from collections import defaultdict, OrderedDict
import logging
from nengo import Ensemble, Network, Node, Probe
from nengo.builder import Model as NengoModel
from nengo.builder.builder import Builder as NengoBuilder
from nengo.builder.network import build_network
from nengo.cache import NoDecoderCache
from nengo_loihi.block import LoihiBlock
from nengo_loihi.decode_neurons import Preset10DecodeNeurons, OnOffDecodeNeurons
from nengo_loihi.inputs import LoihiInput
logger = logging.getLogger(__name__)
[docs]class Model:
"""The data structure for the emulator/hardware simulator.
Defines methods for adding inputs and blocks. Also handles build
functions, and information associated with building the Nengo model.
Some of the Model attributes can be modified before the build process
to change how certain build functions work. Those attributes are listed
first in the attributes section below. To change them, create an instance
of `.Model` and pass it in to `.Simulator` along with your network::
model = nengo_loihi.builder.Model(dt=0.001)
model.pes_error_scale = 50.
with nengo_loihi.Simulator(network, model=model) as sim:
sim.run(1.0)
Parameters
----------
dt : float, optional (Default: 0.001)
The length of a simulator timestep, in seconds.
label : str, optional (Default: None)
A name or description to differentiate models.
builder : Builder, optional (Default: None)
A `.Builder` instance to keep track of build functions.
If None, the default builder will be used.
Attributes
----------
Build parameters
decode_neurons : DecodeNeurons
Type of neurons used to facilitate decoded (NEF-style) connections.
decode_tau : float
Time constant of lowpass synaptic filter used with decode neurons.
intercept_limit : float
Limit for clipping intercepts, to avoid neurons with high gains.
node_neurons : DecodeNeurons
Type of neurons used to convert real-valued node outputs to spikes
for the chip.
pes_error_scale : float
Scaling for PES errors, before rounding and clipping to -127..127.
pes_wgt_exp : int
Learning weight exponent (base 2) for PES learning connections. This
controls the maximum weight magnitude (where a larger exponent means
larger potential weights, but lower weight resolution).
vth_nonspiking : float
Voltage threshold for non-spiking neurons (i.e. voltage decoders).
Internal attributes
blocks : list of LoihiBlock
List of Loihi blocks simulated by this model.
builder : Builder
The build functions used by this model.
dt : float
The length of a simulator timestep, in seconds.
chip2host_params : dict
Mapping from Nengo objects to any additional parameters associated
with those objects for use during the build process.
inputs : list of LoihiInput
List of inputs to this model.
label : str or None
A name or description to differentiate models.
objs : dict
Dictionary mapping from Nengo objects to Nengo Loihi objects.
params : dict
Mapping from objects to namedtuples containing parameters generated
in the build process.
probes : list
List of all probes. Probes must be added to this list in the build
process, as this list is used by Simulator.
seeded : dict
All objects are assigned a seed, whether the user defined the seed
or it was automatically generated. 'seeded' keeps track of whether
the seed is user-defined. We consider the seed to be user-defined
if it was set directly on the object, or if a seed was set on the
network in which the object resides, or if a seed was set on any
ancestor network of the network in which the object resides.
seeds : dict
Mapping from objects to the integer seed assigned to that object.
"""
def __init__(self, dt=0.001, label=None, builder=None):
self.dt = dt
self.label = label
self.builder = Builder() if builder is None else builder
self.build_callback = None
self.decoder_cache = NoDecoderCache()
# TODO: these models may not look/behave exactly the same as
# standard nengo models, because they don't have a toplevel network
# built into them or configs set
self.host_pre = NengoModel(
dt=float(dt),
label="%s:host_pre, dt=%f" % (label, dt),
decoder_cache=NoDecoderCache(),
)
self.host = NengoModel(
dt=float(dt),
label="%s:host, dt=%f" % (label, dt),
decoder_cache=NoDecoderCache(),
)
# Objects created by the model for simulation on Loihi
self.inputs = OrderedDict()
self.blocks = OrderedDict()
# Will be filled in by the simulator __init__
self.split = None
# Will be filled in by the network builder
self.toplevel = None
self.config = None
# Resources used by the build process
self.objs = defaultdict(dict)
self.params = {} # Holds data generated when building objects
self.probes = []
self.probe_conns = {}
self.seeds = {}
self.seeded = {}
# --- other (typically standard) parameters
# Filter on decode neurons
self.decode_tau = 0.005
# ^TODO: how to choose this filter? Even though the input is spikes,
# it may not be absolutely necessary since tau_rc provides a filter,
# and maybe we don't want double filtering if connection has a filter
self.decode_neurons = Preset10DecodeNeurons(dt=dt)
self.node_neurons = OnOffDecodeNeurons(dt=dt)
# voltage threshold for non-spiking neurons (i.e. voltage decoders)
self.vth_nonspiking = 10
# limit for clipping intercepts, to avoid neurons with high gains
self.intercept_limit = 0.95
# scaling for PES errors, before rounding and clipping to -127..127
self.pes_error_scale = 100.0
# learning weight exponent for PES (controls the maximum weight
# magnitude/weight resolution)
self.pes_wgt_exp = 4
# Used to track interactions between host models
self.chip2host_params = {}
self.chip2host_receivers = OrderedDict()
self.host2chip_senders = OrderedDict()
self.needs_sender = {}
def __getstate__(self):
raise NotImplementedError("Can't pickle nengo_loihi.builder.Model")
def __setstate__(self, state):
raise NotImplementedError("Can't pickle nengo_loihi.builder.Model")
def __str__(self):
return "%s(%s)" % (type(self).__name__, self.label)
def add_input(self, input):
assert isinstance(input, LoihiInput)
assert input not in self.inputs
self.inputs[input] = len(self.inputs)
def add_block(self, block):
assert isinstance(block, LoihiBlock)
assert block not in self.blocks
self.blocks[block] = len(self.blocks)
def build(self, obj, *args, **kwargs):
# Don't build the objects marked as "to_remove" by PassthroughSplit
if obj in self.split.passthrough.to_remove:
return None
if not isinstance(obj, (Node, Ensemble, Probe)):
model = self
elif self.split.on_chip(obj):
model = self
else:
# Note: callbacks for the host_model will not be invoked
model = self.host_model(obj)
# done for compatibility with nengo<=2.8.0
# otherwise we could just copy over the initial
# seeding to all other models
model.seeds[obj] = self.seeds[obj]
model.seeded[obj] = self.seeded[obj]
built = model.builder.build(model, obj, *args, **kwargs)
if self.build_callback is not None:
self.build_callback(obj)
return built
def has_built(self, obj):
return obj in self.params
[docs] def host_model(self, obj):
"""Returns the Model corresponding to where obj should be built."""
if self.split.is_precomputable(obj):
return self.host_pre
else:
return self.host
[docs]class Builder(NengoBuilder):
"""Fills in the Loihi Model object based on the Nengo Network.
We cannot use the Nengo builder as is because we make normal Nengo
networks for host-to-chip and chip-to-host communication. To keep
Nengo and Nengo Loihi builders separate, we make a blank subclass,
which effectively copies the class.
"""
builders = {}
Builder.register(Network)(build_network)
