nmigen_soc/scheduler.py

   1 from nmigen import *
   2
   3
   4 __all__ = ["RoundRobin"]
   5
   6
   7 class RoundRobin(Elaboratable):
   8     """A round-robin scheduler.
   9
  10     Parameters
  11     ----------
  12     n : int
  13         Maximum number of requests to handle.
  14
  15     Attributes
  16     ----------
  17     request : Signal(n)
  18         Signal where a '1' on the i-th bit represents an incoming request from the i-th device.
  19     grant : Signal(range(n))
  20         Signal that equals to the index of the device which is currently granted access.
  21     """
  22     def __init__(self, n):
  23         self.n = n
  24         self.request = Signal(n)
  25         self.grant = Signal(range(n))
  26
  27     def elaborate(self, platform):
  28         m = Module()
  29
  30         with m.Switch(self.grant):
  31             for i in range(self.n):
  32                 with m.Case(i):
  33                     with m.If(~self.request[i]):
  34                         for j in reversed(range(i+1, i+self.n)):
  35                             t = j % self.n
  36                             with m.If(self.request[t]):
  37                                 m.d.sync += self.grant.eq(t)
  38
  39         return m