unused_please_ignore_completely/TLB/AddressEncoder.py

   1 from nmigen import Module, Signal, Elaboratable
   2 from nmigen.lib.coding import Encoder, PriorityEncoder
   3
   4
   5 class AddressEncoder(Elaboratable):
   6     """Address Encoder
   7
   8        The purpose of this module is to take in a vector and
   9        encode the bits that are one hot into an address. This module
  10        combines both nmigen's Encoder and PriorityEncoder and will state
  11        whether the input line has a single bit hot, multiple bits hot,
  12        or no bits hot. The output line will always have the lowest value
  13        address output.
  14
  15        Usage:
  16        The output is valid when either single or multiple match is high.
  17        Otherwise output is 0.
  18     """
  19
  20     def __init__(self, width):
  21         """ Arguments:
  22             * width: The desired length of the input vector
  23         """
  24         # Internal
  25         self.encoder = Encoder(width)
  26         self.p_encoder = PriorityEncoder(width)
  27
  28         # Input
  29         self.i = Signal(width)
  30
  31         # Output
  32         self.single_match = Signal(1)
  33         self.multiple_match = Signal(1)
  34         self.o = Signal(range(width))
  35
  36     def elaborate(self, platform=None):
  37         m = Module()
  38
  39         # Add internal submodules
  40         m.submodules.encoder = self.encoder
  41         m.submodules.p_encoder = self.p_encoder
  42
  43         m.d.comb += [
  44             self.encoder.i.eq(self.i),
  45             self.p_encoder.i.eq(self.i)
  46         ]
  47
  48         # Steps:
  49         # 1. check if the input vector is non-zero
  50         # 2. if non-zero, check if single match or multiple match
  51         # 3. set output line to be lowest value address output
  52
  53         # If the priority encoder recieves an input of 0
  54         # If n is 1 then the output is not valid
  55         with m.If(self.p_encoder.n):
  56             m.d.comb += [
  57                 self.single_match.eq(0),
  58                 self.multiple_match.eq(0),
  59                 self.o.eq(0)
  60             ]
  61         # If the priority encoder recieves an input > 0
  62         with m.Else():
  63             # Multiple Match if encoder n is invalid
  64             with m.If(self.encoder.n):
  65                 m.d.comb += [
  66                     self.single_match.eq(0),
  67                     self.multiple_match.eq(1)
  68                 ]
  69             # Single Match if encoder n is valid
  70             with m.Else():
  71                 m.d.comb += [
  72                     self.single_match.eq(1),
  73                     self.multiple_match.eq(0)
  74                 ]
  75             # Always set output based on priority encoder output
  76             m.d.comb += self.o.eq(self.p_encoder.o)
  77         return m