src/TLB/ariane/tlb_content.py

   1 from nmigen import Signal, Module, Cat, Const, Elaboratable
   2
   3 from TLB.ariane.ptw import TLBUpdate, PTE
   4
   5
   6 class TLBEntry:
   7     def __init__(self, asid_width):
   8         self.asid = Signal(asid_width)
   9         # SV39 defines three levels of page tables
  10         self.vpn0 = Signal(9)
  11         self.vpn1 = Signal(9)
  12         self.vpn2 = Signal(9)
  13         self.is_2M = Signal()
  14         self.is_1G = Signal()
  15         self.valid = Signal()
  16
  17     def flatten(self):
  18         return Cat(*self.ports())
  19
  20     def eq(self, x):
  21         return self.flatten().eq(x.flatten())
  22
  23     def ports(self):
  24         return [self.asid, self.vpn0, self.vpn1, self.vpn2,
  25                 self.is_2M, self.is_1G, self.valid]
  26
  27 class TLBContent(Elaboratable):
  28     def __init__(self, pte_width, asid_width):
  29         self.asid_width = asid_width
  30         self.pte_width = pte_width
  31         self.flush_i = Signal()  # Flush signal
  32         # Update TLB
  33         self.update_i = TLBUpdate(asid_width)
  34         self.vpn2 = Signal(9)
  35         self.vpn1 = Signal(9)
  36         self.vpn0 = Signal(9)
  37         self.replace_en_i = Signal() # replace the following entry,
  38                                      # set by replacement strategy
  39         # Lookup signals
  40         self.lu_asid_i = Signal(asid_width)
  41         self.lu_content_o = Signal(pte_width)
  42         self.lu_is_2M_o = Signal()
  43         self.lu_is_1G_o = Signal()
  44         self.lu_hit_o = Signal()
  45
  46     def elaborate(self, platform):
  47         m = Module()
  48
  49         tags = TLBEntry(self.asid_width)
  50         content = Signal(self.pte_width)
  51
  52         m.d.comb += [self.lu_hit_o.eq(0),
  53                      self.lu_is_2M_o.eq(0),
  54                      self.lu_is_1G_o.eq(0)]
  55
  56         # temporaries for 1st level match
  57         asid_ok = Signal(reset_less=True)
  58         vpn2_ok = Signal(reset_less=True)
  59         tags_ok = Signal(reset_less=True)
  60         vpn2_hit = Signal(reset_less=True)
  61         m.d.comb += [tags_ok.eq(tags.valid),
  62                      asid_ok.eq(tags.asid == self.lu_asid_i),
  63                      vpn2_ok.eq(tags.vpn2 == self.vpn2),
  64                      vpn2_hit.eq(tags_ok & asid_ok & vpn2_ok)]
  65         # temporaries for 2nd level match
  66         vpn1_ok = Signal(reset_less=True)
  67         tags_2M = Signal(reset_less=True)
  68         vpn0_ok = Signal(reset_less=True)
  69         vpn0_or_2M = Signal(reset_less=True)
  70         m.d.comb += [vpn1_ok.eq(self.vpn1 == tags.vpn1),
  71                      tags_2M.eq(tags.is_2M),
  72                      vpn0_ok.eq(self.vpn0 == tags.vpn0),
  73                      vpn0_or_2M.eq(tags_2M | vpn0_ok)]
  74         # first level match, this may be a giga page,
  75         # check the ASID flags as well
  76         with m.If(vpn2_hit):
  77             # second level
  78             with m.If (tags.is_1G):
  79                 m.d.comb += [ self.lu_content_o.eq(content),
  80                               self.lu_is_1G_o.eq(1),
  81                               self.lu_hit_o.eq(1),
  82                             ]
  83             # not a giga page hit so check further
  84             with m.Elif(vpn1_ok):
  85                 # this could be a 2 mega page hit or a 4 kB hit
  86                 # output accordingly
  87                 with m.If(vpn0_or_2M):
  88                     m.d.comb += [ self.lu_content_o.eq(content),
  89                                   self.lu_is_2M_o.eq(tags.is_2M),
  90                                   self.lu_hit_o.eq(1),
  91                                 ]
  92         # ------------------
  93         # Update or Flush
  94         # ------------------
  95
  96         # temporaries
  97         replace_valid = Signal(reset_less=True)
  98         m.d.comb += replace_valid.eq(self.update_i.valid & self.replace_en_i)
  99
 100         # flush
 101         with m.If (self.flush_i):
 102             # invalidate (flush) conditions: all if zero or just this ASID
 103             with m.If (self.lu_asid_i == Const(0, self.asid_width) |
 104                       (self.lu_asid_i == tags.asid)):
 105                 m.d.sync += tags.valid.eq(0)
 106
 107         # normal replacement
 108         with m.Elif(replace_valid):
 109             m.d.sync += [ # update tag array
 110                           tags.asid.eq(self.update_i.asid),
 111                           tags.vpn2.eq(self.update_i.vpn[18:27]),
 112                           tags.vpn1.eq(self.update_i.vpn[9:18]),
 113                           tags.vpn0.eq(self.update_i.vpn[0:9]),
 114                           tags.is_1G.eq(self.update_i.is_1G),
 115                           tags.is_2M.eq(self.update_i.is_2M),
 116                           tags.valid.eq(1),
 117                           # and content as well
 118                           content.eq(self.update_i.content.flatten())
 119                         ]
 120         return m
 121
 122     def ports(self):
 123         return [self.flush_i,
 124                  self.lu_asid_i,
 125                  self.lu_is_2M_o, self.lu_is_1G_o, self.lu_hit_o,
 126                 ] + self.update_i.content.ports() + self.update_i.ports()