lfsr: Add LFSR descrambler module and testbench

Signed-off-by: Alex Forencich <alex@alexforencich.com>
2025-12-09 08:58:40 -08:00 · 2025-02-05 15:29:12 -08:00
parent e6ea90be36
commit f479a85155
3 changed files with 423 additions and 0 deletions
--- a/tb/lfsr/taxi_lfsr_descramble/Makefile
+++ b/tb/lfsr/taxi_lfsr_descramble/Makefile
@@ -0,0 +1,51 @@
+# SPDX-License-Identifier: CERN-OHL-S-2.0
+#
+# Copyright (c) 2023-2025 FPGA Ninja, LLC
+#
+# Authors:
+# - Alex Forencich
+
+TOPLEVEL_LANG = verilog
+
+SIM ?= verilator
+WAVES ?= 0
+
+COCOTB_HDL_TIMEUNIT = 1ns
+COCOTB_HDL_TIMEPRECISION = 1ps
+
+DUT      = taxi_lfsr_descramble
+COCOTB_TEST_MODULES = test_$(DUT)
+COCOTB_TOPLEVEL     = $(DUT)
+MODULE   = $(COCOTB_TEST_MODULES)
+TOPLEVEL = $(COCOTB_TOPLEVEL)
+VERILOG_SOURCES += ../../../rtl/lfsr/$(DUT).sv
+VERILOG_SOURCES += ../../../rtl/lfsr/taxi_lfsr.sv
+
+# handle file list files
+process_f_file = $(call process_f_files,$(addprefix $(dir $1),$(shell cat $1)))
+process_f_files = $(foreach f,$1,$(if $(filter %.f,$f),$(call process_f_file,$f),$f))
+uniq_base = $(if $1,$(call uniq_base,$(foreach f,$1,$(if $(filter-out $(notdir $(lastword $1)),$(notdir $f)),$f,))) $(lastword $1))
+VERILOG_SOURCES := $(call uniq_base,$(call process_f_files,$(VERILOG_SOURCES)))
+
+# module parameters
+export PARAM_LFSR_W ?= 58
+export PARAM_LFSR_POLY ?= "58'h8000000001"
+export PARAM_LFSR_INIT ?= "'1"
+export PARAM_LFSR_GALOIS ?= "1'b0"
+export PARAM_REVERSE ?= "1'b1"
+export PARAM_DATA_W ?= 8
+
+ifeq ($(SIM), icarus)
+	PLUSARGS += -fst
+
+	COMPILE_ARGS += $(foreach v,$(filter PARAM_%,$(.VARIABLES)),-P $(COCOTB_TOPLEVEL).$(subst PARAM_,,$(v))=$($(v)))
+else ifeq ($(SIM), verilator)
+	COMPILE_ARGS += $(foreach v,$(filter PARAM_%,$(.VARIABLES)),-G$(subst PARAM_,,$(v))=$($(v)))
+
+	ifeq ($(WAVES), 1)
+		COMPILE_ARGS += --trace-fst
+		VERILATOR_TRACE = 1
+	endif
+endif
+
+include $(shell cocotb-config --makefiles)/Makefile.sim
--- a/tb/lfsr/taxi_lfsr_descramble/test_taxi_lfsr_descramble.py
+++ b/tb/lfsr/taxi_lfsr_descramble/test_taxi_lfsr_descramble.py
@@ -0,0 +1,187 @@
+#!/usr/bin/env python
+# SPDX-License-Identifier: CERN-OHL-S-2.0
+"""
+
+Copyright (c) 2023-2025 FPGA Ninja, LLC
+
+Authors:
+- Alex Forencich
+
+"""
+
+import itertools
+import logging
+import os
+
+import pytest
+import cocotb_test.simulator
+
+import cocotb
+from cocotb.clock import Clock
+from cocotb.triggers import RisingEdge
+from cocotb.regression import TestFactory
+
+
+class TB:
+    def __init__(self, dut):
+        self.dut = dut
+
+        self.log = logging.getLogger("cocotb.tb")
+        self.log.setLevel(logging.DEBUG)
+
+        cocotb.start_soon(Clock(dut.clk, 10, units="ns").start())
+
+        dut.data_in.setimmediatevalue(0)
+        dut.data_in_valid.setimmediatevalue(0)
+
+    async def reset(self):
+        self.dut.rst.setimmediatevalue(0)
+        await RisingEdge(self.dut.clk)
+        await RisingEdge(self.dut.clk)
+        self.dut.rst.value = 1
+        await RisingEdge(self.dut.clk)
+        await RisingEdge(self.dut.clk)
+        self.dut.rst.value = 0
+        await RisingEdge(self.dut.clk)
+        await RisingEdge(self.dut.clk)
+
+
+def chunks(lst, n, padvalue=None):
+    return itertools.zip_longest(*[iter(lst)]*n, fillvalue=padvalue)
+
+
+def scramble_64b66b(data, state=0x3ffffffffffffff):
+    data_out = bytearray()
+    for d in data:
+        b = 0
+        for i in range(8):
+            if bool(state & (1 << 38)) ^ bool(state & (1 << 57)) ^ bool(d & (1 << i)):
+                state = ((state & 0x1ffffffffffffff) << 1) | 1
+                b = b | (1 << i)
+            else:
+                state = (state & 0x1ffffffffffffff) << 1
+        data_out.append(b)
+    return data_out
+
+
+def descramble_64b66b(data, state=0x3ffffffffffffff):
+    data_out = bytearray()
+    for d in data:
+        b = 0
+        for i in range(8):
+            if bool(state & (1 << 38)) ^ bool(state & (1 << 57)) ^ bool(d & (1 << i)):
+                b = b | (1 << i)
+            state = (state & 0x1ffffffffffffff) << 1 | bool(d & (1 << i))
+        data_out += bytearray([b])
+    return data_out
+
+
+async def run_test_descramble(dut, ref_scramble):
+
+    data_width = len(dut.data_in)
+    byte_lanes = data_width // 8
+
+    tb = TB(dut)
+
+    await tb.reset()
+
+    block = bytearray(itertools.islice(itertools.cycle(range(256)), 1024))
+
+    scr = scramble_64b66b(block)
+
+    dscr = descramble_64b66b(scr)
+
+    assert dscr == block
+
+    ref_iter = iter(chunks(block, byte_lanes))
+
+    first = True
+    for b in chunks(scr, byte_lanes):
+        dut.data_in.value = int.from_bytes(b, 'little')
+        dut.data_in_valid.value = 1
+        await RisingEdge(dut.clk)
+
+        val = dut.data_out.value.integer
+
+        if not first:
+            ref = int.from_bytes(bytes(next(ref_iter)), 'little')
+
+            tb.log.info("Descrambled: 0x%x (ref: 0x%x)", val, ref)
+
+            assert ref == val
+
+        first = False
+
+    dut.data_in_valid.value = 0
+
+    await RisingEdge(dut.clk)
+
+
+if cocotb.SIM_NAME:
+
+    # if cocotb.top.LFSR_POLY.value == 0x8000000001:
+    if int(cocotb.top.LFSR_W.value) == 58:
+        factory = TestFactory(run_test_descramble)
+        factory.add_option("ref_scramble", [scramble_64b66b])
+        factory.generate_tests()
+
+
+# cocotb-test
+
+tests_dir = os.path.abspath(os.path.dirname(__file__))
+rtl_dir = os.path.abspath(os.path.join(tests_dir, '..', '..', '..', 'rtl'))
+
+
+def process_f_files(files):
+    lst = {}
+    for f in files:
+        if f[-2:].lower() == '.f':
+            with open(f, 'r') as fp:
+                l = fp.read().split()
+            for f in process_f_files([os.path.join(os.path.dirname(f), x) for x in l]):
+                lst[os.path.basename(f)] = f
+        else:
+            lst[os.path.basename(f)] = f
+    return list(lst.values())
+
+
+@pytest.mark.parametrize(("lfsr_w", "lfsr_poly", "lfsr_init", "lfsr_galois", "reverse", "data_w"), [
+            (58,  "58'h8000000001", "'1", 0, 1, 8),
+            (58,  "58'h8000000001", "'1", 0, 1, 64),
+        ])
+def test_taxi_lfsr_descramble(request, lfsr_w, lfsr_poly, lfsr_init, lfsr_galois, reverse, data_w):
+    dut = "taxi_lfsr_descramble"
+    module = os.path.splitext(os.path.basename(__file__))[0]
+    toplevel = dut
+
+    verilog_sources = [
+        os.path.join(rtl_dir, "lfsr", f"{dut}.sv"),
+        os.path.join(rtl_dir, "lfsr", "taxi_lfsr.sv"),
+    ]
+
+    verilog_sources = process_f_files(verilog_sources)
+
+    parameters = {}
+
+    parameters['LFSR_W'] = lfsr_w
+    parameters['LFSR_POLY'] = lfsr_poly
+    parameters['LFSR_INIT'] = lfsr_init
+    parameters['LFSR_GALOIS'] = f"1'b{lfsr_galois}"
+    parameters['REVERSE'] = f"1'b{reverse}"
+    parameters['DATA_W'] = data_w
+
+    extra_env = {f'PARAM_{k}': str(v) for k, v in parameters.items()}
+
+    sim_build = os.path.join(tests_dir, "sim_build",
+        request.node.name.replace('[', '-').replace(']', ''))
+
+    cocotb_test.simulator.run(
+        simulator="verilator",
+        python_search=[tests_dir],
+        verilog_sources=verilog_sources,
+        toplevel=toplevel,
+        module=module,
+        parameters=parameters,
+        sim_build=sim_build,
+        extra_env=extra_env,
+    )