nmigen.lib.scheduler: add RoundRobin.

nmigen/compat/genlib/roundrobin.py

@@ -0,0 +1,56 @@
+from ..._utils import deprecated
+from ..fhdl.module import CompatModule
+
+
+__all__ = ["RoundRobin", "SP_WITHDRAW", "SP_CE"]
+
+(SP_WITHDRAW, SP_CE) = range(2)
+
+class CompatRoundRobin(CompatModule):
+    def __init__(self, n, switch_policy=SP_WITHDRAW):
+        self.request = Signal(n)
+        self.grant = Signal(max=max(2, n))
+        self.switch_policy = switch_policy
+        if self.switch_policy == SP_CE:
+            warnings.warn("instead of `migen.genlib.roundrobin.RoundRobin`, "
+                          "use `nmigen.lib.scheduler.RoundRobin`; note that RoundRobin does not "
+                          "require a policy anymore but to get the same behavior as SP_CE you"
+                          "should use an EnableInserter",
+                          DeprecationWarning, stacklevel=1)
+            self.ce = Signal()
+        else:
+            warnings.warn("instead of `migen.genlib.roundrobin.RoundRobin`, "
+                          "use `nmigen.lib.scheduler.RoundRobin`; note that RoundRobin does not "
+                          "require a policy anymore",
+                          DeprecationWarning, stacklevel=1)
+
+        ###
+
+        if n > 1:
+            cases = {}
+            for i in range(n):
+                switch = []
+                for j in reversed(range(i+1, i+n)):
+                    t = j % n
+                    switch = [
+                        If(self.request[t],
+                            self.grant.eq(t)
+                        ).Else(
+                            *switch
+                        )
+                    ]
+                if self.switch_policy == SP_WITHDRAW:
+                    case = [If(~self.request[i], *switch)]
+                else:
+                    case = switch
+                cases[i] = case
+            statement = Case(self.grant, cases)
+            if self.switch_policy == SP_CE:
+                statement = If(self.ce, statement)
+            self.sync += statement
+        else:
+            self.comb += self.grant.eq(0)
+
+
+
+RoundRobin = CompatRoundRobin