OpenRAM/compiler/pgates/pinv.py

# See LICENSE for licensing information.
#
# Copyright (c) 2016-2021 Regents of the University of California and The Board
# of Regents for the Oklahoma Agricultural and Mechanical College
# (acting for and on behalf of Oklahoma State University)
# All rights reserved.
#
import contact
import pgate
import debug
import operator
from tech import drc, parameter, spice
from vector import vector
from math import ceil
from globals import OPTS
from utils import round_to_grid
import logical_effort
from sram_factory import factory
from errors import drc_error
from tech import cell_properties as cell_props


class pinv(pgate.pgate):
    """
    Pinv generates gds of a parametrically sized inverter. The
    size is specified as the drive size (relative to minimum NMOS) and
    a beta value for choosing the pmos size.  The inverter's cell
    height is usually the same as the 6t library cell and is measured
    from center of rail to rail.
    """
    # binning %error tracker
    bin_count = 0
    bin_error = 0

    def __init__(self, name, size=1, beta=parameter["beta"], height=None, add_wells=True):

        debug.info(2,
                   "creating pinv structure {0} with size of {1}".format(name,
                                                                         size))
        self.add_comment("size: {}".format(size))

        self.size = size
        debug.check(self.size >= 1, "Must have a size greater than or equal to 1.")
        self.nmos_size = size
        self.pmos_size = beta * size
        self.beta = beta

        super().__init__(name, height, add_wells)

    def create_netlist(self):
        """ Calls all functions related to the generation of the netlist """
        self.add_pins()
        self.determine_tx_mults()
        self.add_ptx()
        self.create_ptx()

    def create_layout(self):
        """ Calls all functions related to the generation of the layout """
        self.place_ptx()
        if self.add_wells:
            self.add_well_contacts()
        self.determine_width()
        self.extend_wells()
        self.route_input_gate(self.pmos_inst,
                              self.nmos_inst,
                              self.output_pos.y,
                              "A",
                              position="farleft")
        self.route_outputs()
        self.route_supply_rails()
        self.connect_rails()
        self.add_boundary()

    def add_pins(self):
        """ Adds pins for spice netlist """
        pin_list = ["A", "Z", "vdd", "gnd"]
        dir_list = ["INPUT", "OUTPUT", "POWER", "GROUND"]
        self.add_pin_list(pin_list, dir_list)

    def determine_tx_mults(self):
        """
        Determines the number of fingers needed to achieve the size within
        the height constraint. This may fail if the user has a tight height.
        """

        # This may make the result differ when the layout is created...
        if OPTS.netlist_only:
            self.tx_mults = 1
            self.nmos_width = self.nmos_size * drc("minwidth_tx")
            self.pmos_width = self.pmos_size * drc("minwidth_tx")
            if cell_props.ptx.bin_spice_models:
                (self.nmos_width, self.tx_mults) = pgate.pgate.best_bin("nmos", self.nmos_width)
                (self.pmos_width, self.tx_mults) = pgate.pgate.best_bin("pmos", self.pmos_width)
            return

        # Do a quick sanity check and bail if unlikely feasible height
        # Sanity check. can we make an inverter in the height
        # with minimum tx sizes?
        # Assume we need 3 metal 1 pitches (2 power rails, one
        # between the tx for the drain)
        # plus the tx height
        nmos = factory.create(module_type="ptx",
                              tx_type="nmos")
        pmos = factory.create(module_type="ptx",
                              width=drc("minwidth_tx"),
                              tx_type="pmos")
        tx_height = nmos.poly_height + pmos.poly_height
        # rotated m1 pitch or poly to active spacing
        min_channel = max(contact.poly_contact.width + self.m1_space,
                          contact.poly_contact.width + 2 * self.poly_to_active)

        total_height = tx_height + min_channel + 2 * self.top_bottom_space
        # debug.check(self.height > total_height,
        #             "Cell height {0} too small for simple min height {1}.".format(self.height,
        # total_height))
        if total_height > self.height:
            msg = "Cell height {0} too small for simple min height {1}.".format(self.height, total_height)
            raise drc_error(msg)

        # Determine the height left to the transistors to determine
        # the number of fingers
        tx_height_available = self.height - min_channel - 2 * self.top_bottom_space
        # Divide the height in half. Could divide proportional to beta,
        # but this makes connecting wells of multiple cells easier.
        # Subtract the poly space under the rail of the tx
        nmos_height_available = 0.5 * tx_height_available - 0.5 * self.poly_space
        pmos_height_available = 0.5 * tx_height_available - 0.5 * self.poly_space

        debug.info(2,
                   "Height avail {0:.4f} PMOS {1:.4f} NMOS {2:.4f}".format(tx_height_available,
                                                                           nmos_height_available,
                                                                           pmos_height_available))

        # Determine the number of mults for each to fit width
        # into available space
        if not cell_props.ptx.bin_spice_models:
            self.nmos_width = self.nmos_size * drc("minwidth_tx")
            self.pmos_width = self.pmos_size * drc("minwidth_tx")
            nmos_required_mults = max(int(ceil(self.nmos_width / nmos_height_available)), 1)
            pmos_required_mults = max(int(ceil(self.pmos_width / pmos_height_available)), 1)
            # The mults must be the same for easy connection of poly
            self.tx_mults = max(nmos_required_mults, pmos_required_mults)

            # Recompute each mult width and check it isn't too small
            # This could happen if the height is narrow and the size is small
            # User should pick a bigger size to fix it...
            # We also need to round the width to the grid or we will end up
            # with LVS property mismatch errors when fingers are not a grid
            # length and get rounded in the offset geometry.
            self.nmos_width = round_to_grid(self.nmos_width / self.tx_mults)
            # debug.check(self.nmos_width >= drc("minwidth_tx"),
            #            "Cannot finger NMOS transistors to fit cell height.")
            if self.nmos_width < drc("minwidth_tx"):
                raise drc_error("Cannot finger NMOS transistors to fit cell height.")

            self.pmos_width = round_to_grid(self.pmos_width / self.tx_mults)
            #debug.check(self.pmos_width >= drc("minwidth_tx"),
            #            "Cannot finger PMOS transistors to fit cell height.")
            if self.pmos_width < drc("minwidth_tx"):
                raise drc_error("Cannot finger NMOS transistors to fit cell height.")
        else:
            self.nmos_width = self.nmos_size * drc("minwidth_tx")
            self.pmos_width = self.pmos_size * drc("minwidth_tx")
            nmos_bins = self.scaled_bins("nmos", self.nmos_width)
            pmos_bins = self.scaled_bins("pmos", self.pmos_width)

            valid_pmos = []
            for bin in pmos_bins:
                if abs(self.bin_accuracy(self.pmos_width, bin[0])) > OPTS.accuracy_requirement and abs(self.bin_accuracy(self.pmos_width, bin[0])) <= 1:
                    valid_pmos.append(bin)
            valid_pmos.sort(key = operator.itemgetter(1))

            valid_nmos = []
            for bin in nmos_bins:
                if abs(self.bin_accuracy(self.nmos_width, bin[0])) > OPTS.accuracy_requirement and abs(self.bin_accuracy(self.nmos_width, bin[0])) <= 1:
                    valid_nmos.append(bin)
            valid_nmos.sort(key = operator.itemgetter(1))

            for bin in valid_pmos:
                if bin[0]/bin[1] < pmos_height_available:
                    self.pmos_width = bin[0]/bin[1]
                    pmos_mults = bin[1]
                    break

            for bin in valid_nmos:
                if bin[0]/bin[1] < nmos_height_available:
                    self.nmos_width = bin[0]/bin[1]
                    nmos_mults = bin[1]
                    break

            self.tx_mults = max(pmos_mults, nmos_mults)
            debug.info(2, "prebinning {0} tx, target: {4}, found {1} x {2} = {3}".format("pmos", self.pmos_width, pmos_mults, self.pmos_width * pmos_mults, self.pmos_size * drc("minwidth_tx")))
            debug.info(2, "prebinning {0} tx, target: {4}, found {1} x {2} = {3}".format("nmos", self.nmos_width, nmos_mults, self.nmos_width * nmos_mults, self.nmos_size * drc("minwidth_tx")))
            pinv.bin_count += 1
            pinv.bin_error += abs(((self.pmos_width * pmos_mults) - (self.pmos_size * drc("minwidth_tx")))/(self.pmos_size * drc("minwidth_tx")))
            pinv.bin_count += 1
            pinv.bin_error += abs(((self.nmos_width * nmos_mults) - (self.nmos_size * drc("minwidth_tx")))/(self.nmos_size * drc("minwidth_tx")))
            debug.info(2, "pinv bin count: {0} pinv bin error: {1} percent error {2}".format(pinv.bin_count, pinv.bin_error, pinv.bin_error/pinv.bin_count))

    def add_ptx(self):
        """ Create the PMOS and NMOS transistors. """
        self.nmos = factory.create(module_type="ptx",
                                   width=self.nmos_width,
                                   mults=self.tx_mults,
                                   tx_type="nmos",
                                   add_source_contact=self.route_layer,
                                   add_drain_contact=self.route_layer,
                                   connect_poly=True,
                                   connect_drain_active=True)
        self.add_mod(self.nmos)

        self.pmos = factory.create(module_type="ptx",
                                   width=self.pmos_width,
                                   mults=self.tx_mults,
                                   tx_type="pmos",
                                   add_source_contact=self.route_layer,
                                   add_drain_contact=self.route_layer,
                                   connect_poly=True,
                                   connect_drain_active=True)
        self.add_mod(self.pmos)

    def create_ptx(self):
        """
        Create the PMOS and NMOS netlist.
        """

        self.pmos_inst = self.add_inst(name="pinv_pmos",
                                       mod=self.pmos)
        self.connect_inst(["Z", "A", "vdd", "vdd"])

        self.nmos_inst = self.add_inst(name="pinv_nmos",
                                      mod=self.nmos)
        self.connect_inst(["Z", "A", "gnd", "gnd"])

    def place_ptx(self):
        """
        Place PMOS and NMOS to the layout at the upper-most and lowest position
        to provide maximum routing in channel
        """

        # place PMOS so it is half a poly spacing down from the top
        self.pmos_pos = self.pmos.active_offset.scale(1, 0) \
                        + vector(0,
                                 self.height - self.pmos.active_height - self.top_bottom_space)
        self.pmos_inst.place(self.pmos_pos)

        # place NMOS so that it is half a poly spacing up from the bottom
        self.nmos_pos = self.nmos.active_offset.scale(1, 0) \
                        + vector(0, self.top_bottom_space)
        self.nmos_inst.place(self.nmos_pos)

        # Output position will be in between the PMOS and NMOS drains
        pmos_drain_pos = self.pmos_inst.get_pin("D").ll()
        nmos_drain_pos = self.nmos_inst.get_pin("D").ul()
        self.output_pos = vector(0, 0.5 * (pmos_drain_pos.y + nmos_drain_pos.y))

    def route_outputs(self):
        """
        Route the output (drains) together.
        Optionally, routes output to edge.
        """

        # Get the drain pins
        nmos_drain_pin = self.nmos_inst.get_pin("D")
        pmos_drain_pin = self.pmos_inst.get_pin("D")

        # Pick point at right most of NMOS and connect down to PMOS
        nmos_drain_pos = nmos_drain_pin.bc()
        pmos_drain_pos = vector(nmos_drain_pos.x, pmos_drain_pin.uc().y)
        self.add_path(self.route_layer, [nmos_drain_pos, pmos_drain_pos])

        # Remember the mid for the output
        mid_drain_offset = vector(nmos_drain_pos.x, self.output_pos.y)

        # This leaves the output as an internal pin (min sized)
        output_offset = mid_drain_offset + vector(0.5 * self.route_layer_width, 0)
        self.add_layout_pin_rect_center(text="Z",
                                        layer=self.route_layer,
                                        offset=output_offset)

    def add_well_contacts(self):
        """ Add n/p well taps to the layout and connect to supplies """

        self.add_nwell_contact(self.pmos, self.pmos_pos)

        self.add_pwell_contact(self.nmos, self.nmos_pos)

    def connect_rails(self):
        """ Connect the nmos and pmos to its respective power rails """

        self.connect_pin_to_rail(self.nmos_inst, "S", "gnd")

        self.connect_pin_to_rail(self.pmos_inst, "S", "vdd")

    def analytical_power(self, corner, load):
        """Returns dynamic and leakage power. Results in nW"""
        c_eff = self.calculate_effective_capacitance(load)
        freq = spice["default_event_frequency"]
        power_dyn = self.calc_dynamic_power(corner, c_eff, freq)
        power_leak = spice["inv_leakage"]

        total_power = self.return_power(power_dyn, power_leak)
        return total_power

    def calculate_effective_capacitance(self, load):
        """Computes effective capacitance. Results in fF"""
        c_load = load
        # In fF
        c_para = spice["min_tx_drain_c"] * (self.nmos_size / parameter["min_tx_size"])
        transition_prob = 0.5
        return transition_prob * (c_load + c_para)

    def input_load(self):
        """
        Return the capacitance of the gate connection in generic capacitive
        units relative to the minimum width of a transistor
        """
        return self.nmos_size + self.pmos_size

    def get_stage_effort(self, cout, inp_is_rise=True):
        """
        Returns an object representing the parameters for delay in tau units.
        Optional is_rise refers to the input direction rise/fall.
        Input inverted by this stage.
        """
        parasitic_delay = 1
        return logical_effort.logical_effort(self.name,
                                             self.size,
                                             self.input_load(),
                                             cout,
                                             parasitic_delay,
                                             not inp_is_rise)

    def build_graph(self, graph, inst_name, port_nets):
        """
        Adds edges based on inputs/outputs.
        Overrides base class function.
        """
        self.add_graph_edges(graph, port_nets)
        
    def is_non_inverting(self):
        """Return input to output polarity for module"""
        
        return False