TLB/CAM.py

   1 from nmigen import Array, Module, Signal
   2 from nmigen.lib.coding import Encoder
   3 from nmigen.cli import main
   4
   5 from math import log
   6
   7 from CamEntry import CamEntry
   8
   9 class CAM():
  10     def __init__(self, key_size, data_size, cam_size):
  11         # Internal
  12         entry_array = Array(CamEntry(key_size, data_size) \
  13                             for x in range(cam_size))
  14         encoder_input = Signal(cam_size)
  15
  16         # Input
  17         self.write = Signal(1) # Denotes read (0) or write (1)
  18         self.address = Signal(max=cam_size) # address of the CAM to be written
  19         self.key = Signal(key_size) # The key to search for or to be written
  20         self.data_in = Signal(key_size) # The data to be written
  21
  22         # Output
  23         self.data_hit = Signal(1) # Denotes a key data pair was stored at key_in
  24         self.data_out = Signal(data_size) # The data mapped to by key_in
  25
  26         def elaborate(self, platform):
  27             m = Module()
  28
  29             m.d.submodules.encoder = encoder = Encoder(cam_size)
  30
  31             # Set the key value for every CamEntry
  32             for index in range(cam_size):
  33                 m.d.sync += [
  34                     If(self.write == 0,
  35                        entry_array[index].write.eq(self.write),
  36                        entry_array[index].key_in.eq(self.key),
  37                        entry_array[index].data_in.eq(self.data_in),
  38                        encoder_input[index].eq(entry_array[index].match)
  39                     )
  40                 ]
  41
  42
  43             m.d.sync += [
  44                 encoder.i.eq(encoder_input),
  45                 #  1. Read request
  46                 #  2. Write request
  47                 If(self.write == 0,
  48                    # 0 denotes a mapping was found
  49                    If(encoder.n == 0,
  50                       self.data_hit.eq(0),
  51                       self.data_out.eq(entry_array[encoder.o].data)
  52                     ).Else(
  53                        self.data_hit.eq(1)
  54                     )
  55                 ).Else(
  56                     entry_array[self.address].key_in.eq(self.key_in),
  57                     entry_array[self.address].data.eq(self.data_in)
  58                 )
  59
  60             ]
  61
  62             return m