# See LICENSE for licensing information. # # Copyright (c) 2016-2019 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 debug import design from tech import drc, spice from vector import vector from globals import OPTS from sram_factory import factory import logical_effort class bitcell_array(design.design): """ Creates a rows x cols array of memory cells. Assumes bit-lines and word line is connected by abutment. Connects the word lines and bit lines. """ def __init__(self, cols, rows, name): design.design.__init__(self, name) debug.info(1, "Creating {0} {1} x {2}".format(self.name, rows, cols)) self.add_comment("rows: {0} cols: {1}".format(rows, cols)) self.column_size = cols self.row_size = rows self.create_netlist() if not OPTS.netlist_only: self.create_layout() # We don't offset this because we need to align # the replica bitcell in the control logic #self.offset_all_coordinates() def create_netlist(self): """ Create and connect the netlist """ self.add_modules() self.add_pins() self.create_instances() def create_layout(self): # We increase it by a well enclosure so the precharges don't overlap our wells self.height = self.row_size*self.cell.height self.width = self.column_size*self.cell.width xoffset = 0.0 for col in range(self.column_size): yoffset = 0.0 for row in range(self.row_size): name = "bit_r{0}_c{1}".format(row, col) if row % 2: tempy = yoffset + self.cell.height dir_key = "MX" else: tempy = yoffset dir_key = "" self.cell_inst[row,col].place(offset=[xoffset, tempy], mirror=dir_key) yoffset += self.cell.height xoffset += self.cell.width self.add_layout_pins() self.add_boundary() self.DRC_LVS() def add_pins(self): row_list = self.cell.get_all_wl_names() column_list = self.cell.get_all_bitline_names() for col in range(self.column_size): for cell_column in column_list: self.add_pin(cell_column+"_{0}".format(col)) for row in range(self.row_size): for cell_row in row_list: self.add_pin(cell_row+"_{0}".format(row)) self.add_pin("vdd") self.add_pin("gnd") def add_modules(self): """ Add the modules used in this design """ self.cell = factory.create(module_type="bitcell") self.add_mod(self.cell) def get_bitcell_pins(self, col, row): """ Creates a list of connections in the bitcell, indexed by column and row, for instance use in bitcell_array """ bitcell_pins = [] pin_names = self.cell.get_all_bitline_names() for pin in pin_names: bitcell_pins.append(pin+"_{0}".format(col)) pin_names = self.cell.get_all_wl_names() for pin in pin_names: bitcell_pins.append(pin+"_{0}".format(row)) bitcell_pins.append("vdd") bitcell_pins.append("gnd") return bitcell_pins def create_instances(self): """ Create the module instances used in this design """ self.cell_inst = {} for col in range(self.column_size): for row in range(self.row_size): name = "bit_r{0}_c{1}".format(row, col) self.cell_inst[row,col]=self.add_inst(name=name, mod=self.cell) self.connect_inst(self.get_bitcell_pins(col, row)) def add_layout_pins(self): """ Add the layout pins """ row_list = self.cell.get_all_wl_names() column_list = self.cell.get_all_bitline_names() for col in range(self.column_size): for cell_column in column_list: bl_pin = self.cell_inst[0,col].get_pin(cell_column) self.add_layout_pin(text=cell_column+"_{0}".format(col), layer=bl_pin.layer, offset=bl_pin.ll().scale(1,0), width=bl_pin.width(), height=self.height) for row in range(self.row_size): for cell_row in row_list: wl_pin = self.cell_inst[row,0].get_pin(cell_row) self.add_layout_pin(text=cell_row+"_{0}".format(row), layer=wl_pin.layer, offset=wl_pin.ll().scale(0,1), width=self.width, height=wl_pin.height()) # For every second row and column, add a via for gnd and vdd for row in range(self.row_size): for col in range(self.column_size): inst = self.cell_inst[row,col] for pin_name in ["vdd", "gnd"]: for pin in inst.get_pins(pin_name): self.add_power_pin(name=pin_name, loc=pin.center(), vertical=True, start_layer=pin.layer) def analytical_delay(self, corner, slew, load): """Returns relative delay of the bitline in the bitcell array""" from tech import parameter #The load being driven/drained is mostly the bitline but could include the sense amp or the column mux. #The load from the bitlines is due to the drain capacitances from all the other bitlines and wire parasitics. drain_load = logical_effort.convert_farad_to_relative_c(parameter['bitcell_drain_cap']) wire_unit_load = .05 * drain_load #Wires add 5% to this. bitline_load = (drain_load+wire_unit_load)*self.row_size return [self.cell.analytical_delay(corner, slew, load+bitline_load)] def analytical_power(self, corner, load): """Power of Bitcell array and bitline in nW.""" from tech import drc, parameter # Dynamic Power from Bitline bl_wire = self.gen_bl_wire() cell_load = 2 * bl_wire.return_input_cap() bl_swing = OPTS.rbl_delay_percentage freq = spice["default_event_rate"] bitline_dynamic = self.calc_dynamic_power(corner, cell_load, freq, swing=bl_swing) #Calculate the bitcell power which currently only includes leakage cell_power = self.cell.analytical_power(corner, load) #Leakage power grows with entire array and bitlines. total_power = self.return_power(cell_power.dynamic + bitline_dynamic * self.column_size, cell_power.leakage * self.column_size * self.row_size) return total_power def gen_wl_wire(self): if OPTS.netlist_only: width = 0 else: width = self.width wl_wire = self.generate_rc_net(int(self.column_size), width, drc("minwidth_metal1")) wl_wire.wire_c = 2*spice["min_tx_gate_c"] + wl_wire.wire_c # 2 access tx gate per cell return wl_wire def gen_bl_wire(self): if OPTS.netlist_only: height = 0 else: height = self.height bl_pos = 0 bl_wire = self.generate_rc_net(int(self.row_size-bl_pos), height, drc("minwidth_metal1")) bl_wire.wire_c =spice["min_tx_drain_c"] + bl_wire.wire_c # 1 access tx d/s per cell return bl_wire def output_load(self, bl_pos=0): bl_wire = self.gen_bl_wire() return bl_wire.wire_c # sense amp only need to charge small portion of the bl # set as one segment for now def input_load(self): wl_wire = self.gen_wl_wire() return wl_wire.return_input_cap() def get_wordline_cin(self): """Get the relative input capacitance from the wordline connections in all the bitcell""" #A single wordline is connected to all the bitcells in a single row meaning the capacitance depends on the # of columns bitcell_wl_cin = self.cell.get_wl_cin() total_cin = bitcell_wl_cin * self.column_size return total_cin def graph_exclude_bits(self, targ_row, targ_col): """Excludes bits in column from being added to graph except target""" #Function is not robust with column mux configurations for row in range(self.row_size): for col in range(self.column_size): if row == targ_row and col == targ_col: continue self.graph_inst_exclude.add(self.cell_inst[row,col]) def get_cell_name(self, inst_name, row, col): """Gets the spice name of the target bitcell.""" return inst_name+'.x'+self.cell_inst[row,col].name, self.cell_inst[row,col]