ethernet/tb/pmd.py

import random
from statistics import NormalDist

import cocotb
from cocotb.binary import BinaryValue
from cocotb.clock import Clock
from cocotb.regression import TestFactory
from cocotb.triggers import RisingEdge, Timer

from .util import timeout

def print_list_at(l, i):
    print(' ' * max(50 - i, 0), *l[max(i - 50, 0):i+50], sep='')

BITS = 1000

def random_delays(count):
    # Target BER is 1e9 and the maximum jitter is 1.4ns
    # This is just random jitter (not DDJ or DCJ) but it'll do
    delay_dist = NormalDist(8000, 1400 / NormalDist().inv_cdf(1-2e-9))
    return (int(delay) for delay in delay_dist.samples(count))

def mindelays(count):
    return (7900,) * count

def maxdelays(count):
    return (8100,) * count

@timeout(100, 'us')
async def test_rx(pmd, delays):
    pmd.signal_detect.value = 0
    await Timer(1)
    await cocotb.start(Clock(pmd.rx_clk_125, 8, units='ns').start())
    # random phase
    await Timer(random.randrange(1, 8000), units='ps')
    await cocotb.start(Clock(pmd.rx_clk_250, 4, units='ns').start())

    ins = [random.randrange(2) for _ in range(BITS)]
    async def generate_bits():
        # random phase
        await Timer(random.randrange(1, 8000), units='ps')
        pmd.signal_detect.value = 1
        for i, delay in zip(ins, delays(len(ins))):
            pmd.rx.value = i
            try:
                pmd.delay.value = delay
            except AttributeError:
                pass
            await Timer(delay, units='ps')
        pmd.signal_detect.value = 0
    await cocotb.start(generate_bits())

    # Wait for things to stabilize
    await RisingEdge(pmd.signal_status)
    outs = []
    while pmd.signal_status.value:
        await RisingEdge(pmd.rx_clk_125)
        valid = pmd.pmd_data_rx_valid.value
        if valid == 0:
            pass
        elif valid == 1:
            outs.append(pmd.pmd_data_rx[1].value)
        else:
            outs.append(pmd.pmd_data_rx[1].value)
            outs.append(pmd.pmd_data_rx[0].value)

    best_corr = -1
    best_off = None
    for off in range(16):
        corr = sum(i == o for i, o in zip(ins[off:], outs))
        if corr > best_corr:
            best_corr = corr
            best_off = off

    print(f"best offset is {best_off} correlation {best_corr/(len(ins) - best_off)}")
    for idx, (i, o) in enumerate(zip(ins[best_off:], outs)):
        if i != o:
            print(idx)
            print_list_at(ins, idx + best_off)
            print_list_at(outs, idx)
            assert False
    # There will be a few bits at the end not recorded because signal_detect
    # isn't delayed like the data signals
    assert best_corr > len(ins) - best_off - 10

rx_tests = TestFactory(test_rx)
rx_tests.add_option('delays', (random_delays, mindelays, maxdelays))
rx_tests.generate_tests()