litex/gen/genlib/roundrobin.py

   1 from litex.gen.fhdl.structure import *
   2 from litex.gen.fhdl.module import Module
   3
   4
   5 (SP_WITHDRAW, SP_CE) = range(2)
   6
   7
   8 class RoundRobin(Module):
   9     def __init__(self, n, switch_policy=SP_WITHDRAW):
  10         self.request = Signal(n)
  11         self.grant = Signal(max=max(2, n))
  12         self.switch_policy = switch_policy
  13         if self.switch_policy == SP_CE:
  14             self.ce = Signal()
  15
  16         ###
  17
  18         if n > 1:
  19             cases = {}
  20             for i in range(n):
  21                 switch = []
  22                 for j in reversed(range(i+1, i+n)):
  23                     t = j % n
  24                     switch = [
  25                         If(self.request[t],
  26                             self.grant.eq(t)
  27                         ).Else(
  28                             *switch
  29                         )
  30                     ]
  31                 if self.switch_policy == SP_WITHDRAW:
  32                     case = [If(~self.request[i], *switch)]
  33                 else:
  34                     case = switch
  35                 cases[i] = case
  36             statement = Case(self.grant, cases)
  37             if self.switch_policy == SP_CE:
  38                 statement = If(self.ce, statement)
  39             self.sync += statement
  40         else:
  41             self.comb += self.grant.eq(0)