ls2: add support for the Nexys Video board

[ls2.git] / src / ls2.py

# Copyright (c) 2020 LambdaConcept <contact@lambdaconcept.com>
# Copyright (c) 2021 Luke Kenneth Casson Leighton <lkcl@lkcl.net>
# Copyright (C) 2022 Raptor Engineering, LLC <support@raptorengineering.com>
#
# Based on code from LambaConcept, from the gram example which is BSD-2-License
# https://github.com/jeanthom/gram/tree/master/examples
#
# Modifications for the Libre-SOC Project funded by NLnet and NGI POINTER
# under EU Grants 871528 and 957073, under the LGPLv3+ License

from nmigen import (Module, Elaboratable, DomainRenamer, Record,
                    Signal, Cat, Const, ClockSignal, ResetSignal,
                    )
from nmigen.build.dsl import Attrs
from nmigen.cli import verilog
from nmigen.lib.cdc import ResetSynchronizer
from nmigen_soc import wishbone, memory
from nmigen_soc.memory import MemoryMap
from nmigen.utils import log2_int
from nmigen_boards.resources.interface import UARTResource
from nmigen_stdio.serial import AsyncSerial

# HyperRAM
from nmigen_boards.resources.memory import HyperRAMResource
from lambdasoc.periph.hyperram import HyperRAM, HyperRAMPads, HyperRAMPHY

from lambdasoc.periph.event import IRQLine
from lambdasoc.periph.intc import GenericInterruptController
from lambdasoc.periph.sram import SRAMPeripheral
from lambdasoc.periph.timer import TimerPeripheral
from lambdasoc.periph import Peripheral
from lambdasoc.soc.base import SoC
from soc.bus.uart_16550 import UART16550 # opencores 16550 uart
from soc.bus.tercel import Tercel # SPI XIP master
from soc.bus.opencores_ethmac import EthMAC # OpenCores 10/100 Ethernet MAC
from soc.bus.external_core import ExternalCore # external libresoc/microwatt
from soc.bus.wb_downconvert import WishboneDownConvert
from soc.bus.wb_async import WBAsyncBridge
from soc.bus.syscon import MicrowattSYSCON
from soc.interrupts.xics import XICS_ICP, XICS_ICS

# DDR3
from gram.common import (PhySettings, get_cl_cw, get_sys_latency,
                        get_sys_phases,)
from gram.core import gramCore
from gram.phy.ecp5ddrphy import ECP5DDRPHY
from gram.phy.fakephy import FakePHY, SDRAM_VERBOSE_STD, SDRAM_VERBOSE_DBG
from gram.modules import MT41K256M16, MT41K64M16
from gram.frontend.wishbone import gramWishbone

# SPI / Ethernet MAC
from nmigen.build import Resource
from nmigen.build import Subsignal
from nmigen.build import Pins

# Board (and simulation) platforms
from nmigen_boards.versa_ecp5 import VersaECP5Platform
from nmigen_boards.versa_ecp5 import VersaECP5Platform85 # custom board
from nmigen_boards.ulx3s import ULX3S_85F_Platform
from nmigen_boards.arty_a7 import ArtyA7_100Platform
# TODO: remove try..catch guards below when Nexys Video support is merged
#       into nmigen-boards
try:
    from nmigen_boards.nexys_video import NexysVideoPlatform
except ImportError:
    NexysVideoPlatform = None
from nmigen_boards.test.blinky import Blinky
from nmigen_boards.orangecrab_r0_2 import OrangeCrabR0_2_85k_Platform
from icarusversa import IcarusVersaPlatform
# Clock-Reset Generator (works for all ECP5 platforms)
from ecp5_crg import ECP5CRG
from arty_crg import ArtyA7CRG

import sys
import os

def sim_ddr3_settings(clk_freq=100e6):
    tck = 2/(2*2*clk_freq)
    nphases = 2
    databits = 16
    nranks = 1
    addressbits = 14
    bankbits = 3
    cl, cwl = get_cl_cw("DDR3", tck)
    cl_sys_latency = get_sys_latency(nphases, cl)
    cwl_sys_latency = get_sys_latency(nphases, cwl)
    rdcmdphase, rdphase = get_sys_phases(nphases, cl_sys_latency, cl)
    wrcmdphase, wrphase = get_sys_phases(nphases, cwl_sys_latency, cwl)
    return PhySettings(
        phytype="ECP5DDRPHY",
        memtype="DDR3",
        databits=databits,
        dfi_databits=4*databits,
        nranks=nranks,
        nphases=nphases,
        rdphase=rdphase,
        wrphase=wrphase,
        rdcmdphase=rdcmdphase,
        wrcmdphase=wrcmdphase,
        cl=cl,
        cwl=cwl,
        read_latency=2 + cl_sys_latency + 2 + log2_int(4//nphases) + 4,
        write_latency=cwl_sys_latency
    )


class WB64to32Convert(Elaboratable):
    """Microwatt IO wishbone slave 64->32 bits converter

    For timing reasons, this adds a one cycle latch on the way both
    in and out. This relaxes timing and routing pressure on the "main"
    memory bus by moving all simple IOs to a slower 32-bit bus.

    This implementation is rather dumb at the moment, no stash buffer,
    so we stall whenever that latch is busy. This can be improved.
    """
    def __init__(self, master, slave):
        self.master = master
        self.slave = slave

    def elaborate(self, platform):
        m = Module()
        comb, sync = m.d.comb, m.d.sync
        master, slave = self.master, self.slave

        has_top = Signal()
        has_top_r = Signal()
        has_bot = Signal()

        with m.FSM() as fsm:
            with m.State("IDLE"):
                # Clear ACK (and has_top_r) in case it was set
                sync += master.ack.eq(0)
                sync += has_top_r.eq(0)

                # Do we have a cycle ?
                with m.If(master.cyc & master.stb):
                    # Stall master until we are done, we are't (yet) pipelining
                    # this, it's all slow IOs.
                    sync += master.stall.eq(1)

                    # Start cycle downstream
                    sync += slave.cyc.eq(1)
                    sync += slave.stb.eq(1)

                    # Do we have a top word and/or a bottom word ?
                    comb += has_top.eq(master.sel[4:].bool())
                    comb += has_bot.eq(master.sel[:4].bool())
                    # record the has_top flag for the next FSM state
                    sync += has_top_r.eq(has_top)

                    # Copy write enable to IO out, copy address as well,
                    # LSB is set later based on HI/LO
                    sync += slave.we.eq(master.we)
                    sync += slave.adr.eq(Cat(0, master.adr))

                    # If we have a bottom word, handle it first, otherwise
                    # send the top word down. XXX Split the actual mux out
                    # and only generate a control signal.
                    with m.If(has_bot):
                        with m.If(master.we):
                            sync += slave.dat_w.eq(master.dat_w[:32])
                        sync += slave.sel.eq(master.sel[:4])

                        # Wait for ack on BOTTOM half
                        m.next = "WAIT_ACK_BOT"

                    with m.Else():
                        with m.If(master.we):
                            sync += slave.dat_w.eq(master.dat_w[32:])
                        sync += slave.sel.eq(master.sel[4:])

                        # Bump LSB of address
                        sync += slave.adr[0].eq(1)

                        # Wait for ack on TOP half
                        m.next = "WAIT_ACK_TOP"


            with m.State("WAIT_ACK_BOT"):
                # If we aren't stalled by the device, clear stb
                if hasattr(slave, "stall"):
                    with m.If(~slave.stall):
                        sync += slave.stb.eq(0)

                # Handle ack
                with m.If(slave.ack):
                    # If it's a read, latch the data
                    with m.If(~slave.we):
                        sync += master.dat_r[:32].eq(slave.dat_r)

                    # Do we have a "top" part as well ?
                    with m.If(has_top_r):
                        # Latch data & sel
                        with m.If(master.we):
                            sync += slave.dat_w.eq(master.dat_w[32:])
                        sync += slave.sel.eq(master.sel[4:])

                        # Bump address and set STB
                        sync += slave.adr[0].eq(1)
                        sync += slave.stb.eq(1)

                        # Wait for new ack
                        m.next = "WAIT_ACK_TOP"

                    with m.Else():
                        # We are done, ack up, clear cyc downstram
                        sync += slave.cyc.eq(0)
                        sync += slave.stb.eq(0)

                        # And ack & unstall upstream
                        sync += master.ack.eq(1)
                        if hasattr(master , "stall"):
                            sync += master.stall.eq(0)

                        # Wait for next one
                        m.next = "IDLE"

            with m.State("WAIT_ACK_TOP"):
                # If we aren't stalled by the device, clear stb
                if hasattr(slave, "stall"):
                    with m.If(~slave.stall):
                        sync += slave.stb.eq(0)

                # Handle ack
                with m.If(slave.ack):
                    # If it's a read, latch the data
                    with m.If(~slave.we):
                        sync += master.dat_r[32:].eq(slave.dat_r)

                    # We are done, ack up, clear cyc downstram
                    sync += slave.cyc.eq(0)
                    sync += slave.stb.eq(0)

                    # And ack & unstall upstream
                    sync += master.ack.eq(1)
                    if hasattr(master, "stall"):
                        sync += master.stall.eq(0)

                    # Wait for next one
                    m.next = "IDLE"

        return m


class DDR3SoC(SoC, Elaboratable):
    def __init__(self, *,
                 fpga,
                 dram_cls=None,
                 uart_pins=None, spi_0_pins=None, ethmac_0_pins=None,
                 ddr_pins=None, ddrphy_addr=None,
                 dramcore_addr=None, ddr_addr=None,
                 fw_addr=0x0000_0000, firmware=None,
                 uart_addr=None, uart_irqno=0,
                 spi0_addr=None, spi0_cfg_addr=None,
                 eth0_cfg_addr=None, eth0_irqno=None,
                 hyperram_addr=None,
                 hyperram_pins=None,
                 xics_icp_addr=None, xics_ics_addr=None,
                 clk_freq=50e6,
                 dram_clk_freq=None,
                 core_clk_freq=50e6,
                 add_cpu=True):

        # wishbone routing is as follows:
        #
        #         SoC
        #       +--+--+
        #       |     |
        #      ibus  dbus
        #       |     |
        #       +--+--+
        #          |
        #      64to32DownCvt
        #          |
        #       arbiter------------------------------------------------------+
        #          |                                                         |
        #   +---decoder----+--------+---------------+-------------+--------+ |
        #   |      |       |        |               |             |        | |
        #   |      |       |  WBAsyncBridge         |             |        | |
        #   |      |       |        |               |             |        | |
        #  uart  XICS    CSRs     DRAM          XIP SPI       HyperRAM   EthMAC

        # set up wishbone bus arbiter and decoder. arbiter routes,
        # decoder maps local-relative addressed satellites to global addresses
        self._arbiter = wishbone.Arbiter(addr_width=30, data_width=32,
                                         granularity=8,
                                         features={"cti", "bte", "stall"})
        self._decoder = wishbone.Decoder(addr_width=30, data_width=32,
                                         granularity=8,
                                         features={"cti", "bte", "stall"})

        # default firmware name
        if firmware is None:
            firmware = "firmware/main.bin"

        # set up clock request generator
        pod_bits = 25
        sync_bits = 26
        need_bridge=False
        if fpga in ['versa_ecp5', 'versa_ecp5_85', 'isim', 'ulx3s',
                    'orangecrab','orangecrab_isim', 'rcs_arctic_tern_bmc_card']:
            if fpga in ['isim','orangecrab_isim']:
                pod_bits = 5
                sync_bits = 6
            if fpga in ['orangecrab', 'orangecrab_sim',
                        'rcs_arctic_tern_bmc_card']:
                need_bridge=True
            self.crg = ECP5CRG(clk_freq, dram_clk_freq=dram_clk_freq,
                               pod_bits=pod_bits, sync_bits=sync_bits,
                               need_bridge=need_bridge)
        if fpga in ['arty_a7', 'nexys_video']:
            self.crg = ArtyA7CRG(clk_freq)

        self.dram_clk_freq = dram_clk_freq
        if self.dram_clk_freq is None:
            self.dram_clk_freq = clk_freq

        # set up CPU, with 64-to-32-bit downconverters, and a delayed Reset
        if add_cpu:
            self.cpu = ExternalCore(name="ext_core")

            cvtdbus = wishbone.Interface(addr_width=30, data_width=32,
                                         granularity=8, features={'stall'})
            cvtibus = wishbone.Interface(addr_width=30, data_width=32,
                                         granularity=8, features={'stall'})
            self.dbusdowncvt = WB64to32Convert(self.cpu.dbus, cvtdbus)
            self.ibusdowncvt = WB64to32Convert(self.cpu.ibus, cvtibus)
            self._arbiter.add(cvtibus) # I-Cache Master
            self._arbiter.add(cvtdbus) # D-Cache Master. TODO JTAG master
            self.cvtibus = cvtibus
            self.cvtdbus = cvtdbus

            # CPU interrupt controller, needs stall to be added, also
            # compat with wishbone.Interface
            self.intc = GenericInterruptController(width=len(self.cpu.irq))
            self.xics_icp = icp = XICS_ICP()
            self.xics_ics = ics = XICS_ICS()
            self.int_level_i = self.xics_ics.int_level_i

            self.pbus = pbus = wishbone.Interface(name="xics_icp_bus",
                                         addr_width=6, data_width=32,
                                         granularity=8, features={'stall'})
            self.sbus = sbus = wishbone.Interface(name="xics_ics_bus",
                                         addr_width=10, data_width=32,
                                         granularity=8, features={'stall'})
            pmap = MemoryMap(addr_width=8, data_width=8, name="icp_map")
            pbus.memory_map = pmap
            self._decoder.add(pbus, addr=xics_icp_addr) # ICP addr

            smap = MemoryMap(addr_width=12, data_width=8, name="ics_map")
            sbus.memory_map = smap
            self._decoder.add(sbus, addr=xics_ics_addr) # ICP addr


        # SRAM (but actually a ROM, for firmware)
        if fw_addr is not None:
            print ("fw at address %x" % fw_addr)
            sram_width = 32
            self.bootmem = SRAMPeripheral(size=0x8000, data_width=sram_width,
                                      writable=True)
            if firmware is not None:
                with open(firmware, "rb") as f:
                    words = iter(lambda: f.read(sram_width // 8), b'')
                    bios  = [int.from_bytes(w, "little") for w in words]
                self.bootmem.init = bios
            self._decoder.add(self.bootmem.bus, addr=fw_addr) # ROM at fw_addr

        # System Configuration info
        # offset executable ELF payload at 6 megabyte offset (2<<20)
        spi_offset = 2<<20 if (spi_0_pins is not None) else None
        dram_offset = ddr_addr if (ddr_pins is not None) else None
        self.syscon = MicrowattSYSCON(sys_clk_freq=clk_freq,
                                      mem_clk_freq=self.dram_clk_freq,
                                      core_clk_freq=core_clk_freq,
                                      has_uart=(uart_pins is not None),
                                      spi_offset=spi_offset,
                                      dram_addr=dram_offset)
        self._decoder.add(self.syscon.bus, addr=0xc0000000) # at 0xc000_0000

        if False:
            # SRAM (read-writeable BRAM)
            self.ram = SRAMPeripheral(size=4096)
            self._decoder.add(self.ram.bus, addr=0x8000000) # at 0x8000_0000

        # UART at 0xC000_2000, convert 32-bit bus down to 8-bit in an odd way
        if uart_pins is not None:
            # sigh actual UART in microwatt is 8-bit
            self.uart_irq = IRQLine()
            self.uart = UART16550(data_width=8, pins=uart_pins,
                                  features={'stall'},
                                  irq=self.uart_irq)
            # but (see soc.vhdl) 8-bit regs are addressed at 32-bit locations
            # strictly speaking this is a nmigen-soc "sparse" arrangement
            # which should be handled by MemoryMap, but needs investigation
            cvtuartbus = wishbone.Interface(addr_width=5, data_width=32,
                                            granularity=8,
                                            features={'stall'})
            umap = MemoryMap(addr_width=7, data_width=8, name="uart_map")
            cvtuartbus.memory_map = umap
            self._decoder.add(cvtuartbus, addr=uart_addr) # 16550 UART addr
            self.cvtuartbus = cvtuartbus
            self.intc.add_irq(self.uart.irq, index=uart_irqno)

        # SDRAM module using opencores sdr_ctrl
        """
        class MT48LC16M16(SDRModule):
            # geometry
            nbanks = 4
            nrows  = 8192
            ncols  = 512
            # timings
            technology_timings = _TechnologyTimings(tREFI=64e6/8192,
                                                    tWTR=(2, None),
                                                    tCCD=(1, None),
                                                    tRRD=(None, 15))
            speedgrade_timings = {"default": _SpeedgradeTimings(tRP=20,
                                                    tRCD=20,
                                                    tWR=15,
                                                    tRFC=(None, 66),
                                                    tFAW=None,
                                                    tRAS=44)}
        """

        # DRAM Module. first, create the (triple) modules:
        # * DDR PHY
        # * gram Core: presents PHY with a DFI Interface
        # * gram Bone (aka gram-with-wishbone) connects wishbone to DFI
        # from there it gets a little complicated because of supporting
        # several options: simulation, synchronous, and asynchronous clocks.
        # dram_clk_freq can *never* be set equal to clk_freq, if it is,
        # it's assumed to be synchronous, and the dram Domains need renaming

        if ddr_pins is not None: # or fpga == 'sim':
            ddrmodule = dram_cls(self.dram_clk_freq, "1:2") # match DDR3 P/N

            # remap both the sync domain (wherever it occurs) and
            # the sync2x domain, if dram frequency is specified and
            # not equal to the core clock
            drs = None
            if dram_clk_freq is not None or fpga == 'sim':
                drs = lambda x: x
            else:
                drs = DomainRenamer({"sync": "dramsync",
                                     "sync2x": "dramsync2x"})

            features = set()
            if dram_clk_freq is None:
                features.add("stall")

            # create the PHY (fake one for sim)
            if fpga == 'sim':
                settings = sim_ddr3_settings(self.dram_clk_freq)
                self.ddrphy = FakePHY(module=ddrmodule,
                                      settings=settings,
                                      verbosity=SDRAM_VERBOSE_DBG,
                                      clk_freq=self.dram_clk_freq)
            else:
                self.ddrphy = drs(ECP5DDRPHY(ddr_pins,
                                             #features=features,
                                             sys_clk_freq=self.dram_clk_freq))

            # create the core (bridge from PHY to DFI)
            dramcore = gramCore(phy=self.ddrphy,
                                geom_settings=ddrmodule.geom_settings,
                                timing_settings=ddrmodule.timing_settings,
                                #features=features,
                                clk_freq=self.dram_clk_freq)
            self.dramcore = drs(dramcore)

            # create the wishbone presentation (wishbone to DFI)
            drambone = gramWishbone(dramcore, features=features)
            self.drambone = drs(drambone)

        # this is the case where sys_clk === dram_clk. no ASync Bridge
        # needed, so just let the phy core and wb-dfi be connected
        # directly to WB decoder.  both are running in "sync" domain
        # (because of the DomainRenamer, above)

        if ddr_pins is not None and dram_clk_freq is None:
            self.ddrphy_bus = self.ddrphy.bus
            self.dramcore_bus = self.dramcore.bus
            self.drambone_bus = self.drambone.bus

        # this covers the case where sys_clk != dram_clk: three separate
        # ASync Bridges are constructed (!) and the interface that's to
        # be wired to the WB decoder is the async bus because that's running
        # in the "sync" domain.

        if ddr_pins is not None and dram_clk_freq is not None:
            # Set up Wishbone asynchronous bridge
            pabus = wishbone.Interface(addr_width=self.ddrphy.bus.addr_width,
                                       data_width=self.ddrphy.bus.data_width,
                                       granularity=self.ddrphy.bus.granularity,
                                       features={'stall'})
            self.ddrphy_bus = pabus
            self.ddrphy_bus.memory_map = self.ddrphy.bus.memory_map

            pabr = WBAsyncBridge(master_bus=self.ddrphy_bus,
                                 slave_bus=self.ddrphy.bus,
                                 master_clock_domain=None,
                                 slave_clock_domain="dramsync",
                                 address_width=self.ddrphy.bus.addr_width,
                                 data_width=self.ddrphy.bus.data_width,
                                 granularity=self.ddrphy.bus.granularity)
            self.ddrphy_async_br = pabr

            # Set up Wishbone asynchronous bridge
            dab = wishbone.Interface(addr_width=self.dramcore.bus.addr_width,
                                     data_width=self.dramcore.bus.data_width,
                                     granularity=self.dramcore.bus.granularity,
                                     features={'stall'})
            self.dramcore_bus = dab
            self.dramcore_bus.memory_map = self.dramcore.bus.memory_map

            dac = WBAsyncBridge(master_bus=self.dramcore_bus,
                                slave_bus=self.dramcore.bus,
                                master_clock_domain=None,
                                slave_clock_domain="dramsync",
                                address_width=self.dramcore.bus.addr_width,
                                data_width=self.dramcore.bus.data_width,
                                granularity=self.dramcore.bus.granularity)
            self.dramcore_async_br = dac

            # Set up Wishbone asynchronous bridge
            bab = wishbone.Interface(addr_width=self.drambone.bus.addr_width,
                                     data_width=self.drambone.bus.data_width,
                                     granularity=self.drambone.bus.granularity,
                                     features={'stall'})
            self.drambone_bus = bab
            self.drambone_bus.memory_map = self.drambone.bus.memory_map

            bab = WBAsyncBridge(master_bus=self.drambone_bus,
                                slave_bus=self.drambone.bus,
                                master_clock_domain=None,
                                slave_clock_domain="dramsync",
                                address_width=self.drambone.bus.addr_width,
                                data_width=self.drambone.bus.data_width,
                                granularity=self.drambone.bus.granularity)
            self.drambone_async_br = bab

        if ddr_pins is not None:
            # Add wishbone decoders
            self._decoder.add(self.dramcore_bus, addr=dramcore_addr)
            self._decoder.add(self.drambone_bus, addr=ddr_addr)
            self._decoder.add(self.ddrphy_bus, addr=ddrphy_addr)

        # additional SRAM at address if DRAM is not also at 0x0
        # (TODO, check Flash, and HyperRAM as well)
        if ((ddr_pins is None or ddr_addr != 0x0) and fw_addr != 0 and
            hyperram_addr[0] != 0x0):
            print ("SRAM 0x8000 at address 0x0")
            sram_width = 32
            self.sram = SRAMPeripheral(size=0x8000,
                                      data_width=sram_width,
                                      writable=True)
            self._decoder.add(self.sram.bus, addr=0x0) # RAM at 0x0

        # SPI controller
        if spi_0_pins is not None and fpga in ['sim',
                                             'isim',
                                             'rcs_arctic_tern_bmc_card',
                                             'orangecrab',
                                             'orangecrab_isim',
                                             'versa_ecp5',
                                             'versa_ecp5_85',
                                             'arty_a7']:
            # The Lattice ECP5 devices require special handling on the
            # dedicated SPI clock line, which is shared with the internal
            # SPI controller used for FPGA bitstream loading.
            spi0_is_lattice_ecp5_clk = False
            if fpga in ['versa_ecp5',
                        'versa_ecp5_85',
                        'rcs_arctic_tern_bmc_card',
                        'orangecrab',
                        'orangecrab_isim',
                        'isim']:
                spi0_is_lattice_ecp5_clk = True

            # Tercel contains two independent Wishbone regions, a
            # configuration region and the direct API access region,
            # Set the SPI 0 access region to 16MB, as the FPGA
            # bitstream Flash device is unlikely to be larger than this.
            # The main SPI Flash (SPI 1) should be set to at
            # least 28 bits (256MB) to allow the use of large 4BA devices.
            self.spi0 = Tercel(data_width=32, spi_region_addr_width=24,
                               adr_offset=spi0_addr,
                               features={'stall'},
                               clk_freq=clk_freq,
                               pins=spi_0_pins,
                               lattice_ecp5_usrmclk=spi0_is_lattice_ecp5_clk)
            self._decoder.add(self.spi0.bus, addr=spi0_addr)
            self._decoder.add(self.spi0.cfg_bus, addr=spi0_cfg_addr)

        # Ethernet MAC
        if ethmac_0_pins is not None and fpga in ['versa_ecp5',
                                                  'versa_ecp5_85',
                                                  'isim']: # not orangecrab
            self.eth_irq = IRQLine()
            # The OpenCores Ethernet MAC contains two independent Wishbone
            # interfaces, a slave (configuration) interface and a master (DMA)
            # interface.
            self.eth0 = EthMAC(pins=ethmac_0_pins, irq=self.eth_irq)
            self._arbiter.add(self.eth0.master_bus)
            self._decoder.add(self.eth0.slave_bus, addr=eth0_cfg_addr)
            self.intc.add_irq(self.eth0.irq, index=eth0_irqno)

        # HyperRAM modules *plural*. Assumes using a Quad PMOD by Piotr
        # Esden, sold by 1bitsquared, only doing one CS_N enable at the
        # moment
        self.hyperram = []
        for i, (pins, hraddr) in enumerate(zip(hyperram_pins, hyperram_addr)):
            hr = HyperRAM(io=pins, phy_kls=HyperRAMPHY,
                             name="hyperram%d" % i,
                             features={'stall'},
                             latency=7) # Winbond W956D8MBYA
            self._decoder.add(hr.bus, addr=hraddr)
            self.hyperram.append(hr)

        self.memory_map = self._decoder.bus.memory_map

        self.clk_freq = clk_freq
        self.fpga = fpga

    def elaborate(self, platform):
        m = Module()
        comb, sync = m.d.comb, m.d.sync

        # add the peripherals and clock-reset-generator
        if platform is not None and hasattr(self, "crg"):
            m.submodules.sysclk = self.crg

        if hasattr(self, "sram"):
            m.submodules.sram = self.sram
        if hasattr(self, "bootmem"):
            m.submodules.bootmem = self.bootmem
        m.submodules.syscon = self.syscon
        if hasattr(self, "ram"):
            m.submodules.ram = self.ram
        if hasattr(self, "uart"):
            m.submodules.uart = self.uart
            comb += self.uart.cts_i.eq(1)
            comb += self.uart.dsr_i.eq(1)
            comb += self.uart.ri_i.eq(0)
            comb += self.uart.dcd_i.eq(1)
            # sigh connect up the wishbone bus manually to deal with
            # the mis-match on the data.  nmigen-soc "sparse" MemoryMap
            # should be able to deal with this. TODO, investigate
            uartbus = self.uart.bus
            comb += uartbus.adr.eq(self.cvtuartbus.adr)
            comb += uartbus.stb.eq(self.cvtuartbus.stb)
            comb += uartbus.cyc.eq(self.cvtuartbus.cyc)
            comb += uartbus.sel.eq(self.cvtuartbus.sel)
            comb += uartbus.we.eq(self.cvtuartbus.we)
            comb += uartbus.dat_w.eq(self.cvtuartbus.dat_w) # drops 8..31
            comb += self.cvtuartbus.dat_r.eq(uartbus.dat_r) # drops 8..31
            comb += self.cvtuartbus.ack.eq(uartbus.ack)
            # aaand with the WB4-pipeline-to-WB3-classic mismatch, sigh
            comb += uartbus.stall.eq(uartbus.cyc & ~uartbus.ack)
            comb += self.cvtuartbus.stall.eq(uartbus.stall)
        if hasattr(self, "cpu"):
            m.submodules.intc = self.intc
            m.submodules.extcore = self.cpu
            m.submodules.dbuscvt = self.dbusdowncvt
            m.submodules.ibuscvt = self.ibusdowncvt

        m.submodules.arbiter = self._arbiter
        m.submodules.decoder = self._decoder
        if hasattr(self, "ddrphy"):
            m.submodules.ddrphy = self.ddrphy
            m.submodules.dramcore = self.dramcore
            m.submodules.drambone = drambone = self.drambone

            # add async wishbone bridges
            if hasattr(self, "ddrphy_async_br"):
                m.submodules.ddrphy_async_br = self.ddrphy_async_br
            if hasattr(self, "dramcore_async_br"):
                m.submodules.dramcore_async_br = self.dramcore_async_br
            if hasattr(self, "drambone_async_br"):
                m.submodules.drambone_async_br = self.drambone_async_br

            # grrr, same problem with WB async bridge: not WB4-pipe compliant
            dab = self.ddrphy_bus
            if hasattr(dab, "stall"):
                comb += dab.stall.eq(dab.cyc & ~dab.ack)
            dab = self.dramcore_bus
            if hasattr(dab, "stall"):
                comb += dab.stall.eq(dab.cyc & ~dab.ack)
            dab = self.drambone_bus
            comb += dab.stall.eq(dab.cyc & ~dab.ack)

            # add wb async bridge verilog source. assumes directory structure
            # where bridge has been checked out in a common subdirectory with:
            # git clone https://github.com/alexforencich/verilog-wishbone.git
            # git checkout d1fa24a0
            verilog_wishbone = "../../verilog-wishbone/rtl"
            pth = os.path.split(__file__)[0]
            pth = os.path.join(pth, verilog_wishbone)
            fname = os.path.abspath(pth)
            print (fname)
            if hasattr(self, "ddrphy_async_br"):
                self.dramcore_async_br.add_verilog_source(fname, platform)
            if hasattr(self, "drambone_async_br"):
                self.drambone_async_br.add_verilog_source(fname, platform)

        # add hyperram module
        for i, hr in enumerate(self.hyperram):
            m.submodules["hyperram%d" % i] = hr
            # grrr, same problem with hyperram: not WB4-pipe compliant
            comb += hr.bus.stall.eq(hr.bus.cyc & ~hr.bus.ack)
            # reset
            if self.fpga == 'arty_a7':
                comb += hr.phy.rst_n.eq(ResetSignal())

        # add blinky lights so we know FPGA is alive
        if platform is not None:
            m.submodules.blinky = Blinky()

        # connect the arbiter (of wishbone masters)
        # to the decoder (addressing wishbone slaves)
        comb += self._arbiter.bus.connect(self._decoder.bus)

        if hasattr(self, "cpu"):
            m.submodules.xics_icp = icp = self.xics_icp
            m.submodules.xics_ics = ics = self.xics_ics
            comb += icp.ics_i.eq(ics.icp_o)           # connect ICS to ICP
            comb += self.cpu.irq.eq(icp.core_irq_o) # connect ICP to core

            # wire up the CPU interrupts from the GenericInterrupt
            comb += self.int_level_i.eq(self.intc.ip)

            # grrr
            comb += self.pbus.stall.eq(self.pbus.cyc & ~self.pbus.ack)
            comb += self.sbus.stall.eq(self.sbus.cyc & ~self.sbus.ack)

            # and also wire up make_wb_layout() to wishbone.Interface.
            # really, XICS_ICS and XICS_ICP both need to be converted
            # to use wishbone.Interface and this all goes
            comb += icp.bus.adr.eq(self.pbus.adr)
            comb += icp.bus.dat_w.eq(self.pbus.dat_w)
            comb += icp.bus.cyc.eq(self.pbus.cyc)
            comb += icp.bus.stb.eq(self.pbus.stb)
            comb += icp.bus.we.eq(self.pbus.we)
            comb += self.pbus.ack.eq(icp.bus.ack)
            comb += self.pbus.dat_r.eq(icp.bus.dat_r)
            comb += ics.bus.adr.eq(self.sbus.adr)
            comb += ics.bus.dat_w.eq(self.sbus.dat_w)
            comb += ics.bus.cyc.eq(self.sbus.cyc)
            comb += ics.bus.stb.eq(self.sbus.stb)
            comb += ics.bus.we.eq(self.sbus.we)
            comb += self.sbus.ack.eq(ics.bus.ack)
            comb += self.sbus.dat_r.eq(ics.bus.dat_r)

        if platform is None:
            return m

        # add uart16550 verilog source. assumes a directory
        # structure where ls2 has been checked out in a common
        # subdirectory as:
        # git clone https://github.com/freecores/uart16550
        opencores_16550 = "../../uart16550/rtl/verilog"
        pth = os.path.split(__file__)[0]
        pth = os.path.join(pth, opencores_16550)
        fname = os.path.abspath(pth)
        print (fname)
        self.uart.add_verilog_source(fname, platform)

        if hasattr(self, "spi0"):
            # add spi submodule
            m.submodules.spi0 = spi = self.spi0
            # gonna drive me nuts, this.
            comb += spi.bus.stall.eq(spi.bus.cyc & ~spi.bus.ack)
            comb += spi.cfg_bus.stall.eq(spi.cfg_bus.cyc & ~spi.cfg_bus.ack)

            # add Tercel verilog source. assumes a directory structure where
            # microwatt has been checked out in a common subdirectory with:
            # git clone https://git.libre-soc.org/git/microwatt.git tercel-qspi
            # git checkout 882ace781e4
            raptor_tercel = "../../tercel-qspi/tercel"
            pth = os.path.split(__file__)[0]
            pth = os.path.join(pth, raptor_tercel)
            fname = os.path.abspath(pth)
            print (fname)
            self.spi0.add_verilog_source(fname, platform)

        if hasattr(self, "eth0"):
            # add ethernet submodule
            m.submodules.eth0 = ethmac = self.eth0

            # add EthMAC verilog source. assumes a directory
            # structure where the opencores ethmac has been checked out
            # in a common subdirectory as:
            # git clone https://github.com/freecores/ethmac
            opencores_ethmac = "../../ethmac/rtl/verilog"
            pth = os.path.split(__file__)[0]
            pth = os.path.join(pth, opencores_ethmac)
            fname = os.path.abspath(pth)
            print (fname)
            self.eth0.add_verilog_source(fname, platform)

        # add the main core
        pth = os.path.split(__file__)[0]
        pth = os.path.join(pth, '../external_core_top.v')
        fname = os.path.abspath(pth)
        with open(fname) as f:
            platform.add_file(fname, f)

        return m

    def ports(self):
        # puzzlingly the only IO ports needed are peripheral pins,
        # and at the moment that's just UART tx/rx.
        ports = []
        ports += [self.uart.tx_o, self.uart.rx_i]
        for hr in self.hyperram:
            ports += list(hr.ports())
        if hasattr(self, "ddrphy"):
            if hasattr(self.ddrphy, "pads"): # real PHY
                ports += list(self.ddrphy.pads.fields.values())
            else: # FakePHY, get at the dfii pads, stops deletion of nets
                for phase in self.dramcore.dfii.master.phases:
                    print ("dfi master", phase)
                    ports += list(phase.fields.values())
                for phase in self.dramcore.dfii.slave.phases:
                    print ("dfi master", phase)
                    ports += list(phase.fields.values())
                for phase in self.dramcore.dfii._inti.phases:
                    print ("dfi master", phase)
                    ports += list(phase.fields.values())
        ports += [ClockSignal(), ResetSignal()]
        return ports

def build_platform(fpga, firmware):

    # create a platform selected from the toolchain.
    platform_kls =  {'versa_ecp5': VersaECP5Platform,
                     'versa_ecp5_85': VersaECP5Platform85,
                     'ulx3s': ULX3S_85F_Platform,
                     'orangecrab': OrangeCrabR0_2_85k_Platform,
                     'arty_a7': ArtyA7_100Platform,
                     'nexys_video': NexysVideoPlatform,
                     'isim': IcarusVersaPlatform,
                     'orangecrab_isim': IcarusVersaPlatform,
                     'rcs_arctic_tern_bmc_card':None, #TODO
                     'sim': None,
                    }[fpga]
    toolchain = {'arty_a7': "yosys_nextpnr",
                 'nexys_video': "yosys_nextpnr",
                 'versa_ecp5': 'Trellis',
                 'versa_ecp5_85': 'Trellis',
                 'orangecrab_isim': 'Trellis',
                 'orangecrab': 'Trellis',
                 'isim': 'Trellis',
                 'ulx3s': 'Trellis',
                 'rcs_arctic_tern_bmc_card': 'Trellis',
                 'sim': None,
                }.get(fpga, None)
    dram_cls = {'arty_a7': None,
                 'nexys_video': None,
                 'versa_ecp5': MT41K64M16,
                 'versa_ecp5_85': MT41K64M16,
                 'orangecrab': MT41K64M16,
                 'orangecrab_isim': MT41K64M16,
                 #'versa_ecp5': MT41K256M16,
                 'ulx3s': None,
                 'rcs_arctic_tern_bmc_card': None, #TODO
                 'sim': MT41K256M16,
                 'isim': MT41K64M16,
                }.get(fpga, None)
    if platform_kls is not None:
        platform = platform_kls(toolchain=toolchain)
        if fpga == 'versa_ecp5_85':
            platform.speed = "7" # HACK. speed grade 7, sigh
    else:
        platform = None

    print ("platform", fpga, firmware, platform)

    # set clock frequency
    clk_freq = 70e6
    dram_clk_freq = None
    if fpga == 'sim':
        clk_freq = 100e6
        dram_clk_freq = clk_freq
    if fpga == 'isim':
        clk_freq = 50e6 # below 50 mhz, stops DRAM being enabled
        #dram_clk_freq = clk_freq
        dram_clk_freq = 100e6
    if fpga == 'versa_ecp5':
        clk_freq = 50e6 # crank right down to timing threshold
        #dram_clk_freq = 55e6
    if fpga == 'versa_ecp5_85':
        # 50MHz works.  100MHz works.  55MHz does NOT work.
        # Stick with multiples of 50MHz...
        clk_freq = 50e6
        dram_clk_freq = 100e6
    if fpga == 'arty_a7':
        clk_freq = 27.0e6 # urrr "working" with the QSPI core (25 mhz does not)
    if fpga == 'nexys_video':
        clk_freq = 25.0e6
    if fpga == 'ulx3s':
        clk_freq = 40.0e6
    if fpga == 'orangecrab' or fpga=='orangecrab_isim':
        clk_freq = 50e6
    core_clk_freq = clk_freq

    # merge dram_clk_freq with clk_freq if the same
    if clk_freq == dram_clk_freq:
        dram_clk_freq = None

    # see if dram can be enabled
    enable_dram = False
    if dram_clk_freq is not None and dram_clk_freq >= 50e6:
        enable_dram = True
    if dram_clk_freq is None and clk_freq >= 50e6:
        enable_dram = True

    # select a firmware address
    fw_addr = None
    if firmware is not None:
        fw_addr = 0xff00_0000 # firmware at HI address, now

    print ("fpga", fpga, "firmware", firmware)

    # get UART resource pins
    if platform is not None:
        if fpga=="orangecrab":
            # assumes an FT232 USB-UART soldered onto these two pins.
            orangecrab_uart = UARTResource(0, rx="M18", tx="N17")
            platform.add_resources([orangecrab_uart])

        uart_pins = platform.request("uart", 0)
    else:
        uart_pins = Record([('tx', 1), ('rx', 1)], name="uart_0")

    # get DDR resource pins, disable if clock frequency is below 50 mhz for now
    ddr_pins = None
    if (enable_dram and platform is not None and
        fpga in ['versa_ecp5', 'versa_ecp5_85', 'isim',
                 'orangecrab','orangecrab_isim']): # not yet 'arty_a7',
        ddr_pins = platform.request("ddr3", 0,
                                    dir={"dq":"-", "dqs":"-"},
                                    xdr={"rst": 4, "clk":4, "a":4,
                                         "ba":4, "clk_en":4,
                                         "odt":4, "ras":4, "cas":4, "we":4,
                                         "cs": 4})
    print ("ddr pins", ddr_pins)

    # Get SPI resource pins
    spi_0_pins = None
    if False and platform is not None and \
       fpga in ['versa_ecp5', 'versa_ecp5_85', 'isim']:
        # Override here to get FlashResource out of the way and enable Tercel
        # direct access to the SPI flash.
        # each pin needs a separate direction control
        spi_0_ios = [
            Resource("spi_0", 0,
                     Subsignal("dq0",   Pins("W2", dir="io")),
                     Subsignal("dq1",   Pins("V2", dir="io")),
                     Subsignal("dq2",   Pins("Y2", dir="io")),
                     Subsignal("dq3",   Pins("W1", dir="io")),
                     Subsignal("cs_n", Pins("R2", dir="o")),
                     Attrs(PULLMODE="NONE", DRIVE="4", IO_TYPE="LVCMOS33"))
        ]
        platform.add_resources(spi_0_ios)
        spi_0_pins = platform.request("spi_0", 0, dir={"cs_n":"o"},
                                                  xdr={"dq0":1, "dq1": 1,
                                                       "dq2":1, "dq3": 1,
                                                       "cs_n":0})

    if platform is not None and \
       fpga in ['arty_a7']:
        # each pin needs a separate direction control
        spi_0_ios = [
            Resource("spi_0", 0,
                     Subsignal("dq0",  Pins("K17", dir="io")),
                     Subsignal("dq1",  Pins("K18", dir="io")),
                     Subsignal("dq2",  Pins("L14", dir="io")),
                     Subsignal("dq3",  Pins("M14", dir="io")),
                     Subsignal("cs_n", Pins("L13", dir="o")),
                     Subsignal("clk",  Pins("L16", dir="o")),
                     # drive support is currently broken on
                     # nextpnx-xilinx/openxc7. Add back DRIVE="4" below
                     # when upstream fixes it.
                     # See: https://github.com/openXC7/nextpnr-xilinx/issues/7
                     Attrs(PULLMODE="NONE", IOSTANDARD="LVCMOS33"))
        ]
        platform.add_resources(spi_0_ios)
        spi_0_pins = platform.request("spi_0", 0)

    orangecrab_enable_spi = False
    if orangecrab_enable_spi and platform is not None and \
       fpga in ['orangecrab']:
       # spi_flash_mosi   <= spi_sdat_o(0) when spi_sdat_oe(0) = '1' else 'Z';
       # spi_flash_miso   <= spi_sdat_o(1) when spi_sdat_oe(1) = '1' else 'Z';
       # spi_flash_wp_n   <= spi_sdat_o(2) when spi_sdat_oe(2) = '1' else 'Z';
       # spi_flash_hold_n <= spi_sdat_o(3) when spi_sdat_oe(3) = '1' else 'Z';
       # cs_n="U17", clk="U16", miso="T18", mosi="U18", wp_n="R18", hold_n="N18"
        # each pin needs a separate direction control
        spi_0_ios = [
            Resource("spi_0", 0,
                     Subsignal("dq0",  Pins("U18", dir="io")), #mosi
                     Subsignal("dq1",  Pins("T18", dir="io")), #miso
                     Subsignal("dq2",  Pins("R18", dir="io")), #wp_n
                     Subsignal("dq3",  Pins("N18", dir="io")), #hold_n
                     # We use USRMCLK instead for clk
                     # todo: read docs
                     Subsignal("cs_n", Pins("U17", dir="o")),
                     # Subsignal("clk",  Pins("U16", dir="o")),
                     Attrs(PULLMODE="NONE", DRIVE="4", IO_TYPE="LVCMOS33"))
        ]
        platform.add_resources(spi_0_ios)
        spi_0_pins = platform.request("spi_0", 0, dir={"cs_n":"o"},
                                                  xdr={"dq0":1, "dq1": 1,
                                                       "dq2":1, "dq3": 1,
                                                       "cs_n":0})

    print ("spiflash pins", spi_0_pins)

    # Get Ethernet RMII resource pins
    ethmac_0_pins = None
    if False and platform is not None and \
       fpga in ['versa_ecp5', 'versa_ecp5_85', 'isim']:
        # Mainly on X3 connector, MDIO on X4 due to lack of pins
        ethmac_0_ios = [
            Resource("ethmac_0", 0,
                     Subsignal("mtx_clk",   Pins("B19", dir="i")),
                     Subsignal("mtxd",      Pins("B12 B9 E6 D6", dir="o")),
                     Subsignal("mtxen",     Pins("E7", dir="o")),
                     Subsignal("mtxerr",    Pins("D7", dir="o")),
                     Subsignal("mrx_clk",   Pins("B11", dir="i")),
                     Subsignal("mrxd",      Pins("B6 E9 D9 B8", dir="i")),
                     Subsignal("mrxdv",     Pins("C8", dir="i")),
                     Subsignal("mrxerr",    Pins("D8", dir="i")),
                     Subsignal("mcoll",     Pins("E8", dir="i")),
                     Subsignal("mcrs",      Pins("C7", dir="i")),
                     Subsignal("mdc",       Pins("B18", dir="o")),
                     Subsignal("md",        Pins("A18", dir="io")),
                     Attrs(PULLMODE="NONE", DRIVE="8", SLEWRATE="FAST",
                           IO_TYPE="LVCMOS33"))
        ]
        platform.add_resources(ethmac_0_ios)
        ethmac_0_pins = platform.request("ethmac_0", 0,
                                        dir={"mtx_clk":"i", "mtxd":"o",
                                             "mtxen":"o",
                                             "mtxerr":"o", "mrx_clk":"i",
                                             "mrxd":"i",
                                             "mrxdv":"i", "mrxerr":"i",
                                             "mcoll":"i",
                                             "mcrs":"i", "mdc":"o", "md":"io"},
                                        xdr={"mtx_clk": 0, "mtxd": 0,
                                             "mtxen": 0,
                                             "mtxerr": 0, "mrx_clk": 0,
                                             "mrxd": 0,
                                             "mrxdv": 0, "mrxerr": 0,
                                             "mcoll": 0,
                                             "mcrs": 0, "mdc": 0, "md": 0})
    print ("ethmac pins", ethmac_0_pins)

    # Get HyperRAM pins
    hyperram_pins = []
    hyperram_addr = [0xa000_0000]
    if platform is None:
        hyperram_pins = [HyperRAMPads()]
    elif fpga in ['isim']:
        hyperram_ios = HyperRAMResource(0, cs_n="B13",
                                        dq="E14 C10 B10 E12 D12 A9 D11 D14",
                                        rwds="C14", rst_n="E13", ck_p="D13",
                                        attrs=Attrs(IO_TYPE="LVCMOS33"))
        platform.add_resources(hyperram_ios)
        hyperram_pins = [platform.request("hyperram")]
        print ("isim a7 hyperram", hyperram_ios)
    # Digilent Arty A7-100t
    elif platform is not None and fpga in ['arty_a7']:
        hyperram_ios = HyperRAMResource(0, cs_n="B11 B18 G13 D13",
                                        dq="E15 E16 D15 C15 J15 K15 J18 J17",
                                        rwds="K16", rst_n="A18", ck_p="A11",
                                        # ck_n="D12" - for later (DDR)
                                        attrs=Attrs(IOSTANDARD="LVCMOS33"))
        platform.add_resources(hyperram_ios)
        hyperram_ios = HyperRAMResource(1, cs_n="V12 V14 U12 U14",
                                        dq="D4 D3 F4 F3 G2 H2 D2 E2",
                                        rwds="U13", rst_n="T13", ck_p="V10",
                                        # ck_n="V11" - for later (DDR)
                                        attrs=Attrs(IOSTANDARD="LVCMOS33"))
        platform.add_resources(hyperram_ios)
        hyperram_pins = [platform.request("hyperram", 0),
                         platform.request("hyperram", 1)]
        print ("arty a7 hyperram", hyperram_ios)
        hyperram_addr=[0x0000_0000,  # HYPERRAM_BASE1
                       0x0200_0000] # HYPERRAM_BASE2
    # VERSA ECP5
    elif False and platform is not None and fpga in \
                ['versa_ecp5', 'versa_ecp5_85']:
        hyperram_ios = HyperRAMResource(0, cs_n="B13",
                                        dq="E14 C10 B10 E12 D12 A9 D11 D14",
                                        rwds="C14", rst_n="E13", ck_p="D13",
                                        attrs=Attrs(IO_TYPE="LVCMOS33"))
        platform.add_resources(hyperram_ios)
        hyperram_pins = [platform.request("hyperram")]
        print ("versa ecp5 hyperram", hyperram_ios)
    print ("hyperram pins", hyperram_pins)

    # set up the SOC
    soc = DDR3SoC(fpga=fpga, dram_cls=dram_cls,
                  # check microwatt_soc.h for these
                  ddrphy_addr=0xfff00000,   # DRAM_INIT_BASE, PHY address
                  dramcore_addr=0xc8000000, # DRAM_CTRL_BASE
                  ddr_addr=0x00000000,      # DRAM_BASE
                  spi0_addr=0xf0000000,     # SPI0_BASE
                  spi0_cfg_addr=0xc0006000, # SPI0_CTRL_BASE
                  eth0_cfg_addr=0xc000c000, # ETH0_CTRL_BASE (4k)
                  eth0_irqno=1,             # ETH0_IRQ number (match microwatt)
                  hyperram_addr=hyperram_addr, # determined above
                  fw_addr=fw_addr,
                  #fw_addr=None,
                  ddr_pins=ddr_pins,
                  uart_pins=uart_pins,
                  uart_irqno=0,             # UART_IRQ number (match microwatt)
                  uart_addr=0xc0002000, # UART0_ADDR
                  spi_0_pins=spi_0_pins,
                  ethmac_0_pins=ethmac_0_pins,
                  hyperram_pins=hyperram_pins,
                  firmware=firmware,
                  xics_icp_addr=0xc000_4000, # XICS_ICP_BASE
                  xics_ics_addr=0xc000_5000, # XICS_ICS_BASE
                  clk_freq=clk_freq,
                  dram_clk_freq=dram_clk_freq,
                  core_clk_freq=core_clk_freq,
                  add_cpu=True)

    if toolchain == 'Trellis':
        # add -abc9 option to yosys synth_ecp5
        os.environ['NMIGEN_synth_opts'] = '-abc9'              # speed
        # os.environ['NMIGEN_synth_opts'] = '-nowidelut'       # size

    if toolchain == 'yosys_nextpnr':
        # add --seed 2 to arty a7 compile-time options
        freq = clk_freq/1e6
        os.environ['NMIGEN_nextpnr_opts'] = '--seed 3 --freq %.1f' % freq
        os.environ['NMIGEN_nextpnr_opts'] += ' --timing-allow-fail'

    if platform is not None:
        # build and upload it
        if fpga == 'isim' or fpga == 'orangecrab_isim':
            platform.build(soc, do_program=False,
                                do_build=True, build_dir="build_simsoc")
        else:
            platform.build(soc, do_program=True)
    else:
        # for now, generate verilog
        vl = verilog.convert(soc, ports=soc.ports())
        with open("ls2.v", "w") as f:
            f.write(vl)


# urrr this gets exec()d by the build process without arguments
# which screws up.  use the arty_a7_ls2.py etc. with no arguments
if __name__ == '__main__':
    fpga = None
    firmware = None
    if len(sys.argv) >= 2:
        fpga = sys.argv[1]
    if len(sys.argv) >= 3:
        firmware = sys.argv[2]
    build_platform(fpga, firmware)