OpenRAM/compiler/modules/rom_dummy_cell.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.
#

from openram.base import design
from openram.base import vector
from openram import OPTS
from openram.sram_factory import factory
from openram.tech import drc


class rom_dummy_cell(design):

    def __init__(self, name="", cell_name=None, add_source_contact=False, add_drain_contact=False, route_layer="m1"):
        super().__init__(name, cell_name)
        self.route_layer = route_layer
        self.add_source_contact=add_source_contact
        self.add_drain_contact=add_drain_contact
        self.create_netlist()
        self.create_layout()

    def create_netlist(self):
        #creates nmos for layout dimensions
        self.add_nmos()

        #set height and width such that the cell will tile perfectly by only ofsetting in the array by its width and height
        
    

    def create_layout(self):
        
        
        self.setup_drc_offsets()
        
        self.add_boundary()
        self.add_poly()
        self.add_metal()
        #self.add_label("0,0", self.route_layer)


    


    # Calculates offsets of cell width and height so that tiling of cells does not violate any drc rules
    def setup_drc_offsets(self):
    
        #nmos contact to gate distance
        self.contact_to_gate = 0.5 * (self.nmos.width - 2 * self.nmos.contact_width - self.nmos.poly_width - 2 * self.active_enclose_contact) 

        #height offset to account for active-to-active spacing between adjacent bitlines
        self.poly_extend_active_spacing = abs( 2 * self.nmos.poly_extend_active - drc("active_to_active") )

        #contact to contact distance, minimum cell width before drc offsets 
        self.base_width = self.nmos.width - 2 * self.active_enclose_contact - self.nmos.contact_width

        #width offset to account for active-to-active spacing between cells on the same bitline
        #this is calculated as a negative value
        self.cell_diffusion_offset = ((self.base_width - 2 * self.active_enclose_contact - self.nmos.contact_width) - drc("active_to_active")) * 0.5

        # width offset to account for poly-active spacing between base and dummy cells on the same bitline
        self.poly_active_offset = 0.5 * (self.base_width - 2 * self.cell_diffusion_offset - (self.poly_width + 2 * self.active_enclose_contact + self.nmos.contact_width)) - self.poly_to_active

        #so that the poly taps are far enough apart 
        self.poly_tap_offset = (self.base_width - self.cell_diffusion_offset - self.poly_contact.width - self.poly_active_offset) - drc("poly_to_poly")
 

    def add_boundary(self):

        #cell width with offsets applied, height becomes width when the cells are rotated 
        # self.width = self.nmos.height + self.poly_extend_active_spacing + 2 * self.nmos.poly_extend_active
        self.width = self.nmos.height + self.poly_extend_active_spacing + 2 * self.nmos.poly_extend_active
        # cell height with offsets applied, width becomes height when the cells are rotated, if the offsets are positive (greater than 0) they are not applied
        self.height = self.base_width - min(self.cell_diffusion_offset, 0) - min(self.poly_active_offset, 0) - min(self.poly_tap_offset, 0)

        super().add_boundary()

        

    def add_poly(self):

        poly_x = 0.5 * (self.nmos.poly_height + self.poly_extend_active_spacing)
        # 0.5 * self.nmos.contact_width + self.contact_to_gate

        self.poly = self.add_rect_center("poly", vector(poly_x, self.base_width * 0.5), 2 * poly_x, self.poly_width)

    def add_metal(self):

        if self.route_layer == "li":
            via = "mcon"
        else:
            via = "via{}".format(self.route_layer[len(self.route_layer) - 1])
        wire_y =  self.height + drc["minwidth_{}".format(via)] * 0.5
        wire_x = 0.5 * (self.width - self.poly_extend_active_spacing)

        wire_start = vector( wire_x, 0)
        wire_end = vector(wire_x, wire_y)

        # if self.route_layer == 'm1':

        #     if self.drain_contact:
        #         self.add_via_center(self.li_stack, [wire_x, wire_y])
        #     if self.source_contact:
        #         self.add_via_center(self.li_stack, [self.width, wire_y])

        self.add_path(self.route_layer, [wire_start, wire_end])   

        # drain_x = 0
        # drain_y = 0.5 * (self.width)
        source_x = 0.5 * (self.width - self.poly_extend_active_spacing)
        source_y = 0
        source_pos = vector(source_x, source_y)
        self.add_layout_pin_rect_center("S", self.route_layer, source_pos)

        drain_pos = vector(source_x, self.height)
        self.add_layout_pin_rect_center("D", self.route_layer, drain_pos)
        
            
    def add_nmos(self):
        #used only for layout constants
        # if not self.source_contact:
        #     add_source = False
        # else:
        #     add_source = self.route_layer

        # if not self.drain_contact:
        #     add_drain = False
        # else:
        #     add_drain = self.route_layer
        self.nmos  = factory.create(module_type="ptx",
                                    module_name="nmos_rom_mod",
                                    tx_type="nmos",
                                    add_source_contact=self.add_source_contact,
                                    add_drain_contact=self.add_drain_contact
                                    )