# 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 vector import vector from globals import OPTS from sram_factory import factory class delay_chain(design.design): """ Generate a delay chain with the given number of stages and fanout. Input is a list contains the electrical effort (fanout) of each stage. Usually, this will be constant, but it could have varied fanout. """ def __init__(self, name, fanout_list): """init function""" super().__init__(name) debug.info(1, "creating delay chain {0}".format(str(fanout_list))) self.add_comment("fanouts: {0}".format(str(fanout_list))) # Two fanouts are needed so that we can route the vdd/gnd connections for f in fanout_list: debug.check(f>=2, "Must have >=2 fanouts for each stage.") # number of inverters including any fanout loads. self.fanout_list = fanout_list self.create_netlist() if not OPTS.netlist_only: self.create_layout() def create_netlist(self): self.add_modules() self.add_pins() self.create_inverters() def create_layout(self): # Each stage is a a row self.height = len(self.fanout_list) * self.inv.height # The width is determined by the largest fanout plus the driver self.width = (max(self.fanout_list) + 1) * self.inv.width self.place_inverters() self.route_inverters() self.route_supplies() self.add_layout_pins() self.add_boundary() self.DRC_LVS() def add_pins(self): """ Add the pins of the delay chain""" self.add_pin("in", "INPUT") self.add_pin("out", "OUTPUT") self.add_pin("vdd", "POWER") self.add_pin("gnd", "GROUND") def add_modules(self): self.inv = factory.create(module_type="pinv") self.add_mod(self.inv) def create_inverters(self): """ Create the inverters and connect them based on the stage list """ self.driver_inst_list = [] self.load_inst_map = {} for stage_num, fanout_size in zip(range(len(self.fanout_list)), self.fanout_list): # Add the inverter cur_driver=self.add_inst(name="dinv{}".format(stage_num), mod=self.inv) # keep track of the inverter instances so we can use them to get the pins self.driver_inst_list.append(cur_driver) # Hook up the driver if stage_num + 1 == len(self.fanout_list): stageout_name = "out" else: stageout_name = "dout_{}".format(stage_num + 1) if stage_num == 0: stagein_name = "in" else: stagein_name = "dout_{}".format(stage_num) self.connect_inst([stagein_name, stageout_name, "vdd", "gnd"]) # Now add the dummy loads to the right self.load_inst_map[cur_driver]=[] for i in range(fanout_size): cur_load=self.add_inst(name="dload_{0}_{1}".format(stage_num, i), mod=self.inv) # Fanout stage is always driven by driver and output is disconnected disconnect_name = "n_{0}_{1}".format(stage_num, i) self.connect_inst([stageout_name, disconnect_name, "vdd", "gnd"]) # Keep track of all the loads to connect their inputs as a load self.load_inst_map[cur_driver].append(cur_load) def place_inverters(self): """ Place the inverters and connect them based on the stage list """ for stage_num, fanout_size in zip(range(len(self.fanout_list)), self.fanout_list): if stage_num % 2: inv_mirror = "MX" inv_offset = vector(0, (stage_num + 1) * self.inv.height) else: inv_mirror = "R0" inv_offset = vector(0, stage_num * self.inv.height) # Add the inverter cur_driver=self.driver_inst_list[stage_num] cur_driver.place(offset=inv_offset, mirror=inv_mirror) # Now add the dummy loads to the right load_list = self.load_inst_map[cur_driver] for i in range(fanout_size): inv_offset += vector(self.inv.width, 0) load_list[i].place(offset=inv_offset, mirror=inv_mirror) def add_route(self, pin1, pin2): """ This guarantees that we route from the top to bottom row correctly. """ pin1_pos = pin1.center() pin2_pos = pin2.center() if pin1_pos.y == pin2_pos.y: self.add_path("m2", [pin1_pos, pin2_pos]) else: mid_point = vector(pin2_pos.x, 0.5 * (pin1_pos.y + pin2_pos.y)) # Written this way to guarantee it goes right first if we are switching rows self.add_path("m2", [pin1_pos, vector(pin1_pos.x, mid_point.y), mid_point, vector(mid_point.x, pin2_pos.y), pin2_pos]) def route_inverters(self): """ Add metal routing for each of the fanout stages """ for i in range(len(self.driver_inst_list)): inv = self.driver_inst_list[i] for load in self.load_inst_map[inv]: # Drop a via on each A pin a_pin = load.get_pin("A") self.add_via_stack_center(from_layer=a_pin.layer, to_layer="m3", offset=a_pin.center()) # Route an M3 horizontal wire to the furthest z_pin = inv.get_pin("Z") a_pin = inv.get_pin("A") a_max = self.load_inst_map[inv][-1].get_pin("A") self.add_via_stack_center(from_layer=a_pin.layer, to_layer="m2", offset=a_pin.center()) self.add_via_stack_center(from_layer=z_pin.layer, to_layer="m3", offset=z_pin.center()) self.add_path("m3", [z_pin.center(), a_max.center()]) # Route Z to the A of the next stage if i + 1 < len(self.driver_inst_list): z_pin = inv.get_pin("Z") next_inv = self.driver_inst_list[i + 1] next_a_pin = next_inv.get_pin("A") y_mid = (z_pin.cy() + next_a_pin.cy()) / 2 mid1_point = vector(z_pin.cx(), y_mid) mid2_point = vector(next_a_pin.cx(), y_mid) self.add_path("m2", [z_pin.center(), mid1_point, mid2_point, next_a_pin.center()]) def route_supplies(self): # Add power and ground to all the cells except: # the fanout driver, the right-most load # The routing to connect the loads is over the first and last cells # We have an even number of drivers and must only do every other # supply rail for inst in self.driver_inst_list: load_list = self.load_inst_map[inst] for pin_name in ["vdd", "gnd"]: pin = load_list[0].get_pin(pin_name) self.add_power_pin(pin_name, pin.rc() - vector(self.m1_pitch, 0), start_layer=pin.layer) pin = load_list[-2].get_pin(pin_name) self.add_power_pin(pin_name, pin.rc() - vector(self.m1_pitch, 0), start_layer=pin.layer) def add_layout_pins(self): # input is A pin of first inverter a_pin = self.driver_inst_list[0].get_pin("A") self.add_via_stack_center(from_layer=a_pin.layer, to_layer="m2", offset=a_pin.center()) self.add_layout_pin(text="in", layer="m2", offset=a_pin.ll().scale(1, 0), height=a_pin.cy()) # output is A pin of last load inverter last_driver_inst = self.driver_inst_list[-1] a_pin = self.load_inst_map[last_driver_inst][-1].get_pin("A") self.add_via_stack_center(from_layer=a_pin.layer, to_layer="m2", offset=a_pin.center()) mid_point = vector(a_pin.cx() + 3 * self.m2_width, a_pin.cy()) self.add_path("m2", [a_pin.center(), mid_point, mid_point.scale(1, 0)]) self.add_layout_pin_segment_center(text="out", layer="m2", start=mid_point, end=mid_point.scale(1, 0))