src/soc/experiment/alu_fsm.py

   1 """Simple example of a FSM-based ALU
   2
   3 This demonstrates a design that follows the valid/ready protocol of the
   4 ALU, but with a FSM implementation, instead of a pipeline.  It is also
   5 intended to comply with both the CompALU API and the nmutil Pipeline API
   6 (Liskov Substitution Principle)
   7
   8 The basic rules are:
   9
  10 1) p.ready_o is asserted on the initial ("Idle") state, otherwise it keeps low.
  11 2) n.valid_o is asserted on the final ("Done") state, otherwise it keeps low.
  12 3) The FSM stays in the Idle state while p.valid_i is low, otherwise
  13    it accepts the input data and moves on.
  14 4) The FSM stays in the Done state while n.ready_i is low, otherwise
  15    it releases the output data and goes back to the Idle state.
  16
  17 """
  18
  19 from nmigen import Elaboratable, Signal, Module, Cat
  20 cxxsim = False
  21 if cxxsim:
  22     from nmigen.sim.cxxsim import Simulator, Settle
  23 else:
  24     from nmigen.back.pysim import Simulator, Settle
  25 from nmigen.cli import rtlil
  26 from math import log2
  27 from nmutil.iocontrol import PrevControl, NextControl
  28
  29 from soc.fu.base_input_record import CompOpSubsetBase
  30 from soc.decoder.power_enums import (MicrOp, Function)
  31
  32 from vcd.gtkw import GTKWSave, GTKWColor
  33
  34
  35 class CompFSMOpSubset(CompOpSubsetBase):
  36     def __init__(self, name=None):
  37         layout = (('sdir', 1),
  38                   )
  39
  40         super().__init__(layout, name=name)
  41
  42
  43
  44 class Dummy:
  45     pass
  46
  47
  48 class Shifter(Elaboratable):
  49     """Simple sequential shifter
  50
  51     Prev port data:
  52     * p.data_i.data:  value to be shifted
  53     * p.data_i.shift: shift amount
  54     *                 When zero, no shift occurs.
  55     *                 On POWER, range is 0 to 63 for 32-bit,
  56     *                 and 0 to 127 for 64-bit.
  57     *                 Other values wrap around.
  58
  59     Operation type
  60     * op.sdir:       shift direction (0 = left, 1 = right)
  61
  62     Next port data:
  63     * n.data_o.data: shifted value
  64     """
  65     class PrevData:
  66         def __init__(self, width):
  67             self.data = Signal(width, name="p_data_i")
  68             self.shift = Signal(width, name="p_shift_i")
  69             self.ctx = Dummy() # comply with CompALU API
  70
  71         def _get_data(self):
  72             return [self.data, self.shift]
  73
  74     class NextData:
  75         def __init__(self, width):
  76             self.data = Signal(width, name="n_data_o")
  77
  78         def _get_data(self):
  79             return [self.data]
  80
  81     def __init__(self, width):
  82         self.width = width
  83         self.p = PrevControl()
  84         self.n = NextControl()
  85         self.p.data_i = Shifter.PrevData(width)
  86         self.n.data_o = Shifter.NextData(width)
  87
  88         # more pieces to make this example class comply with the CompALU API
  89         self.op = CompFSMOpSubset(name="op")
  90         self.p.data_i.ctx.op = self.op
  91         self.i = self.p.data_i._get_data()
  92         self.out = self.n.data_o._get_data()
  93
  94     def elaborate(self, platform):
  95         m = Module()
  96
  97         m.submodules.p = self.p
  98         m.submodules.n = self.n
  99
 100         # Note:
 101         # It is good practice to design a sequential circuit as
 102         # a data path and a control path.
 103
 104         # Data path
 105         # ---------
 106         # The idea is to have a register that can be
 107         # loaded or shifted (left and right).
 108
 109         # the control signals
 110         load = Signal()
 111         shift = Signal()
 112         direction = Signal()
 113         # the data flow
 114         shift_in = Signal(self.width)
 115         shift_left_by_1 = Signal(self.width)
 116         shift_right_by_1 = Signal(self.width)
 117         next_shift = Signal(self.width)
 118         # the register
 119         shift_reg = Signal(self.width, reset_less=True)
 120         # build the data flow
 121         m.d.comb += [
 122             # connect input and output
 123             shift_in.eq(self.p.data_i.data),
 124             self.n.data_o.data.eq(shift_reg),
 125             # generate shifted views of the register
 126             shift_left_by_1.eq(Cat(0, shift_reg[:-1])),
 127             shift_right_by_1.eq(Cat(shift_reg[1:], 0)),
 128         ]
 129         # choose the next value of the register according to the
 130         # control signals
 131         # default is no change
 132         m.d.comb += next_shift.eq(shift_reg)
 133         with m.If(load):
 134             m.d.comb += next_shift.eq(shift_in)
 135         with m.Elif(shift):
 136             with m.If(direction):
 137                 m.d.comb += next_shift.eq(shift_right_by_1)
 138             with m.Else():
 139                 m.d.comb += next_shift.eq(shift_left_by_1)
 140
 141         # register the next value
 142         m.d.sync += shift_reg.eq(next_shift)
 143
 144         # Control path
 145         # ------------
 146         # The idea is to have a SHIFT state where the shift register
 147         # is shifted every cycle, while a counter decrements.
 148         # This counter is loaded with shift amount in the initial state.
 149         # The SHIFT state is left when the counter goes to zero.
 150
 151         # Shift counter
 152         shift_width = int(log2(self.width)) + 1
 153         next_count = Signal(shift_width)
 154         count = Signal(shift_width, reset_less=True)
 155         m.d.sync += count.eq(next_count)
 156
 157         with m.FSM():
 158             with m.State("IDLE"):
 159                 m.d.comb += [
 160                     # keep p.ready_o active on IDLE
 161                     self.p.ready_o.eq(1),
 162                     # keep loading the shift register and shift count
 163                     load.eq(1),
 164                     next_count.eq(self.p.data_i.shift),
 165                 ]
 166                 # capture the direction bit as well
 167                 m.d.sync += direction.eq(self.op.sdir)
 168                 with m.If(self.p.valid_i):
 169                     # Leave IDLE when data arrives
 170                     with m.If(next_count == 0):
 171                         # short-circuit for zero shift
 172                         m.next = "DONE"
 173                     with m.Else():
 174                         m.next = "SHIFT"
 175             with m.State("SHIFT"):
 176                 m.d.comb += [
 177                     # keep shifting, while counter is not zero
 178                     shift.eq(1),
 179                     # decrement the shift counter
 180                     next_count.eq(count - 1),
 181                 ]
 182                 with m.If(next_count == 0):
 183                     # exit when shift counter goes to zero
 184                     m.next = "DONE"
 185             with m.State("DONE"):
 186                 # keep n.valid_o active while the data is not accepted
 187                 m.d.comb += self.n.valid_o.eq(1)
 188                 with m.If(self.n.ready_i):
 189                     # go back to IDLE when the data is accepted
 190                     m.next = "IDLE"
 191
 192         return m
 193
 194     def __iter__(self):
 195         yield self.op.sdir
 196         yield self.p.data_i.data
 197         yield self.p.data_i.shift
 198         yield self.p.valid_i
 199         yield self.p.ready_o
 200         yield self.n.ready_i
 201         yield self.n.valid_o
 202         yield self.n.data_o.data
 203
 204     def ports(self):
 205         return list(self)
 206
 207
 208 # Write a formatted GTKWave "save" file
 209 def write_gtkw_v1(base_name, top_dut_name, loc):
 210     # hierarchy path, to prepend to signal names
 211     dut = top_dut_name + "."
 212     # color styles
 213     style_input = GTKWColor.orange
 214     style_output = GTKWColor.yellow
 215     style_debug = GTKWColor.red
 216     with open(base_name + ".gtkw", "wt") as gtkw_file:
 217         gtkw = GTKWSave(gtkw_file)
 218         gtkw.comment("Auto-generated by " + loc)
 219         gtkw.dumpfile(base_name + ".vcd")
 220         # set a reasonable zoom level
 221         # also, move the marker to an interesting place
 222         gtkw.zoom_markers(-22.9, 10500000)
 223         gtkw.trace(dut + "clk")
 224         # place a comment in the signal names panel
 225         gtkw.blank("Shifter Demonstration")
 226         with gtkw.group("prev port"):
 227             gtkw.trace(dut + "op__sdir", color=style_input)
 228             # demonstrates using decimal base (default is hex)
 229             gtkw.trace(dut + "p_data_i[7:0]", color=style_input,
 230                        datafmt='dec')
 231             gtkw.trace(dut + "p_shift_i[7:0]", color=style_input,
 232                        datafmt='dec')
 233             gtkw.trace(dut + "p_valid_i", color=style_input)
 234             gtkw.trace(dut + "p_ready_o", color=style_output)
 235         with gtkw.group("debug"):
 236             gtkw.blank("Some debug statements")
 237             # change the displayed name in the panel
 238             gtkw.trace("top.zero", alias='zero delay shift',
 239                        color=style_debug)
 240             gtkw.trace("top.interesting", color=style_debug)
 241             gtkw.trace("top.test_case", alias="test case", color=style_debug)
 242             gtkw.trace("top.msg", color=style_debug)
 243         with gtkw.group("internal"):
 244             gtkw.trace(dut + "fsm_state")
 245             gtkw.trace(dut + "count[3:0]")
 246             gtkw.trace(dut + "shift_reg[7:0]", datafmt='dec')
 247         with gtkw.group("next port"):
 248             gtkw.trace(dut + "n_data_o[7:0]", color=style_output,
 249                        datafmt='dec')
 250             gtkw.trace(dut + "n_valid_o", color=style_output)
 251             gtkw.trace(dut + "n_ready_i", color=style_input)
 252
 253
 254 def write_gtkw(gtkw_name, vcd_name, gtkw_style, gtkw_dom,
 255                loc=None, zoom=-22.9, marker=-1):
 256     """ Write a GTKWave document according to the supplied style and DOM.
 257
 258     :param gtkw_name: name of the generated GTKWave document
 259     :param vcd_name: name of the waveform file
 260     :param gtkw_style: style for signals, classes and groups
 261     :param gtkw_dom: DOM style description for the trace pane
 262     :param loc: source code location to include as a comment
 263     :param zoom: initial zoom level, in GTKWave format
 264     :param marker: initial location of a marker
 265
 266     **gtkw_style format**
 267
 268     Syntax: ``{selector: {attribute: value, ...}, ...}``
 269
 270     "selector" can be a signal, class or group
 271
 272     Signal groups propagate most attributes to their children
 273
 274     Attribute choices:
 275
 276     * module: instance path, for prepending to the signal name
 277     * color: trace color
 278     * base: numerical base for value display
 279     * display: alternate text to display in the signal pane
 280     * comment: comment to display in the signal pane
 281
 282     **gtkw_dom format**
 283
 284     Syntax: ``[signal, (signal, class), (group, [children]), comment, ...]``
 285
 286     The DOM is a list of nodes.
 287
 288     Nodes are signals, signal groups or comments.
 289
 290     * signals are strings, or tuples: ``(signal name, class, class, ...)``
 291     * signal groups are tuples: ``(group name, class, class, ..., [nodes])``
 292     * comments are: ``{'comment': 'comment string'}``
 293
 294     In place of a class name, an inline class description can be used.
 295     ``(signal, {attribute: value, ...}, ...)``
 296     """
 297     colors = {
 298         'blue': GTKWColor.blue,
 299         'cycle': GTKWColor.cycle,
 300         'green': GTKWColor.green,
 301         'indigo': GTKWColor.indigo,
 302         'normal': GTKWColor.normal,
 303         'orange': GTKWColor.orange,
 304         'red': GTKWColor.red,
 305         'violet': GTKWColor.violet,
 306         'yellow': GTKWColor.yellow,
 307     }
 308
 309     with open(gtkw_name, "wt") as gtkw_file:
 310         gtkw = GTKWSave(gtkw_file)
 311         if loc is not None:
 312             gtkw.comment("Auto-generated by " + loc)
 313         gtkw.dumpfile(vcd_name)
 314         # set a reasonable zoom level
 315         # also, move the marker to an interesting place
 316         gtkw.zoom_markers(zoom, marker)
 317
 318         if '' in gtkw_style:
 319             root_style = gtkw_style['']
 320         else:
 321             root_style = dict()
 322
 323         # recursively walk the DOM
 324         def walk(dom, style):
 325             for node in dom:
 326                 node_name = None
 327                 children = None
 328                 # copy the style from the parent
 329                 node_style = style.copy()
 330                 # node is a signal name string
 331                 if isinstance(node, str):
 332                     node_name = node
 333                     # apply style from node name, if specified
 334                     if node_name in gtkw_style:
 335                         node_style.update(gtkw_style[node_name])
 336                 # node is a tuple
 337                 # could be a signal or a group
 338                 elif isinstance(node, tuple):
 339                     node_name = node[0]
 340                     # collect styles from the selectors
 341                     # order goes from the most specific to most generic
 342                     # which means earlier selectors override later ones
 343                     for selector in reversed(node):
 344                         # update the node style from the selector
 345                         if isinstance(selector, str):
 346                             if selector in gtkw_style:
 347                                 node_style.update(gtkw_style[selector])
 348                         # apply an inline style description
 349                         elif isinstance(selector, dict):
 350                             node_style.update(selector)
 351                     # node is a group if it has a child list
 352                     if isinstance(node[-1], list):
 353                         children = node[-1]
 354                 # emit the group delimiters and walk over the child list
 355                 if children is not None:
 356                     gtkw.begin_group(node_name)
 357                     # pass on the group style to its children
 358                     walk(children, node_style)
 359                     gtkw.end_group(node_name)
 360                 # emit a trace, if the node is a signal
 361                 elif node_name is not None:
 362                     signal_name = node_name
 363                     # prepend module name to signal
 364                     if 'module' in node_style:
 365                         signal_name = node_style['module'] + '.' + signal_name
 366                     color = None
 367                     if 'color' in node_style:
 368                         color = colors[node_style['color']]
 369                     gtkw.trace(signal_name, color=color)
 370
 371         walk(gtkw_dom, root_style)
 372
 373
 374 def test_shifter():
 375     m = Module()
 376     m.submodules.shf = dut = Shifter(8)
 377     print("Shifter port names:")
 378     for port in dut:
 379         print("-", port.name)
 380     # generate RTLIL
 381     # try "proc; show" in yosys to check the data path
 382     il = rtlil.convert(dut, ports=dut.ports())
 383     with open("test_shifter.il", "w") as f:
 384         f.write(il)
 385
 386     # Write the GTKWave project file
 387     write_gtkw_v1("test_shifter", "top.shf", __file__)
 388
 389     # Describe a GTKWave document
 390
 391     # Style for signals, classes and groups
 392     gtkwave_style = {
 393         # Root selector. Gives default attributes for every signal.
 394         '': {'module': 'top.shf', 'base': 'dec'},
 395         # color the traces, according to class
 396         # class names are not hardcoded, they are just strings
 397         'in': {'color': 'orange'},
 398         'out': {'color': 'yellow'},
 399         # signals in the debug group have a common color and module path
 400         'debug': {'module': 'top', 'color': 'red'},
 401         # display a different string replacing the signal name
 402         'test_case': {'display': 'test case'},
 403     }
 404
 405     # DOM style description for the trace pane
 406     gtkwave_desc = [
 407         # simple signal, without a class
 408         # even so, it inherits the top-level root attributes
 409         'clk',
 410         # comment
 411         {'comment': 'Shifter Demonstration'},
 412         # collapsible signal group
 413         ('prev port', [
 414             # attach a class style for each signal
 415             ('op__sdir', 'in'),
 416             ('p_data_i[7:0]', 'in'),
 417             ('p_shift_i[7:0]', 'in'),
 418             ('p_valid_i', 'in'),
 419             ('p_ready_o', 'out'),
 420         ]),
 421         # Signals in a signal group inherit the group attributes.
 422         # In this case, a different module path and color.
 423         ('debug', [
 424             {'comment': 'Some debug statements'},
 425             # inline attributes, instead of a class name
 426             ('zero', {'display': 'zero delay shift'}),
 427             'interesting',
 428             'test_case',
 429             'msg',
 430         ]),
 431         ('internal', [
 432             'fsm_state',
 433             'count[3:0]',
 434             'shift_reg[7:0]',
 435         ]),
 436         ('next port', [
 437             ('n_data_o[7:0]', 'out'),
 438             ('n_valid_o', 'out'),
 439             ('n_ready_i', 'in'),
 440         ]),
 441     ]
 442
 443     write_gtkw("test_shifter_v2.gtkw", "test_shifter.vcd",
 444                gtkwave_style, gtkwave_desc,
 445                loc=__file__, marker=10500000)
 446
 447     sim = Simulator(m)
 448     sim.add_clock(1e-6)
 449
 450     # demonstrates adding extra debug signal traces
 451     # they end up in the top module
 452     #
 453     zero = Signal()  # mark an interesting place
 454     #
 455     # demonstrates string traces
 456     #
 457     # display a message when the signal is high
 458     # the low level is just an horizontal line
 459     interesting = Signal(decoder=lambda v: 'interesting!' if v else '')
 460     # choose between alternate strings based on numerical value
 461     test_cases = ['', '13>>2', '3<<4', '21<<0']
 462     test_case = Signal(8, decoder=lambda v: test_cases[v])
 463     # hack to display arbitrary strings, like debug statements
 464     msg = Signal(decoder=lambda _: msg.str)
 465     msg.str = ''
 466
 467     def send(data, shift, direction):
 468         # present input data and assert valid_i
 469         yield dut.p.data_i.data.eq(data)
 470         yield dut.p.data_i.shift.eq(shift)
 471         yield dut.op.sdir.eq(direction)
 472         yield dut.p.valid_i.eq(1)
 473         yield
 474         # wait for p.ready_o to be asserted
 475         while not (yield dut.p.ready_o):
 476             yield
 477         # show current operation operation
 478         if direction:
 479             msg.str = f'{data}>>{shift}'
 480         else:
 481             msg.str = f'{data}<<{shift}'
 482         # force dump of the above message by toggling the
 483         # underlying signal
 484         yield msg.eq(0)
 485         yield msg.eq(1)
 486         # clear input data and negate p.valid_i
 487         yield dut.p.valid_i.eq(0)
 488         yield dut.p.data_i.data.eq(0)
 489         yield dut.p.data_i.shift.eq(0)
 490         yield dut.op.sdir.eq(0)
 491
 492     def receive(expected):
 493         # signal readiness to receive data
 494         yield dut.n.ready_i.eq(1)
 495         yield
 496         # wait for n.valid_o to be asserted
 497         while not (yield dut.n.valid_o):
 498             yield
 499         # read result
 500         result = yield dut.n.data_o.data
 501         # negate n.ready_i
 502         yield dut.n.ready_i.eq(0)
 503         # check result
 504         assert result == expected
 505         # finish displaying the current operation
 506         msg.str = ''
 507         yield msg.eq(0)
 508         yield msg.eq(1)
 509
 510     def producer():
 511         # 13 >> 2
 512         yield from send(13, 2, 1)
 513         # 3 << 4
 514         yield from send(3, 4, 0)
 515         # 21 << 0
 516         # use a debug signal to mark an interesting operation
 517         # in this case, it is a shift by zero
 518         yield interesting.eq(1)
 519         yield from send(21, 0, 0)
 520         yield interesting.eq(0)
 521
 522     def consumer():
 523         # the consumer is not in step with the producer, but the
 524         # order of the results are preserved
 525         # 13 >> 2 = 3
 526         yield test_case.eq(1)
 527         yield from receive(3)
 528         # 3 << 4 = 48
 529         yield test_case.eq(2)
 530         yield from receive(48)
 531         # 21 << 0 = 21
 532         yield test_case.eq(3)
 533         # you can look for the rising edge of this signal to quickly
 534         # locate this point in the traces
 535         yield zero.eq(1)
 536         yield from receive(21)
 537         yield zero.eq(0)
 538         yield test_case.eq(0)
 539
 540     sim.add_sync_process(producer)
 541     sim.add_sync_process(consumer)
 542     sim_writer = sim.write_vcd(
 543         "test_shifter.vcd",
 544         # include additional signals in the trace dump
 545         traces=[zero, interesting, test_case, msg],
 546     )
 547     with sim_writer:
 548         sim.run()
 549
 550
 551 if __name__ == "__main__":
 552     test_shifter()