src/scoreboard/issue_unit.py

   1 from nmigen.compat.sim import run_simulation
   2 from nmigen.cli import verilog, rtlil
   3 from nmigen import Module, Signal, Cat, Array, Const, Repl, Elaboratable
   4 from nmigen.lib.coding import Decoder
   5
   6 from scoreboard.group_picker import PriorityPicker
   7
   8
   9 class RegDecode(Elaboratable):
  10     """ decodes registers into unary
  11
  12         Inputs
  13
  14         * :wid:         register file width
  15     """
  16     def __init__(self, wid):
  17         self.reg_width = wid
  18
  19         # inputs
  20         self.enable_i = Signal(reset_less=True) # enable decoders
  21         self.dest_i = Signal(max=wid, reset_less=True) # Dest R# in
  22         self.src1_i = Signal(max=wid, reset_less=True) # oper1 R# in
  23         self.src2_i = Signal(max=wid, reset_less=True) # oper2 R# in
  24
  25         # outputs
  26         self.dest_o = Signal(wid, reset_less=True) # Dest unary out
  27         self.src1_o = Signal(wid, reset_less=True) # oper1 unary out
  28         self.src2_o = Signal(wid, reset_less=True) # oper2 unary out
  29
  30     def elaborate(self, platform):
  31         m = Module()
  32         m.submodules.dest_d = dest_d = Decoder(self.reg_width)
  33         m.submodules.src1_d = src1_d = Decoder(self.reg_width)
  34         m.submodules.src2_d = src2_d = Decoder(self.reg_width)
  35
  36         # dest decoder: write-pending
  37         for d, i, o in [(dest_d, self.dest_i, self.dest_o),
  38                      (src1_d, self.src1_i, self.src1_o),
  39                      (src2_d, self.src2_i, self.src2_o)]:
  40             m.d.comb += d.i.eq(i)
  41             m.d.comb += d.n.eq(~self.enable_i)
  42             m.d.comb += o.eq(d.o)
  43
  44         return m
  45
  46     def __iter__(self):
  47         yield self.enable_i
  48         yield self.dest_i
  49         yield self.src1_i
  50         yield self.src2_i
  51         yield self.dest_o
  52         yield self.src1_o
  53         yield self.src2_o
  54
  55     def ports(self):
  56         return list(self)
  57
  58
  59 class IssueUnitGroup(Elaboratable):
  60     """ Manages a batch of Computation Units all of which can do the same task
  61
  62         A priority picker will allocate one instruction in this cycle based
  63         on whether the others are busy.
  64
  65         insn_i indicates to this module that there is an instruction to be
  66         issued which this group can handle
  67
  68         busy_i is a vector of signals that indicate, in this cycle, which
  69         of the units are currently busy.
  70
  71         busy_o indicates whether it is "safe to proceed" i.e. whether
  72         there is a unit here that can *be* issued an instruction
  73
  74         fn_issue_o indicates, out of the available (non-busy) units,
  75         which one may be selected
  76     """
  77     def __init__(self, n_insns):
  78         """ Set up inputs and outputs for the Group
  79
  80             Input Parameters
  81
  82             * :n_insns:     number of instructions in this issue unit.
  83         """
  84         self.n_insns = n_insns
  85
  86         # inputs
  87         self.insn_i = Signal(reset_less=True, name="insn_i")
  88         self.busy_i = Signal(n_insns, reset_less=True, name="busy_i")
  89
  90         # outputs
  91         self.fn_issue_o = Signal(n_insns, reset_less=True, name="fn_issue_o")
  92         self.busy_o = Signal(reset_less=True)
  93
  94     def elaborate(self, platform):
  95         m = Module()
  96
  97         if self.n_insns == 0:
  98             return m
  99
 100         m.submodules.pick = pick = PriorityPicker(self.n_insns)
 101
 102         # temporaries
 103         allissue = Signal(self.n_insns, reset_less=True)
 104         all1 = Const(-1, self.n_insns)
 105
 106         m.d.comb += allissue.eq(Repl(self.insn_i, self.n_insns))
 107         # Pick one (and only one) of the units to proceed in this cycle
 108         m.d.comb += pick.i.eq(~self.busy_i & allissue)
 109
 110         # "Safe to issue" condition is basically when all units are not busy
 111         m.d.comb += self.g_issue_o.eq((self.busy_i == all1))
 112
 113         # Picker only raises one signal, therefore it's also the fn_issue
 114         m.d.comb += self.fn_issue_o.eq(pick.o)
 115
 116         return m
 117
 118     def __iter__(self):
 119         yield self.insn_i
 120         yield self.busy_i
 121         yield self.fn_issue_o
 122         yield self.g_issue_o
 123
 124     def ports(self):
 125         return list(self)
 126
 127
 128 class IssueUnit(Elaboratable):
 129     """ implements 11.4.14 issue unit, p50
 130
 131         Inputs
 132
 133         * :n_insns:     number of instructions in this issue unit.
 134     """
 135     def __init__(self, n_insns):
 136         self.n_insns = n_insns
 137
 138         # inputs
 139         self.insn_i = Signal(n_insns, reset_less=True, name="insn_i")
 140         self.busy_i = Signal(n_insns, reset_less=True, name="busy_i")
 141
 142         # outputs
 143         self.fn_issue_o = Signal(n_insns, reset_less=True, name="fn_issue_o")
 144         self.g_issue_o = Signal(reset_less=True)
 145
 146     def elaborate(self, platform):
 147         m = Module()
 148
 149         if self.n_insns == 0:
 150             return m
 151
 152         # temporaries
 153         fu_stall = Signal(reset_less=True)
 154
 155         ib_l = []
 156         for i in range(self.n_insns):
 157             ib_l.append(self.insn_i[i] & self.busy_i[i])
 158         m.d.comb += fu_stall.eq(Cat(*ib_l).bool())
 159         m.d.comb += self.g_issue_o.eq(~(fu_stall))
 160         for i in range(self.n_insns):
 161             m.d.comb += self.fn_issue_o[i].eq(self.g_issue_o & self.insn_i[i])
 162
 163         return m
 164
 165     def __iter__(self):
 166         yield self.insn_i
 167         yield self.busy_i
 168         yield self.fn_issue_o
 169         yield self.g_issue_o
 170
 171     def ports(self):
 172         return list(self)
 173
 174
 175 class IntFPIssueUnit(Elaboratable):
 176     def __init__(self, n_int_insns, n_fp_insns):
 177         self.i = IssueUnit(n_int_insns)
 178         self.f = IssueUnit(n_fp_insns)
 179         self.issue_o = Signal(reset_less=True)
 180
 181     def elaborate(self, platform):
 182         m = Module()
 183         m.submodules.intissue = self.i
 184         m.submodules.fpissue = self.f
 185
 186         m.d.comb += self.issue_o.eq(self.i.g_issue_o | self.f.g_issue_o)
 187
 188         return m
 189
 190     def ports(self):
 191         yield self.issue_o
 192         yield from self.i
 193         yield from self.f
 194
 195
 196 def issue_unit_sim(dut):
 197     yield dut.dest_i.eq(1)
 198     yield dut.issue_i.eq(1)
 199     yield
 200     yield dut.issue_i.eq(0)
 201     yield
 202     yield dut.src1_i.eq(1)
 203     yield dut.issue_i.eq(1)
 204     yield
 205     yield
 206     yield
 207     yield dut.issue_i.eq(0)
 208     yield
 209     yield dut.go_rd_i.eq(1)
 210     yield
 211     yield dut.go_rd_i.eq(0)
 212     yield
 213     yield dut.go_wr_i.eq(1)
 214     yield
 215     yield dut.go_wr_i.eq(0)
 216     yield
 217
 218 def test_issue_unit():
 219     dut = IssueUnitGroup(3)
 220     vl = rtlil.convert(dut, ports=dut.ports())
 221     with open("test_issue_unit_group.il", "w") as f:
 222         f.write(vl)
 223
 224     dut = IssueUnit(32, 3)
 225     vl = rtlil.convert(dut, ports=dut.ports())
 226     with open("test_issue_unit.il", "w") as f:
 227         f.write(vl)
 228
 229     dut = IntFPIssueUnit(32, 3, 3)
 230     vl = rtlil.convert(dut, ports=dut.ports())
 231     with open("test_intfp_issue_unit.il", "w") as f:
 232         f.write(vl)
 233
 234     run_simulation(dut, issue_unit_sim(dut), vcd_name='test_issue_unit.vcd')
 235
 236 if __name__ == '__main__':
 237     test_issue_unit()