litex/test/test_ecc.py

#
# This file is part of LiteX.
#
# Copyright (c) 2018-2019 Florent Kermarrec <florent@enjoy-digital.fr>
# SPDX-License-Identifier: BSD-2-Clause

import unittest
import random

from migen import *

from litedram.common import *
from litedram.frontend.ecc import *

from litex.gen.sim import *


class TestECC(unittest.TestCase):
    def test_m_n(self):
        m, n = compute_m_n(15)
        self.assertEqual(m, 5)
        self.assertEqual(n, 20)

    def test_syndrome_positions(self):
        p_pos = compute_syndrome_positions(20)
        p_pos_ref = [1, 2, 4, 8, 16]
        self.assertEqual(p_pos, p_pos_ref)

    def test_data_positions(self):
        d_pos = compute_data_positions(20)
        d_pos_ref = [3, 5, 6, 7, 9, 10, 11, 12, 13, 14, 15, 17, 18, 19, 20]
        self.assertEqual(d_pos, d_pos_ref)

    def test_cover_positions(self):
        c_pos_ref = {
            0 : [1, 3, 5, 7, 9, 11, 13, 15, 17, 19],
            1 : [2, 3, 6, 7, 10, 11, 14, 15, 18, 19],
            2 : [4, 5, 6, 7, 12, 13, 14, 15, 20],
            3 : [8, 9, 10, 11, 12, 13, 14, 15],
            4 : [16, 17, 18, 19, 20]
        }
        for i in range(5):
            c_pos = compute_cover_positions(20, 2**i)
            self.assertEqual(c_pos, c_pos_ref[i])

    def test_ecc(self, k=15):
        class DUT(Module):
            def __init__(self, k):
                m, n = compute_m_n(k)
                self.flip = Signal(n + 1)

                # # #

                self.submodules.encoder = ECCEncoder(k)
                self.submodules.decoder = ECCDecoder(k)

                self.comb += self.decoder.i.eq(self.encoder.o ^ self.flip)

        def generator(dut, k, nvalues, nerrors):
            dut.errors = 0
            prng = random.Random(42)
            yield dut.decoder.enable.eq(1)
            for i in range(nvalues):
                data = prng.randrange(2**k-1)
                yield dut.encoder.i.eq(data)
                # FIXME: error when fliping parity bit
                if nerrors == 1:
                    flip_bit1 = (prng.randrange(len(dut.flip)-2) + 1)
                    yield dut.flip.eq(1<<flip_bit1)
                elif nerrors == 2:
                    flip_bit1 = (prng.randrange(len(dut.flip)-2) + 1)
                    flip_bit2 = flip_bit1
                    while flip_bit2 == flip_bit1:
                        flip_bit2 = (prng.randrange(len(dut.flip)-2) + 1)
                    yield dut.flip.eq((1<<flip_bit1) | (1<<flip_bit2))
                yield
                # if less than 2 errors, check data
                if nerrors < 2:
                    if (yield dut.decoder.o) != data:
                        dut.errors += 1
                # if 0 error, verify sec == 0 / ded == 0
                if nerrors == 0:
                    if (yield dut.decoder.sec) != 0:
                        dut.errors += 1
                    if (yield dut.decoder.ded) != 0:
                        dut.errors += 1
                # if 1 error, verify sec == 1 / dec == 0
                elif nerrors == 1:
                    if (yield dut.decoder.sec) != 1:
                        dut.errors += 1
                    if (yield dut.decoder.ded) != 0:
                        dut.errors += 1
                # if 2 errors, verify sec == 0 / ded == 1
                elif nerrors == 2:
                    if (yield dut.decoder.sec) != 0:
                        dut.errors += 1
                    if (yield dut.decoder.ded) != 1:
                        dut.errors += 1

        for i in range(3):
            dut = DUT(k)
            run_simulation(dut, generator(dut, k, 128, i))
            self.assertEqual(dut.errors, 0)