TLB/src/CamEntry.py

   1 from nmigen import Module, Signal
   2
   3 class CamEntry:
   4     """ Content Addressable Memory (CAM) Entry
   5
   6         The purpose of this module is to represent an entry within a CAM.
   7         This module when given a read command will compare  the given key
   8         and output whether a match was found or not. When given a write
   9         command it will write the given key and data into internal registers.
  10     """
  11
  12     def __init__(self, key_size, data_size):
  13         """ Arguments:
  14             * key_size: (bit count) The size of the key
  15             * data_size: (bit count) The size of the data
  16         """
  17         # Internal
  18         self.key = Signal(key_size)
  19
  20         # Input
  21         self.command = Signal(2) # 00 => NA 01 => Read 10 => Write 11 => Reset
  22         self.key_in = Signal(key_size) # Reference key for the CAM
  23         self.data_in = Signal(data_size) # Data input when writing
  24
  25         # Output
  26         self.match = Signal(1) # Result of the internal/input key comparison
  27         self.data = Signal(data_size)
  28
  29     def elaborate(self, platform=None):
  30         m = Module()
  31         with m.Switch(self.command):
  32             with m.Case("00"):
  33                 m.d.sync += self.match.eq(0)
  34             with m.Case("01"):
  35                 with m.If(self.key_in == self.key):
  36                     m.d.sync += self.match.eq(1)
  37                 with m.Else():
  38                     m.d.sync += self.match.eq(0)
  39             with m.Case("10"):
  40                 m.d.sync += [
  41                     self.key.eq(self.key_in),
  42                     self.data.eq(self.data_in),
  43                     self.match.eq(0)
  44                 ]
  45             with m.Case():
  46                 m.d.sync += [
  47                     self.match.eq(0),
  48                     self.data.eq(0),
  49                     self.key.eq(0)
  50                 ]
  51
  52         return m