76 lines
1.6 KiB
Python
76 lines
1.6 KiB
Python
from migen.fhdl.structure import *
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from migen.corelogic.misc import timeline
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from migen.corelogic.fsm import FSM
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from milkymist.asmicon.multiplexer import *
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class Refresher:
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def __init__(self, a, ba, tRP, tREFI, tRFC):
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self.tRP = tRP
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self.tREFI = tREFI
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self.tRFC = tRFC
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self.req = Signal()
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self.ack = Signal() # 1st command 1 cycle after assertion of ack
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self.cmd = CommandRequest(a, ba)
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def get_fragment(self):
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comb = []
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sync = []
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# Refresh sequence generator:
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# PRECHARGE ALL --(tRP)--> AUTO REFRESH --(tRFC)--> done
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seq_start = Signal()
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seq_done = Signal()
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sync += [
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self.cmd.a.eq(2**10),
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self.cmd.ba.eq(0),
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self.cmd.cas_n.eq(1),
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self.cmd.ras_n.eq(1),
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self.cmd.we_n.eq(1),
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seq_done.eq(0)
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]
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sync += timeline(seq_start, [
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(1, [
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self.cmd.ras_n.eq(0),
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self.cmd.we_n.eq(0)
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]),
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(1+self.tRP, [
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self.cmd.cas_n.eq(0),
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self.cmd.ras_n.eq(0)
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]),
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(1+self.tRP+self.tRFC, [
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seq_done.eq(1)
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])
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])
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# Periodic refresh counter
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counter = Signal(max=self.tREFI)
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start = Signal()
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sync += [
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start.eq(0),
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If(counter == 0,
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start.eq(1),
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counter.eq(self.tREFI - 1)
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).Else(
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counter.eq(counter - 1)
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)
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]
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# Control FSM
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fsm = FSM("IDLE", "WAIT_GRANT", "WAIT_SEQ")
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fsm.act(fsm.IDLE, If(start, fsm.next_state(fsm.WAIT_GRANT)))
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fsm.act(fsm.WAIT_GRANT,
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self.req.eq(1),
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If(self.ack,
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seq_start.eq(1),
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fsm.next_state(fsm.WAIT_SEQ)
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)
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)
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fsm.act(fsm.WAIT_SEQ,
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self.req.eq(1),
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If(seq_done, fsm.next_state(fsm.IDLE))
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)
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return Fragment(comb, sync) + fsm.get_fragment()
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