move "exception happened" detection from TestIssuer to Core

[soc.git] / src / soc / simple / issuer.py

"""simple core issuer

not in any way intended for production use.  this runs a FSM that:

* reads the Program Counter from StateRegs
* reads an instruction from a fixed-size Test Memory
* issues it to the Simple Core
* waits for it to complete
* increments the PC
* does it all over again

the purpose of this module is to verify the functional correctness
of the Function Units in the absolute simplest and clearest possible
way, and to at provide something that can be further incrementally
improved.
"""

from nmigen import (Elaboratable, Module, Signal, ClockSignal, ResetSignal,
                    ClockDomain, DomainRenamer, Mux, Const, Repl, Cat)
from nmigen.cli import rtlil
from nmigen.cli import main
import sys

from nmigen.lib.coding import PriorityEncoder

from openpower.decoder.power_decoder import create_pdecode
from openpower.decoder.power_decoder2 import PowerDecode2, SVP64PrefixDecoder
from openpower.decoder.decode2execute1 import IssuerDecode2ToOperand
from openpower.decoder.decode2execute1 import Data
from openpower.decoder.power_enums import (MicrOp, SVP64PredInt, SVP64PredCR,
                                     SVP64PredMode)
from openpower.state import CoreState
from openpower.consts import (CR, SVP64CROffs)
from soc.experiment.testmem import TestMemory # test only for instructions
from soc.regfile.regfiles import StateRegs, FastRegs
from soc.simple.core import NonProductionCore
from soc.config.test.test_loadstore import TestMemPspec
from soc.config.ifetch import ConfigFetchUnit
from soc.debug.dmi import CoreDebug, DMIInterface
from soc.debug.jtag import JTAG
from soc.config.pinouts import get_pinspecs
from soc.interrupts.xics import XICS_ICP, XICS_ICS
from soc.bus.simple_gpio import SimpleGPIO
from soc.bus.SPBlock512W64B8W import SPBlock512W64B8W
from soc.clock.select import ClockSelect
from soc.clock.dummypll import DummyPLL
from openpower.sv.svstate import SVSTATERec


from nmutil.util import rising_edge

def get_insn(f_instr_o, pc):
    if f_instr_o.width == 32:
        return f_instr_o
    else:
        # 64-bit: bit 2 of pc decides which word to select
        return f_instr_o.word_select(pc[2], 32)

# gets state input or reads from state regfile
def state_get(m, core_rst, state_i, name, regfile, regnum):
    comb = m.d.comb
    sync = m.d.sync
    # read the PC
    res = Signal(64, reset_less=True, name=name)
    res_ok_delay = Signal(name="%s_ok_delay" % name)
    with m.If(~core_rst):
        sync += res_ok_delay.eq(~state_i.ok)
        with m.If(state_i.ok):
            # incoming override (start from pc_i)
            comb += res.eq(state_i.data)
        with m.Else():
            # otherwise read StateRegs regfile for PC...
            comb += regfile.ren.eq(1<<regnum)
        # ... but on a 1-clock delay
        with m.If(res_ok_delay):
            comb += res.eq(regfile.o_data)
    return res

def get_predint(m, mask, name):
    """decode SVP64 predicate integer mask field to reg number and invert
    this is identical to the equivalent function in ISACaller except that
    it doesn't read the INT directly, it just decodes "what needs to be done"
    i.e. which INT reg, whether it is shifted and whether it is bit-inverted.

    * all1s is set to indicate that no mask is to be applied.
    * regread indicates the GPR register number to be read
    * invert is set to indicate that the register value is to be inverted
    * unary indicates that the contents of the register is to be shifted 1<<r3
    """
    comb = m.d.comb
    regread = Signal(5, name=name+"regread")
    invert = Signal(name=name+"invert")
    unary = Signal(name=name+"unary")
    all1s = Signal(name=name+"all1s")
    with m.Switch(mask):
        with m.Case(SVP64PredInt.ALWAYS.value):
            comb += all1s.eq(1)      # use 0b1111 (all ones)
        with m.Case(SVP64PredInt.R3_UNARY.value):
            comb += regread.eq(3)
            comb += unary.eq(1)        # 1<<r3 - shift r3 (single bit)
        with m.Case(SVP64PredInt.R3.value):
            comb += regread.eq(3)
        with m.Case(SVP64PredInt.R3_N.value):
            comb += regread.eq(3)
            comb += invert.eq(1)
        with m.Case(SVP64PredInt.R10.value):
            comb += regread.eq(10)
        with m.Case(SVP64PredInt.R10_N.value):
            comb += regread.eq(10)
            comb += invert.eq(1)
        with m.Case(SVP64PredInt.R30.value):
            comb += regread.eq(30)
        with m.Case(SVP64PredInt.R30_N.value):
            comb += regread.eq(30)
            comb += invert.eq(1)
    return regread, invert, unary, all1s

def get_predcr(m, mask, name):
    """decode SVP64 predicate CR to reg number field and invert status
    this is identical to _get_predcr in ISACaller
    """
    comb = m.d.comb
    idx = Signal(2, name=name+"idx")
    invert = Signal(name=name+"crinvert")
    with m.Switch(mask):
        with m.Case(SVP64PredCR.LT.value):
            comb += idx.eq(CR.LT)
            comb += invert.eq(0)
        with m.Case(SVP64PredCR.GE.value):
            comb += idx.eq(CR.LT)
            comb += invert.eq(1)
        with m.Case(SVP64PredCR.GT.value):
            comb += idx.eq(CR.GT)
            comb += invert.eq(0)
        with m.Case(SVP64PredCR.LE.value):
            comb += idx.eq(CR.GT)
            comb += invert.eq(1)
        with m.Case(SVP64PredCR.EQ.value):
            comb += idx.eq(CR.EQ)
            comb += invert.eq(0)
        with m.Case(SVP64PredCR.NE.value):
            comb += idx.eq(CR.EQ)
            comb += invert.eq(1)
        with m.Case(SVP64PredCR.SO.value):
            comb += idx.eq(CR.SO)
            comb += invert.eq(0)
        with m.Case(SVP64PredCR.NS.value):
            comb += idx.eq(CR.SO)
            comb += invert.eq(1)
    return idx, invert


class TestIssuerInternal(Elaboratable):
    """TestIssuer - reads instructions from TestMemory and issues them

    efficiency and speed is not the main goal here: functional correctness
    and code clarity is.  optimisations (which almost 100% interfere with
    easy understanding) come later.
    """
    def __init__(self, pspec):

        # test is SVP64 is to be enabled
        self.svp64_en = hasattr(pspec, "svp64") and (pspec.svp64 == True)

        # and if regfiles are reduced
        self.regreduce_en = (hasattr(pspec, "regreduce") and
                                            (pspec.regreduce == True))

        # JTAG interface.  add this right at the start because if it's
        # added it *modifies* the pspec, by adding enable/disable signals
        # for parts of the rest of the core
        self.jtag_en = hasattr(pspec, "debug") and pspec.debug == 'jtag'
        self.dbg_domain = "sync" # sigh "dbgsunc" too problematic
        #self.dbg_domain = "dbgsync" # domain for DMI/JTAG clock
        if self.jtag_en:
            # XXX MUST keep this up-to-date with litex, and
            # soc-cocotb-sim, and err.. all needs sorting out, argh
            subset = ['uart',
                      'mtwi',
                      'eint', 'gpio', 'mspi0',
                      # 'mspi1', - disabled for now
                      # 'pwm', 'sd0', - disabled for now
                       'sdr']
            self.jtag = JTAG(get_pinspecs(subset=subset),
                             domain=self.dbg_domain)
            # add signals to pspec to enable/disable icache and dcache
            # (or data and intstruction wishbone if icache/dcache not included)
            # https://bugs.libre-soc.org/show_bug.cgi?id=520
            # TODO: do we actually care if these are not domain-synchronised?
            # honestly probably not.
            pspec.wb_icache_en = self.jtag.wb_icache_en
            pspec.wb_dcache_en = self.jtag.wb_dcache_en
            self.wb_sram_en = self.jtag.wb_sram_en
        else:
            self.wb_sram_en = Const(1)

        # add 4k sram blocks?
        self.sram4x4k = (hasattr(pspec, "sram4x4kblock") and
                         pspec.sram4x4kblock == True)
        if self.sram4x4k:
            self.sram4k = []
            for i in range(4):
                self.sram4k.append(SPBlock512W64B8W(name="sram4k_%d" % i,
                                                    #features={'err'}
                                                    ))

        # add interrupt controller?
        self.xics = hasattr(pspec, "xics") and pspec.xics == True
        if self.xics:
            self.xics_icp = XICS_ICP()
            self.xics_ics = XICS_ICS()
            self.int_level_i = self.xics_ics.int_level_i

        # add GPIO peripheral?
        self.gpio = hasattr(pspec, "gpio") and pspec.gpio == True
        if self.gpio:
            self.simple_gpio = SimpleGPIO()
            self.gpio_o = self.simple_gpio.gpio_o

        # main instruction core.  suitable for prototyping / demo only
        self.core = core = NonProductionCore(pspec)
        self.core_rst = ResetSignal("coresync")

        # instruction decoder.  goes into Trap Record
        #pdecode = create_pdecode()
        self.cur_state = CoreState("cur") # current state (MSR/PC/SVSTATE)
        self.pdecode2 = PowerDecode2(None, state=self.cur_state,
                                     opkls=IssuerDecode2ToOperand,
                                     svp64_en=self.svp64_en,
                                     regreduce_en=self.regreduce_en)
        pdecode = self.pdecode2.dec

        if self.svp64_en:
            self.svp64 = SVP64PrefixDecoder() # for decoding SVP64 prefix

        # Test Instruction memory
        self.imem = ConfigFetchUnit(pspec).fu

        # DMI interface
        self.dbg = CoreDebug()

        # instruction go/monitor
        self.pc_o = Signal(64, reset_less=True)
        self.pc_i = Data(64, "pc_i") # set "ok" to indicate "please change me"
        self.svstate_i = Data(64, "svstate_i") # ditto
        self.core_bigendian_i = Signal() # TODO: set based on MSR.LE
        self.busy_o = Signal(reset_less=True)
        self.memerr_o = Signal(reset_less=True)

        # STATE regfile read /write ports for PC, MSR, SVSTATE
        staterf = self.core.regs.rf['state']
        self.state_r_pc = staterf.r_ports['cia'] # PC rd
        self.state_w_pc = staterf.w_ports['d_wr1'] # PC wr
        self.state_r_msr = staterf.r_ports['msr'] # MSR rd
        self.state_r_sv = staterf.r_ports['sv'] # SVSTATE rd
        self.state_w_sv = staterf.w_ports['sv'] # SVSTATE wr

        # DMI interface access
        intrf = self.core.regs.rf['int']
        crrf = self.core.regs.rf['cr']
        xerrf = self.core.regs.rf['xer']
        self.int_r = intrf.r_ports['dmi'] # INT read
        self.cr_r = crrf.r_ports['full_cr_dbg'] # CR read
        self.xer_r = xerrf.r_ports['full_xer'] # XER read

        if self.svp64_en:
            # for predication
            self.int_pred = intrf.r_ports['pred'] # INT predicate read
            self.cr_pred = crrf.r_ports['cr_pred'] # CR predicate read

        # hack method of keeping an eye on whether branch/trap set the PC
        self.state_nia = self.core.regs.rf['state'].w_ports['nia']
        self.state_nia.wen.name = 'state_nia_wen'

        # pulse to synchronize the simulator at instruction end
        self.insn_done = Signal()

        if self.svp64_en:
            # store copies of predicate masks
            self.srcmask = Signal(64)
            self.dstmask = Signal(64)

    def fetch_fsm(self, m, core, pc, svstate, nia, is_svp64_mode,
                        fetch_pc_o_ready, fetch_pc_i_valid,
                        fetch_insn_o_valid, fetch_insn_i_ready):
        """fetch FSM

        this FSM performs fetch of raw instruction data, partial-decodes
        it 32-bit at a time to detect SVP64 prefixes, and will optionally
        read a 2nd 32-bit quantity if that occurs.
        """
        comb = m.d.comb
        sync = m.d.sync
        pdecode2 = self.pdecode2
        cur_state = self.cur_state
        dec_opcode_i = pdecode2.dec.raw_opcode_in # raw opcode

        msr_read = Signal(reset=1)

        with m.FSM(name='fetch_fsm'):

            # waiting (zzz)
            with m.State("IDLE"):
                comb += fetch_pc_o_ready.eq(1)
                with m.If(fetch_pc_i_valid):
                    # instruction allowed to go: start by reading the PC
                    # capture the PC and also drop it into Insn Memory
                    # we have joined a pair of combinatorial memory
                    # lookups together.  this is Generally Bad.
                    comb += self.imem.a_pc_i.eq(pc)
                    comb += self.imem.a_i_valid.eq(1)
                    comb += self.imem.f_i_valid.eq(1)
                    sync += cur_state.pc.eq(pc)
                    sync += cur_state.svstate.eq(svstate) # and svstate

                    # initiate read of MSR. arrives one clock later
                    comb += self.state_r_msr.ren.eq(1 << StateRegs.MSR)
                    sync += msr_read.eq(0)

                    m.next = "INSN_READ"  # move to "wait for bus" phase

            # dummy pause to find out why simulation is not keeping up
            with m.State("INSN_READ"):
                # one cycle later, msr/sv read arrives.  valid only once.
                with m.If(~msr_read):
                    sync += msr_read.eq(1) # yeah don't read it again
                    sync += cur_state.msr.eq(self.state_r_msr.o_data)
                with m.If(self.imem.f_busy_o): # zzz...
                    # busy: stay in wait-read
                    comb += self.imem.a_i_valid.eq(1)
                    comb += self.imem.f_i_valid.eq(1)
                with m.Else():
                    # not busy: instruction fetched
                    insn = get_insn(self.imem.f_instr_o, cur_state.pc)
                    if self.svp64_en:
                        svp64 = self.svp64
                        # decode the SVP64 prefix, if any
                        comb += svp64.raw_opcode_in.eq(insn)
                        comb += svp64.bigendian.eq(self.core_bigendian_i)
                        # pass the decoded prefix (if any) to PowerDecoder2
                        sync += pdecode2.sv_rm.eq(svp64.svp64_rm)
                        sync += pdecode2.is_svp64_mode.eq(is_svp64_mode)
                        # remember whether this is a prefixed instruction, so
                        # the FSM can readily loop when VL==0
                        sync += is_svp64_mode.eq(svp64.is_svp64_mode)
                        # calculate the address of the following instruction
                        insn_size = Mux(svp64.is_svp64_mode, 8, 4)
                        sync += nia.eq(cur_state.pc + insn_size)
                        with m.If(~svp64.is_svp64_mode):
                            # with no prefix, store the instruction
                            # and hand it directly to the next FSM
                            sync += dec_opcode_i.eq(insn)
                            m.next = "INSN_READY"
                        with m.Else():
                            # fetch the rest of the instruction from memory
                            comb += self.imem.a_pc_i.eq(cur_state.pc + 4)
                            comb += self.imem.a_i_valid.eq(1)
                            comb += self.imem.f_i_valid.eq(1)
                            m.next = "INSN_READ2"
                    else:
                        # not SVP64 - 32-bit only
                        sync += nia.eq(cur_state.pc + 4)
                        sync += dec_opcode_i.eq(insn)
                        m.next = "INSN_READY"

            with m.State("INSN_READ2"):
                with m.If(self.imem.f_busy_o):  # zzz...
                    # busy: stay in wait-read
                    comb += self.imem.a_i_valid.eq(1)
                    comb += self.imem.f_i_valid.eq(1)
                with m.Else():
                    # not busy: instruction fetched
                    insn = get_insn(self.imem.f_instr_o, cur_state.pc+4)
                    sync += dec_opcode_i.eq(insn)
                    m.next = "INSN_READY"
                    # TODO: probably can start looking at pdecode2.rm_dec
                    # here or maybe even in INSN_READ state, if svp64_mode
                    # detected, in order to trigger - and wait for - the
                    # predicate reading.
                    if self.svp64_en:
                        pmode = pdecode2.rm_dec.predmode
                    """
                    if pmode != SVP64PredMode.ALWAYS.value:
                        fire predicate loading FSM and wait before
                        moving to INSN_READY
                    else:
                        sync += self.srcmask.eq(-1) # set to all 1s
                        sync += self.dstmask.eq(-1) # set to all 1s
                        m.next = "INSN_READY"
                    """

            with m.State("INSN_READY"):
                # hand over the instruction, to be decoded
                comb += fetch_insn_o_valid.eq(1)
                with m.If(fetch_insn_i_ready):
                    m.next = "IDLE"

    def fetch_predicate_fsm(self, m,
                            pred_insn_i_valid, pred_insn_o_ready,
                            pred_mask_o_valid, pred_mask_i_ready):
        """fetch_predicate_fsm - obtains (constructs in the case of CR)
           src/dest predicate masks

        https://bugs.libre-soc.org/show_bug.cgi?id=617
        the predicates can be read here, by using IntRegs r_ports['pred']
        or CRRegs r_ports['pred'].  in the case of CRs it will have to
        be done through multiple reads, extracting one relevant at a time.
        later, a faster way would be to use the 32-bit-wide CR port but
        this is more complex decoding, here.  equivalent code used in
        ISACaller is "from openpower.decoder.isa.caller import get_predcr"

        note: this ENTIRE FSM is not to be called when svp64 is disabled
        """
        comb = m.d.comb
        sync = m.d.sync
        pdecode2 = self.pdecode2
        rm_dec = pdecode2.rm_dec # SVP64RMModeDecode
        predmode = rm_dec.predmode
        srcpred, dstpred = rm_dec.srcpred, rm_dec.dstpred
        cr_pred, int_pred = self.cr_pred, self.int_pred   # read regfiles
        # get src/dst step, so we can skip already used mask bits
        cur_state = self.cur_state
        srcstep = cur_state.svstate.srcstep
        dststep = cur_state.svstate.dststep
        cur_vl = cur_state.svstate.vl

        # decode predicates
        sregread, sinvert, sunary, sall1s = get_predint(m, srcpred, 's')
        dregread, dinvert, dunary, dall1s = get_predint(m, dstpred, 'd')
        sidx, scrinvert = get_predcr(m, srcpred, 's')
        didx, dcrinvert = get_predcr(m, dstpred, 'd')

        # store fetched masks, for either intpred or crpred
        # when src/dst step is not zero, the skipped mask bits need to be
        # shifted-out, before actually storing them in src/dest mask
        new_srcmask = Signal(64, reset_less=True)
        new_dstmask = Signal(64, reset_less=True)

        with m.FSM(name="fetch_predicate"):

            with m.State("FETCH_PRED_IDLE"):
                comb += pred_insn_o_ready.eq(1)
                with m.If(pred_insn_i_valid):
                    with m.If(predmode == SVP64PredMode.INT):
                        # skip fetching destination mask register, when zero
                        with m.If(dall1s):
                            sync += new_dstmask.eq(-1)
                            # directly go to fetch source mask register
                            # guaranteed not to be zero (otherwise predmode
                            # would be SVP64PredMode.ALWAYS, not INT)
                            comb += int_pred.addr.eq(sregread)
                            comb += int_pred.ren.eq(1)
                            m.next = "INT_SRC_READ"
                        # fetch destination predicate register
                        with m.Else():
                            comb += int_pred.addr.eq(dregread)
                            comb += int_pred.ren.eq(1)
                            m.next = "INT_DST_READ"
                    with m.Elif(predmode == SVP64PredMode.CR):
                        # go fetch masks from the CR register file
                        sync += new_srcmask.eq(0)
                        sync += new_dstmask.eq(0)
                        m.next = "CR_READ"
                    with m.Else():
                        sync += self.srcmask.eq(-1)
                        sync += self.dstmask.eq(-1)
                        m.next = "FETCH_PRED_DONE"

            with m.State("INT_DST_READ"):
                # store destination mask
                inv = Repl(dinvert, 64)
                with m.If(dunary):
                    # set selected mask bit for 1<<r3 mode
                    dst_shift = Signal(range(64))
                    comb += dst_shift.eq(self.int_pred.o_data & 0b111111)
                    sync += new_dstmask.eq(1 << dst_shift)
                with m.Else():
                    # invert mask if requested
                    sync += new_dstmask.eq(self.int_pred.o_data ^ inv)
                # skip fetching source mask register, when zero
                with m.If(sall1s):
                    sync += new_srcmask.eq(-1)
                    m.next = "FETCH_PRED_SHIFT_MASK"
                # fetch source predicate register
                with m.Else():
                    comb += int_pred.addr.eq(sregread)
                    comb += int_pred.ren.eq(1)
                    m.next = "INT_SRC_READ"

            with m.State("INT_SRC_READ"):
                # store source mask
                inv = Repl(sinvert, 64)
                with m.If(sunary):
                    # set selected mask bit for 1<<r3 mode
                    src_shift = Signal(range(64))
                    comb += src_shift.eq(self.int_pred.o_data & 0b111111)
                    sync += new_srcmask.eq(1 << src_shift)
                with m.Else():
                    # invert mask if requested
                    sync += new_srcmask.eq(self.int_pred.o_data ^ inv)
                m.next = "FETCH_PRED_SHIFT_MASK"

            # fetch masks from the CR register file
            # implements the following loop:
            # idx, inv = get_predcr(mask)
            # mask = 0
            # for cr_idx in range(vl):
            #     cr = crl[cr_idx + SVP64CROffs.CRPred]  # takes one cycle
            #     if cr[idx] ^ inv:
            #         mask |= 1 << cr_idx
            # return mask
            with m.State("CR_READ"):
                # CR index to be read, which will be ready by the next cycle
                cr_idx = Signal.like(cur_vl, reset_less=True)
                # submit the read operation to the regfile
                with m.If(cr_idx != cur_vl):
                    # the CR read port is unary ...
                    # ren = 1 << cr_idx
                    # ... in MSB0 convention ...
                    # ren = 1 << (7 - cr_idx)
                    # ... and with an offset:
                    # ren = 1 << (7 - off - cr_idx)
                    idx = SVP64CROffs.CRPred + cr_idx
                    comb += cr_pred.ren.eq(1 << (7 - idx))
                    # signal data valid in the next cycle
                    cr_read = Signal(reset_less=True)
                    sync += cr_read.eq(1)
                    # load the next index
                    sync += cr_idx.eq(cr_idx + 1)
                with m.Else():
                    # exit on loop end
                    sync += cr_read.eq(0)
                    sync += cr_idx.eq(0)
                    m.next = "FETCH_PRED_SHIFT_MASK"
                with m.If(cr_read):
                    # compensate for the one cycle delay on the regfile
                    cur_cr_idx = Signal.like(cur_vl)
                    comb += cur_cr_idx.eq(cr_idx - 1)
                    # read the CR field, select the appropriate bit
                    cr_field = Signal(4)
                    scr_bit = Signal()
                    dcr_bit = Signal()
                    comb += cr_field.eq(cr_pred.o_data)
                    comb += scr_bit.eq(cr_field.bit_select(sidx, 1) ^ scrinvert)
                    comb += dcr_bit.eq(cr_field.bit_select(didx, 1) ^ dcrinvert)
                    # set the corresponding mask bit
                    bit_to_set = Signal.like(self.srcmask)
                    comb += bit_to_set.eq(1 << cur_cr_idx)
                    with m.If(scr_bit):
                        sync += new_srcmask.eq(new_srcmask | bit_to_set)
                    with m.If(dcr_bit):
                        sync += new_dstmask.eq(new_dstmask | bit_to_set)

            with m.State("FETCH_PRED_SHIFT_MASK"):
                # shift-out skipped mask bits
                sync += self.srcmask.eq(new_srcmask >> srcstep)
                sync += self.dstmask.eq(new_dstmask >> dststep)
                m.next = "FETCH_PRED_DONE"

            with m.State("FETCH_PRED_DONE"):
                comb += pred_mask_o_valid.eq(1)
                with m.If(pred_mask_i_ready):
                    m.next = "FETCH_PRED_IDLE"

    def issue_fsm(self, m, core, pc_changed, sv_changed, nia,
                  dbg, core_rst, is_svp64_mode,
                  fetch_pc_o_ready, fetch_pc_i_valid,
                  fetch_insn_o_valid, fetch_insn_i_ready,
                  pred_insn_i_valid, pred_insn_o_ready,
                  pred_mask_o_valid, pred_mask_i_ready,
                  exec_insn_i_valid, exec_insn_o_ready,
                  exec_pc_o_valid, exec_pc_i_ready):
        """issue FSM

        decode / issue FSM.  this interacts with the "fetch" FSM
        through fetch_insn_ready/valid (incoming) and fetch_pc_ready/valid
        (outgoing). also interacts with the "execute" FSM
        through exec_insn_ready/valid (outgoing) and exec_pc_ready/valid
        (incoming).
        SVP64 RM prefixes have already been set up by the
        "fetch" phase, so execute is fairly straightforward.
        """

        comb = m.d.comb
        sync = m.d.sync
        pdecode2 = self.pdecode2
        cur_state = self.cur_state

        # temporaries
        dec_opcode_i = pdecode2.dec.raw_opcode_in # raw opcode

        # for updating svstate (things like srcstep etc.)
        update_svstate = Signal() # set this (below) if updating
        new_svstate = SVSTATERec("new_svstate")
        comb += new_svstate.eq(cur_state.svstate)

        # precalculate srcstep+1 and dststep+1
        cur_srcstep = cur_state.svstate.srcstep
        cur_dststep = cur_state.svstate.dststep
        next_srcstep = Signal.like(cur_srcstep)
        next_dststep = Signal.like(cur_dststep)
        comb += next_srcstep.eq(cur_state.svstate.srcstep+1)
        comb += next_dststep.eq(cur_state.svstate.dststep+1)

        # note if an exception happened.  in a pipelined or OoO design
        # this needs to be accompanied by "shadowing" (or stalling)
        exc_happened = self.core.o.exc_happened

        with m.FSM(name="issue_fsm"):

            # sync with the "fetch" phase which is reading the instruction
            # at this point, there is no instruction running, that
            # could inadvertently update the PC.
            with m.State("ISSUE_START"):
                # wait on "core stop" release, before next fetch
                # need to do this here, in case we are in a VL==0 loop
                with m.If(~dbg.core_stop_o & ~core_rst):
                    comb += fetch_pc_i_valid.eq(1) # tell fetch to start
                    with m.If(fetch_pc_o_ready):   # fetch acknowledged us
                        m.next = "INSN_WAIT"
                with m.Else():
                    # tell core it's stopped, and acknowledge debug handshake
                    comb += dbg.core_stopped_i.eq(1)
                    # while stopped, allow updating the PC and SVSTATE
                    with m.If(self.pc_i.ok):
                        comb += self.state_w_pc.wen.eq(1 << StateRegs.PC)
                        comb += self.state_w_pc.i_data.eq(self.pc_i.data)
                        sync += pc_changed.eq(1)
                    with m.If(self.svstate_i.ok):
                        comb += new_svstate.eq(self.svstate_i.data)
                        comb += update_svstate.eq(1)
                        sync += sv_changed.eq(1)

            # wait for an instruction to arrive from Fetch
            with m.State("INSN_WAIT"):
                comb += fetch_insn_i_ready.eq(1)
                with m.If(fetch_insn_o_valid):
                    # loop into ISSUE_START if it's a SVP64 instruction
                    # and VL == 0.  this because VL==0 is a for-loop
                    # from 0 to 0 i.e. always, always a NOP.
                    cur_vl = cur_state.svstate.vl
                    with m.If(is_svp64_mode & (cur_vl == 0)):
                        # update the PC before fetching the next instruction
                        # since we are in a VL==0 loop, no instruction was
                        # executed that we could be overwriting
                        comb += self.state_w_pc.wen.eq(1 << StateRegs.PC)
                        comb += self.state_w_pc.i_data.eq(nia)
                        comb += self.insn_done.eq(1)
                        m.next = "ISSUE_START"
                    with m.Else():
                        if self.svp64_en:
                            m.next = "PRED_START"  # start fetching predicate
                        else:
                            m.next = "DECODE_SV"  # skip predication

            with m.State("PRED_START"):
                comb += pred_insn_i_valid.eq(1)  # tell fetch_pred to start
                with m.If(pred_insn_o_ready):  # fetch_pred acknowledged us
                    m.next = "MASK_WAIT"

            with m.State("MASK_WAIT"):
                comb += pred_mask_i_ready.eq(1) # ready to receive the masks
                with m.If(pred_mask_o_valid): # predication masks are ready
                    m.next = "PRED_SKIP"

            # skip zeros in predicate
            with m.State("PRED_SKIP"):
                with m.If(~is_svp64_mode):
                    m.next = "DECODE_SV"  # nothing to do
                with m.Else():
                    if self.svp64_en:
                        pred_src_zero = pdecode2.rm_dec.pred_sz
                        pred_dst_zero = pdecode2.rm_dec.pred_dz

                        # new srcstep, after skipping zeros
                        skip_srcstep = Signal.like(cur_srcstep)
                        # value to be added to the current srcstep
                        src_delta = Signal.like(cur_srcstep)
                        # add leading zeros to srcstep, if not in zero mode
                        with m.If(~pred_src_zero):
                            # priority encoder (count leading zeros)
                            # append guard bit, in case the mask is all zeros
                            pri_enc_src = PriorityEncoder(65)
                            m.submodules.pri_enc_src = pri_enc_src
                            comb += pri_enc_src.i.eq(Cat(self.srcmask,
                                                         Const(1, 1)))
                            comb += src_delta.eq(pri_enc_src.o)
                        # apply delta to srcstep
                        comb += skip_srcstep.eq(cur_srcstep + src_delta)
                        # shift-out all leading zeros from the mask
                        # plus the leading "one" bit
                        # TODO count leading zeros and shift-out the zero
                        #      bits, in the same step, in hardware
                        sync += self.srcmask.eq(self.srcmask >> (src_delta+1))

                        # same as above, but for dststep
                        skip_dststep = Signal.like(cur_dststep)
                        dst_delta = Signal.like(cur_dststep)
                        with m.If(~pred_dst_zero):
                            pri_enc_dst = PriorityEncoder(65)
                            m.submodules.pri_enc_dst = pri_enc_dst
                            comb += pri_enc_dst.i.eq(Cat(self.dstmask,
                                                         Const(1, 1)))
                            comb += dst_delta.eq(pri_enc_dst.o)
                        comb += skip_dststep.eq(cur_dststep + dst_delta)
                        sync += self.dstmask.eq(self.dstmask >> (dst_delta+1))

                        # TODO: initialize mask[VL]=1 to avoid passing past VL
                        with m.If((skip_srcstep >= cur_vl) |
                                  (skip_dststep >= cur_vl)):
                            # end of VL loop. Update PC and reset src/dst step
                            comb += self.state_w_pc.wen.eq(1 << StateRegs.PC)
                            comb += self.state_w_pc.i_data.eq(nia)
                            comb += new_svstate.srcstep.eq(0)
                            comb += new_svstate.dststep.eq(0)
                            comb += update_svstate.eq(1)
                            # synchronize with the simulator
                            comb += self.insn_done.eq(1)
                            # go back to Issue
                            m.next = "ISSUE_START"
                        with m.Else():
                            # update new src/dst step
                            comb += new_svstate.srcstep.eq(skip_srcstep)
                            comb += new_svstate.dststep.eq(skip_dststep)
                            comb += update_svstate.eq(1)
                            # proceed to Decode
                            m.next = "DECODE_SV"

                        # pass predicate mask bits through to satellite decoders
                        # TODO: for SIMD this will be *multiple* bits
                        sync += core.i.sv_pred_sm.eq(self.srcmask[0])
                        sync += core.i.sv_pred_dm.eq(self.dstmask[0])

            # after src/dst step have been updated, we are ready
            # to decode the instruction
            with m.State("DECODE_SV"):
                # decode the instruction
                sync += core.i.e.eq(pdecode2.e)
                sync += core.i.state.eq(cur_state)
                sync += core.i.raw_insn_i.eq(dec_opcode_i)
                sync += core.i.bigendian_i.eq(self.core_bigendian_i)
                if self.svp64_en:
                    sync += core.i.sv_rm.eq(pdecode2.sv_rm)
                    # set RA_OR_ZERO detection in satellite decoders
                    sync += core.i.sv_a_nz.eq(pdecode2.sv_a_nz)
                    # and svp64 detection
                    sync += core.i.is_svp64_mode.eq(is_svp64_mode)
                    # and svp64 bit-rev'd ldst mode
                    ldst_dec = pdecode2.use_svp64_ldst_dec
                    sync += core.i.use_svp64_ldst_dec.eq(ldst_dec)
                # after decoding, reset any previous exception condition,
                # allowing it to be set again during the next execution
                sync += pdecode2.ldst_exc.eq(0)

                m.next = "INSN_EXECUTE"  # move to "execute"

            # handshake with execution FSM, move to "wait" once acknowledged
            with m.State("INSN_EXECUTE"):
                comb += exec_insn_i_valid.eq(1) # trigger execute
                with m.If(exec_insn_o_ready):   # execute acknowledged us
                    m.next = "EXECUTE_WAIT"

            with m.State("EXECUTE_WAIT"):
                # wait on "core stop" release, at instruction end
                # need to do this here, in case we are in a VL>1 loop
                with m.If(~dbg.core_stop_o & ~core_rst):
                    comb += exec_pc_i_ready.eq(1)
                    # see https://bugs.libre-soc.org/show_bug.cgi?id=636
                    # the exception info needs to be blatted into
                    # pdecode.ldst_exc, and the instruction "re-run".
                    # when ldst_exc.happened is set, the PowerDecoder2
                    # reacts very differently: it re-writes the instruction
                    # with a "trap" (calls PowerDecoder2.trap()) which
                    # will *overwrite* whatever was requested and jump the
                    # PC to the exception address, as well as alter MSR.
                    # nothing else needs to be done other than to note
                    # the change of PC and MSR (and, later, SVSTATE)
                    with m.If(exc_happened):
                        sync += pdecode2.ldst_exc.eq(core.fus.get_exc("ldst0"))

                    with m.If(exec_pc_o_valid):

                        # was this the last loop iteration?
                        is_last = Signal()
                        cur_vl = cur_state.svstate.vl
                        comb += is_last.eq(next_srcstep == cur_vl)

                        # return directly to Decode if Execute generated an
                        # exception.
                        with m.If(pdecode2.ldst_exc.happened):
                            m.next = "DECODE_SV"

                        # if either PC or SVSTATE were changed by the previous
                        # instruction, go directly back to Fetch, without
                        # updating either PC or SVSTATE
                        with m.Elif(pc_changed | sv_changed):
                            m.next = "ISSUE_START"

                        # also return to Fetch, when no output was a vector
                        # (regardless of SRCSTEP and VL), or when the last
                        # instruction was really the last one of the VL loop
                        with m.Elif((~pdecode2.loop_continue) | is_last):
                            # before going back to fetch, update the PC state
                            # register with the NIA.
                            # ok here we are not reading the branch unit.
                            # TODO: this just blithely overwrites whatever
                            #       pipeline updated the PC
                            comb += self.state_w_pc.wen.eq(1 << StateRegs.PC)
                            comb += self.state_w_pc.i_data.eq(nia)
                            # reset SRCSTEP before returning to Fetch
                            if self.svp64_en:
                                with m.If(pdecode2.loop_continue):
                                    comb += new_svstate.srcstep.eq(0)
                                    comb += new_svstate.dststep.eq(0)
                                    comb += update_svstate.eq(1)
                            else:
                                comb += new_svstate.srcstep.eq(0)
                                comb += new_svstate.dststep.eq(0)
                                comb += update_svstate.eq(1)
                            m.next = "ISSUE_START"

                        # returning to Execute? then, first update SRCSTEP
                        with m.Else():
                            comb += new_svstate.srcstep.eq(next_srcstep)
                            comb += new_svstate.dststep.eq(next_dststep)
                            comb += update_svstate.eq(1)
                            # return to mask skip loop
                            m.next = "PRED_SKIP"

                with m.Else():
                    comb += dbg.core_stopped_i.eq(1)
                    # while stopped, allow updating the PC and SVSTATE
                    with m.If(self.pc_i.ok):
                        comb += self.state_w_pc.wen.eq(1 << StateRegs.PC)
                        comb += self.state_w_pc.i_data.eq(self.pc_i.data)
                        sync += pc_changed.eq(1)
                    with m.If(self.svstate_i.ok):
                        comb += new_svstate.eq(self.svstate_i.data)
                        comb += update_svstate.eq(1)
                        sync += sv_changed.eq(1)

        # check if svstate needs updating: if so, write it to State Regfile
        with m.If(update_svstate):
            comb += self.state_w_sv.wen.eq(1<<StateRegs.SVSTATE)
            comb += self.state_w_sv.i_data.eq(new_svstate)
            sync += cur_state.svstate.eq(new_svstate) # for next clock

    def execute_fsm(self, m, core, pc_changed, sv_changed,
                    exec_insn_i_valid, exec_insn_o_ready,
                    exec_pc_o_valid, exec_pc_i_ready):
        """execute FSM

        execute FSM. this interacts with the "issue" FSM
        through exec_insn_ready/valid (incoming) and exec_pc_ready/valid
        (outgoing). SVP64 RM prefixes have already been set up by the
        "issue" phase, so execute is fairly straightforward.
        """

        comb = m.d.comb
        sync = m.d.sync
        pdecode2 = self.pdecode2

        # temporaries
        core_busy_o = ~core.p.o_ready                # core is busy
        core_ivalid_i = core.p.i_valid              # instruction is valid
        core_issue_i = core.i.issue_i               # instruction is issued
        insn_type = core.i.e.do.insn_type           # instruction MicroOp type

        with m.FSM(name="exec_fsm"):

            # waiting for instruction bus (stays there until not busy)
            with m.State("INSN_START"):
                comb += exec_insn_o_ready.eq(1)
                with m.If(exec_insn_i_valid):
                    comb += core_ivalid_i.eq(1)  # instruction is valid
                    comb += core_issue_i.eq(1)  # and issued
                    sync += sv_changed.eq(0)
                    sync += pc_changed.eq(0)
                    m.next = "INSN_ACTIVE"  # move to "wait completion"

            # instruction started: must wait till it finishes
            with m.State("INSN_ACTIVE"):
                with m.If(insn_type != MicrOp.OP_NOP):
                    comb += core_ivalid_i.eq(1) # instruction is valid
                # note changes to PC and SVSTATE
                with m.If(self.state_nia.wen & (1<<StateRegs.SVSTATE)):
                    sync += sv_changed.eq(1)
                with m.If(self.state_nia.wen & (1<<StateRegs.PC)):
                    sync += pc_changed.eq(1)
                with m.If(~core_busy_o): # instruction done!
                    comb += exec_pc_o_valid.eq(1)
                    with m.If(exec_pc_i_ready):
                        # when finished, indicate "done".
                        # however, if there was an exception, the instruction
                        # is *not* yet done.  this is an implementation
                        # detail: we choose to implement exceptions by
                        # taking the exception information from the LDST
                        # unit, putting that *back* into the PowerDecoder2,
                        # and *re-running the entire instruction*.
                        # if we erroneously indicate "done" here, it is as if
                        # there were *TWO* instructions:
                        # 1) the failed LDST 2) a TRAP.
                        with m.If(~pdecode2.ldst_exc.happened):
                            comb += self.insn_done.eq(1)
                        m.next = "INSN_START"  # back to fetch

    def setup_peripherals(self, m):
        comb, sync = m.d.comb, m.d.sync

        # okaaaay so the debug module must be in coresync clock domain
        # but NOT its reset signal. to cope with this, set every single
        # submodule explicitly in coresync domain, debug and JTAG
        # in their own one but using *external* reset.
        csd = DomainRenamer("coresync")
        dbd = DomainRenamer(self.dbg_domain)

        m.submodules.core = core = csd(self.core)
        m.submodules.imem = imem = csd(self.imem)
        m.submodules.dbg = dbg = dbd(self.dbg)
        if self.jtag_en:
            m.submodules.jtag = jtag = dbd(self.jtag)
            # TODO: UART2GDB mux, here, from external pin
            # see https://bugs.libre-soc.org/show_bug.cgi?id=499
            sync += dbg.dmi.connect_to(jtag.dmi)

        cur_state = self.cur_state

        # 4x 4k SRAM blocks.  these simply "exist", they get routed in litex
        if self.sram4x4k:
            for i, sram in enumerate(self.sram4k):
                m.submodules["sram4k_%d" % i] = csd(sram)
                comb += sram.enable.eq(self.wb_sram_en)

        # XICS interrupt handler
        if self.xics:
            m.submodules.xics_icp = icp = csd(self.xics_icp)
            m.submodules.xics_ics = ics = csd(self.xics_ics)
            comb += icp.ics_i.eq(ics.icp_o)           # connect ICS to ICP
            sync += cur_state.eint.eq(icp.core_irq_o) # connect ICP to core

        # GPIO test peripheral
        if self.gpio:
            m.submodules.simple_gpio = simple_gpio = csd(self.simple_gpio)

        # connect one GPIO output to ICS bit 15 (like in microwatt soc.vhdl)
        # XXX causes litex ECP5 test to get wrong idea about input and output
        # (but works with verilator sim *sigh*)
        #if self.gpio and self.xics:
        #   comb += self.int_level_i[15].eq(simple_gpio.gpio_o[0])

        # instruction decoder
        pdecode = create_pdecode()
        m.submodules.dec2 = pdecode2 = csd(self.pdecode2)
        if self.svp64_en:
            m.submodules.svp64 = svp64 = csd(self.svp64)

        # convenience
        dmi, d_reg, d_cr, d_xer, = dbg.dmi, dbg.d_gpr, dbg.d_cr, dbg.d_xer
        intrf = self.core.regs.rf['int']

        # clock delay power-on reset
        cd_por  = ClockDomain(reset_less=True)
        cd_sync = ClockDomain()
        core_sync = ClockDomain("coresync")
        m.domains += cd_por, cd_sync, core_sync
        if self.dbg_domain != "sync":
            dbg_sync = ClockDomain(self.dbg_domain)
            m.domains += dbg_sync

        ti_rst = Signal(reset_less=True)
        delay = Signal(range(4), reset=3)
        with m.If(delay != 0):
            m.d.por += delay.eq(delay - 1)
        comb += cd_por.clk.eq(ClockSignal())

        # power-on reset delay
        core_rst = ResetSignal("coresync")
        comb += ti_rst.eq(delay != 0 | dbg.core_rst_o | ResetSignal())
        comb += core_rst.eq(ti_rst)

        # debug clock is same as coresync, but reset is *main external*
        if self.dbg_domain != "sync":
            dbg_rst = ResetSignal(self.dbg_domain)
            comb += dbg_rst.eq(ResetSignal())

        # busy/halted signals from core
        core_busy_o = ~core.p.o_ready                # core is busy
        comb += self.busy_o.eq(core_busy_o)
        comb += pdecode2.dec.bigendian.eq(self.core_bigendian_i)

        # temporary hack: says "go" immediately for both address gen and ST
        l0 = core.l0
        ldst = core.fus.fus['ldst0']
        st_go_edge = rising_edge(m, ldst.st.rel_o)
        m.d.comb += ldst.ad.go_i.eq(ldst.ad.rel_o) # link addr-go direct to rel
        m.d.comb += ldst.st.go_i.eq(st_go_edge) # link store-go to rising rel

    def elaborate(self, platform):
        m = Module()
        # convenience
        comb, sync = m.d.comb, m.d.sync
        cur_state = self.cur_state
        pdecode2 = self.pdecode2
        dbg = self.dbg
        core = self.core

        # set up peripherals and core
        core_rst = self.core_rst
        self.setup_peripherals(m)

        # reset current state if core reset requested
        with m.If(core_rst):
            m.d.sync += self.cur_state.eq(0)

        # PC and instruction from I-Memory
        comb += self.pc_o.eq(cur_state.pc)
        pc_changed = Signal() # note write to PC
        sv_changed = Signal() # note write to SVSTATE

        # read state either from incoming override or from regfile
        # TODO: really should be doing MSR in the same way
        pc = state_get(m, core_rst, self.pc_i,
                            "pc",                  # read PC
                            self.state_r_pc, StateRegs.PC)
        svstate = state_get(m, core_rst, self.svstate_i,
                            "svstate",   # read SVSTATE
                            self.state_r_sv, StateRegs.SVSTATE)

        # don't write pc every cycle
        comb += self.state_w_pc.wen.eq(0)
        comb += self.state_w_pc.i_data.eq(0)

        # don't read msr every cycle
        comb += self.state_r_msr.ren.eq(0)

        # address of the next instruction, in the absence of a branch
        # depends on the instruction size
        nia = Signal(64)

        # connect up debug signals
        # TODO comb += core.icache_rst_i.eq(dbg.icache_rst_o)
        comb += dbg.terminate_i.eq(core.o.core_terminate_o)
        comb += dbg.state.pc.eq(pc)
        comb += dbg.state.svstate.eq(svstate)
        comb += dbg.state.msr.eq(cur_state.msr)

        # pass the prefix mode from Fetch to Issue, so the latter can loop
        # on VL==0
        is_svp64_mode = Signal()

        # there are *THREE^WFOUR-if-SVP64-enabled* FSMs, fetch (32/64-bit)
        # issue, decode/execute, now joined by "Predicate fetch/calculate".
        # these are the handshake signals between each

        # fetch FSM can run as soon as the PC is valid
        fetch_pc_i_valid = Signal() # Execute tells Fetch "start next read"
        fetch_pc_o_ready = Signal() # Fetch Tells SVSTATE "proceed"

        # fetch FSM hands over the instruction to be decoded / issued
        fetch_insn_o_valid = Signal()
        fetch_insn_i_ready = Signal()

        # predicate fetch FSM decodes and fetches the predicate
        pred_insn_i_valid = Signal()
        pred_insn_o_ready = Signal()

        # predicate fetch FSM delivers the masks
        pred_mask_o_valid = Signal()
        pred_mask_i_ready = Signal()

        # issue FSM delivers the instruction to the be executed
        exec_insn_i_valid = Signal()
        exec_insn_o_ready = Signal()

        # execute FSM, hands over the PC/SVSTATE back to the issue FSM
        exec_pc_o_valid = Signal()
        exec_pc_i_ready = Signal()

        # the FSMs here are perhaps unusual in that they detect conditions
        # then "hold" information, combinatorially, for the core
        # (as opposed to using sync - which would be on a clock's delay)
        # this includes the actual opcode, valid flags and so on.

        # Fetch, then predicate fetch, then Issue, then Execute.
        # Issue is where the VL for-loop # lives.  the ready/valid
        # signalling is used to communicate between the four.

        self.fetch_fsm(m, core, pc, svstate, nia, is_svp64_mode,
                       fetch_pc_o_ready, fetch_pc_i_valid,
                       fetch_insn_o_valid, fetch_insn_i_ready)

        self.issue_fsm(m, core, pc_changed, sv_changed, nia,
                       dbg, core_rst, is_svp64_mode,
                       fetch_pc_o_ready, fetch_pc_i_valid,
                       fetch_insn_o_valid, fetch_insn_i_ready,
                       pred_insn_i_valid, pred_insn_o_ready,
                       pred_mask_o_valid, pred_mask_i_ready,
                       exec_insn_i_valid, exec_insn_o_ready,
                       exec_pc_o_valid, exec_pc_i_ready)

        if self.svp64_en:
            self.fetch_predicate_fsm(m,
                                     pred_insn_i_valid, pred_insn_o_ready,
                                     pred_mask_o_valid, pred_mask_i_ready)

        self.execute_fsm(m, core, pc_changed, sv_changed,
                         exec_insn_i_valid, exec_insn_o_ready,
                         exec_pc_o_valid, exec_pc_i_ready)

        # whatever was done above, over-ride it if core reset is held
        with m.If(core_rst):
            sync += nia.eq(0)

        # this bit doesn't have to be in the FSM: connect up to read
        # regfiles on demand from DMI
        self.do_dmi(m, dbg)

        # DEC and TB inc/dec FSM.  copy of DEC is put into CoreState,
        # (which uses that in PowerDecoder2 to raise 0x900 exception)
        self.tb_dec_fsm(m, cur_state.dec)

        return m

    def do_dmi(self, m, dbg):
        """deals with DMI debug requests

        currently only provides read requests for the INT regfile, CR and XER
        it will later also deal with *writing* to these regfiles.
        """
        comb = m.d.comb
        sync = m.d.sync
        dmi, d_reg, d_cr, d_xer, = dbg.dmi, dbg.d_gpr, dbg.d_cr, dbg.d_xer
        intrf = self.core.regs.rf['int']

        with m.If(d_reg.req): # request for regfile access being made
            # TODO: error-check this
            # XXX should this be combinatorial?  sync better?
            if intrf.unary:
                comb += self.int_r.ren.eq(1<<d_reg.addr)
            else:
                comb += self.int_r.addr.eq(d_reg.addr)
                comb += self.int_r.ren.eq(1)
        d_reg_delay  = Signal()
        sync += d_reg_delay.eq(d_reg.req)
        with m.If(d_reg_delay):
            # data arrives one clock later
            comb += d_reg.data.eq(self.int_r.o_data)
            comb += d_reg.ack.eq(1)

        # sigh same thing for CR debug
        with m.If(d_cr.req): # request for regfile access being made
            comb += self.cr_r.ren.eq(0b11111111) # enable all
        d_cr_delay  = Signal()
        sync += d_cr_delay.eq(d_cr.req)
        with m.If(d_cr_delay):
            # data arrives one clock later
            comb += d_cr.data.eq(self.cr_r.o_data)
            comb += d_cr.ack.eq(1)

        # aaand XER...
        with m.If(d_xer.req): # request for regfile access being made
            comb += self.xer_r.ren.eq(0b111111) # enable all
        d_xer_delay  = Signal()
        sync += d_xer_delay.eq(d_xer.req)
        with m.If(d_xer_delay):
            # data arrives one clock later
            comb += d_xer.data.eq(self.xer_r.o_data)
            comb += d_xer.ack.eq(1)

    def tb_dec_fsm(self, m, spr_dec):
        """tb_dec_fsm

        this is a FSM for updating either dec or tb.  it runs alternately
        DEC, TB, DEC, TB.  note that SPR pipeline could have written a new
        value to DEC, however the regfile has "passthrough" on it so this
        *should* be ok.

        see v3.0B p1097-1099 for Timeer Resource and p1065 and p1076
        """

        comb, sync = m.d.comb, m.d.sync
        fast_rf = self.core.regs.rf['fast']
        fast_r_dectb = fast_rf.r_ports['issue'] # DEC/TB
        fast_w_dectb = fast_rf.w_ports['issue'] # DEC/TB

        with m.FSM() as fsm:

            # initiates read of current DEC
            with m.State("DEC_READ"):
                comb += fast_r_dectb.addr.eq(FastRegs.DEC)
                comb += fast_r_dectb.ren.eq(1)
                m.next = "DEC_WRITE"

            # waits for DEC read to arrive (1 cycle), updates with new value
            with m.State("DEC_WRITE"):
                new_dec = Signal(64)
                # TODO: MSR.LPCR 32-bit decrement mode
                comb += new_dec.eq(fast_r_dectb.o_data - 1)
                comb += fast_w_dectb.addr.eq(FastRegs.DEC)
                comb += fast_w_dectb.wen.eq(1)
                comb += fast_w_dectb.i_data.eq(new_dec)
                sync += spr_dec.eq(new_dec) # copy into cur_state for decoder
                m.next = "TB_READ"

            # initiates read of current TB
            with m.State("TB_READ"):
                comb += fast_r_dectb.addr.eq(FastRegs.TB)
                comb += fast_r_dectb.ren.eq(1)
                m.next = "TB_WRITE"

            # waits for read TB to arrive, initiates write of current TB
            with m.State("TB_WRITE"):
                new_tb = Signal(64)
                comb += new_tb.eq(fast_r_dectb.o_data + 1)
                comb += fast_w_dectb.addr.eq(FastRegs.TB)
                comb += fast_w_dectb.wen.eq(1)
                comb += fast_w_dectb.i_data.eq(new_tb)
                m.next = "DEC_READ"

        return m

    def __iter__(self):
        yield from self.pc_i.ports()
        yield self.pc_o
        yield self.memerr_o
        yield from self.core.ports()
        yield from self.imem.ports()
        yield self.core_bigendian_i
        yield self.busy_o

    def ports(self):
        return list(self)

    def external_ports(self):
        ports = self.pc_i.ports()
        ports += [self.pc_o, self.memerr_o, self.core_bigendian_i, self.busy_o,
                ]

        if self.jtag_en:
            ports += list(self.jtag.external_ports())
        else:
            # don't add DMI if JTAG is enabled
            ports += list(self.dbg.dmi.ports())

        ports += list(self.imem.ibus.fields.values())
        ports += list(self.core.l0.cmpi.wb_bus().fields.values())

        if self.sram4x4k:
            for sram in self.sram4k:
                ports += list(sram.bus.fields.values())

        if self.xics:
            ports += list(self.xics_icp.bus.fields.values())
            ports += list(self.xics_ics.bus.fields.values())
            ports.append(self.int_level_i)

        if self.gpio:
            ports += list(self.simple_gpio.bus.fields.values())
            ports.append(self.gpio_o)

        return ports

    def ports(self):
        return list(self)


class TestIssuer(Elaboratable):
    def __init__(self, pspec):
        self.ti = TestIssuerInternal(pspec)
        self.pll = DummyPLL(instance=True)

        # PLL direct clock or not
        self.pll_en = hasattr(pspec, "use_pll") and pspec.use_pll
        if self.pll_en:
            self.pll_test_o = Signal(reset_less=True)
            self.pll_vco_o = Signal(reset_less=True)
            self.clk_sel_i = Signal(2, reset_less=True)
            self.ref_clk =  ClockSignal() # can't rename it but that's ok
            self.pllclk_clk = ClockSignal("pllclk")

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

        # TestIssuer nominally runs at main clock, actually it is
        # all combinatorial internally except for coresync'd components
        m.submodules.ti = ti = self.ti

        if self.pll_en:
            # ClockSelect runs at PLL output internal clock rate
            m.submodules.wrappll = pll = self.pll

            # add clock domains from PLL
            cd_pll = ClockDomain("pllclk")
            m.domains += cd_pll

            # PLL clock established.  has the side-effect of running clklsel
            # at the PLL's speed (see DomainRenamer("pllclk") above)
            pllclk = self.pllclk_clk
            comb += pllclk.eq(pll.clk_pll_o)

            # wire up external 24mhz to PLL
            #comb += pll.clk_24_i.eq(self.ref_clk)
            # output 18 mhz PLL test signal, and analog oscillator out
            comb += self.pll_test_o.eq(pll.pll_test_o)
            comb += self.pll_vco_o.eq(pll.pll_vco_o)

            # input to pll clock selection
            comb += pll.clk_sel_i.eq(self.clk_sel_i)

            # now wire up ResetSignals.  don't mind them being in this domain
            pll_rst = ResetSignal("pllclk")
            comb += pll_rst.eq(ResetSignal())

        # internal clock is set to selector clock-out.  has the side-effect of
        # running TestIssuer at this speed (see DomainRenamer("intclk") above)
        # debug clock runs at coresync internal clock
        cd_coresync = ClockDomain("coresync")
        #m.domains += cd_coresync
        if self.ti.dbg_domain != 'sync':
            cd_dbgsync = ClockDomain("dbgsync")
            #m.domains += cd_dbgsync
        intclk = ClockSignal("coresync")
        dbgclk = ClockSignal(self.ti.dbg_domain)
        # XXX BYPASS PLL XXX
        # XXX BYPASS PLL XXX
        # XXX BYPASS PLL XXX
        if self.pll_en:
            comb += intclk.eq(self.ref_clk)
        else:
            comb += intclk.eq(ClockSignal())
        if self.ti.dbg_domain != 'sync':
            dbgclk = ClockSignal(self.ti.dbg_domain)
            comb += dbgclk.eq(intclk)

        return m

    def ports(self):
        return list(self.ti.ports()) + list(self.pll.ports()) + \
               [ClockSignal(), ResetSignal()]

    def external_ports(self):
        ports = self.ti.external_ports()
        ports.append(ClockSignal())
        ports.append(ResetSignal())
        if self.pll_en:
            ports.append(self.clk_sel_i)
            ports.append(self.pll.clk_24_i)
            ports.append(self.pll_test_o)
            ports.append(self.pll_vco_o)
            ports.append(self.pllclk_clk)
            ports.append(self.ref_clk)
        return ports


if __name__ == '__main__':
    units = {'alu': 1, 'cr': 1, 'branch': 1, 'trap': 1, 'logical': 1,
             'spr': 1,
             'div': 1,
             'mul': 1,
             'shiftrot': 1
            }
    pspec = TestMemPspec(ldst_ifacetype='bare_wb',
                         imem_ifacetype='bare_wb',
                         addr_wid=48,
                         mask_wid=8,
                         reg_wid=64,
                         units=units)
    dut = TestIssuer(pspec)
    vl = main(dut, ports=dut.ports(), name="test_issuer")

    if len(sys.argv) == 1:
        vl = rtlil.convert(dut, ports=dut.external_ports(), name="test_issuer")
        with open("test_issuer.il", "w") as f:
            f.write(vl)