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         # SV48 defines four levels of page tables
  10         self.vpn0 = Signal(9)
  11         self.vpn1 = Signal(9)
  12         self.vpn2 = Signal(9)
  13         self.vpn3 = Signal(9)
  14         #TODO_PLATEN: use that signal
  15         self.is_2M = Signal()
  16         self.is_1G = Signal()
  17         self.valid = Signal()
  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 class TLBContent(Elaboratable):
  30     def __init__(self, pte_width, asid_width):
  31         self.asid_width = asid_width
  32         self.pte_width = pte_width
  33         self.flush_i = Signal()  # Flush signal
  34         # Update TLB
  35         self.update_i = TLBUpdate(asid_width)
  36         self.vpn2 = Signal(9)
  37         self.vpn1 = Signal(9)
  38         self.vpn0 = Signal(9)
  39         self.replace_en_i = Signal() # replace the following entry,
  40                                      # set by replacement strategy
  41         # Lookup signals
  42         self.lu_asid_i = Signal(asid_width)
  43         self.lu_content_o = Signal(pte_width)
  44         self.lu_is_2M_o = Signal()
  45         self.lu_is_1G_o = Signal()
  46         self.lu_hit_o = Signal()
  47
  48     def elaborate(self, platform):
  49         m = Module()
  50
  51         tags = TLBEntry(self.asid_width)
  52         content = Signal(self.pte_width)
  53
  54         m.d.comb += [self.lu_hit_o.eq(0),
  55                      self.lu_is_2M_o.eq(0),
  56                      self.lu_is_1G_o.eq(0)]
  57
  58         # temporaries for 1st level match
  59         asid_ok = Signal(reset_less=True)
  60         vpn2_ok = Signal(reset_less=True)
  61         tags_ok = Signal(reset_less=True)
  62         vpn2_hit = Signal(reset_less=True)
  63         m.d.comb += [tags_ok.eq(tags.valid),
  64                      asid_ok.eq(tags.asid == self.lu_asid_i),
  65                      vpn2_ok.eq(tags.vpn2 == self.vpn2),
  66                      vpn2_hit.eq(tags_ok & asid_ok & vpn2_ok)]
  67         # temporaries for 2nd level match
  68         vpn1_ok = Signal(reset_less=True)
  69         tags_2M = Signal(reset_less=True)
  70         vpn0_ok = Signal(reset_less=True)
  71         vpn0_or_2M = Signal(reset_less=True)
  72         m.d.comb += [vpn1_ok.eq(self.vpn1 == tags.vpn1),
  73                      tags_2M.eq(tags.is_2M),
  74                      vpn0_ok.eq(self.vpn0 == tags.vpn0),
  75                      vpn0_or_2M.eq(tags_2M | vpn0_ok)]
  76         # first level match, this may be a giga page,
  77         # check the ASID flags as well
  78         with m.If(vpn2_hit):
  79             # second level
  80             with m.If (tags.is_1G):
  81                 m.d.comb += [ self.lu_content_o.eq(content),
  82                               self.lu_is_1G_o.eq(1),
  83                               self.lu_hit_o.eq(1),
  84                             ]
  85             # not a giga page hit so check further
  86             with m.Elif(vpn1_ok):
  87                 # this could be a 2 mega page hit or a 4 kB hit
  88                 # output accordingly
  89                 with m.If(vpn0_or_2M):
  90                     m.d.comb += [ self.lu_content_o.eq(content),
  91                                   self.lu_is_2M_o.eq(tags.is_2M),
  92                                   self.lu_hit_o.eq(1),
  93                                 ]
  94         # ------------------
  95         # Update or Flush
  96         # ------------------
  97
  98         # temporaries
  99         replace_valid = Signal(reset_less=True)
 100         m.d.comb += replace_valid.eq(self.update_i.valid & self.replace_en_i)
 101
 102         # flush
 103         with m.If (self.flush_i):
 104             # invalidate (flush) conditions: all if zero or just this ASID
 105             with m.If (self.lu_asid_i == Const(0, self.asid_width) |
 106                       (self.lu_asid_i == tags.asid)):
 107                 m.d.sync += tags.valid.eq(0)
 108
 109         # normal replacement
 110         with m.Elif(replace_valid):
 111             m.d.sync += [ # update tag array
 112                           tags.asid.eq(self.update_i.asid),
 113                           tags.vpn2.eq(self.update_i.vpn[18:27]),
 114                           tags.vpn1.eq(self.update_i.vpn[9:18]),
 115                           tags.vpn0.eq(self.update_i.vpn[0:9]),
 116                           tags.is_1G.eq(self.update_i.is_1G),
 117                           tags.is_2M.eq(self.update_i.is_2M),
 118                           tags.valid.eq(1),
 119                           # and content as well
 120                           content.eq(self.update_i.content.flatten())
 121                         ]
 122         return m
 123
 124     def ports(self):
 125         return [self.flush_i,
 126                  self.lu_asid_i,
 127                  self.lu_is_2M_o, self.lu_is_1G_o, self.lu_hit_o,
 128                 ] + self.update_i.content.ports() + self.update_i.ports()