nmigen/back/rtlil.py

   1 import io
   2 import textwrap
   3 from collections import defaultdict, OrderedDict
   4 from contextlib import contextmanager
   5
   6 from ..tools import bits_for
   7 from ..hdl import ast, ir, mem, xfrm
   8
   9
  10 class _Namer:
  11     def __init__(self):
  12         super().__init__()
  13         self._index = 0
  14         self._names = set()
  15
  16     def _make_name(self, name, local):
  17         if name is None:
  18             self._index += 1
  19             name = "${}".format(self._index)
  20         elif not local and name[0] not in "\\$":
  21             name = "\\{}".format(name)
  22         while name in self._names:
  23             self._index += 1
  24             name = "{}${}".format(name, self._index)
  25         self._names.add(name)
  26         return name
  27
  28
  29 class _Bufferer:
  30     _escape_map = str.maketrans({
  31         "\"": "\\\"",
  32         "\\": "\\\\",
  33         "\t": "\\t",
  34         "\r": "\\r",
  35         "\n": "\\n",
  36     })
  37     def __init__(self):
  38         super().__init__()
  39         self._buffer = io.StringIO()
  40
  41     def __str__(self):
  42         return self._buffer.getvalue()
  43
  44     def _append(self, fmt, *args, **kwargs):
  45         self._buffer.write(fmt.format(*args, **kwargs))
  46
  47     def attribute(self, name, value, indent=0):
  48         if isinstance(value, str):
  49             self._append("{}attribute \\{} \"{}\"\n",
  50                          "  " * indent, name, value.translate(self._escape_map))
  51         else:
  52             self._append("{}attribute \\{} {}\n",
  53                          "  " * indent, name, int(value))
  54
  55     def _src(self, src):
  56         if src:
  57             self.attribute("src", src)
  58
  59
  60 class _Builder(_Namer, _Bufferer):
  61     def module(self, name=None, attrs={}):
  62         name = self._make_name(name, local=False)
  63         return _ModuleBuilder(self, name, attrs)
  64
  65
  66 class _ModuleBuilder(_Namer, _Bufferer):
  67     def __init__(self, rtlil, name, attrs):
  68         super().__init__()
  69         self.rtlil = rtlil
  70         self.name  = name
  71         self.attrs = {"generator": "nMigen"}
  72         self.attrs.update(attrs)
  73
  74     def __enter__(self):
  75         for name, value in self.attrs.items():
  76             self.attribute(name, value, indent=0)
  77         self._append("module {}\n", self.name)
  78         return self
  79
  80     def __exit__(self, *args):
  81         self._append("end\n")
  82         self.rtlil._buffer.write(str(self))
  83
  84     def attribute(self, name, value, indent=1):
  85         super().attribute(name, value, indent)
  86
  87     def wire(self, width, port_id=None, port_kind=None, name=None, src=""):
  88         self._src(src)
  89         name = self._make_name(name, local=False)
  90         if port_id is None:
  91             self._append("  wire width {} {}\n", width, name)
  92         else:
  93             assert port_kind in ("input", "output", "inout")
  94             self._append("  wire width {} {} {} {}\n", width, port_kind, port_id, name)
  95         return name
  96
  97     def connect(self, lhs, rhs):
  98         self._append("  connect {} {}\n", lhs, rhs)
  99
 100     def memory(self, width, size, name=None, src=""):
 101         self._src(src)
 102         name = self._make_name(name, local=False)
 103         self._append("  memory width {} size {} {}\n", width, size, name)
 104         return name
 105
 106     def cell(self, kind, name=None, params={}, ports={}, src=""):
 107         self._src(src)
 108         name = self._make_name(name, local=False)
 109         self._append("  cell {} {}\n", kind, name)
 110         for param, value in params.items():
 111             if isinstance(value, str):
 112                 self._append("    parameter \\{} \"{}\"\n",
 113                              param, value.translate(self._escape_map))
 114             else:
 115                 self._append("    parameter \\{} {:d}\n",
 116                              param, value)
 117         for port, wire in ports.items():
 118             self._append("    connect {} {}\n", port, wire)
 119         self._append("  end\n")
 120         return name
 121
 122     def process(self, name=None, src=""):
 123         name = self._make_name(name, local=True)
 124         return _ProcessBuilder(self, name, src)
 125
 126
 127 class _ProcessBuilder(_Bufferer):
 128     def __init__(self, rtlil, name, src):
 129         super().__init__()
 130         self.rtlil = rtlil
 131         self.name  = name
 132         self.src   = src
 133
 134     def __enter__(self):
 135         self._src(self.src)
 136         self._append("  process {}\n", self.name)
 137         return self
 138
 139     def __exit__(self, *args):
 140         self._append("  end\n")
 141         self.rtlil._buffer.write(str(self))
 142
 143     def case(self):
 144         return _CaseBuilder(self, indent=2)
 145
 146     def sync(self, kind, cond=None):
 147         return _SyncBuilder(self, kind, cond)
 148
 149
 150 class _CaseBuilder:
 151     def __init__(self, rtlil, indent):
 152         self.rtlil  = rtlil
 153         self.indent = indent
 154
 155     def __enter__(self):
 156         return self
 157
 158     def __exit__(self, *args):
 159         pass
 160
 161     def assign(self, lhs, rhs):
 162         self.rtlil._append("{}assign {} {}\n", "  " * self.indent, lhs, rhs)
 163
 164     def switch(self, cond):
 165         return _SwitchBuilder(self.rtlil, cond, self.indent)
 166
 167
 168 class _SwitchBuilder:
 169     def __init__(self, rtlil, cond, indent):
 170         self.rtlil  = rtlil
 171         self.cond   = cond
 172         self.indent = indent
 173
 174     def __enter__(self):
 175         self.rtlil._append("{}switch {}\n", "  " * self.indent, self.cond)
 176         return self
 177
 178     def __exit__(self, *args):
 179         self.rtlil._append("{}end\n", "  " * self.indent)
 180
 181     def case(self, value=None):
 182         if value is None:
 183             self.rtlil._append("{}case\n", "  " * (self.indent + 1))
 184         else:
 185             self.rtlil._append("{}case {}'{}\n", "  " * (self.indent + 1),
 186                                len(value), value)
 187         return _CaseBuilder(self.rtlil, self.indent + 2)
 188
 189
 190 class _SyncBuilder:
 191     def __init__(self, rtlil, kind, cond):
 192         self.rtlil = rtlil
 193         self.kind  = kind
 194         self.cond  = cond
 195
 196     def __enter__(self):
 197         if self.cond is None:
 198             self.rtlil._append("    sync {}\n", self.kind)
 199         else:
 200             self.rtlil._append("    sync {} {}\n", self.kind, self.cond)
 201         return self
 202
 203     def __exit__(self, *args):
 204         pass
 205
 206     def update(self, lhs, rhs):
 207         self.rtlil._append("      update {} {}\n", lhs, rhs)
 208
 209
 210 def src(src_loc):
 211     file, line = src_loc
 212     return "{}:{}".format(file, line)
 213
 214
 215 class LegalizeValue(Exception):
 216     def __init__(self, value, branches):
 217         self.value    = value
 218         self.branches = list(branches)
 219
 220
 221 class _ValueCompilerState:
 222     def __init__(self, rtlil):
 223         self.rtlil  = rtlil
 224         self.wires  = ast.SignalDict()
 225         self.driven = ast.SignalDict()
 226         self.ports  = ast.SignalDict()
 227
 228         self.expansions = ast.ValueDict()
 229
 230     def add_driven(self, signal, sync):
 231         self.driven[signal] = sync
 232
 233     def add_port(self, signal, kind):
 234         assert kind in ("i", "o", "io")
 235         if kind == "i":
 236             kind = "input"
 237         elif kind == "o":
 238             kind = "output"
 239         elif kind == "io":
 240             kind = "inout"
 241         self.ports[signal] = (len(self.ports), kind)
 242
 243     def resolve(self, signal, prefix=None):
 244         if signal in self.wires:
 245             return self.wires[signal]
 246
 247         if signal in self.ports:
 248             port_id, port_kind = self.ports[signal]
 249         else:
 250             port_id = port_kind = None
 251         if prefix is not None:
 252             wire_name = "{}_{}".format(prefix, signal.name)
 253         else:
 254             wire_name = signal.name
 255
 256         for attr_name, attr_signal in signal.attrs.items():
 257             self.rtlil.attribute(attr_name, attr_signal)
 258         wire_curr = self.rtlil.wire(width=signal.nbits, name=wire_name,
 259                                     port_id=port_id, port_kind=port_kind,
 260                                     src=src(signal.src_loc))
 261         if signal in self.driven:
 262             wire_next = self.rtlil.wire(width=signal.nbits, name=wire_curr + "$next",
 263                                         src=src(signal.src_loc))
 264         else:
 265             wire_next = None
 266         self.wires[signal] = (wire_curr, wire_next)
 267
 268         return wire_curr, wire_next
 269
 270     def resolve_curr(self, signal, prefix=None):
 271         wire_curr, wire_next = self.resolve(signal, prefix)
 272         return wire_curr
 273
 274     def expand(self, value):
 275         if not self.expansions:
 276             return value
 277         return self.expansions.get(value, value)
 278
 279     @contextmanager
 280     def expand_to(self, value, expansion):
 281         try:
 282             assert value not in self.expansions
 283             self.expansions[value] = expansion
 284             yield
 285         finally:
 286             del self.expansions[value]
 287
 288
 289 class _ValueCompiler(xfrm.ValueVisitor):
 290     def __init__(self, state):
 291         self.s = state
 292
 293     def on_value(self, value):
 294         return super().on_value(self.s.expand(value))
 295
 296     def on_unknown(self, value):
 297         if value is None:
 298             return None
 299         else:
 300             super().on_unknown(value)
 301
 302     def on_ClockSignal(self, value):
 303         raise NotImplementedError # :nocov:
 304
 305     def on_ResetSignal(self, value):
 306         raise NotImplementedError # :nocov:
 307
 308     def on_Cat(self, value):
 309         return "{{ {} }}".format(" ".join(reversed([self(o) for o in value.parts])))
 310
 311     def _prepare_value_for_Slice(self, value):
 312         raise NotImplementedError # :nocov:
 313
 314     def on_Slice(self, value):
 315         if value.start == 0 and value.end == len(value.value):
 316             return self(value.value)
 317
 318         sigspec = self._prepare_value_for_Slice(value.value)
 319         if value.start + 1 == value.end:
 320             return "{} [{}]".format(sigspec, value.start)
 321         else:
 322             return "{} [{}:{}]".format(sigspec, value.end - 1, value.start)
 323
 324     def on_ArrayProxy(self, value):
 325         index = self.s.expand(value.index)
 326         if isinstance(index, ast.Const):
 327             if index.value < len(value.elems):
 328                 return self(value.elems[index.value])
 329             else:
 330                 return self(value.elems[-1])
 331         else:
 332             raise LegalizeValue(value.index, range(len(value.elems)))
 333
 334
 335 class _RHSValueCompiler(_ValueCompiler):
 336     operator_map = {
 337         (1, "~"):    "$not",
 338         (1, "-"):    "$neg",
 339         (1, "b"):    "$reduce_bool",
 340         (2, "+"):    "$add",
 341         (2, "-"):    "$sub",
 342         (2, "*"):    "$mul",
 343         (2, "/"):    "$div",
 344         (2, "%"):    "$mod",
 345         (2, "**"):   "$pow",
 346         (2, "<<"):   "$sshl",
 347         (2, ">>"):   "$sshr",
 348         (2, "&"):    "$and",
 349         (2, "^"):    "$xor",
 350         (2, "|"):    "$or",
 351         (2, "=="):   "$eq",
 352         (2, "!="):   "$ne",
 353         (2, "<"):    "$lt",
 354         (2, "<="):   "$le",
 355         (2, ">"):    "$gt",
 356         (2, ">="):   "$ge",
 357         (3, "m"):    "$mux",
 358     }
 359
 360     def on_Const(self, value):
 361         if isinstance(value.value, str):
 362             return "{}'{}".format(value.nbits, value.value)
 363         else:
 364             return "{}'{:0{}b}".format(value.nbits, value.value, value.nbits)
 365
 366     def on_Signal(self, value):
 367         wire_curr, wire_next = self.s.resolve(value)
 368         return wire_curr
 369
 370     def on_Operator_unary(self, value):
 371         arg, = value.operands
 372         arg_bits, arg_sign = arg.shape()
 373         res_bits, res_sign = value.shape()
 374         res = self.s.rtlil.wire(width=res_bits)
 375         self.s.rtlil.cell(self.operator_map[(1, value.op)], ports={
 376             "\\A": self(arg),
 377             "\\Y": res,
 378         }, params={
 379             "A_SIGNED": arg_sign,
 380             "A_WIDTH": arg_bits,
 381             "Y_WIDTH": res_bits,
 382         }, src=src(value.src_loc))
 383         return res
 384
 385     def match_shape(self, value, new_bits, new_sign):
 386         if isinstance(value, ast.Const):
 387             return self(ast.Const(value.value, (new_bits, new_sign)))
 388
 389         value_bits, value_sign = value.shape()
 390         if new_bits <= value_bits:
 391             return self(ast.Slice(value, 0, new_bits))
 392
 393         res = self.s.rtlil.wire(width=new_bits)
 394         self.s.rtlil.cell("$pos", ports={
 395             "\\A": self(value),
 396             "\\Y": res,
 397         }, params={
 398             "A_SIGNED": value_sign,
 399             "A_WIDTH": value_bits,
 400             "Y_WIDTH": new_bits,
 401         }, src=src(value.src_loc))
 402         return res
 403
 404     def on_Operator_binary(self, value):
 405         lhs, rhs = value.operands
 406         lhs_bits, lhs_sign = lhs.shape()
 407         rhs_bits, rhs_sign = rhs.shape()
 408         if lhs_sign == rhs_sign:
 409             lhs_wire = self(lhs)
 410             rhs_wire = self(rhs)
 411         else:
 412             lhs_sign = rhs_sign = True
 413             lhs_bits = rhs_bits = max(lhs_bits, rhs_bits)
 414             lhs_wire = self.match_shape(lhs, lhs_bits, lhs_sign)
 415             rhs_wire = self.match_shape(rhs, rhs_bits, rhs_sign)
 416         res_bits, res_sign = value.shape()
 417         res = self.s.rtlil.wire(width=res_bits)
 418         self.s.rtlil.cell(self.operator_map[(2, value.op)], ports={
 419             "\\A": lhs_wire,
 420             "\\B": rhs_wire,
 421             "\\Y": res,
 422         }, params={
 423             "A_SIGNED": lhs_sign,
 424             "A_WIDTH": lhs_bits,
 425             "B_SIGNED": rhs_sign,
 426             "B_WIDTH": rhs_bits,
 427             "Y_WIDTH": res_bits,
 428         }, src=src(value.src_loc))
 429         return res
 430
 431     def on_Operator_mux(self, value):
 432         sel, val1, val0 = value.operands
 433         val1_bits, val1_sign = val1.shape()
 434         val0_bits, val0_sign = val0.shape()
 435         res_bits, res_sign = value.shape()
 436         val1_bits = val0_bits = res_bits = max(val1_bits, val0_bits, res_bits)
 437         val1_wire = self.match_shape(val1, val1_bits, val1_sign)
 438         val0_wire = self.match_shape(val0, val0_bits, val0_sign)
 439         res = self.s.rtlil.wire(width=res_bits)
 440         self.s.rtlil.cell("$mux", ports={
 441             "\\A": val0_wire,
 442             "\\B": val1_wire,
 443             "\\S": self(sel),
 444             "\\Y": res,
 445         }, params={
 446             "WIDTH": res_bits
 447         }, src=src(value.src_loc))
 448         return res
 449
 450     def on_Operator(self, value):
 451         if len(value.operands) == 1:
 452             return self.on_Operator_unary(value)
 453         elif len(value.operands) == 2:
 454             return self.on_Operator_binary(value)
 455         elif len(value.operands) == 3:
 456             assert value.op == "m"
 457             return self.on_Operator_mux(value)
 458         else:
 459             raise TypeError # :nocov:
 460
 461     def _prepare_value_for_Slice(self, value):
 462         if isinstance(value, (ast.Signal, ast.Slice, ast.Cat)):
 463             sigspec = self(value)
 464         else:
 465             sigspec = self.s.rtlil.wire(len(value))
 466             self.s.rtlil.connect(sigspec, self(value))
 467         return sigspec
 468
 469     def on_Part(self, value):
 470         lhs, rhs = value.value, value.offset
 471         lhs_bits, lhs_sign = lhs.shape()
 472         rhs_bits, rhs_sign = rhs.shape()
 473         res_bits, res_sign = value.shape()
 474         res = self.s.rtlil.wire(width=res_bits)
 475         # Note: Verilog's x[o+:w] construct produces a $shiftx cell, not a $shift cell.
 476         # However, Migen's semantics defines the out-of-range bits to be zero, so it is correct
 477         # to use a $shift cell here instead, even though it produces less idiomatic Verilog.
 478         self.s.rtlil.cell("$shift", ports={
 479             "\\A": self(lhs),
 480             "\\B": self(rhs),
 481             "\\Y": res,
 482         }, params={
 483             "A_SIGNED": lhs_sign,
 484             "A_WIDTH": lhs_bits,
 485             "B_SIGNED": rhs_sign,
 486             "B_WIDTH": rhs_bits,
 487             "Y_WIDTH": res_bits,
 488         }, src=src(value.src_loc))
 489         return res
 490
 491     def on_Repl(self, value):
 492         return "{{ {} }}".format(" ".join(self(value.value) for _ in range(value.count)))
 493
 494
 495 class _LHSValueCompiler(_ValueCompiler):
 496     def on_Const(self, value):
 497         raise TypeError # :nocov:
 498
 499     def on_Operator(self, value):
 500         raise TypeError # :nocov:
 501
 502     def on_Signal(self, value):
 503         wire_curr, wire_next = self.s.resolve(value)
 504         if wire_next is None:
 505             raise ValueError("No LHS wire for non-driven signal {}".format(repr(value)))
 506         return wire_next
 507
 508     def _prepare_value_for_Slice(self, value):
 509         assert isinstance(value, (ast.Signal, ast.Slice, ast.Cat))
 510         return self(value)
 511
 512     def on_Part(self, value):
 513         offset = self.s.expand(value.offset)
 514         if isinstance(offset, ast.Const):
 515             return self(ast.Slice(value.value, offset.value, offset.value + value.width))
 516         else:
 517             raise LegalizeValue(value.offset, range((1 << len(value.offset)) - 1))
 518
 519     def on_Repl(self, value):
 520         raise TypeError # :nocov:
 521
 522
 523 class _StatementCompiler(xfrm.StatementVisitor):
 524     def __init__(self, state, rhs_compiler, lhs_compiler):
 525         self.state        = state
 526         self.rhs_compiler = rhs_compiler
 527         self.lhs_compiler = lhs_compiler
 528
 529         self._group = None
 530         self._case  = None
 531
 532         self._test_cache = {}
 533
 534     @contextmanager
 535     def case(self, switch, value):
 536         try:
 537             old_case = self._case
 538             with switch.case(value) as self._case:
 539                 yield
 540         finally:
 541             self._case = old_case
 542
 543     def on_Assign(self, stmt):
 544         # The invariant provided by LHSGroupAnalyzer is that all signals that ever appear together
 545         # on LHS are a part of the same group, so it is sufficient to check any of them.
 546         any_lhs_signal = next(iter(stmt.lhs._lhs_signals()))
 547         if any_lhs_signal not in self._group:
 548             return
 549
 550         lhs_bits, lhs_sign = stmt.lhs.shape()
 551         rhs_bits, rhs_sign = stmt.rhs.shape()
 552         if lhs_bits == rhs_bits:
 553             rhs_sigspec = self.rhs_compiler(stmt.rhs)
 554         else:
 555             # In RTLIL, LHS and RHS of assignment must have exactly same width.
 556             rhs_sigspec = self.rhs_compiler.match_shape(
 557                 stmt.rhs, lhs_bits, rhs_sign)
 558         self._case.assign(self.lhs_compiler(stmt.lhs), rhs_sigspec)
 559
 560     def on_Switch(self, stmt):
 561         if stmt not in self._test_cache:
 562             self._test_cache[stmt] = self.rhs_compiler(stmt.test)
 563         test_sigspec = self._test_cache[stmt]
 564
 565         with self._case.switch(test_sigspec) as switch:
 566             for value, stmts in stmt.cases.items():
 567                 with self.case(switch, value):
 568                     self.on_statements(stmts)
 569
 570     def on_statement(self, stmt):
 571         try:
 572             super().on_statement(stmt)
 573         except LegalizeValue as legalize:
 574             with self._case.switch(self.rhs_compiler(legalize.value)) as switch:
 575                 bits, sign = legalize.value.shape()
 576                 tests = ["{:0{}b}".format(v, bits) for v in legalize.branches]
 577                 tests[-1] = "-" * bits
 578                 for branch, test in zip(legalize.branches, tests):
 579                     with self.case(switch, test):
 580                         branch_value = ast.Const(branch, (bits, sign))
 581                         with self.state.expand_to(legalize.value, branch_value):
 582                             super().on_statement(stmt)
 583
 584     def on_statements(self, stmts):
 585         for stmt in stmts:
 586             self.on_statement(stmt)
 587
 588
 589 def convert_fragment(builder, fragment, name, top):
 590     if isinstance(fragment, ir.Instance):
 591         port_map = OrderedDict()
 592         for port_name, value in fragment.named_ports.items():
 593             port_map["\\{}".format(port_name)] = value
 594
 595         if fragment.type[0] == "$":
 596             return fragment.type, port_map
 597         else:
 598             return "\\{}".format(fragment.type), port_map
 599
 600     with builder.module(name or "anonymous", attrs={"top": 1} if top else {}) as module:
 601         compiler_state = _ValueCompilerState(module)
 602         rhs_compiler   = _RHSValueCompiler(compiler_state)
 603         lhs_compiler   = _LHSValueCompiler(compiler_state)
 604         stmt_compiler  = _StatementCompiler(compiler_state, rhs_compiler, lhs_compiler)
 605
 606         # Register all signals driven in the current fragment. This must be done first, as it
 607         # affects further codegen; e.g. whether sig$next signals will be generated and used.
 608         for domain, signal in fragment.iter_drivers():
 609             compiler_state.add_driven(signal, sync=domain is not None)
 610
 611         # Transform all signals used as ports in the current fragment eagerly and outside of
 612         # any hierarchy, to make sure they get sensible (non-prefixed) names.
 613         for signal in fragment.ports:
 614             compiler_state.add_port(signal, fragment.ports[signal])
 615             compiler_state.resolve_curr(signal)
 616
 617         # Transform all clocks clocks and resets eagerly and outside of any hierarchy, to make
 618         # sure they get sensible (non-prefixed) names. This does not affect semantics.
 619         for domain, _ in fragment.iter_sync():
 620             cd = fragment.domains[domain]
 621             compiler_state.resolve_curr(cd.clk)
 622             if cd.rst is not None:
 623                 compiler_state.resolve_curr(cd.rst)
 624
 625         # Transform all subfragments to their respective cells. Transforming signals connected
 626         # to their ports into wires eagerly makes sure they get sensible (prefixed with submodule
 627         # name) names.
 628         memories = OrderedDict()
 629         for subfragment, sub_name in fragment.subfragments:
 630             if not subfragment.ports:
 631                 continue
 632
 633             sub_params = OrderedDict()
 634             if hasattr(subfragment, "parameters"):
 635                 for param_name, param_value in subfragment.parameters.items():
 636                     if isinstance(param_value, mem.Memory):
 637                         memory = param_value
 638                         if memory not in memories:
 639                             memories[memory] = module.memory(width=memory.width, size=memory.depth,
 640                                                              name=memory.name)
 641                             addr_bits = bits_for(memory.depth)
 642                             for addr in range(memory.depth):
 643                                 if addr < len(memory.init):
 644                                     data = memory.init[addr]
 645                                 else:
 646                                     data = 0
 647                                 module.cell("$meminit", ports={
 648                                     "\\ADDR": rhs_compiler(ast.Const(addr, addr_bits)),
 649                                     "\\DATA": rhs_compiler(ast.Const(data, memory.width)),
 650                                 }, params={
 651                                     "MEMID": memories[memory],
 652                                     "ABITS": addr_bits,
 653                                     "WIDTH": memory.width,
 654                                     "WORDS": 1,
 655                                     "PRIORITY": 0,
 656                                 })
 657
 658                         param_value = memories[memory]
 659
 660                     sub_params[param_name] = param_value
 661
 662             sub_type, sub_port_map = \
 663                 convert_fragment(builder, subfragment, top=False, name=sub_name)
 664
 665             sub_ports = OrderedDict()
 666             for port, value in sub_port_map.items():
 667                 for signal in value._rhs_signals():
 668                     compiler_state.resolve_curr(signal, prefix=sub_name)
 669                 sub_ports[port] = rhs_compiler(value)
 670
 671             module.cell(sub_type, name=sub_name, ports=sub_ports, params=sub_params)
 672
 673         lhs_grouper = xfrm.LHSGroupAnalyzer()
 674         lhs_grouper.on_statements(fragment.statements)
 675         for group, group_signals in lhs_grouper.groups().items():
 676             with module.process(name="$group_{}".format(group)) as process:
 677                 with process.case() as case:
 678                     # For every signal in comb domain, assign \sig$next to the reset value.
 679                     # For every signal in sync domains, assign \sig$next to the current
 680                     # value (\sig).
 681                     for domain, signal in fragment.iter_drivers():
 682                         if signal not in group_signals:
 683                             continue
 684                         if domain is None:
 685                             prev_value = ast.Const(signal.reset, signal.nbits)
 686                         else:
 687                             prev_value = signal
 688                         case.assign(lhs_compiler(signal), rhs_compiler(prev_value))
 689
 690                     # Convert statements into decision trees.
 691                     stmt_compiler._group = group_signals
 692                     stmt_compiler._case = case
 693                     stmt_compiler(fragment.statements)
 694
 695                 # For every signal in the sync domain, assign \sig's initial value (which will
 696                 # end up as the \init reg attribute) to the reset value.
 697                 with process.sync("init") as sync:
 698                     for domain, signal in fragment.iter_sync():
 699                         if signal not in group_signals:
 700                             continue
 701                         wire_curr, wire_next = compiler_state.resolve(signal)
 702                         sync.update(wire_curr, rhs_compiler(ast.Const(signal.reset, signal.nbits)))
 703
 704                 # For every signal in every domain, assign \sig to \sig$next. The sensitivity list,
 705                 # however, differs between domains: for comb domains, it is `always`, for sync
 706                 # domains with sync reset, it is `posedge clk`, for sync domains with async reset
 707                 # it is `posedge clk or posedge rst`.
 708                 for domain, signals in fragment.drivers.items():
 709                     signals = signals & group_signals
 710                     if not signals:
 711                         continue
 712
 713                     triggers = []
 714                     if domain is None:
 715                         triggers.append(("always",))
 716                     else:
 717                         cd = fragment.domains[domain]
 718                         triggers.append(("posedge", compiler_state.resolve_curr(cd.clk)))
 719                         if cd.async_reset:
 720                             triggers.append(("posedge", compiler_state.resolve_curr(cd.rst)))
 721
 722                     for trigger in triggers:
 723                         with process.sync(*trigger) as sync:
 724                             for signal in signals:
 725                                 wire_curr, wire_next = compiler_state.resolve(signal)
 726                                 sync.update(wire_curr, wire_next)
 727
 728     # Finally, collect the names we've given to our ports in RTLIL, and correlate these with
 729     # the signals represented by these ports. If we are a submodule, this will be necessary
 730     # to create a cell for us in the parent module.
 731     port_map = OrderedDict()
 732     for signal in fragment.ports:
 733         port_map[compiler_state.resolve_curr(signal)] = signal
 734
 735     return module.name, port_map
 736
 737
 738 def convert(fragment, name="top", **kwargs):
 739     fragment = fragment.prepare(**kwargs)
 740     builder = _Builder()
 741     convert_fragment(builder, fragment, name=name, top=True)
 742     return str(builder)