misoclib/lasmicon/refresher.py

   1 from migen.fhdl.std import *
   2 from migen.genlib.misc import timeline
   3 from migen.genlib.fsm import FSM
   4
   5 from misoclib.lasmicon.multiplexer import *
   6
   7 class Refresher(Module):
   8         def __init__(self, a, ba, tRP, tREFI, tRFC):
   9                 self.req = Signal()
  10                 self.ack = Signal() # 1st command 1 cycle after assertion of ack
  11                 self.cmd = CommandRequest(a, ba)
  12
  13                 ###
  14
  15                 # Refresh sequence generator:
  16                 # PRECHARGE ALL --(tRP)--> AUTO REFRESH --(tRFC)--> done
  17                 seq_start = Signal()
  18                 seq_done = Signal()
  19                 self.sync += [
  20                         self.cmd.a.eq(2**10),
  21                         self.cmd.ba.eq(0),
  22                         self.cmd.cas_n.eq(1),
  23                         self.cmd.ras_n.eq(1),
  24                         self.cmd.we_n.eq(1),
  25                         seq_done.eq(0)
  26                 ]
  27                 self.sync += timeline(seq_start, [
  28                         (1, [
  29                                 self.cmd.ras_n.eq(0),
  30                                 self.cmd.we_n.eq(0)
  31                         ]),
  32                         (1+tRP, [
  33                                 self.cmd.cas_n.eq(0),
  34                                 self.cmd.ras_n.eq(0)
  35                         ]),
  36                         (1+tRP+tRFC, [
  37                                 seq_done.eq(1)
  38                         ])
  39                 ])
  40
  41                 # Periodic refresh counter
  42                 counter = Signal(max=tREFI)
  43                 start = Signal()
  44                 self.sync += [
  45                         start.eq(0),
  46                         If(counter == 0,
  47                                 start.eq(1),
  48                                 counter.eq(tREFI - 1)
  49                         ).Else(
  50                                 counter.eq(counter - 1)
  51                         )
  52                 ]
  53
  54                 # Control FSM
  55                 fsm = FSM()
  56                 self.submodules += fsm
  57                 fsm.act("IDLE", If(start, NextState("WAIT_GRANT")))
  58                 fsm.act("WAIT_GRANT",
  59                         self.req.eq(1),
  60                         If(self.ack,
  61                                 seq_start.eq(1),
  62                                 NextState("WAIT_SEQ")
  63                         )
  64                 )
  65                 fsm.act("WAIT_SEQ",
  66                         self.req.eq(1),
  67                         If(seq_done, NextState("IDLE"))
  68                 )