    def __init__(self):
        self.sink = stream.Endpoint(word_layout_dchar)
        self.source = stream.Endpoint(word_layout_dchar)
        # # #
        # TODO: decode Image header, line break
 class Pixel_Decoder(Module):
    def __init__(self, pixel_format="mono16"):
        assert pixel_format == "mono16"
        self.sink = stream.Endpoint(word_layout_dchar)
        self.source = stream.Endpoint(word_layout_dchar)
        # # #
        # TODO: support mono16 for now?
 class Streams_Dispatcher(Module):
    def __init__(self, downconns):
        n_downconn = len(downconns)
        self.submodules.mux = mux = stream.Multiplexer(word_layout_dchar, n_downconn)
        for i, c in enumerate(downconns):
            # if i == 0:
            self.comb += [
                # no backpressure
                c.source.ack.eq(1),
                c.source.connect(getattr(mux, "sink"+str(i)))
            ]
        self.source = stream.Endpoint(word_layout_dchar)
        self.submodules.fsm = fsm = FSM(reset_state="WAIT_HEADER")
        # TODO: add different downstream
        # stream_id = Signal()
        # case = dict((i, mux.source.connect(b.sink)) for i, b in enumerate(buffers))
        fsm.act(
            "WAIT_HEADER",
            mux.source.connect(self.source),
            If(mux.source.eop,
                NextState("SWITCH_CONN"),
            ),
        )
        read_mask = Signal(max=n_downconn)
        self.comb += mux.sel.eq(read_mask)
        fsm.act(
            "SWITCH_CONN",
            If(read_mask == n_downconn - 1,
                NextValue(read_mask, read_mask.reset),
            ).Else(
                NextValue(read_mask, read_mask + 1),
            ),
            NextState("WAIT_HEADER"),
        )
 def reverse_bytes(s):
    assert len(s) % 8 == 0
    char = [s[i*8:(i+1)*8] for i in range(len(s)//8)]
    return Cat(char[::-1])
@ResetInserter()
@CEInserter()
 class CXPCRC32(Module):
    # Section 9.2.2.2 (CXP-001-2021)
    width = 32
    polynom = 0x04C11DB7
    seed = 2**width - 1
    check = 0x00000000
    def __init__(self, data_width):
        self.data = Signal(data_width)
        self.value = Signal(self.width)
        self.error = Signal()
        # # #
        self.submodules.engine = LiteEthMACCRCEngine(
            data_width, self.width, self.polynom
        )
        reg = Signal(self.width, reset=self.seed)
        self.sync += reg.eq(self.engine.next)
        self.comb += [
            # the CRC Engine use Big Endian, need to reverse the bytes
            self.engine.data.eq(reverse_bytes(self.data)),
            self.engine.last.eq(reg),
            self.value.eq(reverse_bytes(reg[::-1])),
            self.error.eq(reg != self.check),
        ]
 class CXPCRC32Inserter(Module):
    def __init__(self):
        self.sink = stream.Endpoint(word_layout)
        self.source = stream.Endpoint(word_layout)
        # # #
        self.submodules.crc = crc = CXPCRC32(word_dw)
        self.submodules.fsm = fsm = FSM(reset_state="IDLE")
        fsm.act("IDLE",
            crc.reset.eq(1),
            self.sink.ack.eq(1),
            If(self.sink.stb,
                self.sink.ack.eq(0),
                NextState("COPY"),
            )
        )
        fsm.act("COPY",
            crc.ce.eq(self.sink.stb & self.source.ack),
            crc.data.eq(self.sink.data),
            self.sink.connect(self.source),
            self.source.eop.eq(0),
            If(self.sink.stb & self.sink.eop & self.source.ack,
                NextState("INSERT"),
            )
        )        
        fsm.act("INSERT",
            self.source.stb.eq(1),
            self.source.eop.eq(1),
            self.source.data.eq(crc.value),
            If(self.source.ack, NextState("IDLE"))
        )
 class StreamPacket_Wrapper(Module):
    def __init__(self):
        self.sink = stream.Endpoint(word_layout)
        self.source = stream.Endpoint(word_layout)
        # # #
        self.submodules.fsm = fsm = FSM(reset_state="IDLE")
        fsm.act("IDLE",
            self.sink.ack.eq(1),
            If(self.sink.stb,
                self.sink.ack.eq(0),
                NextState("INSERT_HEADER_0"),
            )
        )
        fsm.act("INSERT_HEADER_0",
            self.sink.ack.eq(0),
            self.source.stb.eq(1),
            self.source.data.eq(Replicate(KCode["pak_start"], 4)),
            self.source.k.eq(Replicate(1, 4)),
            If(self.source.ack, NextState("INSERT_HEADER_1")),
        )
        fsm.act("INSERT_HEADER_1",
            self.sink.ack.eq(0),
            self.source.stb.eq(1),
            self.source.data.eq(Replicate(C(0x01, char_width), 4)),
            self.source.k.eq(Replicate(0, 4)),
            If(self.source.ack, NextState("COPY")),
        )
        fsm.act("COPY",
            self.sink.connect(self.source),
            self.source.eop.eq(0),
            If(self.sink.stb & self.sink.eop & self.source.ack,
                NextState("INSERT_FOOTER"),
            ),
        )
        fsm.act("INSERT_FOOTER",
            self.sink.ack.eq(0),
            self.source.stb.eq(1),
            self.source.data.eq(Replicate(KCode["pak_end"], 4)),
            self.source.k.eq(Replicate(1, 4)),
            # Simulate RX don't have eop tagged
            # self.source.eop.eq(1),
            If(self.source.ack, NextState("IDLE")),
        )
 # With KCode & 0x01*4
 class StreamData_Generator(Module):
    def __init__(self):
        # should be big enough for all test
        self.submodules.buffer = buffer = stream.SyncFIFO(word_layout, 32)
        self.submodules.crc_inserter = crc_inserter = CXPCRC32Inserter()
        self.submodules.wrapper = wrapper = StreamPacket_Wrapper()
        # # #
        pipeline = [buffer, crc_inserter, wrapper]
        for s, d in zip(pipeline, pipeline[1:]):
            self.comb += s.source.connect(d.sink)
        self.sink = pipeline[0].sink
        self.source = pipeline[-1].source
 # For verifying crc in stream data packet
 class Double_Stream_Buffer(Module):
    # default size is 2 kBtyes - Section 9.5.2 (CXP-001-2021)
    def __init__(self, size=16000):
        # detect and tag end of packet for crc
        # self.submodules.eop_marker = eop_marker = EOP_Marker()
        # self.sink = eop_marker.sink
        self.sink = stream.Endpoint(word_layout_dchar)
        self.submodules.crc = crc = CXPCRC32(word_dw)
        self.comb += crc.data.eq(self.sink.data)
        self.submodules.fsm = fsm = FSM(reset_state="RESET")
        write_mask = Signal()
        self.submodules.line_buffer0 = line_buffer0 = ResetInserter()(stream.SyncFIFO(word_layout_dchar, 2**bits_for(size//word_dw)))
        self.submodules.line_buffer1 = line_buffer1 = ResetInserter()(stream.SyncFIFO(word_layout_dchar, 2**bits_for(size//word_dw)))
        fsm.act("RESET",
            Case(write_mask,
                {
                     0: line_buffer0.reset.eq(1),
                     1: line_buffer1.reset.eq(1),
                }
            ),
            crc.reset.eq(1),
            NextState("CHECKING"),
        )
        fsm.act("CHECKING",
            self.sink.ack.eq(1),
            If(self.sink.stb,
                crc.ce.eq(1),
                If(self.sink.eop,
                    # discard the crc at the end
                    NextState("SWITCH_BUFFER")
                ).Else(
                    If(write_mask == 0,
                        self.sink.connect(line_buffer0.sink),
                    ).Else(
                        self.sink.connect(line_buffer1.sink),
                    ),
                )
            )
        )
        # only valid data will be passed to downstream
        fsm.act("SWITCH_BUFFER",
            If(~crc.error,
                NextValue(write_mask, ~write_mask),
            ),
            NextState("RESET"),
        )
        self.submodules.mux = mux = stream.Multiplexer(word_layout_dchar, 2)
        self.comb += [
            line_buffer0.source.connect(mux.sink0),
            line_buffer1.source.connect(mux.sink1),
            mux.sel.eq(~write_mask),
        ]
        self.source = mux.source
        # DEBUG:
        self.write = Signal()
        self.error = Signal()
        self.comb += [
            self.write.eq(write_mask),
            self.error.eq(crc.error),
        ]
        # # to add eop in the same cycle
        # # the tricks relies on the fact source lags sink one cycle
        # # but fsm .connect by default use combinational logic which the same cycle rising/falling edge check immpossible
        # fsm.act("CHECKING",
        #     NextValue(self.source.payload.raw_bits(), 0),
        #     NextValue(self.source.stb, 0),
        #     If(self.sink.stb,
        #         crc.ce.eq(1),
        #         If(self.sink.eop,
        #             NextState("RESET")
        #         ).Else(
        #             NextValue(self.source.payload.raw_bits(), self.sink.payload.raw_bits()),
        #             NextValue(self.source.stb, 1),
        #         )
        #     )
        # )
        # last_eop = Signal()
        # self.comb += self.source.eop.eq(~last_eop & self.sink.eop)
--- a/sim_stream.py
+++ b/sim_stream.py
@ -1,159 +0,0 @@
 from migen import *
 from misoc.interconnect import stream
 from sim_pipeline import *
 from src.gateware.cxp_pipeline import *
 class CXP_Links(Module):
    def __init__(self):
        # TODO: select the correct buffer to read from
        # NOTE: although there are double buffer in each connect, the reading must be faster than writing to avoid data loss
        self.downconns = []
        for i in range(2):
            downconn = Pipeline()
            setattr(self.submodules, "cxp_conn"+str(i), downconn)
            self.downconns.append(downconn)
        self.submodules.dispatcher = dispatcher = Streams_Dispatcher(self.downconns)
        # TODO: add extractor
        # self.submodules.double_buffer = double_buffer = Double_Stream_Buffer()
        pipeline = [dispatcher]
        for s, d in zip(pipeline, pipeline[1:]):
            self.comb += s.source.connect(d.sink)
        self.source = pipeline[-1].source
        # no backpressure
        self.sync += self.source.ack.eq(1)
 class Pipeline(Module):
    def __init__(self):
        self.submodules.generator = generator = StreamData_Generator()
        self.submodules.dchar_decoder = dchar_decoder = Duplicated_Char_Decoder()
        self.submodules.data_decoder = data_decoder = RX_Bootstrap()
        self.submodules.eop_marker = eop_marker = EOP_Marker()
        # # #
        pipeline = [generator, dchar_decoder, data_decoder, eop_marker]
        for s, d in zip(pipeline, pipeline[1:]):
            self.comb += s.source.connect(d.sink)
        self.sink = pipeline[0].sink
        self.source = pipeline[-1].source
        # self.comb += self.source.ack.eq(1)
 dut = CXP_Links()
 def check_case(packet=[]):
    print("=================TEST========================")
    downconns = dut.downconns
    ch = 0
    for i, p in enumerate(packet):
        for x in range(len(downconns)):
            if x == ch:
                yield downconns[x].sink.data.eq(p["data"])
                yield downconns[x].sink.k.eq(p["k"])
                yield downconns[x].sink.stb.eq(1)
            else:
                yield downconns[x].sink.data.eq(0)
                yield downconns[x].sink.k.eq(0)
                yield downconns[x].sink.stb.eq(0)
                yield downconns[x].sink.eop.eq(0)
        if "eop" in p:
            yield downconns[ch].sink.eop.eq(1)
            # compensate for delay
            # yield
            # yield downconns[ch].sink.data.eq(0)
            # yield downconns[ch].sink.k.eq(0)
            # yield downconns[ch].sink.stb.eq(0)
            # yield downconns[ch].sink.eop.eq(0)
            # yield
            # yield
            # yield
            ch = (ch + 1) % len(downconns)
        else:
            yield downconns[ch].sink.eop.eq(0)
        # check cycle result
        yield
        source = dut.dispatcher.mux.source
        print(
            f"\nCYCLE#{i} : source char = {yield source.data:#X} k = {yield source.k:#X} stb = {yield source.stb} ack = {yield source.ack} eop = {yield source.eop}"
            # f" source dchar = {yield source.dchar:#X} dchar_k = {yield source.dchar_k:#X}"
            f"\nCYCLE#{i} : read mask = {yield dut.dispatcher.mux.sel}"
            # f"\nCYCLE#{i} : stream id = {yield decoder.stream_id:#X} pak_tag = {yield decoder.pak_tag:#X}"
            # f" stream_pak_size = {yield decoder.stream_pak_size:#X}"
        )
        # crc = downconns[1].generator.crc_inserter.crc
        # crc = dut.double_buffer.crc
        # print(
        #     f"CYCLE#{i} : crc error = {yield crc.error:#X} crc value = {yield crc.value:#X}"
        #     f" crc data = {yield crc.data:#X} engine next = {yield crc.engine.next:#X} ce = {yield crc.ce}"
        # )
    # extra clk cycles
    cyc = i + 1
    for i in range(cyc, cyc + 30):
        for x in range(len(downconns)):
            # yield won't reset every cycle
            yield downconns[x].sink.data.eq(0)
            yield downconns[x].sink.k.eq(0)
            yield downconns[x].sink.stb.eq(0)
            yield downconns[x].sink.eop.eq(0)
        yield
        print(
            f"\nCYCLE#{i} : source char = {yield source.data:#X} k = {yield source.k:#X} stb = {yield source.stb} ack = {yield source.ack} eop = {yield source.eop}"
            # f" source dchar = {yield source.dchar:#X} dchar_k = {yield source.dchar_k:#X}"
            f"\nCYCLE#{i} : read mask = {yield dut.dispatcher.mux.sel}"
            # f"\nCYCLE#{i} : stream id = {yield decoder.stream_id:#X} pak_tag = {yield decoder.pak_tag:#X}"
            # f" stream_pak_size = {yield decoder.stream_pak_size:#X}"
        )
    assert True
 def testbench():
    stream_id = 0x69
    streams = [
        [
            {"data": 0x11111111, "k": Replicate(0, 4)},
            {"data": 0xB105F00D, "k": Replicate(0, 4)},
        ],
        [
            {"data": 0x22222222, "k": Replicate(0, 4)},
            {"data": 0xC00010FF, "k": Replicate(0, 4)},
        ],
        [
            {"data": 0x33333333, "k": Replicate(0, 4)},
            {"data": 0xC0A79AE5, "k": Replicate(0, 4)},
        ],
    ]
    packet = []
    for i, s in enumerate(streams):
        s[-1]["eop"] = 0
        packet += [
            {"data": Replicate(C(stream_id, char_width), 4), "k": Replicate(0, 4)},
            {"data": Replicate(C(i, char_width), 4), "k": Replicate(0, 4)},
            {
                "data": Replicate(C(len(s) >> 8 & 0xFF, char_width), 4),
                "k": Replicate(0, 4),
            },
            {"data": Replicate(C(len(s) & 0xFF, char_width), 4), "k": Replicate(0, 4)},
            *s,
        ]
    yield from check_case(packet)
 run_simulation(dut, testbench(), vcd_name="sim-cxp.vcd")
--- a/src/gateware/cxp_downconn.py
+++ b/src/gateware/cxp_downconn.py
@ -58,7 +58,7 @@ class Receiver(Module):
        data_valid = Signal()
        self.sync.cxp_gtx_rx += [
-            data_valid.eq(gtx.comma_aligner.rxfsm.ongoing("READY")),
+            data_valid.eq(gtx.comma_checker.rxfsm.ongoing("READY")),
            self.source.stb.eq(0),
            If(data_valid & self.source.ack & ~((gtx.decoders[0].d == 0xBC) & (gtx.decoders[0].k == 1)),
@ -218,33 +218,9 @@ class QPLL(Module, AutoCSR):
            ),
        ]
 class RX_Resetter(Module):
    def __init__(self, reset_period=10_000_000):
        self.rx_ready = Signal()
        self.rx_reset = Signal()
        # # #
        # periodically reset rx until rx is connected and receiving valid data
        # as after connecting RXP/RXN, the whole RX need to be reset 
        reset_counter = Signal(reset=reset_period-1, max=reset_period)
        self.sync += [
            self.rx_reset.eq(0),
            If(~self.rx_ready,
                If(reset_counter == 0,
                    reset_counter.eq(reset_counter.reset),
                    self.rx_reset.eq(1),
                ).Else(
                    reset_counter.eq(reset_counter - 1),
                )
            )
        ]
 # Warning: Xilinx transceivers are LSB first, and comma needs to be flipped
 # compared to the usual 8b10b binary representation.
-class Comma_Aligner(Module):
+class Comma_Checker(Module):
    def __init__(self, comma, reset_period=10_000_000):
        self.data = Signal(20)
        self.comma_aligned = Signal()
@ -253,9 +229,28 @@ class Comma_Aligner(Module):
        self.aligner_en = Signal()
        self.ready_sys = Signal()
        self.restart_sys = Signal()
        # # #
        # periodically reset rx until rx is connected and receiving valid data
        # as after connecting RXP/RXN, the whole RX need to be reset 
        reset_counter = Signal(reset=reset_period-1, max=reset_period)
        self.sync += [
            self.restart_sys.eq(0),
            If(~self.ready_sys,
                If(reset_counter == 0,
                    reset_counter.eq(reset_counter.reset),
                    self.restart_sys.eq(1),
                ).Else(
                    reset_counter.eq(reset_counter - 1),
                )
            )
        ]
        # Data and comma checker
        # From UG476 (v1.12.1) p.228
        # The built-in RXBYTEISALIGNED can be falsely asserted at linerate higher than 5Gbps
@ -699,29 +694,14 @@ class GTX(Module):
            Instance("BUFG", i_I=txpll_clkout, o_O=self.cd_cxp_gtx_tx.clk),
            AsyncResetSynchronizer(self.cd_cxp_gtx_tx, ~self.txpll_locked & ~tx_init.done)
        ]
        self.comb += tx_init.restart.eq(self.tx_restart)
        # RX clocking
        # the CDR matches the required frequency for RXUSRCLK, no need for PLL 
-
+        self.clock_domains.cd_cxp_gtx_rx = ClockDomain()
-        # Slave Rx will use cxp_gtx_rx instead
+        self.specials += [
-        if rx_mode == "single" or rx_mode == "master":
+            Instance("BUFG", i_I=self.rxoutclk, o_O=self.cd_cxp_gtx_rx.clk),
-            self.clock_domains.cd_cxp_gtx_rx = ClockDomain()
+            AsyncResetSynchronizer(self.cd_cxp_gtx_rx, ~rx_init.done)
-            self.specials += [
+        ]
                Instance("BUFG", i_I=self.rxoutclk, o_O=self.cd_cxp_gtx_rx.clk),
                AsyncResetSynchronizer(self.cd_cxp_gtx_rx, ~rx_init.done)
            ]
            self.submodules.rx_resetter = rx_resetter = RX_Resetter()
            self.comb += [
                rx_resetter.rx_ready.eq(self.rx_ready),
                rx_init.restart.eq(self.rx_restart | rx_resetter.rx_reset),
            ]
        else:
            self.comb += rx_init.restart.eq(self.rx_restart),
        # 8b10b Encoder/Decoder
        self.comb += [
            txdata.eq(Cat(self.encoder.output[0], self.encoder.output[1], self.encoder.output[2], self.encoder.output[3])),
@ -731,12 +711,16 @@ class GTX(Module):
            self.decoders[3].input.eq(rxdata[30:]),
        ]
-        self.submodules.comma_aligner = comma_aligner = Comma_Aligner(0b0101111100)
+
        self.submodules.comma_checker = comma_checker = Comma_Checker(0b0101111100)
        self.comb += [
-            comma_aligner.data.eq(rxdata),
+            comma_checker.data.eq(rxdata),
-            comma_aligner.comma_aligned.eq(comma_aligned),
+            comma_checker.comma_aligned.eq(comma_aligned),
-            comma_aligner.comma_realigned.eq(comma_realigned),
+            comma_checker.comma_realigned.eq(comma_realigned),
-            comma_aligner.comma_det.eq(comma_det),
+            comma_checker.comma_det.eq(comma_det),
-            comma_aligner_en.eq(comma_aligner.aligner_en),
+            comma_aligner_en.eq(comma_checker.aligner_en),
-            self.rx_ready.eq(comma_aligner.ready_sys),
+            self.rx_ready.eq(comma_checker.ready_sys),
            rx_init.restart.eq(self.rx_restart | comma_checker.restart_sys),
            tx_init.restart.eq(self.tx_restart),
        ]
--- a/src/gateware/cxp_pipeline.py
+++ b/src/gateware/cxp_pipeline.py
@ -2,6 +2,7 @@ from migen import *
 from migen.genlib.cdc import MultiReg 
 from misoc.interconnect.csr import *
 from misoc.interconnect import stream
 from misoc.cores.liteeth_mini.mac.crc import LiteEthMACCRCEngine, LiteEthMACCRCChecker
 from functools import reduce
 from itertools import combinations
@ -290,6 +291,7 @@ class RX_Debug_Buffer(Module,AutoCSR):
 class Duplicated_Char_Decoder(Module):
    def __init__(self):
        self.sink = stream.Endpoint(word_layout)
        self.buffer = stream.Endpoint(word_layout)
        self.source = stream.Endpoint(word_layout_dchar)
        # # #
@ -312,23 +314,22 @@ class Duplicated_Char_Decoder(Module):
        # Hence, a pipeline approach is needed to avoid any s/h violation, where the majority voting result are pre-calculate and injected into the bus immediate after the PHY.
        # And any downstream modules can access the voting result without implementing the voting logic inside the decoder
        # cycle 1 - buffer data & calculate intermediate result  
        buffer = stream.Endpoint(word_layout)
        self.sync += [
-            If((~buffer.stb | buffer.ack),
+            self.sink.ack.eq(self.buffer.ack),
-                buffer.stb.eq(self.sink.stb),
+            self.buffer.stb.eq(self.sink.stb),
-                buffer.payload.eq(self.sink.payload),
+            If(self.sink.stb,
-            )
+                self.buffer.data.eq(self.sink.data),
                self.buffer.k.eq(self.sink.k),
            ),
        ]
-        self.comb += self.sink.ack.eq(~buffer.stb | buffer.ack)
+
-        
+        # cycle 1 - calculate ABC, ABD, ACD & BCD  
        # calculate ABC, ABD, ACD, BCD  
        char = [[self.sink.data[i*8:(i+1)*8], self.sink.k[i]] for i in range(4)]
        voters = [Record([("data", 8), ("k", 1)]) for _ in range(4)]
        for i, comb in enumerate(combinations(char, 3)):
            self.sync += [
-                If((~buffer.stb | buffer.ack),
+                If(self.sink.stb,
                    voters[i].data.eq(reduce(and_, [code[0] for code in comb])),
                    voters[i].k.eq(reduce(and_, [code[1] for code in comb])),
                )
@ -337,16 +338,15 @@ class Duplicated_Char_Decoder(Module):
        # cycle 2 - inject the voting result 
        self.sync += [
-            If((~self.source.stb | self.source.ack),
+            self.buffer.ack.eq(self.source.ack),
-                self.source.stb.eq(buffer.stb),
+            self.source.stb.eq(self.buffer.stb),
-                self.source.data.eq(buffer.data),
+            If(self.buffer.stb,
-                self.source.k.eq(buffer.k),
+                self.source.data.eq(self.buffer.data),
                self.source.k.eq(self.buffer.k),
                self.source.dchar.eq(Replicate(reduce(or_, [v.data for v in voters]), 4)),
                self.source.dchar_k.eq(Replicate(reduce(or_, [v.k for v in voters]), 4)),
-            )
+            ),
        ]
        self.comb += buffer.ack.eq(~self.source.stb | self.source.ack)
@FullMemoryWE()
 class RX_Bootstrap(Module):
@ -523,3 +523,34 @@ class Trigger_Ack_Checker(Module, AutoCSR):
                )
            )
        )
@ResetInserter()
@CEInserter()
 class CXPCRC32(Module):
    # Section 9.2.2.2 (CXP-001-2021)
    width = 32
    polynom = 0x04C11DB7
    seed = 2**width-1
    check = 0x00000000
    def __init__(self, data_width):
        self.data = Signal(data_width)
        self.value = Signal(self.width)
        self.error = Signal()
        # # #
        self.submodules.engine = LiteEthMACCRCEngine(data_width, self.width, self.polynom)
        reg = Signal(self.width, reset=self.seed)
        self.sync += reg.eq(self.engine.next)
        self.comb += [
            self.engine.data.eq(self.data),
            self.engine.last.eq(reg),
            self.value.eq(reg[::-1]),
            self.error.eq(self.engine.next != self.check)
        ]
 # For verifying crc in stream data packet
 class CXPCRC32Checker(LiteEthMACCRCChecker):
    def __init__(self, layout):
        LiteEthMACCRCChecker.__init__(self, CXPCRC32, layout)