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
 181             ###############
 182             # TDI/TWI/TD/TW.  v3.0B p90-91
 183
 184             with m.Case(MicrOp.OP_TRAP):
 185                 # trap instructions (tw, twi, td, tdi)
 186                 with m.If(should_trap):
 187                     # generate trap-type program interrupt
 188                     self.trap(m, trapaddr<<4, cia_i)
 189                     with m.If(traptype == 0):
 190                         # say trap occurred (see 3.0B Book III 6.5.9 p1074-6)
 191                         comb += srr1_o.data[PI.TRAP].eq(1)
 192                     with m.If(traptype & TT.PRIV):
 193                         comb += srr1_o.data[PI.PRIV].eq(1)
 194                     with m.If(traptype & TT.FP):
 195                         comb += srr1_o.data[PI.FP].eq(1)
 196                     with m.If(traptype & TT.ADDR):
 197                         comb += srr1_o.data[PI.ADR].eq(1)
 198                     with m.If(traptype & TT.ILLEG):
 199                         comb += srr1_o.data[PI.ILLEG].eq(1)
 200                     comb += srr1_o.ok.eq(1)
 201
 202                     # when SRR1 is written to, update MSR bits
 203                     self.msr_exception(m, trapaddr)
 204
 205             ###################
 206             # MTMSR/D.  v3.0B p TODO - move to MSR
 207
 208             with m.Case(MicrOp.OP_MTMSRD, MicrOp.OP_MTMSR):
 209                 L = self.fields.FormX.L[0:-1] # X-Form field L
 210                 # start with copy of msr
 211                 comb += msr_o.eq(msr_i)
 212                 with m.If(L):
 213                     # just update RI..EE
 214                     comb += msr_o.data[MSR.RI].eq(a_i[MSR.RI])
 215                     comb += msr_o.data[MSR.EE].eq(a_i[MSR.EE])
 216                 with m.Else():
 217                     # Architecture says to leave out bits 3 (HV), 51 (ME)
 218                     # and 63 (LE) (IBM bit numbering)
 219                     with m.If(op.insn_type == MicrOp.OP_MTMSRD):
 220                         # not MSB0 notation here!
 221                         for stt, end in [(1,12), (13, 60), (61, 64)]:
 222                             comb += msr_o.data[stt:end].eq(a_i[stt:end])
 223                         # put *back* bits 29-31 (MSB0 notation)
 224                         bits = field_slice(29, 31)
 225                         with m.If((msr_i[bits] == Const(0b010, 3)) &
 226                                   (a_i[bits] == Const(0b000, 3))):
 227                             comb += msr_o.data[bits].eq(msr_i[bits])
 228
 229                     with m.Else():
 230                         # mtmsr - 32-bit, only room for bottom 32 LSB flags
 231                         for stt, end in [(1,12), (13, 32)]:
 232                             comb += msr_o.data[stt:end].eq(a_i[stt:end])
 233                     msr_check_pr(m, msr_o.data)
 234
 235                 # Per https://bugs.libre-soc.org/show_bug.cgi?id=325#c123,
 236                 # this actually *is* in the microwatt code now.
 237                 #
 238                 # hypervisor stuff.  here: bits 3 (HV) and 51 (ME) were
 239                 # copied over by msr_copy but if HV was not set we need
 240                 # the *original* (msr_i) bits
 241                 with m.If(~msr_i[MSR.HV]):
 242                     comb += msr_o.data[MSR.HV].eq(msr_i[MSR.HV])
 243                     comb += msr_o.data[MSR.ME].eq(msr_i[MSR.ME])
 244
 245                 comb += msr_o.ok.eq(1)
 246
 247             ###################
 248             # MFMSR.  v3.0B p TODO - move from MSR
 249
 250             with m.Case(MicrOp.OP_MFMSR):
 251                 # some of the bits need zeroing?  apparently not
 252                 comb += o.data.eq(msr_i)
 253                 comb += o.ok.eq(1)
 254
 255             ###################
 256             # RFID.  v3.0B p955
 257
 258             with m.Case(MicrOp.OP_RFID):
 259
 260                 # return addr was in srr0
 261                 comb += nia_o.data.eq(br_ext(srr0_i[2:]))
 262                 comb += nia_o.ok.eq(1)
 263
 264                 # MSR was in srr1: copy it over, however *caveats below*
 265                 comb += msr_copy(msr_o.data, srr1_i, zero_me=False) # don't zero
 266
 267                 with m.If(~self.i.ctx.op.insn[9]): # XXX BAD HACK! (hrfid)
 268                     with m.If(field(msr_i, 3)): # HV
 269                         comb += field(msr_o, 51).eq(field(srr1_i, 51)) # ME
 270                     with m.Else():
 271                         comb += field(msr_o, 51).eq(field(msr_i, 51)) # ME
 272
 273                 # check problem state
 274                 msr_check_pr(m, msr_o.data)
 275
 276                 # don't understand but it's in the spec.  again: bits 32-34
 277                 # are copied from srr1_i and need *restoring* to msr_i
 278
 279                 bits = field_slice(29, 31)  # bits 29, 30, 31 (Power notation)
 280                 with m.If((msr_i[bits] == Const(0b010, 3)) &
 281                           (srr1_i[bits] == Const(0b000, 3))):
 282                     comb += msr_o.data[bits].eq(msr_i[bits])
 283
 284                 comb += msr_o.ok.eq(1)
 285
 286             #################
 287             # SC.  v3.0B p952
 288
 289             with m.Case(MicrOp.OP_SC):
 290                 # scv is not covered here. currently an illegal instruction.
 291                 # raising "illegal" is the decoder's job, not ours, here.
 292
 293                 # According to V3.0B, Book II, section 3.3.1, the System Call
 294                 # instruction allows you to trap directly into the hypervisor
 295                 # if the opcode's LEV sub-field is equal to 1.
 296                 # however we are following *microwatt* - which has
 297                 # not implemented hypervisor.
 298
 299                 # jump to the trap address, return at cia+4
 300                 self.trap(m, 0xc00, cia_i+4)
 301                 self.msr_exception(m, 0xc00)
 302
 303             # TODO (later)
 304             #with m.Case(MicrOp.OP_ADDPCIS):
 305             #    pass
 306
 307         comb += self.o.ctx.eq(self.i.ctx)
 308
 309         return m