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/* Copyright (c) 2012 Massachusetts Institute of Technology
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#include "model/optical/OpticalLinkBackendTx.h"
#include "util/Constants.h"
#include "model/PortInfo.h"
#include "model/TransitionInfo.h"
#include "model/EventInfo.h"
#include "model/electrical/MuxTreeSerializer.h"
#include "model/electrical/BarrelShifter.h"
#include "model/electrical/Multiplexer.h"
#include <cmath>
namespace DSENT
{
// TODO: Kind of don't like the way thermal tuning is written here. Maybe will switch
// to curve fitting the CICC paper, which uses results from a monte-carlo sim
OpticalLinkBackendTx::OpticalLinkBackendTx(const String& instance_name_, const TechModel* tech_model_)
: ElectricalModel(instance_name_, tech_model_)
{
initParameters();
initProperties();
}
OpticalLinkBackendTx::~OpticalLinkBackendTx()
{}
void OpticalLinkBackendTx::initParameters()
{
addParameterName("InBits");
addParameterName("CoreDataRate");
addParameterName("LinkDataRate");
addParameterName("RingTuningMethod");
addParameterName("BitDuplicate");
return;
}
void OpticalLinkBackendTx::initProperties()
{
return;
}
void OpticalLinkBackendTx::constructModel()
{
unsigned int in_bits = getParameter("InBits");
double core_data_rate = getParameter("CoreDataRate");
double link_data_rate = getParameter("LinkDataRate");
const String& tuning_method = getParameter("RingTuningMethod");;
bool bit_duplicate = getParameter("BitDuplicate");
// Calculate serialization ratio
unsigned int serialization_ratio = (unsigned int) floor(link_data_rate / core_data_rate);
ASSERT(serialization_ratio == link_data_rate / core_data_rate,
"[Error] " + getInstanceName() + " -> Cannot have non-integer serialization ratios " +
"(" + (String) (core_data_rate / link_data_rate) + ")!");
// Calculate output width
ASSERT(floor((double) in_bits / serialization_ratio) == (double) in_bits / serialization_ratio,
"[Error] " + getInstanceName() + " -> Input width (" + (String) in_bits + ") " +
"must be a multiple of the serialization ratio (" + (String) serialization_ratio + ")!");
unsigned int out_bits = in_bits / serialization_ratio;
getGenProperties()->set("SerializationRatio", serialization_ratio);
getGenProperties()->set("OutBits", out_bits);
// Create ports
createInputPort("In", makeNetIndex(0, in_bits-1));
createInputPort("LinkCK");
createOutputPort("Out", makeNetIndex(0, out_bits-1));
//Create energy, power, and area results
createElectricalResults();
// Create ring heating power cost
addNddPowerResult(new AtomicResult("RingTuning"));
// Create process bits event
createElectricalEventResult("ProcessBits");
getEventInfo("ProcessBits")->setTransitionInfo("LinkCK", TransitionInfo(0.0, (double) serialization_ratio / 2.0, 0.0));
// Set conditions during idle state
getEventInfo("Idle")->setStaticTransitionInfos();
getEventInfo("Idle")->setTransitionInfo("LinkCK", TransitionInfo(0.0, (double) serialization_ratio / 2.0, 0.0));
// Create serializer
const String& serializer_name = "Serializer";
MuxTreeSerializer* serializer = new MuxTreeSerializer(serializer_name, getTechModel());
serializer->setParameter("InBits", in_bits);
serializer->setParameter("InDataRate", core_data_rate);
serializer->setParameter("OutDataRate", link_data_rate);
serializer->setParameter("BitDuplicate", bit_duplicate);
serializer->construct();
addSubInstances(serializer, 1.0);
addElectricalSubResults(serializer, 1.0);
getEventResult("ProcessBits")->addSubResult(serializer->getEventResult("Serialize"), serializer_name, 1.0);
if ((tuning_method == "ThermalWithBitReshuffle") || (tuning_method == "ElectricalAssistWithBitReshuffle"))
{
// If a bit reshuffling backend is present, create the reshuffling backend
unsigned int reorder_degree = getBitReorderDegree();
// Create intermediate nets
createNet("SerializerIn", makeNetIndex(0, in_bits-1));
createNet("ReorderIn", makeNetIndex(0, out_bits+reorder_degree-1));
assign("ReorderIn", makeNetIndex(out_bits, out_bits+reorder_degree-1), "ReorderIn", makeNetIndex(0, reorder_degree-1));
// Create barrelshifter
unsigned int shift_index_min = (unsigned int)ceil(log2(serialization_ratio));
unsigned int shift_index_max = std::max(shift_index_min, (unsigned int) ceil(log2(in_bits)) - 1);
// Remember some things
getGenProperties()->set("ReorderDegree", reorder_degree);
getGenProperties()->set("ShiftIndexMin", shift_index_min);
getGenProperties()->set("ShiftIndexMax", shift_index_max);
const String& barrel_shift_name = "BarrelShifter";
BarrelShifter* barrel_shift = new BarrelShifter(barrel_shift_name, getTechModel());
barrel_shift->setParameter("NumberBits", in_bits);
barrel_shift->setParameter("ShiftIndexMax", shift_index_max);
barrel_shift->setParameter("ShiftIndexMin", shift_index_min);
barrel_shift->setParameter("BitDuplicate", bit_duplicate);
barrel_shift->construct();
// Create bit reorder muxes
const String& reorder_mux_name = "ReorderMux";
Multiplexer* reorder_mux = new Multiplexer(reorder_mux_name, getTechModel());
reorder_mux->setParameter("NumberBits", out_bits);
reorder_mux->setParameter("NumberInputs", reorder_degree);
reorder_mux->setParameter("BitDuplicate", bit_duplicate);
reorder_mux->construct();
// Connect barrelshifter
// TODO: Connect barrelshift shifts!
portConnect(barrel_shift, "In", "In");
portConnect(barrel_shift, "Out", "SerializerIn");
// Connect serializer
portConnect(serializer, "In", "SerializerIn");
portConnect(serializer, "Out", "ReorderIn", makeNetIndex(0, out_bits-1));
portConnect(serializer, "OutCK", "LinkCK");
// Connect bit reorder muxes
// TODO: Connect re-order multiplex select signals!
for (unsigned int i = 0; i < reorder_degree; i++)
portConnect(reorder_mux, "In" + (String) i, "ReorderIn", makeNetIndex(i, i+out_bits-1));
portConnect(reorder_mux, "Out", "Out");
addSubInstances(barrel_shift, 1.0);
addSubInstances(reorder_mux, 1.0);
addElectricalSubResults(barrel_shift, 1.0);
addElectricalSubResults(reorder_mux, 1.0);
getEventResult("ProcessBits")->addSubResult(barrel_shift->getEventResult("BarrelShift"), barrel_shift_name, 1.0);
getEventResult("ProcessBits")->addSubResult(reorder_mux->getEventResult("Mux"), reorder_mux_name, 1.0); // This happens multiple times
}
else if ((tuning_method == "FullThermal") || (tuning_method == "AthermalWithTrim"))
{
// If no bit reshuffling backend is present, then just connect serializer up
portConnect(serializer, "In", "In");
portConnect(serializer, "Out", "Out");
portConnect(serializer, "OutCK", "LinkCK");
}
else
{
ASSERT(false, "[Error] " + getInstanceName() + " -> Unknown ring tuning method '" + tuning_method + "'!");
}
return;
}
void OpticalLinkBackendTx::updateModel()
{
// Update everyone
Model::updateModel();
// Update ring tuning power
getNddPowerResult("RingTuning")->setValue(getRingTuningPower());
return;
}
void OpticalLinkBackendTx::propagateTransitionInfo()
{
// Get parameters
const String& tuning_method = getParameter("RingTuningMethod");
// Update the serializer
if ((tuning_method == "ThermalWithBitReshuffle") || (tuning_method == "ElectricalAssistWithBitReshuffle"))
{
// Get generated properties
unsigned int reorder_degree = getGenProperties()->get("ReorderDegree").toUInt();
unsigned int shift_index_min = getGenProperties()->get("ShiftIndexMin").toUInt();
unsigned int shift_index_max = getGenProperties()->get("ShiftIndexMax").toUInt();
// Update barrel shifter
const String& barrel_shift_name = "BarrelShifter";
ElectricalModel* barrel_shift = (ElectricalModel*) getSubInstance(barrel_shift_name);
propagatePortTransitionInfo(barrel_shift, "In", "In");
// Set shift transitions to be very low (since it is affected by slow temperature time constants)
for (unsigned int i = shift_index_min; i <= shift_index_max; ++i)
barrel_shift->getInputPort("Shift" + (String) i)->setTransitionInfo(TransitionInfo(0.499, 0.001, 0.499));
barrel_shift->use();
// Set serializer transition info
ElectricalModel* serializer = (ElectricalModel*) getSubInstance("Serializer");
propagatePortTransitionInfo(serializer, "In", barrel_shift, "Out");
propagatePortTransitionInfo(serializer, "OutCK", "LinkCK");
serializer->use();
// Reorder mux shift select bits
unsigned int reorder_sel_bits = (unsigned int)ceil(log2(reorder_degree));
// Reorder mux probabilities
const String& reorder_mux_name = "ReorderMux";
ElectricalModel* reorder_mux = (ElectricalModel*) getSubInstance(reorder_mux_name);
for (unsigned int i = 0; i < reorder_degree; ++i)
propagatePortTransitionInfo(reorder_mux, "In" + (String) i, serializer, "Out");
// Set select transitions to be 0, since these are statically configured
for (unsigned int i = 0; i < reorder_sel_bits; ++i)
reorder_mux->getInputPort("Sel" + (String) i)->setTransitionInfo(TransitionInfo(0.5, 0.0, 0.5));
reorder_mux->use();
// Set output transition info
propagatePortTransitionInfo("Out", reorder_mux, "Out");
}
else if ((tuning_method == "FullThermal") || (tuning_method == "AthermalWithTrim"))
{
// Set serializer transition info
ElectricalModel* serializer = (ElectricalModel*) getSubInstance("Serializer");
propagatePortTransitionInfo(serializer, "In", "In");
propagatePortTransitionInfo(serializer, "OutCK", "LinkCK");
serializer->use();
// Set output transition info
propagatePortTransitionInfo("Out", serializer, "Out");
}
return;
}
double OpticalLinkBackendTx::getRingTuningPower()
{
// Get properties
const String& tuning_method = getParameter("RingTuningMethod");;
unsigned int number_rings = getGenProperties()->get("OutBits");
// Get tech model parameters
double R = getTechModel()->get("Ring->Radius");
double n_g = getTechModel()->get("Ring->GroupIndex");
double heating_efficiency = getTechModel()->get("Ring->HeatingEfficiency");
// This can actually be derived if we know thermo-optic coefficient (delta n / delta T)
double tuning_efficiency = getTechModel()->get("Ring->TuningEfficiency");
double sigma_r_local = getTechModel()->get("Ring->LocalVariationSigma");
double sigma_r_systematic = getTechModel()->get("Ring->SystematicVariationSigma");
double T_max = getTechModel()->get("Ring->TemperatureMax");
double T_min = getTechModel()->get("Ring->TemperatureMin");
double T = getTechModel()->get("Temperature");
// Get constants
double c = Constants::c;
double pi = Constants::pi;
double tuning_power = 0.0;
if (tuning_method == "ThermalWithBitReshuffle")
{
// When an electrical backend is present, rings only have to tune to the nearest channel
// This can be approximated as each ring tuning to something exactly 1 channel away
// Setup calculations
double L = 2 * pi * R; // Optical length
double FSR = c / (n_g * L); // Free spectral range
double freq_sep = FSR / number_rings; // Channel separation
// Calculate tuning power
tuning_power = number_rings * freq_sep / (tuning_efficiency * heating_efficiency);
}
else if (tuning_method == "ElectricalAssistWithBitReshuffle")
{
// Electrical assistance allows for a fraction of the tuning range to be
// covered electrically. This is most pronounced when the tuning range is small,
// such is the case when bit reshuffling is applied. The electrically
// assisted part of it pretty much comes for free...
// Get electrically tunable range
double max_assist = getTechModel()->get("Ring->MaxElectricallyTunableFreq");
// Setup calculations
double L = 2 * pi * R; // Optical length
double FSR = c / (n_g * L); // Free spectral range
double freq_sep = FSR / number_rings; // Channel separation
double heating_range = std::max(0.0, freq_sep - max_assist); // The distance needed to bridge using heaters
// Calculate tuning power, which is really only the power spent on heating since
// distance tuned electrically is pretty much free
tuning_power = number_rings * heating_range / (tuning_efficiency * heating_efficiency);
}
else if (tuning_method == "FullThermal")
{
// If there is no bit reshuffling backend, each ring must tune to an
// absolute channel frequency. Since we can only heat rings (and not cool),
// we can only red-shift (decrease frequency). Thus, a fabrication bias
// must be applied such that under any process and temperature corner, the
// ring resonance remains above channel resonance
// I'll use 3 sigmas of sigma_r_local and sigma_r_systematic, and bias against
// the full temperature range
double fabrication_bias_freq = 3.0 * sqrt(pow(sigma_r_local, 2) + pow(sigma_r_systematic, 2)) +
(T_max - T_min) * tuning_efficiency;
// The local/systematic variations are 0 on average. Thus, the tuning distance can be calculated as
double tuning_distance = fabrication_bias_freq - (T - T_min) * tuning_efficiency;
// Tuning power needed is just the number of rings * tuning distance / (tuning and heating efficiencies)
tuning_power = number_rings * tuning_distance / (tuning_efficiency * heating_efficiency);
}
else if (tuning_method == "AthermalWithTrim")
{
// Athermal! Each ring's process variations are trimmed! Everything is free!
// Basically an ideal scenario
tuning_power = 0;
}
else
{
ASSERT(false, "[Error] " + getInstanceName() + " -> Unknown ring tuning method '" + tuning_method + "'!");
}
return tuning_power;
}
unsigned int OpticalLinkBackendTx::getBitReorderDegree()
{
// Get properties
unsigned int number_rings = getGenProperties()->get("OutBits");
// Get tech model parameters
double R = getTechModel()->get("Ring->Radius");
double n_g = getTechModel()->get("Ring->GroupIndex");
// This can actually be derived if we know thermo-optic coefficient (delta n / delta T)
double sigma_r_local = getTechModel()->get("Ring->LocalVariationSigma");
// Get constants
double c = Constants::c;
double pi = Constants::pi;
// Calculates the degree of bit re-order multiplexing needed for bit-reshuffling backend
// Bit reshuffling tuning is largely unaffected by sigma_r_systematic. However, sigma_r_local
// Can potentially throw each ring to a channel several channels away. This just calculates
// the degree of bit reorder muxing needed to realign bits in the correct order
// Setup calculations
double L = 2 * pi * R; // Optical length
double FSR = c / (n_g * L); // Free spectral range
double freq_sep = FSR / number_rings; // Channel separation
// Using 4 sigmas as the worst re-ordering case (must double to get both sides)
unsigned int worst_case_channels = (unsigned int)ceil(2.0 * 4.0 * sigma_r_local / freq_sep);
return worst_case_channels;
}
} // namespace DSENT