litex/migen/corelogic/roundrobin.py

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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
self.request = Signal(nbits=self.n)
self.grant = Signal(max=self.n)
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self.switch_policy = switch_policy
if self.switch_policy == SP_CE:
self.ce = Signal()
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def get_fragment(self):
if self.n > 1:
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cases = {}
for i in range(self.n):
switch = []
for j in reversed(range(i+1,i+self.n)):
t = j % self.n
switch = [
If(self.request[t],
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self.grant.eq(t)
).Else(
*switch
)
]
if self.switch_policy == SP_WITHDRAW:
case = [If(~self.request[i], *switch)]
else:
case = switch
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cases[i] = case
statement = Case(self.grant, cases)
if self.switch_policy == SP_CE:
statement = If(self.ce, statement)
return Fragment(sync=[statement])
else:
return Fragment([self.grant.eq(0)])