OpenRAM/compiler/bitcell_array.py

import debug
import design
from tech import drc, spice
from vector import vector
from globals import OPTS



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="bitcell_array"):
        design.design.__init__(self, name)
        debug.info(1, "Creating {0} {1} x {2}".format(self.name, rows, cols))


        self.column_size = cols
        self.row_size = rows

        c = reload(__import__(OPTS.bitcell))
        self.mod_bitcell = getattr(c, OPTS.bitcell)
        self.cell = self.mod_bitcell()
        self.add_mod(self.cell)

        self.height = self.row_size*self.cell.height 
        self.width = self.column_size*self.cell.width 
        
        self.add_pins()
        self.create_layout()
        self.add_layout_pins()
        self.DRC_LVS()

    def add_pins(self):
        for col in range(self.column_size):
            self.add_pin("bl[{0}]".format(col))
            self.add_pin("br[{0}]".format(col))
        for row in range(self.row_size):
            self.add_pin("wl[{0}]".format(row))
        self.add_pin("vdd")
        self.add_pin("gnd")

    def create_layout(self):
        xoffset = 0.0
        self.cell_inst = {}
        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]=self.add_inst(name=name,
                                                      mod=self.cell,
                                                      offset=[xoffset, tempy],
                                                      mirror=dir_key)
                self.connect_inst(["bl[{0}]".format(col),
                                   "br[{0}]".format(col),
                                   "wl[{0}]".format(row),
                                   "vdd",
                                   "gnd"])
                yoffset += self.cell.height
            xoffset += self.cell.width


    def add_layout_pins(self):
        
        # Our cells have multiple gnd pins for now.
        # FIXME: fix for multiple vdd too
        vdd_pin = self.cell.get_pin("vdd")

        # shift it up by the overlap amount (gnd_pin) too
        # must find the lower gnd pin to determine this overlap
        lower_y = self.cell.height
        gnd_pins = self.cell.get_pins("gnd")
        for gnd_pin in gnd_pins:
            if gnd_pin.layer=="metal2" and gnd_pin.by()<lower_y:
                lower_y=gnd_pin.by()

        # lower_y is negative, so subtract off double this amount for each pair of
        # overlapping cells
        full_height = self.height - 2*lower_y
        
        vdd_pin = self.cell.get_pin("vdd")
        lower_x = vdd_pin.lx()
        # lower_x is negative, so subtract off double this amount for each pair of
        # overlapping cells
        full_width = self.width - 2*lower_x
        
        offset = vector(0.0, 0.0)
        for col in range(self.column_size):
            # get the pin of the lower row cell and make it the full width
            bl_pin = self.cell_inst[0,col].get_pin("BL")
            br_pin = self.cell_inst[0,col].get_pin("BR")
            self.add_layout_pin(text="bl[{0}]".format(col),
                                layer="metal2",
                                offset=bl_pin.ll(),
                                width=bl_pin.width(),
                                height=full_height)
            self.add_layout_pin(text="br[{0}]".format(col),
                                layer="metal2",
                                offset=br_pin.ll(),
                                width=br_pin.width(),
                                height=full_height)

            # gnd offset is 0 in our cell, but it be non-zero
            gnd_pins = self.cell_inst[0,col].get_pins("gnd")
            for gnd_pin in gnd_pins:
                # avoid duplicates by only doing even rows
                # also skip if it isn't the pin that spans the entire cell down to the bottom
                if gnd_pin.layer=="metal2" and gnd_pin.by()==lower_y:
                    self.add_layout_pin(text="gnd", 
                                        layer="metal2",
                                        offset=gnd_pin.ll(),
                                        width=gnd_pin.width(),
                                        height=full_height)
                    
            # increments to the next column width
            offset.x += self.cell.width

        offset.x = 0.0
        for row in range(self.row_size):
            wl_pin = self.cell_inst[row,0].get_pin("WL")
            vdd_pins = self.cell_inst[row,0].get_pins("vdd")
            gnd_pins = self.cell_inst[row,0].get_pins("gnd")

            for gnd_pin in gnd_pins:
                if gnd_pin.layer=="metal1":
                    self.add_layout_pin(text="gnd", 
                                        layer="metal1",
                                        offset=gnd_pin.ll(),
                                        width=full_width,
                                        height=drc["minwidth_metal1"])
                
            # add vdd label and offset
            # only add to even rows to avoid duplicates
            for vdd_pin in vdd_pins:
                if row % 2 == 0 and vdd_pin.layer=="metal1":
                    self.add_layout_pin(text="vdd",
                                        layer="metal1",
                                        offset=vdd_pin.ll(),
                                        width=full_width,
                                        height=drc["minwidth_metal1"])
                
            # add wl label and offset
            self.add_layout_pin(text="wl[{0}]".format(row),
                                layer="metal1",
                                offset=wl_pin.ll(),
                                width=full_width,
                                height=wl_pin.height())

            # increments to the next row height
            offset.y += self.cell.height

    def analytical_delay(self, slew, load=0):
        from tech import drc
        wl_wire = self.gen_wl_wire()
        wl_wire.return_delay_over_wire(slew)

        wl_to_cell_delay = wl_wire.return_delay_over_wire(slew)
        # hypothetical delay from cell to bl end without sense amp
        bl_wire = self.gen_bl_wire()
        cell_load = 2 * bl_wire.return_input_cap() # we ingore the wire r
                                                   # hence just use the whole c
        bl_swing = 0.1
        cell_delay = self.cell.analytical_delay(wl_to_cell_delay.slew, cell_load, swing = bl_swing)

        #we do not consider the delay over the wire for now
        return self.return_delay(cell_delay.delay+wl_to_cell_delay.delay,
                                 wl_to_cell_delay.slew)

    def gen_wl_wire(self):
        wl_wire = self.generate_rc_net(int(self.column_size), self.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):
        bl_pos = 0
        bl_wire = self.generate_rc_net(int(self.row_size-bl_pos), self.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()