40 lines
1009 B
Python
40 lines
1009 B
Python
from migen.fhdl.structure import *
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(SP_WITHDRAW, SP_CE) = range(2)
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class RoundRobin:
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def __init__(self, n, switch_policy=SP_WITHDRAW):
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self.n = n
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self.bn = bits_for(self.n-1)
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self.request = Signal(BV(self.n))
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self.grant = Signal(BV(self.bn))
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self.switch_policy = switch_policy
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if self.switch_policy == SP_CE:
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self.ce = Signal()
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def get_fragment(self):
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if self.n > 1:
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cases = []
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for i in range(self.n):
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switch = []
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for j in reversed(range(i+1,i+self.n)):
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t = j % self.n
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switch = [
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If(self.request[t],
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self.grant.eq(Constant(t, BV(self.bn)))
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).Else(
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*switch
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)
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]
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if self.switch_policy == SP_WITHDRAW:
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case = [If(~self.request[i], *switch)]
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else:
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case = switch
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cases.append([Constant(i, BV(self.bn))] + case)
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statement = Case(self.grant, *cases)
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if self.switch_policy == SP_CE:
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statement = If(self.ce, statement)
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return Fragment(sync=[statement])
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else:
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return Fragment([self.grant.eq(0)])
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