src/soc/fu/trap/main_stage.py

   1 """Trap Pipeline
   2
   3 Deals with td/tw/tdi/twi as well as mfmsr/mtmsr, sc and rfid. addpcis TODO.
   4 Also used generally for interrupts (as a micro-coding mechanism) by
   5 actually modifying the decoded instruction in PowerDecode2.
   6
   7 * https://bugs.libre-soc.org/show_bug.cgi?id=325
   8 * https://bugs.libre-soc.org/show_bug.cgi?id=344
   9 * https://libre-soc.org/openpower/isa/fixedtrap/
  10 """
  11
  12 from nmigen import (Module, Signal, Cat, Mux, Const, signed)
  13 from nmutil.pipemodbase import PipeModBase
  14 from nmutil.extend import exts
  15 from soc.fu.trap.pipe_data import TrapInputData, TrapOutputData
  16 from soc.fu.branch.main_stage import br_ext
  17 from soc.decoder.power_enums import MicrOp
  18
  19 from soc.decoder.power_fields import DecodeFields
  20 from soc.decoder.power_fieldsn import SignalBitRange
  21
  22 from soc.consts import MSR, PI, TT, field, field_slice
  23
  24
  25 def msr_copy(msr_o, msr_i, zero_me=True):
  26     """msr_copy
  27     ISA says this:
  28     Defined MSR bits are classified as either full func tion or partial
  29     function. Full function MSR bits are saved in SRR1 or HSRR1 when
  30     an interrupt other than a System Call Vectored interrupt occurs and
  31     restored by rfscv, rfid, or hrfid, while partial function MSR bits
  32     are not saved or restored.  Full function MSR bits lie in the range
  33     0:32, 37:41, and 48:63, and partial function MSR bits lie in the
  34     range 33:36 and 42:47. (Note this is IBM bit numbering).
  35     """
  36     l = []
  37     if zero_me:
  38         l.append(msr_o.eq(0))
  39     for stt, end in [(0,16), (22, 27), (31, 64)]:
  40         l.append(msr_o[stt:end].eq(msr_i[stt:end]))
  41     return l
  42
  43
  44 def msr_check_pr(m, msr):
  45     """msr_check_pr: checks "problem state"
  46     """
  47     comb = m.d.comb
  48     with m.If(msr[MSR.PR]):
  49         comb += msr[MSR.EE].eq(1) # set external interrupt bit
  50         comb += msr[MSR.IR].eq(1) # set instruction relocation bit
  51         comb += msr[MSR.DR].eq(1) # set data relocation bit
  52
  53
  54 class TrapMainStage(PipeModBase):
  55     def __init__(self, pspec):
  56         super().__init__(pspec, "main")
  57         self.fields = DecodeFields(SignalBitRange, [self.i.ctx.op.insn])
  58         self.fields.create_specs()
  59
  60     def trap(self, m, trap_addr, return_addr):
  61         """trap.  sets new PC, stores MSR and old PC in SRR1 and SRR0
  62         """
  63         comb  = m.d.comb
  64         op = self.i.ctx.op
  65         msr_i = op.msr
  66         nia_o, srr0_o, srr1_o = self.o.nia, self.o.srr0, self.o.srr1
  67
  68         # trap address
  69         comb += nia_o.data.eq(trap_addr)
  70         comb += nia_o.ok.eq(1)
  71
  72         # addr to begin from on return
  73         comb += srr0_o.data.eq(return_addr)
  74         comb += srr0_o.ok.eq(1)
  75
  76         # take a copy of the current MSR in SRR1
  77         comb += msr_copy(srr1_o.data, msr_i) # old MSR
  78         comb += srr1_o.ok.eq(1)
  79
  80     def msr_exception(self, m, trap_addr, msr_hv=None):
  81         """msr_exception - sets bits in MSR specific to an exception.
  82         the full list of what needs to be done is given in V3.0B
  83         Book III Section 6.5 p1063 however it turns out that for the
  84         majority of cases (microwatt showing the way, here), all these
  85         bits are all set by all (implemented) interrupt types.  this
  86         may change in the future, hence the (unused) trap_addr argument
  87         """
  88         comb  = m.d.comb
  89         op = self.i.ctx.op
  90         msr_i, msr_o = op.msr, self.o.msr
  91         comb += msr_o.data.eq(msr_i) # copy msr, first, then modify
  92         comb += msr_o.data[MSR.SF].eq(1)
  93         comb += msr_o.data[MSR.EE].eq(0)
  94         comb += msr_o.data[MSR.PR].eq(0)
  95         comb += msr_o.data[MSR.IR].eq(0)
  96         comb += msr_o.data[MSR.DR].eq(0)
  97         comb += msr_o.data[MSR.RI].eq(0)
  98         comb += msr_o.data[MSR.LE].eq(1)
  99         comb += msr_o.data[MSR.FE0].eq(0)
 100         comb += msr_o.data[MSR.FE1].eq(0)
 101         comb += msr_o.data[MSR.VSX].eq(0)
 102         comb += msr_o.data[MSR.TM].eq(0)
 103         comb += msr_o.data[MSR.VEC].eq(0)
 104         comb += msr_o.data[MSR.FP].eq(0)
 105         comb += msr_o.data[MSR.PMM].eq(0)
 106         comb += msr_o.data[MSR.TEs].eq(0) # this is only 2 bits
 107         comb += msr_o.data[MSR.TEe].eq(0) # so just zero them both
 108         comb += msr_o.data[MSR.UND].eq(0)
 109         if msr_hv is not None:
 110             comb += msr_o.data[MSR.HV].eq(msr_hv)
 111         comb += msr_o.ok.eq(1)
 112
 113     def ispec(self):
 114         return TrapInputData(self.pspec)
 115
 116     def ospec(self):
 117         return TrapOutputData(self.pspec)
 118
 119     def elaborate(self, platform):
 120         m = Module()
 121         comb = m.d.comb
 122         op = self.i.ctx.op
 123
 124         # convenience variables
 125         a_i, b_i, cia_i, msr_i = self.i.a, self.i.b, op.cia, op.msr
 126         srr0_i, srr1_i = self.i.srr0, self.i.srr1
 127         o, msr_o, nia_o = self.o.o, self.o.msr, self.o.nia
 128         srr0_o, srr1_o = self.o.srr0, self.o.srr1
 129         traptype, trapaddr = op.traptype, op.trapaddr
 130
 131         # take copy of D-Form TO field
 132         i_fields = self.fields.FormD
 133         to = Signal(i_fields.TO[0:-1].shape())
 134         comb += to.eq(i_fields.TO[0:-1])
 135
 136         # signed/unsigned temporaries for RA and RB
 137         a_s = Signal(signed(64), reset_less=True)
 138         b_s = Signal(signed(64), reset_less=True)
 139
 140         a = Signal(64, reset_less=True)
 141         b = Signal(64, reset_less=True)
 142
 143         # set up A and B comparison (truncate/sign-extend if 32 bit)
 144         with m.If(op.is_32bit):
 145             comb += a_s.eq(exts(a_i, 32, 64))
 146             comb += b_s.eq(exts(b_i, 32, 64))
 147             comb += a.eq(a_i[0:32])
 148             comb += b.eq(b_i[0:32])
 149         with m.Else():
 150             comb += a_s.eq(a_i)
 151             comb += b_s.eq(b_i)
 152             comb += a.eq(a_i)
 153             comb += b.eq(b_i)
 154
 155         # establish comparison bits
 156         lt_s = Signal(reset_less=True)
 157         gt_s = Signal(reset_less=True)
 158         lt_u = Signal(reset_less=True)
 159         gt_u = Signal(reset_less=True)
 160         equal = Signal(reset_less=True)
 161
 162         comb += lt_s.eq(a_s < b_s)
 163         comb += gt_s.eq(a_s > b_s)
 164         comb += lt_u.eq(a < b)
 165         comb += gt_u.eq(a > b)
 166         comb += equal.eq(a == b)
 167
 168         # They're in reverse bit order because POWER.
 169         # Check V3.0B Book 1, Appendix C.6 for chart
 170         trap_bits = Signal(5, reset_less=True)
 171         comb += trap_bits.eq(Cat(gt_u, lt_u, equal, gt_s, lt_s))
 172
 173         # establish if the trap should go ahead (any tests requested in TO)
 174         # or if traptype is set already
 175         should_trap = Signal(reset_less=True)
 176         comb += should_trap.eq((trap_bits & to).any() | traptype.any())
 177
 178         # TODO: some #defines for the bits n stuff.
 179         with m.Switch(op.insn_type):
 180             #### trap ####
 181             with m.Case(MicrOp.OP_TRAP):
 182                 # trap instructions (tw, twi, td, tdi)
 183                 with m.If(should_trap):
 184                     # generate trap-type program interrupt
 185                     self.trap(m, trapaddr<<4, cia_i)
 186                     with m.If(traptype == 0):
 187                         # say trap occurred (see 3.0B Book III 6.5.9 p1074-6)
 188                         comb += srr1_o.data[PI.TRAP].eq(1)
 189                     with m.If(traptype & TT.PRIV):
 190                         comb += srr1_o.data[PI.PRIV].eq(1)
 191                     with m.If(traptype & TT.FP):
 192                         comb += srr1_o.data[PI.FP].eq(1)
 193                     with m.If(traptype & TT.ADDR):
 194                         comb += srr1_o.data[PI.ADR].eq(1)
 195                     with m.If(traptype & TT.ILLEG):
 196                         comb += srr1_o.data[PI.ILLEG].eq(1)
 197                     comb += srr1_o.ok.eq(1)
 198
 199                     # when SRR1 is written to, update MSR bits
 200                     self.msr_exception(m, trapaddr)
 201
 202             # move to MSR
 203             with m.Case(MicrOp.OP_MTMSRD, MicrOp.OP_MTMSR):
 204                 L = self.fields.FormX.L[0:-1] # X-Form field L
 205                 # start with copy of msr
 206                 comb += msr_o.eq(msr_i)
 207                 with m.If(L):
 208                     # just update RI..EE
 209                     comb += msr_o.data[MSR.RI].eq(a_i[MSR.RI])
 210                     comb += msr_o.data[MSR.EE].eq(a_i[MSR.EE])
 211                 with m.Else():
 212                     # Architecture says to leave out bits 3 (HV), 51 (ME)
 213                     # and 63 (LE) (IBM bit numbering)
 214                     with m.If(op.insn_type == MicrOp.OP_MTMSRD):
 215                         for stt, end in [(1,12), (13, 60), (61, 64)]:
 216                             comb += msr_o.data[stt:end].eq(a_i[stt:end])
 217                     with m.Else():
 218                         # mtmsr - 32-bit, only room for bottom 32 LSB flags
 219                         for stt, end in [(1,12), (13, 32)]:
 220                             comb += msr_o.data[stt:end].eq(a_i[stt:end])
 221                     msr_check_pr(m, msr_o.data)
 222
 223                 # Per https://bugs.libre-soc.org/show_bug.cgi?id=325#c123,
 224                 # this actually *is* in the microwatt code now.
 225                 #
 226                 # hypervisor stuff.  here: bits 3 (HV) and 51 (ME) were
 227                 # copied over by msr_copy but if HV was not set we need
 228                 # the *original* (msr_i) bits
 229                 with m.If(~msr_i[MSR.HV]):
 230                     comb += msr_o.data[MSR.HV].eq(msr_i[MSR.HV])
 231                     comb += msr_o.data[MSR.ME].eq(msr_i[MSR.ME])
 232
 233                 comb += msr_o.ok.eq(1)
 234
 235             # move from MSR
 236             with m.Case(MicrOp.OP_MFMSR):
 237                 # some of the bits need zeroing?  apparently not
 238                 comb += o.data.eq(msr_i)
 239                 comb += o.ok.eq(1)
 240
 241             with m.Case(MicrOp.OP_RFID):
 242                 # XXX f_out.virt_mode <= b_in(MSR.IR) or b_in(MSR.PR);
 243                 # XXX f_out.priv_mode <= not b_in(MSR.PR);
 244
 245                 # return addr was in srr0
 246                 comb += nia_o.data.eq(br_ext(srr0_i[2:]))
 247                 comb += nia_o.ok.eq(1)
 248
 249                 # MSR was in srr1: copy it over, however *caveats below*
 250                 comb += msr_copy(msr_o.data, srr1_i, zero_me=False) # don't zero
 251
 252                 with m.If(field(msr_i, 3)): # HV
 253                     comb += field(msr_o, 51).eq(field(srr1_i, 51)) # ME
 254                 with m.Else():
 255                     comb += field(msr_o, 51).eq(field(msr_i, 51)) # ME
 256
 257                 # check problem state
 258                 msr_check_pr(m, msr_o.data)
 259
 260                 # don't understand but it's in the spec.  again: bits 32-34
 261                 # are copied from srr1_i and need *restoring* to msr_i
 262
 263                 bits = field_slice(29, 31)  # bits 29, 30, 31 (Power notation)
 264                 with m.If((msr_i[bits] == Const(0b010, 3)) &
 265                           (srr1_i[bits] == Const(0b000, 3))):
 266                     comb += msr_o.data[bits].eq(msr_i[bits])
 267
 268                 comb += msr_o.ok.eq(1)
 269
 270             # OP_SC
 271             with m.Case(MicrOp.OP_SC):
 272                 # scv is not covered here. currently an illegal instruction.
 273                 # raising "illegal" is the decoder's job, not ours, here.
 274
 275                 # According to V3.0B, Book II, section 3.3.1, the System Call
 276                 # instruction allows you to trap directly into the hypervisor
 277                 # if the opcode's LEV sub-field is equal to 1.
 278                 # however we are following *microwatt* - which has
 279                 # not implemented hypervisor.
 280
 281                 # jump to the trap address, return at cia+4
 282                 self.trap(m, 0xc00, cia_i+4)
 283                 self.msr_exception(m, 0xc00)
 284
 285             # TODO (later)
 286             #with m.Case(MicrOp.OP_ADDPCIS):
 287             #    pass
 288
 289         comb += self.o.ctx.eq(self.i.ctx)
 290
 291         return m