src/soc/fu/trap/main_stage.py

   1 """Trap Pipeline
   2
   3 * https://bugs.libre-soc.org/show_bug.cgi?id=325
   4 * https://bugs.libre-soc.org/show_bug.cgi?id=344
   5 * https://libre-soc.org/openpower/isa/fixedtrap/
   6 """
   7
   8 from nmigen import (Module, Signal, Cat, Mux, Const, signed)
   9 from nmutil.pipemodbase import PipeModBase
  10 from nmutil.extend import exts
  11 from soc.fu.trap.pipe_data import TrapInputData, TrapOutputData
  12 from soc.fu.branch.main_stage import br_ext
  13 from soc.decoder.power_enums import InternalOp
  14
  15 from soc.decoder.power_fields import DecodeFields
  16 from soc.decoder.power_fieldsn import SignalBitRange
  17
  18
  19 # Listed in V3.0B Book III Chap 4.2.1
  20 # MSR bit numbers
  21 MSR_SF  = (63 - 0)     # Sixty-Four bit mode
  22 MSR_HV  = (63 - 3)     # Hypervisor state
  23 MSR_S   = (63 - 41)    # Secure state
  24 MSR_EE  = (63 - 48)    # External interrupt Enable
  25 MSR_PR  = (63 - 49)    # PRoblem state
  26 MSR_FP  = (63 - 50)    # FP available
  27 MSR_ME  = (63 - 51)    # Machine Check int enable
  28 MSR_IR  = (63 - 58)    # Instruction Relocation
  29 MSR_DR  = (63 - 59)    # Data Relocation
  30 MSR_PMM = (63 - 60)    # Performance Monitor Mark
  31 MSR_RI  = (63 - 62)    # Recoverable Interrupt
  32 MSR_LE  = (63 - 63)    # Little Endian
  33
  34 # Listed in V3.0B Book III 7.5.9 "Program Interrupt"
  35
  36 # note that these correspond to trap_input_record.traptype bits 0,1,2,3
  37 # (TODO: add more?)
  38
  39 PI_FP   = (63 - 43)    # 1 if FP exception
  40 PI_PRIV = (63 - 45)    # 1 if privileged interrupt
  41 PI_TRAP = (63 - 46)    # 1 if exception is "trap" type
  42 PI_ADR  = (63 - 47)    # 0 if SRR0 = address of instruction causing exception
  43
  44
  45 def msr_copy(msr_o, msr_i, zero_me=True):
  46     """
  47     -- ISA says this:
  48     --  Defined MSR bits are classified as either full func-
  49     --  tion or partial function. Full function MSR bits are
  50     --  saved in SRR1 or HSRR1 when an interrupt other
  51     --  than a System Call Vectored interrupt occurs and
  52     --  restored by rfscv, rfid, or hrfid, while partial func-
  53     --  tion MSR bits are not saved or restored.
  54     --  Full function MSR bits lie in the range 0:32, 37:41, and
  55     --  48:63, and partial function MSR bits lie in the range
  56     --  33:36 and 42:47. (Note this is IBM bit numbering).
  57     msr_out := (others => '0');
  58     msr_out(63 downto 31) := msr(63 downto 31);
  59     msr_out(26 downto 22) := msr(26 downto 22);
  60     msr_out(15 downto 0)  := msr(15 downto 0);
  61     """
  62     l = []
  63     if zero_me:
  64         l.append(msr_o.eq(0))
  65     for stt, end in [(0,16), (22, 27), (31, 64)]:
  66         l.append(msr_o[stt:end].eq(msr_i[stt:end]))
  67     return l
  68
  69
  70 def msr_check_pr(m, msr_o):
  71     """msr_check_pr: checks "problem state"
  72     """
  73     comb = m.d.comb
  74     with m.If(msrdata[MSR_PR]):
  75         comb += msr[MSR_EE].eq(1) # set external interrupt bit
  76         comb += msr[MSR_IR].eq(1) # set instruction relocation bit
  77         comb += msr[MSR_DR].eq(1) # set data relocation bit
  78
  79
  80 class TrapMainStage(PipeModBase):
  81     def __init__(self, pspec):
  82         super().__init__(pspec, "main")
  83         self.fields = DecodeFields(SignalBitRange, [self.i.ctx.op.insn])
  84         self.fields.create_specs()
  85
  86     def trap(self, m, return_addr, trap_addr):
  87         """trap """ # TODO add descriptive docstring
  88         comb  = m.d.comb
  89         nia_o, srr0_o, srr1_o = self.o.nia, self.o.srr0, self.o.srr1
  90
  91         # trap address
  92         comb += nia_o.data.eq(trap_addr)
  93         comb += nia_o.ok.eq(1)
  94
  95         # addr to begin from on return
  96         comb += srr0_o.data.eq(return_addr)
  97         comb += srr0_o.ok.eq(1)
  98
  99         # take a copy of the current MSR in SRR1
 100         comb += msr_copy(srr1_o.data, msr_i) # old MSR
 101         comb += srr1_o.ok.eq(1)
 102
 103     def ispec(self):
 104         return TrapInputData(self.pspec)
 105
 106     def ospec(self):
 107         return TrapOutputData(self.pspec)
 108
 109     def elaborate(self, platform):
 110         m = Module()
 111         comb = m.d.comb
 112         op = self.i.ctx.op
 113
 114         # convenience variables
 115         a_i, b_i, cia_i, msr_i = self.i.a, self.i.b, self.i.cia, self.i.msr
 116         o, msr_o, nia_o = self.o.o, self.o.msr, self.o.nia
 117         srr0_o, srr1_o = self.o.srr0, self.o.srr1
 118
 119         # take copy of D-Form TO field
 120         i_fields = self.fields.FormD
 121         to = Signal(i_fields.TO[0:-1].shape())
 122         comb += to.eq(i_fields.TO[0:-1])
 123
 124         # signed/unsigned temporaries for RA and RB
 125         a_s = Signal(signed(64), reset_less=True)
 126         b_s = Signal(signed(64), reset_less=True)
 127
 128         a = Signal(64, reset_less=True)
 129         b = Signal(64, reset_less=True)
 130
 131         # set up A and B comparison (truncate/sign-extend if 32 bit)
 132         with m.If(op.is_32bit):
 133             comb += a_s.eq(exts(a_i, 32, 64))
 134             comb += b_s.eq(exts(b_i, 32, 64))
 135             comb += a.eq(a_i[0:32])
 136             comb += b.eq(b_i[0:32])
 137         with m.Else():
 138             comb += a_s.eq(a_i)
 139             comb += b_s.eq(b_i)
 140             comb += a.eq(a_i)
 141             comb += b.eq(b_i)
 142
 143         # establish comparison bits
 144         lt_s = Signal(reset_less=True)
 145         gt_s = Signal(reset_less=True)
 146         lt_u = Signal(reset_less=True)
 147         gt_u = Signal(reset_less=True)
 148         equal = Signal(reset_less=True)
 149
 150         comb += lt_s.eq(a_s < b_s)
 151         comb += gt_s.eq(a_s > b_s)
 152         comb += lt_u.eq(a < b)
 153         comb += gt_u.eq(a > b)
 154         comb += equal.eq(a == b)
 155
 156         # They're in reverse bit order because POWER.
 157         # Check V3.0B Book 1, Appendix C.6 for chart
 158         trap_bits = Signal(5)
 159         comb += trap_bits.eq(Cat(gt_u, lt_u, equal, gt_s, lt_s))
 160
 161         # establish if the trap should go ahead (any tests requested in TO)
 162         should_trap = Signal()
 163         comb += should_trap.eq((trap_bits & to).any())
 164
 165         # TODO: some #defines for the bits n stuff.
 166         with m.Switch(op):
 167             #### trap ####
 168             with m.Case(InternalOp.OP_TRAP):
 169                 # trap instructions (tw, twi, td, tdi)
 170                 with m.If(should_trap):
 171                     # generate trap-type program interrupt
 172                     self.trap(0x700, cia_i)
 173                     # set bit 46 to say trap occurred (see 3.0B Book III 7.5.9)
 174                     comb += srr1_o.data[PI_TRAP].eq(1)
 175
 176             # move to MSR
 177             with m.Case(InternalOp.OP_MTMSR):
 178                 L = self.fields.FormX.L[0:-1] # X-Form field L
 179                 with m.If(L):
 180                     # just update EE and RI
 181                     comb += msr_o.data[MSR_EE].eq(a_i[MSR_EE])
 182                     comb += msr_o.data[MSR_RI].eq(a_i[MSR_RI])
 183                 with m.Else():
 184                     # Architecture says to leave out bits 3 (HV), 51 (ME)
 185                     # and 63 (LE) (IBM bit numbering)
 186                     for stt, end in [(1,12), (13, 60), (61, 64)]:
 187                         comb += msr_o.data[stt:end].eq(a_i[stt:end])
 188                     msr_check_pr(m, msr_o.data)
 189                 comb += msr_o.ok.eq(1)
 190
 191             # move from MSR
 192             with m.Case(InternalOp.OP_MFMSR):
 193                 # TODO: some of the bits need zeroing?  apparently not
 194                 comb += o.data.eq(msr_i)
 195                 comb += o.ok.eq(1)
 196
 197             with m.Case(InternalOp.OP_RFID):
 198                 # XXX f_out.virt_mode <= b_in(MSR_IR) or b_in(MSR_PR);
 199                 # XXX f_out.priv_mode <= not b_in(MSR_PR);
 200
 201                 # return addr was in srr0
 202                 comb += nia_o.data.eq(br_ext(srr0_i[2:]))
 203                 comb += nia_o.ok.eq(1)
 204                 # MSR was in srr1
 205                 comb += msr_copy(msr_o.data, srr1_i, zero_me=False) # don't zero
 206                 msr_check_pr(m, msr_o.data)
 207                 comb += msr_o.ok.eq(1)
 208
 209             with m.Case(InternalOp.OP_SC):
 210                 # TODO: scv must generate illegal instruction.  this is
 211                 # the decoder's job, not ours, here.
 212
 213                 # jump to the trap address, return at cia+4
 214                 self.trap(0xc00, cia_i+4)
 215
 216             # TODO (later)
 217             #with m.Case(InternalOp.OP_ADDPCIS):
 218             #    pass
 219
 220         comb += self.o.ctx.eq(self.i.ctx)
 221
 222         return m