gateware/serwb: add scrambling, reduce cdc fifo depth

artiq/gateware/serwb/core.py

@@ -2,38 +2,54 @@ from migen import *
 
 from misoc.interconnect import stream
 
-from artiq.gateware.serwb.packet import Depacketizer, Packetizer
+from artiq.gateware.serwb.scrambler import Scrambler, Descrambler
+from artiq.gateware.serwb.packet import Packetizer, Depacketizer
 from artiq.gateware.serwb.etherbone import Etherbone
 
 
 class SERWBCore(Module):
-    def __init__(self, phy, clk_freq, mode):
+    def __init__(self, phy, clk_freq, mode, with_scrambling=False):
+        # etherbone
         self.submodules.etherbone = etherbone = Etherbone(mode)
+
+        # packetizer / depacketizer
         depacketizer = Depacketizer(clk_freq)
         packetizer = Packetizer()
         self.submodules += depacketizer, packetizer
-        tx_cdc = stream.AsyncFIFO([("data", 32)], 32)
-        tx_cdc = ClockDomainsRenamer({"write": "sys", "read": "serwb_serdes"})(tx_cdc)
-        self.submodules += tx_cdc
-        rx_cdc = stream.AsyncFIFO([("data", 32)], 32)
-        rx_cdc = ClockDomainsRenamer({"write": "serwb_serdes", "read": "sys"})(rx_cdc)
-        self.submodules += rx_cdc
-        self.comb += [
-            # core <--> etherbone
-            depacketizer.source.connect(etherbone.sink),
-            etherbone.source.connect(packetizer.sink),
 
-            # core --> serdes
+        # clock domain crossing
+        tx_cdc = stream.AsyncFIFO([("data", 32)], 16)
+        tx_cdc = ClockDomainsRenamer({"write": "sys", "read": phy.cd})(tx_cdc)
+        rx_cdc = stream.AsyncFIFO([("data", 32)], 16)
+        rx_cdc = ClockDomainsRenamer({"write": phy.cd, "read": "sys"})(rx_cdc)
+        self.submodules += tx_cdc, rx_cdc
+
+        # scrambling
+        scrambler =  ClockDomainsRenamer(phy.cd)(Scrambler(enable=with_scrambling))
+        descrambler = ClockDomainsRenamer(phy.cd)(Descrambler(enable=with_scrambling))
+        self.submodules += scrambler, descrambler
+
+        # modules connection
+        self.comb += [
+            # core --> phy
             packetizer.source.connect(tx_cdc.sink),
+            tx_cdc.source.connect(scrambler.sink),
             If(phy.init.ready,
-                If(tx_cdc.source.stb,
+                If(scrambler.source.stb,
-                    phy.serdes.tx_data.eq(tx_cdc.source.data)
+                    phy.serdes.tx_k.eq(scrambler.source.k),
+                    phy.serdes.tx_d.eq(scrambler.source.d)
                 ),
-                tx_cdc.source.ack.eq(1)
+                scrambler.source.ack.eq(1)
             ),
 
-            # serdes --> core
+            # phy --> core
-            rx_cdc.sink.stb.eq(phy.init.ready),
+            descrambler.sink.stb.eq(phy.init.ready),
-            rx_cdc.sink.data.eq(phy.serdes.rx_data),
+            descrambler.sink.k.eq(phy.serdes.rx_k),
+            descrambler.sink.d.eq(phy.serdes.rx_d),
+            descrambler.source.connect(rx_cdc.sink),
             rx_cdc.source.connect(depacketizer.sink),
+
+            # etherbone <--> core
+            depacketizer.source.connect(etherbone.sink),
+            etherbone.source.connect(packetizer.sink)
         ]

artiq/gateware/serwb/kusphy.py

@@ -8,8 +8,10 @@ from misoc.cores.code_8b10b import Encoder, Decoder
 
 class KUSSerdes(Module):
     def __init__(self, pll, pads, mode="master"):
-        self.tx_data = Signal(32)
+        self.tx_k = Signal(4)
-        self.rx_data = Signal(32)
+        self.tx_d = Signal(32)
+        self.rx_k = Signal(4)
+        self.rx_d = Signal(32)
 
         self.tx_idle = Signal()
         self.tx_comma = Signal()
@@ -111,10 +113,14 @@ class KUSSerdes(Module):
                 self.encoder.k[0].eq(1),
                 self.encoder.d[0].eq(0xbc)
             ).Else(
-                self.encoder.d[0].eq(self.tx_data[0:8]),
+                self.encoder.k[0].eq(self.tx_k[0]),
-                self.encoder.d[1].eq(self.tx_data[8:16]),
+                self.encoder.k[1].eq(self.tx_k[1]),
-                self.encoder.d[2].eq(self.tx_data[16:24]),
+                self.encoder.k[2].eq(self.tx_k[2]),
-                self.encoder.d[3].eq(self.tx_data[24:32])
+                self.encoder.k[3].eq(self.tx_k[3]),
+                self.encoder.d[0].eq(self.tx_d[0:8]),
+                self.encoder.d[1].eq(self.tx_d[8:16]),
+                self.encoder.d[2].eq(self.tx_d[16:24]),
+                self.encoder.d[3].eq(self.tx_d[24:32])
             )
         ]
         self.sync.serwb_serdes += \
@@ -217,7 +223,8 @@ class KUSSerdes(Module):
             self.decoders[1].input.eq(self.rx_bitslip.o[10:20]),
             self.decoders[2].input.eq(self.rx_bitslip.o[20:30]),
             self.decoders[3].input.eq(self.rx_bitslip.o[30:40]),
-            self.rx_data.eq(Cat(*[self.decoders[i].d for i in range(4)])),
+            self.rx_k.eq(Cat(*[self.decoders[i].k for i in range(4)])),
+            self.rx_d.eq(Cat(*[self.decoders[i].d for i in range(4)])),
             rx_idle.eq(self.rx_bitslip.o == 0),
             rx_comma.eq(((self.decoders[0].d == 0xbc) & (self.decoders[0].k == 1)) &
                         ((self.decoders[1].d == 0x00) & (self.decoders[1].k == 0)) &

artiq/gateware/serwb/phy.py

@@ -376,6 +376,7 @@ class SERWBPLL(Module):
 
 
 class SERWBPHY(Module, AutoCSR):
+    cd = "serwb_serdes"
     def __init__(self, device, pll, pads, mode="master"):
         assert mode in ["master", "slave"]
         if device[:4] == "xcku":

artiq/gateware/serwb/s7phy.py

@@ -8,8 +8,10 @@ from misoc.cores.code_8b10b import Encoder, Decoder
 
 class S7Serdes(Module):
     def __init__(self, pll, pads, mode="master"):
-        self.tx_data = Signal(32)
+        self.tx_k = Signal(4)
-        self.rx_data = Signal(32)
+        self.tx_d = Signal(32)
+        self.rx_k = Signal(4)
+        self.rx_d = Signal(32)
 
         self.tx_idle = Signal()
         self.tx_comma = Signal()
@@ -99,10 +101,14 @@ class S7Serdes(Module):
                 self.encoder.k[0].eq(1),
                 self.encoder.d[0].eq(0xbc)
             ).Else(
-                self.encoder.d[0].eq(self.tx_data[0:8]),
+                self.encoder.k[0].eq(self.tx_k[0]),
-                self.encoder.d[1].eq(self.tx_data[8:16]),
+                self.encoder.k[1].eq(self.tx_k[1]),
-                self.encoder.d[2].eq(self.tx_data[16:24]),
+                self.encoder.k[2].eq(self.tx_k[2]),
-                self.encoder.d[3].eq(self.tx_data[24:32])
+                self.encoder.k[3].eq(self.tx_k[3]),
+                self.encoder.d[0].eq(self.tx_d[0:8]),
+                self.encoder.d[1].eq(self.tx_d[8:16]),
+                self.encoder.d[2].eq(self.tx_d[16:24]),
+                self.encoder.d[3].eq(self.tx_d[24:32])
             )
         ]
         self.sync.serwb_serdes += \
@@ -213,7 +219,8 @@ class S7Serdes(Module):
             self.decoders[1].input.eq(self.rx_bitslip.o[10:20]),
             self.decoders[2].input.eq(self.rx_bitslip.o[20:30]),
             self.decoders[3].input.eq(self.rx_bitslip.o[30:40]),
-            self.rx_data.eq(Cat(*[self.decoders[i].d for i in range(4)])),
+            self.rx_k.eq(Cat(*[self.decoders[i].k for i in range(4)])),
+            self.rx_d.eq(Cat(*[self.decoders[i].d for i in range(4)])),
             rx_idle.eq(self.rx_bitslip.o == 0),
             rx_comma.eq(((self.decoders[0].d == 0xbc) & (self.decoders[0].k == 1)) &
                         ((self.decoders[1].d == 0x00) & (self.decoders[1].k == 0)) &

artiq/gateware/serwb/scrambler.py

@@ -0,0 +1,99 @@
+from functools import reduce
+from operator import xor
+
+from migen import *
+
+from misoc.interconnect import stream
+
+
+def K(x, y):
+    return (y << 5) | x
+
+
+@ResetInserter()
+class _Scrambler(Module):
+    def __init__(self, n_io, n_state=23, taps=[17, 22]):
+        self.i = Signal(n_io)
+        self.o = Signal(n_io)
+
+        # # #
+
+        state = Signal(n_state, reset=1)
+        curval = [state[i] for i in range(n_state)]
+        for i in reversed(range(n_io)):
+            flip = reduce(xor, [curval[tap] for tap in taps])
+            self.comb += self.o[i].eq(flip ^ self.i[i])
+            curval.insert(0, flip)
+            curval.pop()
+
+        self.sync += state.eq(Cat(*curval[:n_state]))
+
+
+class Scrambler(Module):
+    def __init__(self, sync_interval=1024, enable=True):
+        self.sink = sink = stream.Endpoint([("data", 32)])
+        self.source = source = stream.Endpoint([("d", 32), ("k", 4)])
+
+        # # #
+
+        if enable:
+            # scrambler
+            scrambler = _Scrambler(32)
+            self.submodules += scrambler
+            self.comb += scrambler.i.eq(sink.data)
+
+            # insert K.29.7 as sync character
+            # every sync_interval cycles
+            count = Signal(max=sync_interval)
+            self.sync += count.eq(count + 1)
+            self.comb += [
+                If(count == 0,
+                    scrambler.reset.eq(1),
+                    source.stb.eq(1),
+                    source.k[0].eq(1),
+                    source.d[:8].eq(K(29, 7))
+                ).Else(
+                    sink.ack.eq(source.ack),
+                    source.stb.eq(sink.stb),
+                    source.d.eq(scrambler.o)
+                )
+            ]
+        else:
+            self.comb += [
+                sink.connect(source, omit={"data"}),
+                source.k.eq(0b0000),
+                source.d.eq(sink.data)
+            ]
+
+
+class Descrambler(Module):
+    def __init__(self, enable=True):
+        self.sink = sink = stream.Endpoint([("d", 32), ("k", 4)])
+        self.source = source = stream.Endpoint([("data", 32)])
+
+        # # #
+
+        if enable:
+            # descrambler
+            descrambler = _Scrambler(32)
+            self.submodules += descrambler
+            self.comb += descrambler.i.eq(sink.d)
+
+            # detect K29.7 and synchronize descrambler
+            self.comb += [
+                descrambler.reset.eq(0),
+                If((sink.k[0] == 1) &
+                   (sink.d[:8] == K(29,7)),
+                    sink.ack.eq(1),
+                    descrambler.reset.eq(1)
+                ).Else(
+                    sink.ack.eq(source.ack),
+                    source.stb.eq(sink.stb),
+                    source.data.eq(descrambler.o)
+                )
+            ]
+        else:
+            self.comb += [
+                sink.connect(source, omit={"d", "k"}),
+                source.data.eq(sink.d)
+            ]