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,name="ent_asid")
   9         # SV48 defines four levels of page tables
  10         self.vpn0 = Signal(9,name="ent_vpn0")
  11         self.vpn1 = Signal(9,name="ent_vpn1")
  12         self.vpn2 = Signal(9,name="ent_vpn2")
  13         self.vpn3 = Signal(9,name="ent_vpn3")
  14         self.is_2M = Signal(name="ent_is_2M")
  15         self.is_1G = Signal(name="ent_is_1G")
  16         self.is_512G = Signal(name="ent_is_512G")
  17         self.valid = Signal(name="ent_valid")
  18
  19     def flatten(self):
  20         return Cat(*self.ports())
  21
  22     def eq(self, x):
  23         return self.flatten().eq(x.flatten())
  24
  25     def ports(self):
  26         return [self.asid, self.vpn0, self.vpn1, self.vpn2,
  27                 self.is_2M, self.is_1G, self.valid]
  28
  29
  30 class TLBContent(Elaboratable):
  31     def __init__(self, pte_width, asid_width):
  32         self.asid_width = asid_width
  33         self.pte_width = pte_width
  34         self.flush_i = Signal()  # Flush signal
  35         # Update TLB
  36         self.update_i = TLBUpdate(asid_width)
  37         self.vpn3 = Signal(9)
  38         self.vpn2 = Signal(9)
  39         self.vpn1 = Signal(9)
  40         self.vpn0 = Signal(9)
  41         self.replace_en_i = Signal() # replace the following entry,
  42                                      # set by replacement strategy
  43         # Lookup signals
  44         self.lu_asid_i = Signal(asid_width)
  45         self.lu_content_o = Signal(pte_width)
  46         self.lu_is_512G_o = Signal()
  47         self.lu_is_2M_o = Signal()
  48         self.lu_is_1G_o = Signal()
  49         self.lu_hit_o = Signal()
  50
  51     def elaborate(self, platform):
  52         m = Module()
  53
  54         tags = TLBEntry(self.asid_width)
  55
  56
  57         content = Signal(self.pte_width)
  58
  59         m.d.comb += [self.lu_hit_o.eq(0),
  60                      self.lu_is_512G_o.eq(0),
  61                      self.lu_is_2M_o.eq(0),
  62                      self.lu_is_1G_o.eq(0)]
  63
  64         # temporaries for lookup
  65         asid_ok = Signal(reset_less=True)
  66         # tags_ok = Signal(reset_less=True)
  67
  68         vpn3_ok = Signal(reset_less=True)
  69         vpn2_ok = Signal(reset_less=True)
  70         vpn1_ok = Signal(reset_less=True)
  71         vpn0_ok = Signal(reset_less=True)
  72
  73         #tags_2M = Signal(reset_less=True)
  74         vpn0_or_2M = Signal(reset_less=True)
  75
  76         m.d.comb += [
  77                      #compare asid and vpn*
  78                      asid_ok.eq(tags.asid == self.lu_asid_i),
  79                      vpn3_ok.eq(tags.vpn3 == self.vpn3),
  80                      vpn2_ok.eq(tags.vpn2 == self.vpn2),
  81                      vpn1_ok.eq(tags.vpn1 == self.vpn1),
  82                      vpn0_ok.eq(tags.vpn0 == self.vpn0),
  83                      vpn0_or_2M.eq(tags.is_2M | vpn0_ok)
  84         ]
  85
  86
  87         with m.If(asid_ok & tags.valid):
  88             # first level, only vpn3 needs to match
  89             with m.If (tags.is_512G & vpn3_ok):
  90                 m.d.comb += [ self.lu_content_o.eq(content),
  91                               self.lu_is_512G_o.eq(1),
  92                               self.lu_hit_o.eq(1),
  93                             ]
  94             # second level , second level vpn2 and vpn3 need to match
  95             with m.Elif (tags.is_1G & vpn2_ok & vpn3_ok):
  96                 m.d.comb += [ self.lu_content_o.eq(content),
  97                               self.lu_is_1G_o.eq(1),
  98                               self.lu_hit_o.eq(1),
  99                             ]
 100             # not a giga page hit nor a tera page hit so check further
 101             with m.Elif(vpn1_ok):
 102                 # this could be a 2 mega page hit or a 4 kB hit
 103                 # output accordingly
 104                 with m.If(vpn0_or_2M):
 105                     m.d.comb += [ self.lu_content_o.eq(content),
 106                                   self.lu_is_2M_o.eq(tags.is_2M),
 107                                   self.lu_hit_o.eq(1),
 108                                 ]
 109         # ------------------
 110         # Update or Flush
 111         # ------------------
 112
 113         # temporaries
 114         replace_valid = Signal(reset_less=True)
 115         m.d.comb += replace_valid.eq(self.update_i.valid & self.replace_en_i)
 116
 117         # flush
 118         with m.If (self.flush_i):
 119             # invalidate (flush) conditions: all if zero or just this ASID
 120             with m.If (self.lu_asid_i == Const(0, self.asid_width) |
 121                       (self.lu_asid_i == tags.asid)):
 122                 m.d.sync += tags.valid.eq(0)
 123
 124         # normal replacement
 125         with m.Elif(replace_valid):
 126             m.d.sync += [ # update tag array
 127                           tags.asid.eq(self.update_i.asid),
 128                           tags.vpn3.eq(self.update_i.vpn[27:36]),
 129                           tags.vpn2.eq(self.update_i.vpn[18:27]),
 130                           tags.vpn1.eq(self.update_i.vpn[9:18]),
 131                           tags.vpn0.eq(self.update_i.vpn[0:9]),
 132                           tags.is_512G.eq(self.update_i.is_512G),
 133                           tags.is_1G.eq(self.update_i.is_1G),
 134                           tags.is_2M.eq(self.update_i.is_2M),
 135                           tags.valid.eq(1),
 136                           # and content as well
 137                           content.eq(self.update_i.content.flatten())
 138                         ]
 139         return m
 140
 141     def ports(self):
 142         return [self.flush_i,
 143                  self.lu_asid_i,
 144                  self.lu_is_2M_o, self.lu_is_1G_o,self.lu_is_512G_o, self.lu_hit_o,
 145                 ] + self.update_i.content.ports() + self.update_i.ports()