예제 #1
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def test_negative_cxbase(request, seed):
    n_axons = 3

    model = Model()

    input = SpikeInput(n_axons)
    input.add_spikes(1, list(range(n_axons)))
    model.add_input(input)

    axon = Axon(n_axons)
    input.add_axon(axon)

    block = LoihiBlock(3)
    block.compartment.configure_relu()
    model.add_block(block)

    synapse = Synapse(n_axons)
    weights = [0.1, 0.1, 0.1]
    indices = [0, 1, 2]
    axon_to_weight_map = list(range(n_axons))
    cx_bases = [0, 1, -1]
    synapse.set_population_weights(weights,
                                   indices,
                                   axon_to_weight_map,
                                   cx_bases,
                                   pop_type=32)
    axon.target = synapse
    block.add_synapse(synapse)

    probe = Probe(target=block, key='voltage')
    block.add_probe(probe)

    discretize_model(model)

    n_steps = 2
    if request.config.getoption("--target") == 'loihi':
        with HardwareInterface(model, use_snips=False, seed=seed) as sim:
            sim.run_steps(n_steps)
            y = sim.get_probe_output(probe)
    else:
        with EmulatorInterface(model, seed=seed) as sim:
            sim.run_steps(n_steps)
            y = sim.get_probe_output(probe)

    # Compartments 0 and 2 should change from axons 0 and 1.
    # Axon 2 should have no effect, and not change compartment 1 (the sum of
    # its cx_base and index), or other compartments (e.g. 2 if cx_base ignored)
    assert np.allclose(y[1, 1], 0), "Third axon not ignored"
    assert np.allclose(y[1, 0], y[1, 2]), "Third axon targeting another"
    assert not np.allclose(y[1], y[0]), "Voltage not changing"
예제 #2
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    def __init__(  # noqa: C901
            self,
            network,
            dt=0.001,
            seed=None,
            model=None,
            precompute=False,
            target=None,
            progress_bar=None,
            remove_passthrough=True,
            hardware_options=None,
    ):
        # initialize values used in __del__ and close() first
        self.closed = True
        self.precompute = precompute
        self.networks = None
        self.sims = OrderedDict()
        self._run_steps = None

        hardware_options = {} if hardware_options is None else hardware_options

        if progress_bar:
            warnings.warn("nengo-loihi does not support progress bars")

        if HAS_DL:
            install_dl_builders()

        if model is None:
            # Call the builder to make a model
            self.model = Model(dt=float(dt), label="%s, dt=%f" % (network, dt))
        else:
            assert isinstance(model, Model), (
                "model is not type 'nengo_loihi.builder.Model'")
            self.model = model
            assert self.model.dt == dt

        if network is not None:
            nengo.rc.set("decoder_cache", "enabled", "False")
            config.add_params(network)

            # ensure seeds are identical to nengo
            seed_network(network, seeds=self.model.seeds,
                         seeded=self.model.seeded)

            # split the host into one, two or three networks
            self.networks = split(
                network,
                precompute=precompute,
                node_neurons=self.model.node_neurons,
                node_tau=self.model.decode_tau,
                remove_passthrough=remove_passthrough,
            )
            network = self.networks.chip

            self.model.chip2host_params = self.networks.chip2host_params

            self.chip = self.networks.chip
            self.host = self.networks.host
            self.host_pre = self.networks.host_pre

            if len(self.host_pre.all_objects) > 0:
                host_pre_model = self._get_host_model(
                    self.host_pre, dt=dt, seeds=self.model.seeds,
                    seeded=self.model.seeded)
                self.sims["host_pre"] = nengo.Simulator(self.host_pre,
                                                        dt=self.dt,
                                                        model=host_pre_model,
                                                        progress_bar=False,
                                                        optimize=False)

            if len(self.host.all_objects) > 0:
                host_model = self._get_host_model(
                    self.host, dt=dt, seeds=self.model.seeds,
                    seeded=self.model.seeded)
                self.sims["host"] = nengo.Simulator(
                    self.host,
                    dt=self.dt,
                    model=host_model,
                    progress_bar=False,
                    optimize=False)
            elif not precompute:
                # If there is no host and precompute=False, then all objects
                # must be on the chip, which is precomputable in the sense that
                # no communication has to happen with the host.
                # We could warn about this, but we want to avoid people having
                # to specify `precompute` unless they absolutely have to.
                self.precompute = True

            # Build the network into the model
            self.model.build(network)

        self._probe_outputs = self.model.params
        self.data = ProbeDict(self._probe_outputs)
        for sim in self.sims.values():
            self.data.add_fallback(sim.data)

        if seed is None:
            if network is not None and network.seed is not None:
                seed = network.seed + 1
            else:
                seed = np.random.randint(npext.maxint)

        if target is None:
            target = 'loihi' if HAS_NXSDK else 'sim'
        self.target = target

        logger.info("Simulator target is %r", target)
        logger.info("Simulator precompute is %r", self.precompute)

        if target != "simreal":
            discretize_model(self.model)

        if target in ("simreal", "sim"):
            self.sims["emulator"] = EmulatorInterface(self.model, seed=seed)
        elif target == 'loihi':
            assert HAS_NXSDK, "Must have NxSDK installed to use Loihi hardware"
            self.sims["loihi"] = HardwareInterface(
                self.model, use_snips=not self.precompute, seed=seed,
                **hardware_options)
        else:
            raise ValidationError("Must be 'simreal', 'sim', or 'loihi'",
                                  attr="target")

        assert "emulator" in self.sims or "loihi" in self.sims

        self.closed = False
        self.reset(seed=seed)
예제 #3
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def test_uv_overflow(n_axons, plt, allclose, monkeypatch):
    # TODO: Currently this is not testing the V overflow, since it is higher
    #  and I haven't been able to figure out a way to make it overflow.
    nt = 15

    model = Model()

    # n_axons controls number of input spikes and thus amount of overflow
    input = SpikeInput(n_axons)
    for t in np.arange(1, nt + 1):
        # send spikes to all axons
        input.add_spikes(t, np.arange(n_axons), permanent=True)
    model.add_input(input)

    block = LoihiBlock(1)
    block.compartment.configure_relu()
    block.compartment.configure_filter(0.1)
    model.add_block(block)

    synapse = Synapse(n_axons)
    synapse.set_weights(np.ones((n_axons, 1)))
    block.add_synapse(synapse)

    axon = Axon(n_axons)
    axon.target = synapse
    input.add_axon(axon)

    probe_u = LoihiProbe(target=block, key="current")
    model.add_probe(probe_u)
    probe_v = LoihiProbe(target=block, key="voltage")
    model.add_probe(probe_v)
    probe_s = LoihiProbe(target=block, key="spiked")
    model.add_probe(probe_s)

    discretize_model(model)

    # must set these after `discretize` to specify discretized values
    block.compartment.vmin = -(2**22) + 1
    block.compartment.vth[:] = VTH_MAX

    assert EmulatorInterface.strict  # Tests should be run in strict mode
    monkeypatch.setattr(EmulatorInterface, "strict", False)
    overflow_var = "q0" if n_axons == 1000 else "current"
    with EmulatorInterface(model) as emu:
        with pytest.warns(UserWarning, match=f"Overflow in {overflow_var}"):
            emu.run_steps(nt)
        emu_u = emu.collect_probe_output(probe_u)
        emu_v = emu.collect_probe_output(probe_v)
        emu_s = emu.collect_probe_output(probe_s)

    with HardwareInterface(model, use_snips=False) as sim:
        sim.run_steps(nt)
        sim_u = sim.collect_probe_output(probe_u)
        sim_v = sim.collect_probe_output(probe_v)
        sim_s = sim.collect_probe_output(probe_s)
        sim_v[sim_s > 0] = 0  # since Loihi has placeholder voltage after spike

    plt.subplot(311)
    plt.plot(emu_u)
    plt.plot(sim_u)

    plt.subplot(312)
    plt.plot(emu_v)
    plt.plot(sim_v)

    plt.subplot(313)
    plt.plot(emu_s)
    plt.plot(sim_s)

    assert allclose(emu_u, sim_u)
    assert allclose(emu_v, sim_v)
예제 #4
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def test_pop_tiny(pop_type, channels_last, nc, request, plt, seed, allclose):
    tau_rc = 0.02
    tau_ref = 0.001
    tau_s = 0.0
    dt = 0.001

    neuron_bias = 1.

    pres_time = 0.4

    sti, stj = 1, 1

    if nc == 1:
        filters = np.array([[-0.5, 2., -0.25], [-0.75, 2., -1.0],
                            [-0.5, 3., -0.5], [-1.0, 6.,
                                               -0.25]]).reshape(1, 4, 1, 3)

        inp_biases = np.array([[1, 5, 1], [2, 1, 2]])
        inp_biases = inp_biases[:, :, None]
    elif nc == 2:
        filters = np.array([[[-0.5, 2., -0.2], [-0.7, 2., -1.0],
                             [-0.5, 3., -0.5], [-1.0, 6., -0.2]],
                            [[-1.0, 2., -1.0], [-0.5, 2., -0.5],
                             [-0.8, 3., -0.2], [-1.0, 4.,
                                                -0.2]]]).reshape(2, 4, 1, 3)

        inp_biases = np.array([[[1, 5, 1], [2, 1, 2]], [[0, 3, 1], [4, 2, 1]]])
        inp_biases = np.transpose(inp_biases, (1, 2, 0))

    # rearrange to (kernel_rows, kernel_cols, in_channels, out_channels)
    filters = np.transpose(filters, (2, 3, 0, 1))

    inp_biases = inp_biases / (inp_biases.max() + 0.001)

    # --- compute nengo_loihi outputs
    ni, nj, nk = inp_biases.shape
    si, sj, nc, nf = filters.shape
    nij = ni * nj
    nyi = 1 + (ni - si) // sti
    nyj = 1 + (nj - sj) // stj
    out_size = nyi * nyj * nf
    assert out_size <= 1024

    model = Model()

    # input block
    inp = LoihiBlock(ni * nj * nk, label='inp')
    assert inp.n_neurons <= 1024
    inp.compartment.configure_relu()
    inp.compartment.bias[:] = inp_biases.ravel()

    inp_ax = Axon(nij, label='inp_ax')

    # we always compute the pixel/channel idxs with channels_last=True
    # (not sure why?), and then set it to the correct value afterwards
    inp_shape = nengo_transforms.ChannelShape((ni, nj, nk), channels_last=True)
    inp_ax.set_compartment_axon_map(target_axons=conv.pixel_idxs(inp_shape),
                                    atoms=conv.channel_idxs(inp_shape))
    inp_shape.shape = (ni, nj, nk) if channels_last else (nk, ni, nj)
    inp_shape.channels_last = channels_last

    inp.add_axon(inp_ax)

    model.add_block(inp)

    # conv block
    neurons = LoihiBlock(out_size, label='neurons')
    assert neurons.n_neurons <= 1024
    neurons.compartment.configure_lif(tau_rc=tau_rc, tau_ref=tau_ref, dt=dt)
    neurons.compartment.configure_filter(tau_s, dt=dt)
    neurons.compartment.bias[:] = neuron_bias

    synapse = Synapse(np.prod(inp_shape.spatial_shape), label='synapse')
    conv2d_transform = nengo_transforms.Convolution(
        nf,
        inp_shape,
        strides=(sti, stj),
        channels_last=channels_last,
        init=filters,
        kernel_size=(1, 3))
    weights, indices, axon_to_weight_map, bases = conv.conv2d_loihi_weights(
        conv2d_transform)
    synapse.set_population_weights(weights,
                                   indices,
                                   axon_to_weight_map,
                                   bases,
                                   pop_type=pop_type)
    neurons.add_synapse(synapse)

    out_probe = Probe(target=neurons, key='spiked')
    neurons.add_probe(out_probe)

    inp_ax.target = synapse
    model.add_block(neurons)

    # simulation
    discretize_model(model)

    n_steps = int(pres_time / dt)
    target = request.config.getoption("--target")
    if target == 'loihi':
        with HardwareInterface(model, use_snips=False, seed=seed) as sim:
            sim.run_steps(n_steps)
            sim_out = sim.get_probe_output(out_probe)
    else:
        with EmulatorInterface(model, seed=seed) as sim:
            sim.run_steps(n_steps)
            sim_out = sim.get_probe_output(out_probe)

    sim_out = np.sum(sim_out, axis=0) * (dt / pres_time)
    if channels_last:
        sim_out.shape = (nyi, nyj, nf)
        sim_out = np.transpose(sim_out, (2, 0, 1))
    else:
        sim_out.shape = (nf, nyi, nyj)

    out_max = sim_out.max()

    # --- plot results
    rows = 1
    cols = 2

    ax = plt.subplot(rows, cols, 1)
    plt.hist(sim_out.ravel(), bins=11)

    ax = plt.subplot(rows, cols, 2)
    tile(sim_out, vmin=0, vmax=out_max, grid=True, ax=ax)

    # ref_out determined by emulator running code known to work
    if nc == 1:
        ref_out = np.array([[0.06, 0.02], [0.055, 0.], [0.0825, 0.0225],
                            [0.125, 0.04]])
    elif nc == 2:
        ref_out = np.array([[0.0975, 0.02], [0.0825, 0.02], [0.125, 0.055],
                            [0.2475, 0.0825]])
    assert allclose(sim_out[:, :, 0], ref_out, rtol=0, atol=1e-7)
예제 #5
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def test_conv2d_weights(channels_last, hw_opts, request, plt, seed, rng,
                        allclose):
    def loihi_rates_n(neuron_type, x, gain, bias, dt):
        """Compute Loihi rates on higher dimensional inputs"""
        y = x.reshape(-1, x.shape[-1])
        gain = np.asarray(gain)
        bias = np.asarray(bias)
        if gain.ndim == 0:
            gain = gain * np.ones(x.shape[-1])
        if bias.ndim == 0:
            bias = bias * np.ones(x.shape[-1])
        rates = loihi_rates(neuron_type, y, gain, bias, dt)
        return rates.reshape(*x.shape)

    if channels_last:
        plt.saveas = None
        pytest.xfail("Blocked by CxBase cannot be > 256 bug")

    target = request.config.getoption("--target")
    if target != 'loihi' and len(hw_opts) > 0:
        pytest.skip("Hardware options only available on hardware")

    pop_type = 32

    # load data
    with open(os.path.join(test_dir, 'mnist10.pkl'), 'rb') as f:
        test10 = pickle.load(f)

    test_x = test10[0][0].reshape(28, 28)
    test_x = test_x[3:24, 3:24]
    test_x = 1.999 * test_x - 0.999

    filters = Gabor(freq=Uniform(0.5, 1)).generate(8, (7, 7), rng=rng)
    sti, stj = 2, 2
    tau_rc = 0.02
    tau_ref = 0.002
    tau_s = 0.005
    dt = 0.001

    encode_type = nengo.SpikingRectifiedLinear()
    encode_gain = 1. / dt
    encode_bias = 0.
    neuron_type = nengo.LIF(tau_rc=tau_rc, tau_ref=tau_ref)
    neuron_gain = 1.
    neuron_bias = 1.

    pres_time = 0.2

    # --- compute ideal outputs
    def conv_pm(x, kernel):
        y0 = scipy.signal.correlate2d(x[0], kernel, mode='valid')[::sti, ::stj]
        y1 = scipy.signal.correlate2d(x[1], kernel, mode='valid')[::sti, ::stj]
        return [y0, -y1]

    ref_out = np.array([test_x, -test_x])
    ref_out = loihi_rates_n(encode_type, ref_out, encode_gain, encode_bias, dt)
    ref_out = ref_out / encode_gain
    ref_out = np.array([conv_pm(ref_out, kernel) for kernel in filters])
    ref_out = ref_out.sum(axis=1)  # sum positive and negative parts
    ref_out = loihi_rates_n(neuron_type, ref_out, neuron_gain, neuron_bias, dt)

    # --- compute nengo_loihi outputs
    inp_biases = np.stack([test_x, -test_x], axis=-1 if channels_last else 0)
    inp_shape = nengo_transforms.ChannelShape(inp_biases.shape,
                                              channels_last=channels_last)

    kernel = np.array([filters, -filters])  # two channels, pos and neg
    kernel = np.transpose(kernel, (2, 3, 0, 1))
    conv2d_transform = nengo_transforms.Convolution(
        8,
        inp_shape,
        strides=(sti, stj),
        channels_last=channels_last,
        kernel_size=(7, 7),
        init=kernel)

    out_size = ref_out.size
    nf, nyi, nyj = ref_out.shape
    assert out_size <= 1024

    model = Model()

    # input block
    inp = LoihiBlock(inp_shape.size, label='inp')
    assert inp.n_neurons <= 1024
    inp.compartment.configure_relu()
    inp.compartment.bias[:] = inp_biases.ravel()

    inp_ax = Axon(np.prod(inp_shape.spatial_shape), label='inp_ax')
    inp_ax.set_compartment_axon_map(target_axons=conv.pixel_idxs(inp_shape),
                                    atoms=conv.channel_idxs(inp_shape))
    inp.add_axon(inp_ax)

    model.add_block(inp)

    # conv block
    neurons = LoihiBlock(out_size, label='neurons')
    assert neurons.n_neurons <= 1024
    neurons.compartment.configure_lif(tau_rc=tau_rc, tau_ref=tau_ref, dt=dt)
    neurons.compartment.configure_filter(tau_s, dt=dt)
    neurons.compartment.bias[:] = neuron_bias

    synapse = Synapse(np.prod(inp_shape.spatial_shape), label='synapse')
    weights, indices, axon_to_weight_map, bases = conv.conv2d_loihi_weights(
        conv2d_transform)
    synapse.set_population_weights(weights,
                                   indices,
                                   axon_to_weight_map,
                                   bases,
                                   pop_type=pop_type)

    neurons.add_synapse(synapse)

    out_probe = Probe(target=neurons, key='spiked')
    neurons.add_probe(out_probe)

    inp_ax.target = synapse
    model.add_block(neurons)

    # simulation
    discretize_model(model)

    n_steps = int(pres_time / dt)
    if target == 'loihi':
        with HardwareInterface(model, use_snips=False, seed=seed,
                               **hw_opts) as sim:
            sim.run_steps(n_steps)
            sim_out = sim.get_probe_output(out_probe)
    else:
        with EmulatorInterface(model, seed=seed) as sim:
            sim.run_steps(n_steps)
            sim_out = sim.get_probe_output(out_probe)

    sim_out = np.sum(sim_out, axis=0) / pres_time
    if channels_last:
        sim_out.shape = (nyi, nyj, nf)
        sim_out = np.transpose(sim_out, (2, 0, 1))
    else:
        sim_out.shape = (nf, nyi, nyj)

    out_max = max(ref_out.max(), sim_out.max())

    # --- plot results
    rows = 2
    cols = 2

    ax = plt.subplot(rows, cols, 1)
    tile(filters, cols=8, ax=ax)

    ax = plt.subplot(rows, cols, 2)
    tile(ref_out, vmin=0, vmax=out_max, cols=8, ax=ax)

    ax = plt.subplot(rows, cols, 3)
    plt.hist(ref_out.ravel(), bins=31)
    plt.hist(sim_out.ravel(), bins=31)

    ax = plt.subplot(rows, cols, 4)
    # tile(sim_out, vmin=0, vmax=1, cols=8, ax=ax)
    tile(sim_out, vmin=0, vmax=out_max, cols=8, ax=ax)

    assert allclose(sim_out, ref_out, atol=10, rtol=1e-3)
예제 #6
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def test_population_input(request, allclose):
    target = request.config.getoption("--target")
    dt = 0.001

    n_inputs = 3
    n_axons = 1
    n_cx = 2

    steps = 6
    spike_times_inds = [(1, [0]), (3, [1]), (5, [2])]

    model = Model()

    input = SpikeInput(n_inputs)
    model.add_input(input)
    spikes = [(input, ti, inds) for ti, inds in spike_times_inds]

    input_axon = Axon(n_axons)
    axon_map = np.zeros(n_inputs, dtype=int)
    atoms = np.arange(n_inputs)
    input_axon.set_axon_map(axon_map, atoms)
    input.add_axon(input_axon)

    block = LoihiBlock(n_cx)
    block.compartment.configure_lif(tau_rc=0., tau_ref=0., dt=dt)
    block.compartment.configure_filter(0, dt=dt)
    model.add_block(block)

    synapse = Synapse(n_axons)
    weights = 0.1 * np.array([[[1, 2], [2, 3], [4, 5]]], dtype=float)
    indices = np.array([[[0, 1], [0, 1], [0, 1]]], dtype=int)
    axon_to_weight_map = np.zeros(n_axons, dtype=int)
    cx_bases = np.zeros(n_axons, dtype=int)
    synapse.set_population_weights(weights,
                                   indices,
                                   axon_to_weight_map,
                                   cx_bases,
                                   pop_type=32)
    block.add_synapse(synapse)
    input_axon.target = synapse

    probe = Probe(target=block, key='voltage')
    block.add_probe(probe)

    discretize_model(model)

    if target == 'loihi':
        with HardwareInterface(model, use_snips=True) as sim:
            sim.run_steps(steps, blocking=False)
            for ti in range(1, steps + 1):
                spikes_i = [spike for spike in spikes if spike[1] == ti]
                sim.host2chip(spikes=spikes_i, errors=[])
                sim.chip2host(probes_receivers={})

            y = sim.get_probe_output(probe)
    else:
        for inp, ti, inds in spikes:
            inp.add_spikes(ti, inds)

        with EmulatorInterface(model) as sim:
            sim.run_steps(steps)
            y = sim.get_probe_output(probe)

    vth = block.compartment.vth[0]
    assert (block.compartment.vth == vth).all()
    z = y / vth
    assert allclose(z[[1, 3, 5]], weights[0], atol=4e-2, rtol=0)
예제 #7
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def test_simulator_noise(exp, request, plt, seed, allclose):
    # TODO: test that the mean falls within a number of standard errors
    # of the expected mean, and that non-zero offsets work correctly.
    # Currently, there is an unexpected negative bias for small noise
    # exponents, apparently because there is a probability of generating
    # the shifted equivalent of -128, whereas with e.g. exp = 7 all the
    # generated numbers fall in [-127, 127].
    offset = 0

    target = request.config.getoption("--target")
    n_cx = 1000

    model = Model()
    block = LoihiBlock(n_cx)
    block.compartment.configure_relu()

    block.compartment.vmin = -1

    block.compartment.enableNoise[:] = 1
    block.compartment.noiseExp0 = exp
    block.compartment.noiseMantOffset0 = offset
    block.compartment.noiseAtDendOrVm = 1

    probe = Probe(target=block, key='voltage')
    block.add_probe(probe)
    model.add_block(block)

    discretize_model(model)
    exp2 = block.compartment.noiseExp0
    offset2 = block.compartment.noiseMantOffset0

    n_steps = 100
    if target == 'loihi':
        with HardwareInterface(model, use_snips=False, seed=seed) as sim:
            sim.run_steps(n_steps)
            y = sim.get_probe_output(probe)
    else:
        with EmulatorInterface(model, seed=seed) as sim:
            sim.run_steps(n_steps)
            y = sim.get_probe_output(probe)

    t = np.arange(1, n_steps + 1)
    bias = offset2 * 2.**(exp2 - 1)
    std = 2.**exp2 / np.sqrt(3)  # divide by sqrt(3) for std of uniform -1..1
    rmean = t * bias
    rstd = np.sqrt(t) * std
    rerr = rstd / np.sqrt(n_cx)
    ymean = y.mean(axis=1)
    ystd = y.std(axis=1)
    diffs = np.diff(np.vstack([np.zeros_like(y[0]), y]), axis=0)

    plt.subplot(311)
    plt.hist(diffs.ravel(), bins=256)

    plt.subplot(312)
    plt.plot(rmean, 'k')
    plt.plot(rmean + 3 * rerr, 'k--')
    plt.plot(rmean - 3 * rerr, 'k--')
    plt.plot(ymean)
    plt.title('mean')

    plt.subplot(313)
    plt.plot(rstd, 'k')
    plt.plot(ystd)
    plt.title('std')

    assert allclose(ystd, rstd, rtol=0.1, atol=1)
예제 #8
0
    def __init__(  # noqa: C901
        self,
        network,
        dt=0.001,
        seed=None,
        model=None,
        precompute=None,
        target=None,
        progress_bar=None,
        remove_passthrough=True,
        hardware_options=None,
    ):
        # initialize values used in __del__ and close() first
        self.closed = True
        self.network = network
        self.sims = OrderedDict()
        self.timers = Timers()
        self.timers.start("build")
        self.seed = seed
        self._n_steps = 0
        self._time = 0

        hardware_options = {} if hardware_options is None else hardware_options

        if progress_bar:
            warnings.warn("nengo-loihi does not support progress bars")

        if model is None:
            self.model = Model(dt=float(dt), label="%s, dt=%f" % (network, dt))
        else:
            assert isinstance(
                model, Model), "model is not type 'nengo_loihi.builder.Model'"
            self.model = model
            assert self.model.dt == dt

        if network is None:
            raise ValidationError("network parameter must not be None",
                                  attr="network")

        if target is None:
            target = "loihi" if HAS_NXSDK else "sim"
        self.target = target
        logger.info("Simulator target is %r", target)

        # Build the network into the model
        self.model.build(
            network,
            precompute=precompute,
            remove_passthrough=remove_passthrough,
            discretize=target != "simreal",
        )

        # Create host_pre and host simulators if necessary
        self.precompute = self.model.split.precompute
        logger.info("Simulator precompute is %r", self.precompute)
        assert precompute is None or precompute == self.precompute
        if self.model.split.precomputable() and not self.precompute:
            warnings.warn(
                "Model is precomputable. Setting precompute=False may slow execution."
            )

        if len(self.model.host_pre.params) > 0:
            assert self.precompute
            self.sims["host_pre"] = nengo.Simulator(
                network=None,
                dt=self.dt,
                model=self.model.host_pre,
                progress_bar=False,
                optimize=False,
            )

        if len(self.model.host.params) > 0:
            self.sims["host"] = nengo.Simulator(
                network=None,
                dt=self.dt,
                model=self.model.host,
                progress_bar=False,
                optimize=False,
            )

        self._probe_outputs = self.model.params
        self.data = SimulationData(self._probe_outputs)
        for sim in self.sims.values():
            self.data.add_fallback(sim.data)

        if seed is None:
            if network is not None and network.seed is not None:
                seed = network.seed + 1
            else:
                seed = np.random.randint(npext.maxint)

        if target in ("simreal", "sim"):
            self.sims["emulator"] = EmulatorInterface(self.model, seed=seed)
        elif target == "loihi":
            assert HAS_NXSDK, "Must have NxSDK installed to use Loihi hardware"
            use_snips = not self.precompute and self.sims.get("host",
                                                              None) is not None
            self.sims["loihi"] = HardwareInterface(self.model,
                                                   use_snips=use_snips,
                                                   seed=seed,
                                                   **hardware_options)
        else:
            raise ValidationError("Must be 'simreal', 'sim', or 'loihi'",
                                  attr="target")

        assert "emulator" in self.sims or "loihi" in self.sims

        self._runner = StepRunner(self.model, self.sims, self.precompute,
                                  self.timers)
        self.closed = False
        self.timers.stop("build")