Add NRZI support

This adds support for encoding and decoding nrzi data.

Signed-off-by: Sean Anderson <seanga2@gmail.com>

Makefile

@@ -63,7 +63,7 @@ endef
 %.post.fst: rtl/%.post.vvp tb/%.py FORCE
 	$(run-vvp)
 
-MODULES := pcs pmd
+MODULES := pcs pmd nrzi_encode nrzi_decode
 
 .PHONY: test
 test: $(addsuffix .fst,$(MODULES)) $(addsuffix .post.fst,$(MODULES))

rtl/nrzi_decode.v

@@ -0,0 +1,39 @@
+// SPDX-License-Identifier: AGPL-3.0-Only
+/*
+ * Copyright (C) 2022 Sean Anderson <seanga2@gmail.com>
+ */
+
+`include "common.vh"
+
+module nrzi_decode (
+	input clk,
+	input [1:0] nrzi,
+	input [1:0] nrzi_valid,
+	output reg [1:0] nrz,
+	output reg [1:0] nrz_valid
+);
+
+	reg [1:0] nrz_next;
+	reg nrzi_last;
+	reg nrzi_last_next;
+
+	always @(*) begin
+		nrz_next[0] = nrzi[1] ^ nrzi[0];
+		nrz_next[1] = nrzi[1] ^ nrzi_last;
+
+		nrzi_last_next = nrzi_last;
+		if (nrzi_valid != 0)
+			nrzi_last_next = nrzi[1];
+		if (nrzi_valid & 2)
+			nrzi_last_next = nrzi[0];
+	end
+
+	always @(posedge clk) begin
+		nrzi_last <= nrzi_last_next;
+		nrz_valid <= nrzi_valid;
+		nrz <= nrz_next;
+	end
+
+	`DUMP(0)
+
+endmodule

rtl/nrzi_encode.v

@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: AGPL-3.0-Only
+/*
+ * Copyright (C) 2022 Sean Anderson <seanga2@gmail.com>
+ */
+
+`include "common.vh"
+
+module nrzi_encode (
+	input clk,
+	input nrz,
+	output reg nrzi
+);
+
+	reg nrzi_next;
+	initial nrzi = 1;
+
+	always @(*)
+		nrzi_next = nrz ^ nrzi;
+
+	always @(posedge clk)
+		nrzi <= nrzi_next;
+
+	`DUMP(0)
+
+endmodule

tb/nrzi_decode.py

@@ -0,0 +1,45 @@
+# SPDX-License-Identifier: AGPL-3.0-Only
+# Copyright (C) 2022 Sean Anderson <seanga2@gmail.com>
+
+import random
+
+import cocotb
+from cocotb.clock import Clock
+from cocotb.regression import TestFactory
+from cocotb.triggers import FallingEdge, RisingEdge, Timer
+
+from .util import compare_lists, timeout, send_recovered_bits, with_valids
+
+def nrzi_decode(bits):
+    last = 1
+    for bit in bits:
+        yield bit ^ last
+        last = bit
+
+@timeout(10, 'us')
+async def test_rx(decoder, valids):
+    decoder.nrzi_valid.value = 0
+    await Timer(1)
+    await cocotb.start(Clock(decoder.clk, 8, units='ns').start())
+
+    ins = [random.randrange(2) for _ in range(1000)]
+    await cocotb.start(send_recovered_bits(decoder.clk, decoder.nrzi,
+                                           decoder.nrzi_valid, ins, valids))
+
+    outs = []
+    await RisingEdge(decoder.clk)
+    for _ in ins:
+        await RisingEdge(decoder.clk)
+        valid = decoder.nrz_valid.value
+        if valid == 0:
+            pass
+        elif valid == 1:
+            outs.append(decoder.nrz[1].value)
+        else:
+            outs.append(decoder.nrz[1].value)
+            outs.append(decoder.nrz[0].value)
+
+    # Ignore the first bit, since it is influenced by the initial value
+    compare_lists(list(nrzi_decode(ins))[1:], outs[1:])
+
+with_valids(globals(), test_rx)

tb/nrzi_encode.py

@@ -0,0 +1,38 @@
+# SPDX-License-Identifier: AGPL-3.0-Only
+# Copyright (C) 2022 Sean Anderson <seanga2@gmail.com>
+
+import random
+
+import cocotb
+from cocotb.clock import Clock
+from cocotb.triggers import FallingEdge, RisingEdge, Timer
+
+from .util import compare_lists
+
+def nrzi_encode(bits):
+    last = 1
+    for bit in bits:
+        yield (last := last ^ bit)
+
+@cocotb.test(timeout_time=100, timeout_unit='us')
+async def text_encode(encoder):
+    ins = [random.randrange(2) for _ in range(1000)]
+    encoder.nrz.value = ins[0]
+    await Timer(1)
+    await cocotb.start(Clock(encoder.clk, 8, units='ns').start())
+
+    async def send_nrz():
+        for bit in ins:
+            await FallingEdge(encoder.clk)
+            encoder.nrz.value = bit
+    await cocotb.start(send_nrz())
+
+    outs = []
+    await RisingEdge(encoder.clk)
+    await RisingEdge(encoder.clk)
+    for _ in ins:
+        await RisingEdge(encoder.clk)
+        outs.append(encoder.nrzi.value)
+
+    # Ignore the first bit, since it is influenced by the initial value
+    compare_lists(list(nrzi_encode(ins[1:])), outs[1:])